ATOMIC SPECTROMETRY UPDATE

X-ray ¯uorescence spectrometry

Philip J. Potts,*a Andrew T. Ellis,b Peter Kregsamer,c Christina Streli,c Margaret Westd and

Peter Wobrauschekc

aDepartment of Earth Sciences, The Open University, Walton Hall, Milton Keynes, UKMK7 6AA

bOxford Instruments, Industrial Analysis Group, Wyndyke Furlong, Abingdon, Oxfordshire,UK OX14 1UJ

cAtominstitut der OÈ sterreichischen UniversitaÈten, SchuÈttelstrasse 115, A-1020, Wien, AustriadMaterials Research Institute, Shef®eld Hallam University, City Campus, Howard Street,Shef®eld, UK S1 1WB

Received 20th September 1999

1 Reviews2 Instrumentation2.1 General instrumentation and excitation sources2.2 Detectors3 Spectral analysis, matrix correction and calibration

procedures3.1 Spectral analysis3.2 Matrix correction and calibration procedures4 X-ray optics4.1 Optical elements4.2 Micro¯uorescence4.3 Capillary waveguides5 Synchrotron radiation5.1 Beamlines and optics5.2 Applications6 Total re¯ection XRF spectrometry6.1 Instrumentation and quanti®cation6.2 Synchrotron radiation-induced TXRF6.3 Surface analysis6.4 Related techniques6.5 Applications7 Portable XRF8 On-line XRF9 Applications9.1 Sample preparation9.2 Preconcentration techniques9.3 Geological9.4 Environmental9.5 Archaeological and forensic9.6 Industrial9.7 Clinical and biological9.8 Thin ®lms9.9 Chemical state analysis and speciation studies10 References

This annual review of X-ray ¯uorescence covers paperspublished over the period 1998±1999 that are judged to havemade a signi®cant contribution to this branch of the analyticalsciences. The review is both comprehensive in scope andselective in the choice of contributions included. The scopeincludes developments in instrumentation and detectors, matrixcorrection and spectrum analysis software, X-ray optics andmicro¯uorescence, synchrotron XRF, TXRF, portable XRFand on-line applications. Also included is a review of

applications, including sample preparation, geological,environmental, archaeological, forensic, biological, clinical,thin ®lms and chemical state analysis, including speciation.Highlights of this year include further work in the developmentof high resolution detector devices based on bothmicrocalorimeters and superconducting tunnel junction devices.However, there continue to be important developments incapillary X-ray optics, portable XRF, on-line applications,TXRF and synchrotron radiation devices. Furthermore, it isnoteworthy that XRF continues to make an essentialcontribution in a wide range of applications where the non-destructive, high precision, simple sample preparationtechniques and well-characterised spectrum interpretation andquanti®cation procedures can be used to advantage.

1 Reviews

XRF continues to go from strength to strength, as indicated bythe number of reports covered in the present review. However,almost all developments in science depend on the strength ofwhat has gone on before, and it is a pleasure to report reviewson various aspects of XRF, published as part of the centenarycelebrations to mark the discovery of X-rays by a group ofdistinguished XRF spectroscopists who did much to lay thefoundations of modern XRF. Ron Jenkins1 considered theevolution of X-ray instrumentation and techniques emphasiz-ing milestone developments, including the acceptance of XRFand XRD techniques in the 1960s, the in¯uence of mini-computers in the 1970s and advances related to the introduc-tion of ED detectors. Hans de Vries2 reviewed the early years ofXRD and X-ray spectrometry from a historic perspective butincluded interesting personal reminiscences from early years atPhilips in Eindhoven. John Gilfrich3 also looked at thehistorical development of XRF, giving a personal view of themost important developments in techniques and applications.The complementary biennial review of X-ray spectrometry byTorok and colleagues has been published in AnalyticalChemistry.4 This review included sections on PIXE andelectron probe microanalysis, techniques not included in thepresent review, and covers the period from November 1995 toAutumn 1997. Other general reviews of XRF included a wide-ranging overview of recent developments from the perspectiveof an individual manufacturer by Uhlig,5 a consideration ofbasic principles and user bene®ts of WDXRF6 and a wide-ranging Chinese language review.7

More targeted reviews included the work of Fitton,8 whopresented an overview of a range of X-ray techniques in

*Review co-ordinator, to whom correspondence should be addressedand from whom reprints may be obtained.

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This Journal is # The Royal Society of Chemistry 1999

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geological applications. Fuentes et al.9 considered the role ofvarious techniques, including XRF, in the determination of theREE, emphasizing the need for chromatographic separation inthe analysis of complex matrices. Harada and Sakurai10

described XRF analysis with high energy photons (40±100 keV) and concluded that this approach had some attractivefeatures, particularly in the determination of high-Z elementsin medium-z matrices in environmental and materials applica-tions. Important aspects were considered to be the in¯uence ofCompton scattering (especially the effect of double scattering),the provision of quasi-monochromatic excitation to attainreasonable detection limits, and opportunities associatedwith synchrotron radiation sources and novel developments inX-ray optics and detectors. A Russian language review11

considered the XRF determination of trace elements.One aspect of scienti®c communication that will become

increasingly important in future years is use of the Internet anddetails of web sites of 31 suppliers of XRF and microanalysisinstrumentation were reported by MacRae.12

Standards will also continue to be an important feature ofscienti®c endeavour and Neelmeijer et al.13 reported on resultsfrom a paper-based multi-element standard for ED detectionusing PIXE, XRF and SEM instrumentation. Evaluation ofresults involved normalizing line intensities of Al±Cu to thatfrom Zn Ka and comparing ratios with those calculated takinginto account known absorbers in the instrument (e.g., detectorberyllium window). Limitations included restrictions to lines ofv4.5 keV in Rh tube excited XRF, w4.5 keV in XRF with anair path and the need to attenuate K-line emissions from C andO from paper when SEM windowless detectors were used.Buhrke et al.14 also discussed the use and availability ofstandards (assumed here to mean reference materials) in XRFanalysis.

Turning now to an aspect that always stimulates a lot ofinterest, Havrilla15 made a conference presentation addressingthe issue of how far can we go in lowering XRF detection limits.Particular instrumental developments considered were TXRFand micro-XRF coupled to the dried spot sample preparation.

It is appropriate to end this section by recording thepublication of two XRF volumes, namely Volume 39 ofAdvances in X-ray Spectrometry, edited by Gilfrich andcolleagues,16 from which papers have already been citedabove, and a special issue of X-ray Spectrometry, edited byHolynska,17 considering X-ray spectrometry in the environ-ment.

2 Instrumentation

2.1 General instrumentation and excitation sources

The fast electron-emission phenomenon from Grimm glow-discharge plasmas was introduced by Tsuji and colleagues18

from the Institute for Materials Research, Tohoku University.In this Japanese language paper, the lamp was operated withHe gas with an applied potential of up to 5 kV, and theapplication of the system to the quantitative analysis of Fe±Sialloys was described. It is pleasing to ®nd that the authorsfollowed up this interesting work with further publications inEnglish during the review period, describing19 a modi®cation tothe lamp by incorporating a 15 mm thick PTFE support toinsulate the cathode from the anode body. Stable high voltagedischarge plasmas were created in the hollow anode near thecathode with gas pressures of 10±100 Pa and discharge currentsof 0.1±10 mA. Transparent ®lms (0.015±0.05 mm thick) wereused as X-ray windows and a Si(Li) detector placed behind theend window was used to record X-ray spectra. When operatedin side window mode, with electrons impinged on the target atan incident angle of 45³ and detected at a take-off angle of 45³through a 0.025 mm thick Be window, higher X-ray intensitieswere obtained with possible opportunities for use as a portable

X-ray tube. Further work by Tsuji et al.20 described theapplication of a compact XRF instrument with a Grimm tubefor the quantitative determination of Mn, Si and Ti in Fe±Mn,Fe±Si and Fe±Ti alloys. The reader is further enticed with thepossibility of observing X-ray diffraction peaks, indicating thatthe structure of the cathode material may also be determined.Work with this glow discharge device, operated with an Al thin®lm target at a discharge voltage of 2.0 kV, a discharge currentof 0.1 mA and a He pressure of y0.2 Torr, was also reportedby this group from Tohoku University21 to produce char-acteristic Al Ka X-rays throughout a discharge time of 1.5 h.

Stuik et al.22 published a new technique based on the use of alaser plasma X-ray source and spherically curved multilayeroptics. The laser light was focused on the sample and a Fe±Schwarzschild mirror used to image the ¯uorescence radiationon a 2-D CCD unit. This con®guration permitted the detectionof C Ka. Recent progress in nickel-like lasers was reported byZhang et al.23 Korobkin et al.24 described monochromatic X-ray sources based on emitters controlled by laser production.Work by Glotin and colleagues25 described the production oftuneable X-rays by optimizing the Compton backscatteredphotons emitted in an IR free-electron laser. The nextgeneration of large, high power lasers was discussed by Suteret al.26 with prospects for ¯uorescence based imaging ofhydrodynamic systems on the National Ignition Facility in theUS. Lee et al.27 compared overlapping areas of research in thedevelopment of X-ray lasers and third generation radiationsources.

Developments in other X-ray excitation sources werepublished by Sakurai et al.,28 who worked on a high poweredX-ray generator equipped with a lanthanum hexaboridecathode for X-ray absorption ®ne structure experiments.Nasonov et al.29 described a general theory of X-ray coherentbremsstrahlung by low energy electrons moving in a crystal.The possibility of creating a high ef®ciency tuneable source ofquasi-monochromatic X-rays was considered. Chesta et al.30

reported a comparison of the ef®ciency of energetic electronsand positrons from low intensity 90Sr and 22Na radioactivesources to produce characteristic radiation. A new experi-mental con®guration for radioisotope excited XRF analysisoffering at least a ten-fold increase in intensity of X-raysemitted by the sample when compared with a conventionalradioactive source was claimed. Among the advantagesclaimed for excitation with energetic beta particles was thefact that the radiation yield changed by less than an order ofmagnitude over the full range of elements investigated. Devanand colleagues31 described their XRF spectrometer with a20 mCi 109Cd source and a 30 mm263 mm Si(Li) detector,having a resolution of 200 eV at 5.9 keV, coupled to a multi-channel analyser for the study of environmental and geologicalsamples in Botswana.

Researchers interested in investigating parametric X-rayradiation (PXR) will bene®t from a review by Shchagin andMaruyama.32 The nature and main properties of this mono-chromatic, polarized, directed, tuneable radiation arising in thevicinity of Bragg directions of a crystal when relativisticparticles pass through were described and possible applicationsproposed.

Several workers published papers on the performance ofmultilayers during this review period. Chernov et al.33

presented ®ndings on the effects of X-ray scattering from aNi±C multilayer and a Ni±C multilayer grating. Barbee34

studied the interfacial structure and the atomic interactionsbetween atoms at interfaces in multilayers or nanolaminates.Salashchenko et al.35 described new experimental results forthe fabrication and X-ray properties of multilayer X-raymirrors based on Cr±Sc and W±Sc for close to normal andBrewster angles of incidence. Holly et al.36 described the designand performance of two new double crystal monochromators(DCM) built at the Madison Physical Sciences Laboratory,

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University of Wisconsin. Aglitskiy et al.37 presented work onthe use of mica as a spherically curved crystal in a spectrometerfor X-ray measurements on an electron beam ion trap. Andre38

gave the principle of a soft X-ray ¯uorescence spectrometerbased on a multilayer interferential transmission plate withillustrations of the Ka emission line of Si and Al samples.Comparison of a mosaic crystal spectrometer to a high-performance solid-state detector for X-ray micro¯uorescenceanalysis was offered by Chung and colleagues.39

Patent claims for innovation in XRF instrumentation this yearincluded Tif®n and Hossain46 for an apparatus and a methodfor determining the elemental composition and relativelocations of particles on the surface of semiconductor wafers.Van de Wal47 described a spectrometer with a doublecollimator mask to provide a facility to irradiate as large asurface of a specimen as possible whilst eliminating ¯uorescentradiation from the specimen holder by the use of a secondcollimator mask behind a solar slit. Virshup and Reynolds48

offered methods for the fabrication of rotating anode X-raytargets with a carbon±carbon matrix into which high Zmaterial was embedded. In a Japanese language patent,Hiraishi et al.49 claimed an invention related to an anode fora transmission target X-ray tube with metals such as Mo, Re,Th, W and their alloys deposited on a substrate by chemicalvapour deposition (CVD). Sipila50 described an inventionrelated to the production of polarized X-ray radiation from aberyllium anode despite its poor effectiveness. An improvedEDXRF con®guration using total external re¯ection wasoffered by O'Hara51 for delivering an increased ¯ux of X-rays onto a detector. The optics could also be used as a lowenergy ®lter by the incorporation of a stop at or near theaperture. Two German language claims by Schwenke et al.52,53

described an apparatus containing movable multi-layeredmirrors for WDXRF. A measuring method and apparatusfor time-averaged, ¯uorescent X-ray interferometry wasclaimed, in Japanese, by Sasaki and Suzuki.54 Similarly,Utaka55 described, in Japanese, an X-ray spectrometercharacterized by the incorporation of a UV radiation sourceto clean the specimen surface prior to analysis. A secondarytarget device claim, again in Japanese by Terada,56 alsoprovided a facility to switch to direct irradiation of a sample.

2.2 Detectors

The cutting edge of detector technology during the reviewperiod continued to be forged by high-resolution cryogenicdetectors. The advances in this rapidly developing area werereviewed by Kraus57 and Wollman et al.58

Members of the NIST, Boulder, CO, group59,60 reported thebest energy resolution to date for a microcalorimeter of 3.1 eVover the energy range 0.1±2 keV. As anticipated, this group hadincreased the size of the device itself to 4006400 mm and thenadded an X-ray polycapillary optic to increase the effectivecollection area to 4 mm2. The best resolution 3.1 eV versus 4 eVwas obtained using a digital pulse processor and the availablecount rate was 500 cps, rising to 1000 cps with beam blanking.Such an impressive performance enabled the straightforwardand direct measurement of chemical shifts in the Fe L serieslines from iron compounds and Al K series lines in aluminiumand alumina. The exciting potential of these high-resolutiondevices has led other groups, such as the one at the Universityof Milan, to fabricate detection systems. Two differentdetectors, one based on a tin absorber and the other on agermanium thermistor, were reported by this group.61 Bothdetectors fully resolved the Mn Ka1 and Ka2 lines, providingan energy resolution of around 5 eV. Improvements in theSQUID ampli®ers for this type of detector were reported byHuber et al.62 and Meier and co-workers,63 whilst the use of animproved SQUID system was found by von Kienlin et al.64 tostabilize the working temperature of the detector. These latter

workers used a 241Am radioisotope source to investigate higherenergy performance and measured an impressive energyresolution of 150 eV at 14 keV and 250 eV at 60 keV. Finally,but importantly, arrays of microcalorimeters have beenreported by two groups during the review period. Silver andcolleagues were awarded a patent65 for a detector systemcomprising an array of four microcalorimeters delivering anenergy resolution of 7±10 eV over the range 0.2±7 keV andcapable of an input rate, for each of the four detectors, of 10±50 cps. The system incorporated analogue pulse processing andthermal pile-up rejection and was claimed to be compact andportable. A second group, at NASA Goddard Space FlightCenter, reported66 the fabrication of a 666 array of siliconmicrocalorimeters, which delivered an energy resolution of10 eV over the energy range 0.4±10 keV. A review by Dieboldet al.67 perhaps best indicated the rapid development of thistype of device by claiming that the microcalorimeter willreplace the traditional Si(Li) detector. Whether and how soonthis happens depends upon many factors, but the future bodeswell as effective areas and count rates increase and predictionsof 0.5±1 eV energy resolution are made.

The second type of high-resolution cryogenic ED detectoris based upon superconducting tunnel junctions (STJ). Frankand colleagues, at the Lawrence Livermore Laboratory,reported68±70 the best performance so far from this type ofdetector. Using a 1416141 mm Nb±Al±Al2O3±Al±Nb STJ, anenergy resolution of 5.9 eV at 277 eV was achieved at severalhundred cps. Upon increasing the count rate, the energyresolution at 277 eV remained below 10 eV up to 10 kcps anddegraded to only 13 eV at 23 kcps. Such count rates aresubstantially higher than those currently available from thehigh-resolution microcalorimeters. The energy resolution ofthis device was shown by Le Grand and colleagues at LLNL71

to be within 15% of the theoretically predicted energyresolution. The largest such device thus far was claimed byworkers at Kyushi University, Japan.72,73 The device was2006200 mm against previous devices of 1006100 mm or1416141 mm and the effect on its operating performance withdifferent magnetic ®eld ramping speeds was investigated. Theenergy resolution of the optimized device was 93 eV at5.9 keV. Kurakado, who has been involved in STJ detectorsthroughout their short history, reviewed74 series-connectedSTJs, which offer not only much larger area devices but also theprospect of obtaining positional information from the samedetector array. Coupled with the very high resolution, highoperating count rate and high detection ef®ciency, the overallcharacteristics of these devices were claimed to make themparticularly attractive. The group working at the EuropeanSpace Agency, Noordwijk, Holland, reported75 the perfor-mance of their tantalum-based 1006100 mm STJ. The energyresolution was 56 eV at 5.9 keV, but this was found to bedominated by spatial non-uniformity in the detecting elementitself. When illuminating selectively only a 5±10 mm spot ontheir device, its energy resolution was substantially improved to22 eV, which corresponds to 15.7 eV for the individual Mn Ka1

and Ka2 lines. This still leaves a further factor of twoimprovement to yield the theoretically predicted energyresolution of 7.3 eV at this energy. Further development bythis group included the use of an NbN passivation layer, whichwas reported by Rando et al.,76 to yield more than a factor oftwo improvement in detector responsiveness. This device wascharacterized by Verhoeve et al.,77 who reported the use of thisNb±Al STJ for photon counting experiments in both the visibleand X-ray energy regions. Perhaps the most exciting develop-ment by the ESA group was the report by Rando andcolleagues78 of a 36-element STJ array detector. The 666 arrayof tantalum-based STJ detectors exhibited an impressiveenergy resolution of 2.5 eV at 270 eV and 6.8 eV at1 keV. The detector energy resolution was reported to belimited by Fano and tunnel noise to about 3 eV at

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1 keV. Although the performance of all the devices in the arraywas consistent to within 5%, the individual detectors showedthe same spatial non-uniformity of energy resolution reportedearlier for a single STJ. A low noise charge sensitivepreampli®er using a 4-terminal JFET was described byUkibe et al.79 and their co-workers Katagiri et al.,80 whoused it in conjunction with a 1786178 mm STJ. The energyresolution at 5.9 keV was claimed to be 66 eV. In-depthcharacterization of STJs was also reported by Cristiano et al.81

and Shimizu and co-workers.82 Low-temperature SEM wasused by Ohkubo and colleagues83 to investigate the doublepeaks arising from the different response of the base andcounter electrode in the STJ.

Clearly, as the volume and advanced nature of the studies onthese two types of very high resolution cryogenic detectorsdemonstrate, the ®eld continues to advance and much can beexpected from it again in the coming year.

Although strongly in¯uenced by a number of papers from asingle Materials Research Society symposium on room-temperature detectors, the review period has seen substantialactivity in CdTe and CdZnTe compound semiconductors forroom-temperature energy dispersive detectors. Redus andcolleagues84 reported the development of a commerciallyavailable CdZnTe detector, the construction of which wasenabled through improvements in the manufacturing processfor CdZnTe detector material. The detector package wasPeltier-cooled to 240 ³C and was capable of an impressiveenergy resolution of 188 eV at 5.9 keV and 482 eV at59.5 keV. Improvements in the detector materials werereviewed by Eisen and colleagues,85 who also reported86 onthe performance of both single and array detectors using theimproved materials. The performance of a new Schottky CdTedetector was reported by a group at ISAS, Kanagawa,Japan.87,88 A 0.5 mm thick high quality 262 mm CdTe crystalwith an indium Schottky contact was used to give a low leakagecurrent, which allowed the detector bias to be increased to400 V, i.e., above that typically used for previous detectors ofthis type. The leakage current was 0.7 nA at room temperatureand less than 1 pA at 270 ³C, yielding an energy resolution of1 keV at 122 keV. Hard X-ray performance is typically themajor interest for these types of compound semiconductordetector. Work at the ESA, The Netherlands, on CdZnTe andGaAs detectors was reported by Kraft et al.89,90 and Bavdazet al.,91 who obtained an energy resolution of 700 eV at 14 keV,which is unattractive for terrestrial XRF but of considerableinterest for hard X-ray space studies. The performance of aPIN-type CdZnTe detector employing less expensive material,which was produced using either the vertical or high-pressureBridgman process, was reported by Sudharsanan and co-workers.92,93 Detectors of large volume (w200 mm3) wereproduced and the new PIN design offered low leakage currentsand no charge polarization effects. Ivanov and colleagues,94,95

reported the use of an M-p-N CdTe detector that exhibited alow leakage current and, when operated at 230 ³C, provided anenergy resolution of 420 eV at 5.9 keV. The application of pulseshape discrimination improved the high-energy resolution from2.4 to 1.5 keV at 662 keV. Matz and Wiedner96 developed anew model for describing charge collection ef®ciency and spacecharge formation in CdZnTe and CdTe detectors. Ruhter andcolleagues at LLNL, Livermore, CA,97 reviewed the applica-tion of CdZnTe detectors in nuclear safeguard measurements.The same group was reported by Lavietes and colleagues98 tohave produced a working, portable spectrometry system basedon a CdZnTe detector, a low power portable MCA and in-house software. The achievable energy resolution was 2.4 keVat 122 keV and the system was well-suited to portableapplications such as nuclear safeguard investigations and on-site high-energy XRF measurements. Although principallytargeted at hard X-ray imaging and astrophysics experiments,there has also been considerable activity during the review

period into CdZnTe array detectors. A collaboration between acommercial supplier and a group at the Harvard-SmithsonianCenter for Astrophysics99±102 resulted in a prototype detectorcomprising a 464 array of PIN CdZnTe detectors, each of1.561.5 mm and 5 mm thick. The array provided a stoppingef®ciency greater than 80% and energy resolution of 3.5 keVat 122 keV. Workers at NASA, Goddard Space FlightCenter,103,104 presented work on prototype CdZnTe stripdetectors that they hoped would allow them to construct anarray of 580 000 pixels, which will offer a staggering total areaof 60 cm2! Yoo et al.105 developed a 16-element linear CdZnTedetector array, which had strong peak tailing and signi®cantcharge sharing for energies less than 60 keV. High energy X-rayimaging CdZnTe detector arrays speci®cally for deployment onspace missions were described by Turner et al.106 and Versrandet al.107 An interesting, though ultimately poorly performing,CdZnTe drift detector was reported by Van Pamelan and Butz-Jorgensen.108 Although the signals could be corrected for holetrapping effects, the energy resolution remained dismal.Finally, Warburton109 described a novel method in whichelectronic signal processing was used for detectors such asCdZnTe strip detectors in which hole transport is poor. Theauthor claimed that this signal processing would allow sub-pixel spatial resolution without signi®cant adverse effects onenergy resolution.

Turning now to the more conventional area of silicon-basedenergy dispersive detectors, Allier and co-workers110,111 made acomparison of Si PIN diodes, drift detectors and avalanchephotodiodes. Pfaustiel et al.112 reported a comparison, fordetectors used in environmental applications in the energyrange 10±450 keV, of silicon and CdZnTe detectors. The mostactive section of published research in this area during thereview period was that of the silicon drift detector (SDD).Strueder and co-workers113 reviewed the key characteristicsand performance of the SDD and reported114,115 their mostrecent developments in this important new area. In the newdevices described, integrated on-chip electronics allowed muchlarger area devices to be prepared, along with the ability toprocess maximum count rates in the region of 26106 cps. Theenergy resolution of 220 eV at 5.9 keV delivered by the newdevices at room temperature remained excellent and improvedto 140 eV when cooled to 253 K using a simple Peltier cooler.The on-chip electronics employed in these devices weredescribed further by Fiorini et al.116 A new geometry forfabricating SDDs was described by Segal et al.,117 who claimedthat the surface leakage current could be substantially reduced,thereby obviating the need for a guard ring. Early results on an8-mm diameter SDD were promising. The Monte Carlo (MC)simulation of X-ray spectra from large area SDDs was reportedby Karvelas and co-workers,118 in which pile-up effects weremodelled based upon four key detector parameters. Acommercially available Peltier-cooled SDD was used byFischer et al.119 for energy dispersive texture mapping. Finally,in the search for SDDs with larger active areas, Gauthier andcolleagues120 reported the development of a 32-channel SDDwith digital signal processing electronics. Two single-channelSDDs with active area of 1 and 10 mm2 were fabricated andtested, as was a monolithic 2 cm2 SDD with eight read-out anodes. Energy resolution of the devices remained in the160±170 eV range and the bene®ts of the new digital pulseprocessing system were described.

Interest in silicon charge coupled device (CCD) detectors hasremained high during the review period although much of thework is for X-ray imaging on space missions or for the very lowX-ray energy region. The European XMM space mission hasbeen the trigger for much work reported in the last year withreports on the technology used in this 36 cm2 monolithic CCDdetector by Struder et al.121 and Holl et al.122,123 These reportsincluded details of the fabrication and testing of theseimpressive devices that offer a detector comprising 12 PN

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CCDs each of 361 cm2 with a total of 768 pixels and each withintegrated, on-chip measurement channels. The dimension ofeach pixel was 1506150 mm2. Measurements and MC model-ling reported by Short and co-workers124 determined that theeffective depletion depth of this detector was 30±35 mm.Meidinger and co-workers125 studied the effects of radiationdamage in this detector and found that, although X-rayhardness was excellent, the energy resolution degraded from135 eV to 175 eV at 5.9 keV after exposure to a 10 MeV proton¯uence of 26109 cm22. Yoshita and co-workers126,127 andTsunemi et al.128 at Osaka University presented a careful studyinto the mechanisms of split events in silicon CCDs. The teamused a highly parallel X-ray beam and a mesh in front of theCCD to restrict the positions at which the events interacted andwere able to describe the nature of 1-, 2-, 3- and 4-pixel eventsin the detector. Further characterization of CCD detectors wasreported by Hashimotodani et al.,129 who used an electron-excited aluminium source as a calibration source; by Prigozhinet al.130 on the precise measurement of quantum ef®ciency from60 to 3000 eV and by Dunn and colleagues131 on the absolutecalibration of CCD detectors over the energy range 8±98 keV. Finally, Simons and colleagues132 concluded that adeep depletion CCD with a frame rate of a few Hz may besuitable as an ED detector, but if rates greater than 1 kHz wererequired its use was expected to be very limited.

Not to be outdone by the new breed of pixellated detectorsbased upon CCD technology, Tull and co-workers133 modelledthe spectral response from an array of multi-element silicondetectors with multi-channel integrated electronics. Deviceswere then fabricated on high resistivity silicon and investigatedusing both conventional 55Fe and 109Cd radioisotope sourcesand a 5 mm beam of 8.5 keV X-rays. Sellar and co-workers134

reported a novel, pixellated detector in which the 16616 silicondetector array was bump-bonded directly onto a 16616 arrayof preampli®er electronics. The output from the preampli®erswas fed into two custom-made 128 channel ICs containing thepulse shaping circuitry and pixel address data. The energyresolution of this interesting new detection system was claimedto be 250 eV at 5.9 keV. Al®eri et al.135 reported a 2-dimensional array of mercuric iodide detectors directly coupledto very low noise ampli®ers. The authors' interest was mostlyfor high X-ray energies and the energy resolution at 60 keV wasa dismal 15%. Finally, Vilhu et al.136 took the conventional butrather expensive route to an array detector of some 750 cm2

active area for X-ray energies in the range 0.5±20 keV. Thesystem comprised an array of 19 conventional Si(Li) detectors,each with an active area of 9.2 mm2 and thickness of 3 mm. Aradiative cooler was used to reach an operating temperature of110±125 K, which resulted in an energy resolution of 200 eV.

There was continuing interest during the review period innon-liquid nitrogen cooling systems for semiconductor detectors.Little137 reviewed the history of Kleemenko cycle coolers,which made use of a new gas mixture and yielded operatingtemperatures in the range 65±150 K. Arai138 was granted apatent for a high purity silicon detector, cooled by a compactgas recycling cooler. A thermoelectric cooling scheme was usedby Shen et al.139 for a 28 mm2 Si(Li) detector. A temperature ofonly 250 ³C was achieved and the resulting energy resolutionof the detector was an abysmal 700 eV at 5.9 keV, which couldreadily be matched by a good quality gas proportional counter.

The Coimbra group continued their work on gas propor-tional scintillation counters (GPSC) and established theoperational parameters needed to operate such detectors,®lled with neon±xenon gas mixtures, in order to improve lowenergy performance.140 In a second study141 on large areaGPSCs this group demonstrated that a shaped curved gridcould retain energy resolution even though the effectivedetector sensitive area was increased by a factor of six. Workwas also reported142 on the good agreement between MonteCarlo (MC) simulation and measured data for the detection of

X-rays and conversion electrons from a 109Cd radioisotopesource in a conventional xenon-®lled GPSC. Calculations byNelson et al.40 showed that signi®cant transmission improve-ments may be gained from the use of ultra-thin windows in gas¯ow proportional detectors. Practitioners who developed skillsin changing 1 mm windows in the past will welcome theinclusion of a supporting grid to allow for pressure cyclingwhich the 0.3 mm detector window will undoubtedly experi-ence. Improvements in the performance of spectrometers usinggas proportional scintillation counters were offered by Simoeset al.41,42 Pulse integration times of several nanoseconds,necessary to reduce the ballistic de®cit in the counter, con¯ictedwith the requirement of shorter integration times when risetime discrimination was applied. Both requirements were metby a 0.1 ms integration of the pulse in the main ampli®er for risetime discrimination followed by digital integration with alonger time constant. This combination was reported toimprove the resolution and peak-to-background ratio whenthe pulse-height distribution of X-rays from a109Cd source wasprocessed.

Other developments included the performance improvementsfrom a semiconductor X-ray detecting system were reported byKuwata et al.43 A new time variant pulse processor wasdescribed as being able to adapt the weighting functionaccording to detector noise characteristics by the addition ofa differentiated signal and an integration of the differentiatedsignal with the same ratio. Hayakawa and colleagues44

designed a WDXRF spectrometer for small area spectroscopywith energy resolution determined by the spatial resolution of aposition sensitive proportional counter. A combination of welldesigned ®lters and non-dispersive X-ray detectors wasdemonstrated by Cazaux45 in various experimental arrange-ments which used CCD cameras for X-ray imaging in TXRFmicroscopy.

3 Spectrum analysis, matrix correction andcalibration procedures

3.1 Spectral analysis

This topic has seen little publication activity during the reviewperiod, although Torres and co-workers143 included some novelfeatures to simplify peak ®tting in their SAX software. Thetechnique used for background correction involved a straight-forward peak stripping algorithm, whilst the peak shape modelwas derived experimentally. A series of samples giving well-separated XRF peaks was used to build a stored peak shapetable whose entries were used in conjunction with parabolicinterpolation to derive measured peak intensities. A leastsquares minimization technique was used to ®t unknownspectra with the peak models and results of the process werereliable for the classic Mn/Fe K series line overlap. The authorsclaimed their spectrum processing procedure was faster and lesscomplex than those which use analytical models of a Gaussianpeak plus exponential tailing and one or more `shelf' features.The use of measured spectra certainly compensates for some ofthe non-ideal and variable line shapes seen with some Si(Li)detectors. Smolniakov and Koltoun144 described the use of aspecial peak deconvolution procedure in which a digital ®lterwas used for background suppression and resolution enhance-ment in conjunction with a least squares ®tting procedure forpeak ®tting. Although similar techniques have been in use sincethe late 1970s, the authors claimed substantial improvements.These improvements resulted in the claim that the effectiveenergy resolution of the EDXRF spectra, using the newtechnique, approaches that obtained from WDXRF scans.

The radiative Auger (RA) X-ray spectrum of Ar was studiedby Muhleisen et al.145 using two high-resolution, curved crystalspectrometers at two separate Institutes. The relative intensityof the K-LM RA to the Ka1,2 peak was measured to be 0.18

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and 0.25% on the instruments used, which was in strongdisagreement with theoretical predictions that are a factor offour greater. This work underlines the importance of the RAeffect in some spectra and the need to obtain more-reliablevalues for the RA peak intensities.

Campbell and others associated with the Guelph groupcontinued to make progress in studies of Si(Li) detector lineshapes. In one study, Campbell and co-workers146 used highlymonochromatized X-ray beams in the energy range 1.8±8.3 keV. The shape and intensity of the longer range, low-energy shelf was accurately predicted using a Monte Carlosimulation based upon a simple electron transport model.Improved data for silicon escape peak relative intensities wereobtained from least squares ®tting of the spectrum features.However, the authors were unable to identify the physicalorigin of the exponential tail on the immediate low energy sideof the parent peak. The features of the derived detectorresponse models were further investigated147 using XPS ofsilicon and front contact metals (gold and nickel). Campbelland co-workers148 measured the intensity ratio of the siliconescape peak to the parent peak in the energy range 2±9 keV inorder to determine accurately the K shell ¯uorescence yield ofsilicon. A value of 0.050 or 0.052 was proposed, which agreedwith earlier values from Kreuse and Bambynek, but wassigni®cantly higher than the recent values presented byHubbell. The detailed evaluation of the spectra obtainedtook into account the double photo-ionization satellites of theescape peaks. The authors noted that such a detailed study ofescape peaks would have been impossible without thesigni®cant improvements to peak tailing delivered throughimproved crystal processing by one detector manufacturer inparticular. Lepy and colleagues149 used heavily monochroma-tized SR in the energy range 1±7 keV to calibrate and study theresponse of a Si(Li) detector. The silicon dead layer wasmeasured experimentally but, interestingly, was claimed tofunction as a partially active layer. The peak shapes were ®ttedusing a Hypermet function similar to that developed byCampbell. Finally, Shima150 reviewed all of the features foundin spectra from Si(Li) detectors.

An equation describing the ef®ciency of planar germaniumdetectors was described by Martinez et al.151 The authorsconcluded that a simple function, which included only theberyllium window absorption and the photoelectric interactionin the bulk, was inadequate, as it did not account for escapepeak losses. Their new model was applied to detectors of 5 and7 mm thick and found to be valid over a wide energy range,although it should be noted that only front-side escape wasaccounted for.

3.2 Matrix correction and calibration procedures

A comprehensive review of in¯uence coef®cient methods waspresented by Lachance,152 in which the concordance betweenthe coef®cients and the algorithms that use them was carefullyexamined. The author made the valuable observation that thein¯uence coef®cients can be highly dependent upon theanalytical context in which they were determined. Conversely,the algorithms themselves tend to be independent of theanalytical context, thus retaining their validity and allowingthem to bene®t from any advances in the de®nition anddetermination of the in¯uence coef®cients. The virtues of thefundamental algorithm were once more expounded byRousseau and Boivin,153 who described how the algorithmbrought together the theoretical exactness of the fundamentalparameter method with the practical convenience of in¯uencecoef®cients and a novel calibration method. In a second paperby Rousseau,154 the theoretical rigour embodied in thefundamental algorithm was used to evaluate three conventionalin¯uence coef®cient models in order to identify the mainsources of error in each. It must be a source of continuing

disappointment to that author as, since the ®rst introduction ofthe fundamental algorithm in 1982, few XRF practitionershave adopted it in favour of the widely-used in¯uencecoef®cient models, despite the errors identi®ed in them bythe fundamental algorithm.

A useful systematic procedure was described by Ochandio-Cardo et al.155 for the preparation of sets of calibrationstandards for XRF spectrometry. A computer program(CALPAT) was developed, which required the user to inputonly the analyte and the required calibration ranges. Theprogram allowed for the use of pure oxides or salts and certi®edreference materials and the authors reported that the programwas being used successfully in a number of ceramic plantsthroughout Spain.

The use of chemometrics in XRF analysis continues togenerate interest despite the large number of in¯uencecoef®cient and fundamental parameter (FP) algorithms thatare already in use. Taking a particularly novel and interestingapproach to determining the light element composition oforganic liquids, Molt and Schramm156 used principalcomponent regression (PCR) and backscatter informationfrom EDXRF spectra. Using an yttrium secondary targetarranged in Cartesian geometry, the authors were able notonly to estimate the overall `dark' matrix, but also to obtainindividual concentration values for C, H and O in a widerange of organic solvents and base oils. The analysis ofunknown samples gave impressive prediction errors of4 mg g21 for H, 30 mg g21 for C and 26 mg g21 forO. Overall, the results were impressive and the PCR techniquelooks promising for use with a wider range of applications inthe future. Urbanski and Kowalska157 used PLS regressionfor the analysis of plating bath solutions and determining thethickness of nickel ®lms on a steel substrate. The procedurewas applied to raw spectral data from low resolution EDXRFinstruments and provided reliable data without the need forexplicit spectrum processing or matrix correction procedures.Such a method is well suited to simple applications like these,as it requires relatively few analytical standards. A PLSregression approach was also adopted by Luo et al.158 for theanalysis of copper alloys. Providing that the top and bottomstandards were included in the calibration set, only fourstandards were required to yield accurate analysis ofunknowns. The authors also reported reliable analysis ofsamples, the analyte concentrations of which lay outside therange of the calibration standards. For more complicatedmatrices, such as geological samples, the authors advocatedcombining PLS with an FP approach. Antoniak et al.159

investigated the use of three spectrum smoothing methodsprior to the application of PLS regression.

An extensive review of the use of expert systems for XRFanalysis was presented by Otto and Flock.160 The system tookinto account all aspects of XRF analysis from the selection ofthe optimum sample preparation methodology, throughselection of instrument parameters to selection of thequantitative model. The inclusion of fuzzy logic in theprograms that were developed allowed semi-quantitativeanalysis of totally unknown samples to be realized.

The development of fundamental parameter (FP) programscontinued during the review period. The powerful combinationof polarized beam EDXRF spectrometry and the FP programTURBOQUANT was presented by Branden161 and Schrammand Heckel.162 The program was set up to cater for many typesof sample without the need for calibration by the user and wasclaimed to provide results for 40 or more major and traceelements in less than 5 min. The performance of the SSQ3000FP analysis program for use with a high power sequentialWDXRF spectrometer was presented by Park.163 Up to 75elements could be determined in a total measuring time of23 min, and the author reported, unsurprisingly, that samplesof known and declared matrix, such as stainless steels, could be

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determined with higher accuracy than totally unknownsamples. Information from the Rh Ka Compton backscatterpeak was used to verify the light element (dark matrix)composition and, unless the matrix was correctly de®ned, theaccuracy of the matrix correction and subsequent analysis wassigni®cantly reduced. Angeyo et al.164 used the AXIL-QXASsoftware (IAEA, Vienna) for the FP determination of traceelements in cellulosic materials such as coffee and tobaccoleaves. The authors investigated the effects of geometry in their109Cd radioisotope source excited EDXRF system and madeuse of the emission-transmission method for the estimation ofthe matrix mass absorption coef®cients. For this work, theauthors assumed that the dark matrix was cellulose andcon®rmed the validity of this simplifying approach by thesuccessful determination of many trace elements in samples ofdried plant material. A suite of in-house FP analysis programswas developed by Bos and Vrielink.165 Accuracy of analysiswas reported to be better than 1% for concentrations greaterthan 1%. The programs allowed for calculations based uponthe following three limitations: all elements measured and thesample mass thickness known; sample mass thicknessunknown; or all elements measured and a balance of oxygenassumed.

Knowledge of the X-ray tube spectrum energy distribution isof great importance for the majority of FP calculationprocedures. An improved model for the tube spectrum wasproposed by Finkelshtein and Pavlova.166 The new modeladdressed the underestimate of the intensity of low energybremsstrahlung that is inherent to models based solely uponKramer's law. In addition, the authors took into account theadditional target K line ¯uorescence excited by the brems-strahlung, which can contribute up to 30% of its total intensity.Results from this valuable new model were compared withthose from the NIST algorithm and those from carefulexperimental studies. A comparison of existing algorithmswas also made by Schossmann et al.,167 who also proposed anew model. The authors' new model was based upon earlierwork by this team at TU Vienna and the improvements made inthe new model led to more accurate ®tting of the characteristicradiation. The provision of high quality experimental data forthe testing of tube spectrum algorithms is of prime importanceand was the subject of work reported by Aiginger andcolleagues168 at the Atominstitut in Vienna. A highlycollimated Si(Li) detector was used to measure directly theenergy spectrum of X-ray tubes with chromium, molybdenum,rhodium or tungsten anodes. Data were presented for varioustube voltages and target take-off angles.

The use for matrix correction of scattered radiation remainsimportant for many FP and in¯uence correction procedures.Bao169 described a new power function that modelled thenon-linear inverse relationship between mass absorptioncoef®cients and scattered continuum radiation. The newmethod was applied to the determination of Sr in pressedpellet samples of geological materials and yielded an accuracyof 2.4% relative compared with 9.7% relative when using theconventional Compton correction procedure. A detailed MCsimulation for X-ray single and multiple scattering from bulksamples of linearly polarized photons in the energy range40±80 keV was described by Vincze and co-workers.170 Theaccuracy of the simulation was con®rmed by measurementsusing a highly monochromatized SR beam on beam line BW5at Hasylab (Hamburg, Germany). Of particular interest wasthe novel use of the Rayleigh and Compton scatter peaks toobtain 3-D information on the distribution and compositionof the sample dark matrix. A very comprehensive MCsimulation for the scattering of polarized X-rays wasdescribed by Fernandez et al.171 The validity of the newcode (MC-SHAPE) was con®rmed by good agreement of itsdata with those from deterministic calculations and experi-mental measurements.

4 X-ray optics

Although X-ray micro¯uorescence represents a relativelyspecialized form of XRF analysis, it is becoming increasinglyadopted in specialized applications because of its uniqueanalytical capabilities and the complementary nature of resultsin comparison with other microprobe techniques. The `bigscience' end of X-ray micro¯uorescence is based on thesynchrotron excitation source, applications of which are alsoreviewed in Section 5. In this section the characteristics ofoptical elements and the design and application of bothsynchrotron and laboratory scale instrumentation are con-sidered. A wide ranging review of this topic, drawing togetherdetails of micro¯uorescence, synchrotron and TXRF techni-ques, was published by Adams et al.172

4.1 Optical elements

The transmission and gain of singly and doubly focusing X-raylenses were investigated by Lengeler et al.173 These devices hadfocal lengths of 1±2 m and were capable of focusing hard X-rays to a spot size in the micrometre range. Proposedapplications included microdiffraction, micro¯uorescence andcoherent imaging. This investigation mainly consisted of astudy of the degree of small angle X-ray scattering from a rangeof low Z materials, since this phenomenon is one of the reasonswhy lens gain is not as high and the focal spot is not as small astheory. Kawata et al.174 described a new water-cooled doubly-bent crystal monochromator designed for Compton scatterexperiments on a synchrotron beamline at the Photon Factory.The device gave a focused beam of 0.562 mm2 for 60 keVphotons and was one order of magnitude higher in brightnessthan the monochromator it replaced. An overview of X-raylenses in XRF analysis was presented by Ding et al.175

Kondrashov et al.176 compared the capabilities and propertiesof an RAP crystal, a nickel±carbon multilayer and a diamond-like carbon X-ray mirror, the properties under considerationbeing the effects of temperature and radiation on re¯ectivityand resolving power. Multilayer diamond-like carbon struc-tures were found to offer stable performance up to 570 ³C.

A rather specialized imaging device based on a square-poremicrochannel plate was described by Martin et al.177 Themultichannel plate was used to relay ¯uorescent radiation ontoa 2-dimensional charge-coupled device capable of bothrecording an image and providing energy information, evenfor low-Z elements such as C, N and O. The picosecond pulsedlaser plasma X-ray source at the Rutherford±AppletonLaboratory was used as the primary source and, unlikecomparable imaging devices, the system had no moving parts.

Improvement in the detection sensitivity of EDXRF traceelement analysis by means of ef®cient X-ray focusing based onstrongly curved highly oriented pyrolytic graphite (HOPG)crystals was presented at the 1997 Denver Conference byBeckhoff and Kanngiesser.178 These co-workers also presenteda paper179 on the excitation of low Z elements by means of acylindrical graded multilayer which was used as a high energycut-off in EDXRF analysis.

In terms of other developments in instrumentation related tooptical elements, Shard et al.180 provided an analysis of theperformance of computer controlled piezoceramic electrostric-tive actuators with specially designed feedback circuits toprovide precise control of the pitch angle of crystals in adouble-mirror monochromator. Chen and Wittry181 describeda microanalysis instrument based on a small laboratory sourcefrom which radiation was monochromatized and focused usinga doubly-curved crystal diffractor. Performance of the devicetested gave a focused beam of 57643 mm2 and detection limitof 1.6 mg g21. However, partially based on predictions from raytracing models and improvements in instrumentation, probesof v10 mm diameter offering ng g21 detection limit perfor-

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mance were thought to be possible. Wittry182 also made apatent claim for a simpli®ed system for the monochromaticexcitation using a number of focusing diffractors, eachprealigned to a source of X-rays excited by an electron beam.

4.2 Micro¯uorescence

A number of applications of laboratory micro¯uorescence havebeen presented, including a paper by Wiess et al.,183 whoanalysed the ash fraction of plants and peats using an `EDminiprobe multi-element analyser'. A LiF(200) crystal wasused as the focusing device for Mo Ka radiation from aconventional X-ray tube. Dry ashing of about 1 g of materialyielded about 35 mg of ash for analysis by X-ray miniprobe andresults for the element of interest, Pb, were generally inagreement with independent ICP-MS data. Flynn andcolleagues184 analysed ®rearm discharge residues by X-raymicro¯uorescence, results being used to differentiate betweendifferent ammunition types and to estimate the shootingdistance in comparison with conventional SEM±EDX analysis.It was anticipated that this application could be extended withhigher speci®cation instrumentation, offering an X-ray tubepower of 100 W, rather than 50 W, and a beam diameter of10 mm, rather than the 100 mm that was available. Gambardellaet al.185 used X-ray micro¯uorescence as well as AAS tomeasure the accumulation of Cu and Fe in the species Idoteabaltica after exposure to these elements. Worley and Havrilla186

used m-XRF to measure the distribution of Ga2O3 in a mixedoxide fuel surrogate feed material in a CeO2 matrix. Thesedeterminations were required to evaluate the effectiveness withwhich Ga was removed during fuel processing as Ga candamage the fuel cladding. A rather specialized technique ofselected area XRF analysis was described by Hossain andLowell187 for the determination of light elements on the surfaceof silicon substrate. The sample surface was excited using amonochromatic beam optimized in energy for the elements ofinterest. The beam was obtained from a high power laboratorysource and formed using collimators, multilayer crystals and aglass capillary waveguide (q.v.) and illuminated an area on thesample from 0.5 to 10 mm in diameter.

A perennial problem for almost all forms of microanalysis isthe lack of suitable reference materials, certi®ed on a micro-scale. The problem was reviewed by Zeisler,188 who proposed aremedy in the creation of a new genre of highly homogeneousnatural matrix materials. The categories of materials consid-ered were single cell biological materials, ®nely dispersedsuspensions or precipitates derived, for example, from airparticulate matter or sediments, or by appropriate pulveriza-tion of complex matrices.

4.3 Capillary waveguides

No doubt partially stimulated by the introduction ofcommercial instrumentation as well as the development of arange of applications, X-ray micro¯uorescence using glasscapillary waveguides continues to attract a lot of interest. Anumber of publications continue to model various aspects of theX-ray transmission properties of glass capillaries. Alexandrovet al.189 investigated the `peculiarities of photon transmissionthrough capillary systems' using a numerical solution of a waveequation and offering an explanation for recently discoveredinterference effects occurring on the multiple re¯ection of X-rays. Parameters such as transmission ef®ciency and intensitygain were calculated by Sanchez and Perez190 for glasscapillaries having different geometric shapes and dimensionsas a function of photon energy. Calculations were undertakenin two dimensions for monochromatic radiation with synchro-tron-like properties (small source with low angular divergence).Refractive index is also important in affecting the transmission

properties of glass capillaries and Liang et al.191 reported datafor Cs- and Na-glass capillaries in a Chinese-language paper.

In what is likely to be an important development in theproduction of commercial instrumentation, a method offabricating tapered glass capillaries was described in a patentapplication by Hirsch.192 The method involved etching a metalor glass wire into a narrowly tapering zone with a shapematching the bore of the desired capillary optics. The wire wasthen coated either by electroplating, by being built up usingelectrodeless plating or by encapsulating in a polymer cylinderto increase the diameter for easier handling and greaterrobustness. The patent also described an apparatus whichcontrolled the rate of removal of the wire from the etching bathin order to control the shape of the taper. An equally in¯uentialcontribution was that of Bilderback and Fontes,193 whofabricated a unique computerized glass puller capable ofmaking parabolic or elliptically tapered glass capillaries fromhollow glass tubing. Two types of capillary have been made.First, capillaries designed for a single `bounce' of the X-raybeam for imaging diffraction patterns from tiny bundles ofcarbon and Kevlar ®bres. Second, capillaries designed formultiple `bounce' for condensing the X-ray beam to create sub-micrometre beams for m-XRF applications, with the aim ofachieving fg sensitivity in the determination of Er and Tbdopants diffused into an optically-active lithium niobate wafer,presumably using a synchrotron X-ray source. A new design ofmicrocapillary lens for X-rays was described by Dudchik andKolchevsky.194 Details of the fabrication of this device weregiven, based on a set of microlenses placed inside a glasscapillary.

Gao and colleagues195 described real and simulated experi-ments to evaluate the performance of tapered monocapillaries incomparison with straight (i.e., parallel bore) capillaries using alaboratory 16 W X-ray source. Intensities transmitted fromtapered capillaries with output diameters of 8 mm and 3.5 mmwere 1.4 and 1.5 times, respectively, greater than thoseobserved from parallel bore capillaries of identical outputdiameter. Tapered monocapillaries were also found to producea signi®cantly lower high energy bremsstrahlung and anincreased stability in transmitted output when the X-raysource was moved slightly. Janssens et al.196 also investigatedproperties of ellipsoidal lead-glass capillaries, in this instancefor microfocusing high energy synchrotron radiation (0±60 keV). At v30 keV, beam diameters of about 4 mm wereproduced in which the ¯ux was ten times greater than that of acollimated beam. At 40±60 keV, the focused beam diameterwas 10 mm. Detection limits for the elements Mn to Gd (Kalines) in silicate materials were 1±10 fg for a 1000 s count time.

With reference to developments in instrumentation, a desk-topcommercial instrument capable of producing a v10 mmdiameter X-ray beam using a miniature X-ray tube and anX-ray waveguide tube with a parabolic inner contour wasdescribed by Hosokawa et al.197 Samples were mounted on anx±y stage and detectors were provided to measure transmittedX-rays as well as ¯uorescence, backscatter and diffracted X-rays whilst scanning the sample. Interesting possibilities werethen described in combining images recorded using differentsignals for the comprehensive analysis of samples such asprinted circuit boards. An instrument with some similaranalytical capabilities was described by Yamamoto.198 Thisinstrument was also capable of making ¯uorescence anddiffraction measurements and incorporated a glass capillarywaveguide with a parabolic inner surface which could becoupled to a transmission target tube. The applicationdescribed in this work was the characterization of the structureof ultra-large-scale integrated circuits which incorporatedtitanium silicide components and aluminium connections ona silicon substrate. Continuing with the theme of semiconduc-tor components, Fougeres et al.199 developed a new micro-¯uorescence instrument comprising an X-ray generator

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coupled to an X-ray focusing capillary with a high resolutionCdZnTe detector (225 eV resolution FWHM at 5.9 keV). Thisinstrument was used to control the concentration of Zn and its¯uctuation in high pressure Bridgman-grown CdZnTe crystals.Features down to 100 mm across could be analysed using aninstrument described by Nicolosi200 which incorporated amicrofocus X-ray tube and capillary X-ray optics. A particularfeature of this instrument was that it was capable ofaccommodating bulky objects 250 mm in diameter and100 mm thick.

Applications of capillary m-XRF include the work ofKuczumow et al.,201 who analysed petri®ed wood usingelectron, X-ray and optical microprobes. These techniquesoffered complementary information and results indicated thatsome samples of petri®ed wood were the chemical negatives ofthe primordial living wood. XRF with a focused X-ray beambased on a glass capillary waveguide was also used byFukumoto et al.202 for the elemental mapping of biologicalsamples. Particular interest was shown in mapping changes inelemental distributions (e.g., Ca, K, Mn) in living leaves afterexposure to both high X-ray doses and arti®cial acid rain. Thecapability of glass capillary m-XRF to characterize glasssamples relevant to forensic applications has also beendescribed.203 Holynska et al.204 used an EDXRF micro¯uor-escence instrument, which incorporated a 1 mm diameter glasscapillary, to analyse air ®lters, using a special collection devicecapable of collecting air particulate material on a ®lter disc,which was progressively exposed over a period of 1 week.Performance of this m-XRF was compared with PIXE andapplied to air samples collected from Cracow, Poland.

The big brother of the glass monocapillary is the `monolithicpolycapillary' lens, usually comprising large numbers (hundredsof thousands) of capillaries bundled together but with eachbent to guide the X-ray beam to the same point of focus. Gaoet al.205 from the State University of New York evaluated sucha device using a 12 W minifocus X-ray source and obtained a21 mm focused spot (FWHM) at 17.4 keV (Mo Ka) with anintensity of 2400 times greater than that observed from the X-ray tube alone, at an equivalent distance of 100 mm. The devicewas used to analyse and map industrial samples. In a secondcontribution from the State University of New York, Hofmannand colleagues206 showed the potential of this device tomeasure diffraction patterns from small lysozyme proteincrystals. Some applications require intense parallel X-raybeams and Dozier et al.207 showed how polycapillary devicescan be designed to achieve this for use in lithography. Themanufacture, measurement of basic characteristics and appli-cations of monolithic polycapillary lenses were described byXie et al.,208 who reported a 30 mm focal spot diameter usingMo Ka radiation with a gain factor of w2000 compared withan equivalent aperture. Transition element detection limits atthe sub-pg level were reported with this device in conjunctionwith a 1 W X-ray source.

Monolithic polycapillary lenses have also found uses in SRapplications and Rath et al.209 performed measurements andcalculations to show the thermal loading effects when exposedto the white beam from a synchrotron bending magnet. After atime of 1 min, the temperature at the input end of thepolycapillary increased by up to 190 ³C. Cooling in anatmosphere of He or using an air ¯ow would substantiallyreduce this effect. The focusing properties of polycapillarydevices in synchrotron applications were considered in afurther contribution from Hofmann et al.210

5 Synchrotron radiation

5.1 Beamlines and optics

The design of a 1.5 GeV compact storage ring that uses 7 Tsuperconducting magnets was presented by Cline et al.212 The

aim of this source was to provide 10±30 keV X-rays ofmoderate brilliance for commercial biotechnological andindustrial applications. The prototype was being designed forUCLA, California. The status of the world's smallest electronstorage ring (50 MeV) for far-IR and incoherent hard X-rays(generated as bremsstrahlung photons) was reported byYamada.213 The design of a new high brilliance VUV andsoft X-ray source for the University of Tokyo was described214

and a grazing incidence re¯ectometer for an undulatorbeamline at Spring-8 intended for TXRF experiments, forexample, was presented.215

Optical components for focusing X-rays were described bySnigirev et al.,216,217 who used compound refractive lenses (ofAl, B, Be and C) for sub-micrometre focusing for energieshigher than 5 keV at ESRF. A tuneable bent Laue mono-chromator, where the ®rst crystal was plane and the second onewas bent and its angle kept constant to make the device stableagainst vibrations, was used at NSLS.218 An article in theJapanese language dealt with a beamline at the Spring-8 facilityfor high resolution XRF.219 A long-standing problem withmonochromators for synchrotron radiation is the high heatload. Two approaches with internal water cooling at wigglerstations at CHESS220 and SSRL, ESRF221 and contact coolingat an undulator insertion device at APS,222 were proved to beeffective. An aberration effect observed with bent Lauemonochromators in combination with wide fan-shaped syn-chrotron radiation X-ray beams, referred to as `beam-smiling',was described and a correction involving asymmetric bendingof focusing elements proposed.223

In a review article, Chevallier et al.224 discussed hard X-raymicrobeam production and applications. Electron microscopesrepresent the most widely used technique for microanalysis, butthe sample must be analysed under vacuum and detection limitsare not as low as is required in many applications. Therefore,high brilliance synchrotron radiation is an attractive alter-native. As an example of such an instrument, an XRFmicroprobe system was developed at Spring-8225 and incorpo-rated ED and WD detection. X-ray ¯uorescence correlationspectroscopy was presented as a method for studying particledynamics in condensed matter.226

5.2 Applications

Synchrotron based XRF microprobes have been used in thesemiconductor, ceramic and glass industries, as exempli®ed bythe report of McHugo et al.,227 who used an instrument with a1 mm spatial resolution to detect and map impurities such as Feand Cu in silicon semiconductor devices using well character-ized standard samples. A synchrotron radiation XRF micro-scope was also used to study multi-metal oxide ceramics thathad been designed to sequester radioactive actinides for long-term storage and disposal.228 The correlation of solar cellperformance with the distribution of metal impurities inpolycrystalline silicon was studied,229 as were unopenedinclusions of gas bubbles in an aluminosilicate glass matrix,using a microbeam to determine Mo, Rb and Xe.230

The continuing interest in atmospheric aerosols was shown inseveral publications, demonstrating that synchrotron excitedXRF is a well suited method for this category of sample. Byapplying principal factor analysis to elemental compositions,the origin of aerosols collected at different Siberian locationswas studied.231 Within the framework of an inter-laboratorycomparison, SRXRF analyses of aerosols collected on ®lterswere compared232 with results from other techniques (NAA,AAS, OES) and the capabilities and limitations of the SRXRFtechnique were evaluated. In a further contribution from theseauthors,233 an evaluation of the use of the SRXRF techniquewas made in assessing the anthropogenic impact of aerosols ina remote area of northern Siberia.

Turning now to biological applications, Janssens et al.234

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determined non-destructively the REE content in fossilizedbone by their K-lines with X-ray micro¯uorescence at theHasylab synchrotron laboratory in Hamburg. The results werediscussed and critically compared with those obtained by NAAand laser ablation microprobe ICP-MS. The Sr : Ca ratio in ®shotoliths can be used as an indicator of salinity changes andassist in clari®ng the migration history of the eel. Nakai et al.235

collected and analysed samples from the Tone and Elbe rivers(which ¯ow into the East China and North Seas, respectively)to evaluate contrasting migration patterns. Studies were alsoundertaken of the site-speci®c lead distribution in scales of carpwhich had been administered Pb236 and of XRS imagingcombined with histochemical staining of the renal section ofmercury-treated rats.237

Several publications concerned the analysis of geologicalsamples, one example being bottom sediments from LakeBaikal of relevance to paleoclimatic reconstruction.238 `Warm'and `cold' periods of climate could be distinguished from thecorresponding mean contents of elements. Data on some toxicelements associated with the different size fractions in thebottom sediments of Novosibirsk reservoir's tributaries werereported by Sokolovskaya et al.239 Bottom sediment sampleswere also studied by Bobrov et al.,240 this time from LakeTeletskoy; results revealed the difference between sedimentlayers associated with rhythmic layer-by-layer oscillations ofmineral compositions and grain size. Ferromanganese nodulesections from the Paci®c Ocean were statistically characterizedby scanning SRXRF to determine the element content oflayers.241 A review by ToÈroÈk et al.242 summarized the principalanalytical techniques based on ion and photon beam excitationused for geological materials. Chemical data obtained by m-SRXRF on sublimates and incrustations of volcanic gases fromFogo Island volcano (Cape Verde Archipelago) were discussedby Figueiredo,243 a particular feature of this work being thepresentation of data for Tl in well identi®ed minerals found involcanic fumarole sublimates. In highland Lunar rocks (Apollo16 and Luna 20 missions), six groups of rocks having variousaluminium and trace element contents were distinguished onthe basis of the distribution of Rb, Sr, Y, Zr and Nb.244

Janssens et al.211 described the XRF analysis of a largenumber of glass ®nds from the 15th to 17th centuries resultingfrom excavations in the centre of Antwerp. Samples wereanalysed by EPMA and m-SRXRF and could be classi®ed into4 major compositional types; the implications of these ®ndingswere discussed.

6 Total re¯ection XRF spectrometry

During the current review period a review article was publishedby Stoev et al.,245 covering grazing incidence X-ray spectro-metry and re¯ectometry. This article gave an overview of recentadvances since 1993 on the application to surface and thin ®lmanalysis, both from theoretical and experimental aspects, with482 references cited. Also, combinations of different grazingincidence techniques were mentioned and their advantages forsurface and interface analysis. Furthermore, the 7th Conferenceon TXRF and Related Techniques took place during the reviewperiod in Austin, Texas. A variety of new developments andapplications were presented, mainly dealing with semiconduc-tor applications, some contributions being mentioned here.

6.1 Instrumentation and quanti®cation

The TXRF group at GKSS published details of the optimiza-tion of curved X-ray multilayer mirrors for TXRF.246 Variousoptical con®gurations combining focusing and monochroma-tization were modelled and system parameters such as mirrorshape, size of X-ray source, angular divergence and shape ofmultilayer were varied and the in¯uence of these designparameters on detection limits studied. Results depended on

the excitation energy and distance from anode source tosample.

Wegrzynek et al.247 compared the performance of afundamental parameter method for the quanti®cation of traceelements from TXRF spectrum evaluation with an empiricalquanti®cation procedure. The ®rst method was reported tooffer advantages, especially for complex matrices with spectracontaining strongly interfering peaks.

Hossain et al.248 claimed a patent on an apparatus andmethod for characterizing particles embedded within a thin ®lmon an underlying semiconductor wafer. For excitation, aradioisotope source was used, the emitted X-rays impingingupon the sample surface at near grazing angles. The identityand quantity of elements in the thin ®lm were determined. Thisis the ®rst time that a radioisotope source has been used forTXRF, because generally a high brilliance source is required toobtain a reasonable photon ¯ux with a suf®ciently smalldivergence for total re¯ection.

The TXRF design group at the Ministry of Geology andMineral Resources, Beijing, published a paper on thedevelopment of a high sensitivity TXRF spectrometer249 andapplied it to the analysis of trace elements in natural water.250

Also, the group at Yantai University, China,251 developed aTXRF spectrometer with detection limits in the pg range.

The Atominstitut group in Vienna published an overview ofsources, samples and detectors,252 as well as a paper dealingwith the excitation of low Z elements in TXRF.253 In this latterwork, a windowless X-ray tube with optimized anodecon®guration and target material (Al, Si) achieved detectionlimits of 15 pg for Na. Light elements were also analysed byTXRF by Fukuda et al.,254 using a special spectrometer.

6.2 Synchrotron radiation-induced TXRF

The ®rst SR-TXRF experiments performed at ESRF ID32 weredescribed by Ortega et al.255 using an undulator beamline.Detection limits of 17 fg or 1.86108 atoms cm22 were achievedusing a Si(111) double crystal monochromator and measure-ments were applied to the impurity analysis of Si wafersurfaces. The authors estimated that it would be possible toreduce the detection limits by a factor of 25 by employingoptimized optics and detectors. Comin256 also presented at theTXRF conference in Austin future plans for an industrialfacility for mapping the distribution of trace impurities on300 mm silicon wafers. The elements to be detected shouldrange from Na to Hg with routine detection limits of108 atoms cm22.

An update on SR-TXRF was given by Brennan et al.257

concerning the already established routine SR-TXRF beamlineat SSRL, with a supplementary presentation by Pianetta258 atthe TXRF conference. Detection limits of 36108 atoms cm22

were reported for this facility. Improvements were planned bythe use of high count rate electronics and an upgrade of thestorage ring to SPEAR 3.

Soo et al.259 investigated the heterojunction interface of solarcells and reported measurements of interfacial roughness,interface height ¯uctuations, the effects of heat treatment andthe diffusion of Te atoms. These measurements were made bygrazing incidence X-ray scattering and the angular dependenceof ¯uorescence radiation using synchrotron radiation.

Wu et al.,260 from the Chinese Academy of Science,published details of SR-TXRF experiments and the applicationto preliminary study of several kinds of biological materials(including pig liver and mouse intestine cells),261 unfortunatelyonly in Chinese.

6.3 Surface analysis

Hockett262 presented a review article on the current activities ofStandards Organisations working in the ®eld of surface

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analysis using TXRF. In another review, De Gendt et al.263

presented results from the European round-robin assessment ofcalibration accuracy of TXRF in the analysis of contaminatedwafers. A second round-robin assessed vapour phase deposi-tion±droplet collection TXRF techniques, both series ofexperiments involved the participation of 7 facilities (includingindustry, research and universities). The vapour phase decom-position (VPD) technique coupled with TXRF was alsodescribed as a standard method for the online inspection ofsurface contamination on silicon wafers in the semiconductorindustry264 and a modular system for the fully automated VPDpreparation and scanning of 300 mm wafers was described.265

Depth pro®ling of cobalt-implanted silicon wafers wastackled by a new approach by KlockenkaÈmper and vonBohlen,266 where a square section of some cm2 on the wafer wasoxidized and precisely etched by HF. The mass of Si in the layerwas determined by differential weighing and the Co content inthe solution measured by TXRF. By repetition of these steps,the depth pro®le could be reconstructed. In anotherapproach,267 depth pro®les were obtained for cobalt-titaniumsilicide ®lms by a combination of ex-situ low energy ion beametching with TXRF. The micro-roughness of polymer thin®lms supported on nickel-coated silicon substrates was studiedby TXRF and atomic force microscopy.268

Shallow impurity depth pro®les for As implanted into siliconwere established by TXRF and compared to ToF-SIMS bySchwenke et al.269 The authors concluded that SIMS andTXRF provided complementary information. TXRF was usedto verify independently the implant doses on a series ofreference samples which were used to quantify ToF-SIMSresults in the analysis of metal contaminants on UV ozonizedGaAs wafer surfaces.270 A comparative study of the As and Inimplant dose in silicon employed TXRF, SIMS and ToF-SIMS271 and claimed a strong correlation between SIMS andTXRF data.

6.4 Related techniques

Grazing emission XRF (GEXRF) with 90 degrees incidence anda shallow angle of detection is an alternative to TXRF for thesurface characterization of certain samples. Detection ispossible with WD methods with consequent bene®ts in thedetermination of the light element. Typical applications,including the determination of light element contaminationon Si and the characterization of TiN and TaN thin layers,were presented by de Bokx et al.272 and Wiener et al.273 For theanalysis of trace elements in drinking water the performance ofthis method and also TXRF were compared with otheranalytical techniques.274 For this study a natural mineralwater was selected, and TXRF was claimed to be suited for thedirect analysis of heavy elements. GEXRF was successfullyapplied to the determination of the low Z elements but resultsfor Mg and Na were systematically low.

6.5 Applications

A survey of sampling techniques for solids suitable for TXRFanalysis was presented by KlockenkaÈmper et al.275 Severaltechniques for solid sampling were investigated and oneexample of each technique was reported, including the directplacing of individual particles, suspensions of powderedmaterial, collection of air dust by impaction, the touchstonetechnique for metals, laser ablation for local analysis, Q-tiptechniques for paintings and inks, freeze-cutting for organicmaterial and direct contamination control of wafers.

A comparison of ICP-MS with a microconcentric nebulizerand TXRF for the analysis of small liquid volume samples wasperformed by Lofthouse et al.276 TXRF was considered to offerthe potential of fast effective screening using only 10 ml ofsolution, and digestion was required prior to the analysis of

polymer samples. ICP-MS offered better detection limits for awide range of elements but at least 90 ml of sample wererequired and digestion was essential.

Turning now to the TXRF analysis of environmental samples,Zaray et al.277 published a survey on trace element determina-tion in organic environmental matter using TXRF, includingthe analysis of xylem sap, mussel and algae biomonitoring, andairborne dust analysis.

TXRF was applied to the analysis of aerosol samples andcompared with other analytical techniques by Ortner et al.278

Neuhauser et al.279 presented results at the 25th AnnualConference of the Federation of Analytical Chemistry andSpectroscopy Societies of on-line monitoring of heavy metals inaerosols which was calibrated with TXRF.

Pettersson280 investigated marine periphyton algae commu-nities by TXRF. Algae were directly grown on ¯oat glass,which was used as a sample re¯ector, without samplepreparation. The method was evaluated by the analysis ofcerti®ed plankton reference materials and by comparativeanalysis of samples using a wet digestion method. In acompanion paper, Pettersson and Olsson281 used a digestionmethod based on nitric acid and hydrogen peroxide, to preparealgae as well as plankton prior to TXRF analysis. Freshwateralgae were also investigated by Varga and colleagues,282,283

who compared the TXRF analysis of slurry samples preparedby soni®cation after freeze drying with solution samplesprepared by vapour phase microwave digestion. Goodagreement was reported between both techniques and it wasconcluded that slurry preparation was suitable for TXRFanalysis.

Experiences in routine food control were presented byZahlbruckner et al.,284 who used TXRF to determine Ag,Cd, Cu, Fe, Pb, Sr and Zn in water. Chinese tea wasinvestigated by Xie et al.285±287 by analysing both digested tealeaves and tea infusions. The main element of interest was Se;the content in the tea leaves ranged from 48 to 570 ng g21 andthe extractable portion from 15 to 27%.

TXRF is also widely used in medical and biologicalapplications. Indeed, TXRF and PIXE were compared forthe analysis of human amniotic ¯uid by Liendo et al.288 toestablish correlations between concentrations of certainelements and fetal malformations. An analytical methodologyfor the analysis of blood plasma was developed by Savage andHaswell,289 where chemical modi®ers were used to compensatefor analyte loss or sample modi®cation during the drying andmatrix decomposition stages. The concentration of trace andnon-trace elements in Mammalian cultured cells was investi-gated using TXRF by Gonzalez et al.290 Results could be usedto evaluate variations in response to modi®ed concentrations inthe extracellular medium. An elemental correlation study incancerous breast tissue was performed by Majerska et al.,291

who observed an inhibition of enzyme activity caused byvariations of trace element concentrations at the clinical stageof cancer.

In the ®eld of industrial applications, TXRF was used for theanalysis of radioactive water from a condensed nuclear reactorby Trabuc et al.;292 provided the activity was less than 7000 Bq(alpha emitters) or 107 Bq (beta/gamma emitters), measure-ments could be undertaken in non-controlled areas. Ferri-electric ®lms of complex oxides were investigated byKrasnolutskii et al.,293 who reported detection limits of10212±10210 g cm22 in comparison with 1028±1026 g cm22

by standard XRF.The application of TXRF to cultural and heritage samples

includes the non-destructive discrimination between elephantivory products and mammoth tusk products, which wasperformed using glancing incidence XRF.294 Results suggestedthat the integrated intensity ratios of Sr Ka/Ca Ka and BrKa/P Ka were valuable in discriminating between these twoproducts. Pigments of a late-mediaeval manuscript were

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investigated by TXRF and micro-Raman spectroscopy byVandenabeele et al.295 as well as Van Hooydonk.296 Aquantitative and qualitative reconstruction of pigments usedin the artists' palettes was possible using data from bothtechniques with the possibility of distinguishing differentminiaturists who worked on the manuscript.

7 Portable XRF

When reviewing this year's reports, it is relevant to note thatthere is a blurring of the distinction between in situ PXRF,which involves direct measurement with the analyser placedagainst the sample, in comparison with in situ in the sense ofmobile laboratory applications, where the PXRF instrument istaken to the site, but where test portions are removed foranalysis after some sample preparation. In archaeologicalapplications the former is the only real option, but inapplications such as the determination of heavy metals in soil,the latter mode of operation is becoming equally popular.Indeed the analysis of contaminated soil is one of the classicalPXRF applications and is illustrated by the work of Rammleret al.,297 who compared three different models of PXRF tomonitor and detect pollutants in waste deposits and pollutedsoil. Muller and Pelzer298 used a mobile XRF spectrometer toanalyse dredged materials. Spittler299 described the use of aportable XRF analyser to analyse lead and other toxic heavymetals in soil contaminated by mining and metallurgicalactivities in the Urals region of Russia. This survey wascomplemented by gas chromatography measurements on waterand soil to determine volatile organic compound residuesresulting from spills and leaks. The use of PXRF was describedby Schneider,300 again as a ®eld screening tool for thedetermination of lead and heavy metals in polluted soil. Itwas reported that PXRF results did not correlate perfectly withAAS data. Interest continued in the use of PXRF incharacterizing contamination at former ®ring ranges (Hender-sen et al.301). In the support of ®eld remediation operations,Waligora302 used PXRF to monitor the removal of chromiumcontaminated soil at a hazardous waste site. Samples wereprepared and analysed in an on-site laboratory and data wereused to con®rm that clean-up had been achieved, as well as todetermine the average Cr content of a stockpile of excavatedsoil. Independent analysis of 32 test samples gave a linearcorrelation coef®cient of 0.985 compared with the XRFtechnique, a comparison in which PXRF presumably bene®tedfrom the homogenization of the sample at the preparationstage.

The cone penetrometer is a rather more specialized device forevaluating heavy metal contaminants in soil and the pre-liminary design considerations of such a device, incorporating aminiature X-ray tube and detector, were presented by Elamand Gilfrich.303 Further details of the analytical performanceof this device, called by the authors SCAPS (site characteriza-tion and analysis penetrometer system), were described byElam et al.,304,305 including reference to the characterization ofPb within a military establishment.

A comparison between XRF data and independent methods ofanalysis was reported by Shefsky,306 who evaluated theeffectiveness of ®eld screening by XRF under a variety ofdifferent site conditions and found, not unexpectedly, thatdrying, grinding, sieving and homogenizing signi®cantlyimproved the quality of data. It was further claimed that insome instances, de®ciencies in ®eld methods can be erroneouslycaused by bias introduced when a sample is split and handled toprovide a test portion for independent laboratory analysis.

Metals in marine sediments were determined by Kirtayet al.307,308 using PXRF and a manufacturer-supplied funda-mental parameter application which was apparently used tocorrect for particle size effects. Cu, Pb and Zn were measured

on samples that were homogenized and analysed wet and alinear correlation was observed with data obtained by astandard method, although PXRF underestimated the truecomposition, an effect that could have arisen because ofdiscrepancies related to the moisture content.

Another classical application of PXRF is in the determina-tion of lead in paint and Afshari et al.309 described a newinstrument designed to overcome many of the limitations ofearlier instruments. Particular features of this dedicated hand-held instrument included optimization of excitation geometryand a mathematical approach which incorporated correctionsfor both systematic errors such as matrix effects and Comptonscatter. In a second contribution, Afshari et al.310 describedfurther aspects of the instrument, which incorporated a 10 mCi57Co source and a CdTe detector. Derbin et al.,311 in a Russianlanguage contribution, also described a PXRF instrument forthe determination of lead in paint: detection limits of from 0.01to 0.1% were reported when elements with Zw50 weremeasured for 15 s.

Archaeological applications is another important area forPXRF and Gigante and Cesareo312 continued their manycontributions in this area by describing the analysis of ancientmetal alloys using an instrument ®tted with an air-cooledminiature X-ray tube and a high resolution semiconductordetector. A new portable XRF instrument designed for non-destructive analysis of archaeological samples was described byLongoni et al.313 This instrument was based on a Peltier-cooledSi drift detector (offering a resolution of better than 160 eV at5.9 keV for a shaping time of 2 ms) and a miniature X-raydetector and was used for the analysis of paintings of differentages and for metal alloys.

Innovative PXRF applications are also possible in the analysisof air and liquids, the former being demonstrated by the workof Kienbusch et al.314 in the analysis of Pb in high volume air®lters in the ®eld. The speci®c application concerned sandblasting of steel structures and the consequent possibility ofairborne dust containing lead paint. Correlation of XRFresults with ICP-AES data indicated that it was feasible to usePXRF instrumentation to provide relatively accurate airquality measurements for Pb. In relation to the analysis ofliquids, Allen et al.315 described a ®lter device designed for theselective extraction of heavy metals down to ng ml21 levels.Extraction ef®ciency was claimed to be 85±95% and thedetection limit in the determination of Pb in drinking waterusing a 500 ml sample were 8 ng ml21. Piorek316,317 alsodescribed the application of a ®eld portable instrumentdesigned for the determination of hazardous metals incontaminated soil for the analysis of liquid hazardous waste,described as a mixture of solids suspended in a liquid medium.With minimal sample preparation, detection limits of 10±20 mg kg21 could be achieved in liquid hazardous wastes.

All of these applications would not be possible withoutcorresponding developments in instrumentation. Warburtonet al.318,319 described a possible extension of `XIA' digitalspectrometer technology to XRF devices for portable andremote applications, including a lead paint detector, a remotecontamination monitor and a space mission spectrometer. Theparticular features of this technology were a very high countrate capability (w50 000 cps), low power consumption anddigital signal processing technology, all originally developedfor multi-detector arrays for use in SR applications. Whenconsidering space mission applications, Sarrazin et al.320

described a miniature XRD±XRF instrument designed forthe in situ characterization of Martian soils and rocks. Theinstrument incorporated a single CCD detector which wasexposed directly to X-rays diffracted and ¯uoresced off thesample. Another combined XRD±XRF instrument, claimed tobe the ®rst capable of making measurements in real time, wasdescribed by Paglietti and Plescia.321 This instrument used thesame miniature detector as was installed on the NASA

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Path®nder mission and X-ray `microtubes' and was capable ofthe chemical and mineralogical characterization of varioustypes of sample. Russell and Feldmann322 described the use ofthe `Joule±Thompson' type cooled detector for ®eld transpor-table XRF analysis of heavy metals in contaminated soil. In aJapanese language contribution, Hirai et al.323 described arelatively conventional PXRF instrument incorporating a SiPIN diode and miniature X-ray tube but with a cylindricalcrystal to monochromatize and ®nely focus the primary X-raybeam, yielding advantages in the reduction of the scattered X-ray background. Finally, although designed for in situ radio-isotope detection, there is some interest in the work of Helmeret al.,324 who compared the performance and ef®ciencies ofthree types of photon detector, an N-type, thin windowgermanium semiconductor detector, a plastic scintillator andan array of six CaF2 detectors. Of particular interest was thecapability of the latter two detector systems to transfermeasurements by telemetry to provide operators with a real-time mapping capability. More details of the Ge detectorsystem were given by Gehrke et al.325

A further prerequisite, if quantitative determinations are tobe achieved by PXRF, is an adequate correction model if solidsamples with irregular surfaces are to be analysed successfully.Liangquan et al.326 addressed this issue in the analysis of rocksby examining the effect of variations in sample analysisdistance, the peak to valley amplitude of the sample surface andthe frequency of concave and convex surfaces. These workersdescribe a correction based on the ratios of the intensities of thecharacteristic-to-scattered radiation, an approach similar tothat proposed by Potts et al.327

8 On-line XRF

A pleasing array of publications is available for this yearsreview, in contrast to the relatively spartan collection inprevious years. Cement has been the subject of discussion byPedersen and Finney,328,329 who described a new commercialon-stream cement raw mix XRF analyser incorporating awindowless powder ¯ow cell. This instrument was claimed tooffer increased accuracy and reliability, particularly in thedetermination of the light elements, Al and Si, avoiding errorsassociated with abrasion and cross-contamination effectsshown by instruments ®tted with conventional ¯ow cells, andpermitting determinations to be made with a 4±5 min cycletime. Whilst talking of ¯ow cells, Miyoshi330 claimed a patentfor a new design.

XRF was also used for the on-line control of a La and Ndextraction process by Li et al.,331 and Casarci et al.332

Instrumentation comprised an 241Am excitation source and ahyperpure germanium detector, which was used to measure theLa Ka and Nd Kb lines to determine these elements in theraf®nate solution from a 16 stage counter-current extractionprocess. Connolly et al.333 described an on-line system for apulverized coal feed line. Pulverized coal travelling along thefeed line was collected in a recessed chamber, resting againstthe X-ray transparent window of the XRF analyser. Afteranalysis, pressurized air blew the accumulated sample backonto the feed line, permitting another sample to be collected.Ringo et al.334 described a different sort of on-line application±instrumentation in which XRF was used as a detector forcapillary electrophoresis. A polyethylene sample cell wasinserted between the fused silica capillary segments to permitcontinuous XRF detection with minimum band broadeningand permitting detection down to 1024 mol l21 of metalcomplexes. Potential applications, particularly with advancesin design that would improve detection limits by one to twoorders of magnitude, were in the ®eld of environmental andbiological analysis. XRF was also reviewed by Shacham-Diamand et al.335 for the on-line analysis of ultra-thin barrier

layers in ULSI applications. This review included theprinciples, system requirements and applications for allforms of X-ray metrology for the determination of composi-tion, crystallographic structure and surface roughness. Aparticular consideration in this application was the need tolimit radiation dose to prevent damage to the semiconductordevice and it was concluded that both high-speed and damage-free XRF metrology is possible. In another demandingapplication for XRF, Connolly and Walker336 described acommercial product designed for the on-line monitoring ofmetals at sub-ng g21 concentrations in waters. The capabilitiesof this instrument, which incorporates a preconcentrationmechanism, were described.

9 Applications

9.1 Sample preparation

Practitioners new to XRF may bene®t from the advice of thosewho have worked and developed successful applications over theyears by consulting papers 338±341 that appeared in a reviewedited by Buhrke et al.337 entitled `A practical guide for the prep-aration of specimens for XRF and XRD analysis', containingcontributions describing all aspects of this topic. Blank andEksperiandova342 also offered a review of what they consideredto be the most suitable preparation procedures published inthe period 1987±1996. Allen343 evaluated the comminutingef®ciency of Syalon 101 (an Al±Si±oxynitride alloy) for thepreparation of geological samples. A system for the automaticpreparation of pressed powders of heavy mineral sands usingan industrial robot was described by Louw and Pedersen.344

A paper by Malmqvist345 described a semi-low dilutionfusion method for oxides and sul®des. Originally intended forXRF applications, the method was also offered for the pre-treatment of samples for ICP-AES and AAS. Samples withsulfur concentrations of up to 50% m/m were quantitativelyconverted into sulfate and analysed with an accuracy of about2%. An algorithm was presented which allowed loss-on-fusion,oxygen content of the non-oxidized components in the sampleand also the ratio of FeII to FeIII to be calculated. Shannon346

discussed fusion techniques and the use of alpha coef®cients forthe analysis of heavy minerals and associated samples.Claisse347 reminded us of the selection criteria for optimizingthe composition of lithium borate ¯uxes for bead preparation.Many readers will sympathize with Merkle and colleagues,348

whose platinum ware reached an untimely end whilst attempt-ing to prepare a bead from SiC after pre-oxidation at 1000 ³C.

Concerning the analysis of liquids, Nielson et al.349 offered anorder of magnitude improvement in detection limits for traceelements in water by using a new sample support for retainingdrops of sample solution in one place and allowing the solutionto dry into a single spot. Wolska and Vrebos350 also describedthe dimpling technique. MeneÁndez-Alonso et al.351 describedthe direct determination of trace metals in bio-environmentalsamples by retention with ion-exchange resins. Eksperiandovaet al.352,353 proposed methods for making organic glassy andquasi-solid specimens by the introduction of a saccharosethickening agent into aqueous concentrates.

Patent claims devoted to sample preparation during thisreview period included Echi354 who described, in a Japaneselanguage claim, a technique for the rapid detection of elementssuch as As, Hg, K and Na in food oils. In a German languagepatent, Neelmeijer et al.355 claimed a technique for metal saltcomponents mounted on a support for use as a secondarymulti-element standard.

9.2 Preconcentration techniques

Carvalho et al.356 described a sensitive method based on thepreconcentration of uranium on powdered foam for the

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determination at ng g21 levels in aqueous samples. Theinterference levels of various ions and ligands were studiedto develop optimum conditions for U in reference materials,waste water, mine drainage and sea-waters. Eksperiandova andcolleagues at the National Academy of Science of Ukraine357

offered methods for the determination of small quantities ofheavy metals in water-soluble salts and natural water. Necemerand Kump358 described a new approach for the radiochemicalseparation of 55Fe in waste waters from the KrsÏko nuclearpower plant. The radionuclides were preconcentrated withammonium pyrrolidinedithiocarbamate (APDC) and sepa-rated by ®ltration through a cellulose nitrate ®lter prior toanalysis. Correjo-Ponce et al.359 proposed a liquid±solidextraction procedure to assist in the determination of Nd,Pr, Sm and Y mixtures using silica gel loaded with 1-(2-pyridylazo)-2-naphthol (PAN).

9.3 Geological

As has been remarked in previous annual reviews, XRF hasbecome one of the standard techniques used for the routineanalysis of geological samples, a theme continued byPotts,360,361 who showed that XRF and ICP-MS was thecombination of techniques most widely adopted for routinegeochemical analysis, although arguing that microprobetechniques were most likely to have a more signi®cantimpact on advances in geochemistry in future years. The roleand capabilities of EDXRF were reviewed by Bacso et al.362

The widespread use of WDXRF in the routine analysis ofrocks is not, as might be expected, illustrated by a large numberof reports published within the reviewing period, since themethod is now well established and few innovations arepossible using normal laboratory instrumentation. However,Borkhodoev363 reported on the XRF determination of Nb, Rb,Sr, Y and Zr in rocks to 2±3 mg g21 detection limits.

By contrast, more work has appeared describing the use ofradioisotope XRF in geological applications. Puri et al.364

reported the analysis of polymetallic nodules from the CentralIndian Basin using 55Fe and 109Cd excitation sources. Sampleswere diluted with cellulose nitrate before being compressed aspowder pellets to reduce matrix effects, although this is notnormally necessary in routine silicate rock analysis. Angeyoet al.365 used starch as a binder for rocks from Kenya, beforepreparing powder pellets for XRF analysis using a 109Cdsource. Devan et al.31 described an arrangement, again basedon 109Cd excitation, used for the analysis of thin polished slicesof ®ve rocks and three ores and ®ve air particulates.

Reports on the analysis of sediments also featured this year.Majchrak and Pencakova367 described EDXRF in thisapplication (stream sediments), as did Somogyi et al.,368 whoemployed a radioisotope instrument unusually incorporating a125I source. In the latter work, a detailed comparison wasundertaken against replicate determinations by ICP-AES withgood agreement for Mn, Sr and Zn but disagreement in Fe andZr data, elements that are normally well-characterized insedimentary samples. INAA was used as a complementarytechnique to XRF by Bounakhla et al.369 in the analysis ofMoroccan marine sediments in a project designed to under-stand the mechanisms of sediment transport from coast to seaand assess coastal pollution. A more sophisticated analyticalprotocol was described by Janssen et al.,370 speci®cally an XRFscanner designed for the semi-quantitative analysis of splitsediment cores. This instrumentation was designed for ship-board operation and produced counts for the elements betweenK and Sr in the Periodic Table. A time of less than 1 h wasrequired to scan a 1 m core section at 2 cm intervals (aresolution of 1 mm was possible), although further develop-ments were planned to improve the calibration procedure andextend the elemental range.

Arguably one of the most important geological applications

during the current review period was that of Rieder et al.,371

who presented analytical results for the composition of Martiansoil and rock. These data were obtained from the alpha-protonX-ray spectrometer carried on the rover of the Mars Path®ndermission. The rocks had unexpectedly high Si and K contentsbut low Mg, in comparison with Martian soil and meteorites,and were similar to terrestrial andesites.

Sul®des are not the easiest sample type to analyse by XRFbecause sample preparation and matrix effects can beproblematic. However, Mihajlovic and Sta®lov372 determinedTl down to the 0.016% m/m level (0.006% m/m using themethod of standard additions). To prepare glass disks, samples(0.5 g) were mixed with KNO3 (0.5 g) and fused with 10 g ofLi2B4O7 at 1100 ³C for 15 min in a Pt±5% Au crucible.

Other studies included the work of Adams and Allen,373 whodescribed an automated wavelength selection method com-bined with a calibration procedure incorporating partial leastsquares regression and applied this method to the analysis of 25geological reference materials. XRF also contributed toreference material characterization studies of Chinese Paci®cOcean polymetallic nodules and sediments374 and also of fournatural soil reference materials.375 Of signi®cant interest, twoconference reports376,377 described the merit of bulk XRFmeasurements combined with laser ablation ICP-AES/MS onthe same glass disk, possibly anticipating full publications ofnovel applications in next year's review.

9.4 Environmental

The performance of EDXRF as a versatile analytical tool forenvironmental studies was tested in an inter-analytical-methodcomparison with ICP-MS and GF-AAS in the analysis of seveninternational biological reference materials by Nguyen et al.378

The same authors379 also published a report on the determina-tion of Hg in environmental samples using EDXRF and CV-AAS and found good agreement between these two methods.

XRF continues to be a valuable analytical method for theanalysis of aerosols and air particle pollution. Braga Marcaz-zan380 investigated particulate pollution within the frameworkof a large research programme on air quality in northern Italy.Sampling campaigns were carried out in different areas in thePo Valley and concentration and composition trends in spaceand time determined as well as main sources of pollution. Themain components were found to be crustal elements and sulfurcompounds. The investigations were performed with EDXRFand PIXE and both techniques turned out to be of greatadvantage. A similar study was undertaken in Chile toinvestigate the chemical characterization and source identi®ca-tion of airborne particulate matter. This study was carried outby Cortes381 under the auspices of IAEA (International AtomicEnergy Agency) and showed that several signi®cant correla-tions were found between a number of elements (As, Cu and S)and also between the mass of the ®ne fraction and blackcarbon, indicating possible sources, including a possiblecontribution from copper smelters. In Sao Paulo, Brazil, oneof the worst air polluted cities, aerosol characterization studieswere performed to develop a database on which a controlstrategy could be developed.382 Particulate matter in theatmosphere was studied in another Brazilian town, Natal, andfound to be less than in Rio de Janeiro and Sao Paulo.383

Nejedly et al.384 presented a report about an inter-laboratorycomparison of air particulate monitoring data using ionchromatography, PIXE and XRF. The results of an inter-laboratory comparison in the multi-element characterization ofthe atmospheric aerosols was published by Shuvayeva et al.385

using different analytical techniques, including INAA, syn-chrotron radiation excited XRF, AAS and AES. Talebi et al.386

from Esfahan, Iran, determined the lead associated withairborne particulate matter by FAAS and WDXRF, showedgood agreement and pointed out the advantages of WDXRF

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which required no time-consuming sample preparation or theuse of environmentally hazardous solvents. Kallithrakas-Kontos and colleagues387 analysed trace elements and theradioactivity in aerosol particles collected near Greek lignitepower plants. The monitoring of urban air pollution withEDXRF was performed by Bandhu et al.388 in Chandigarh,India, soil dust, refuse burning, ®eld burning, automobileexhaust and smelter activity being identi®ed as possiblesources.

A further important topic for environmental studies withXRF is the ®eld of water analysis. Ranaweera et al.389 appliedXRF to the assessment of pollution by heavy metals of LunawaLagoon, Sri Lanka, and the potential of some native plantspecies to remove heavy metals from the waste waters.Eichhornia crassipes was found to be the most ef®cient of thespecies tested in the uptake of As, Cd, Cu, Fe, Pb, Mn, Ni andZn. The heavy metal content of river water in the Jakarta areaof Indonesia was investigated by Surtipanti et al.390 afterpreconcentration with ammonium pyrrolidine diethyldithio-carbamate. Polukhina and colleagues391 published the resultsof the determination of heavy metals in water, suspendedmatter, zooplankton, zoobenthos and bottom sediments ofNovosibirsk reservoir by SR-XRF and AAS. The elementalcomposition of drinking water supplies in three states ofSoutheastern Nigeria was investigated by Nkono et al.392 Theyfound that the Hg value in public tap water violated the WHOlimits of 1 ng g21.

Heavy metal assessment in the sediments of the Ave RiverBasin was performed by Araujo et al.393 Somogyi et al.394

investigated the speciation of elements in lake sediments byXRF and ICP-AES. The feasibility of several EDXRFquanti®cation methods for the multi-element analysis ofmarine biological and sediment samples from CienfuegosBay, Cuba, was studied by Alvarez and colleagues.395 Acomparison of trace element concentrations in Asian clams andsediment from the Concho River, Texas, was performed byWebb et al.396 Johnson et al.397 studied contaminated soilsamples from 2 industrial sites. Rusell et al.398 analysedhazardous liquid waste for Cd and Cl with EDXRF aftermixing the sample with a `matrix-modifying' powder.

It was shown that XRF is a suitable method forbiomonitoring studies. Cahill et al.399 determined elementalconcentrations in feathers using XRF and PIXE. Morespeci®cally, the geographical differences between two popula-tions of brown pelicans were determined as well as the Hgcontamination in birds at Clear Lake, CA. Rautio et al.400

published element concentrations in Scots pine needles onradial transects across a subarctic area. The effect of theemissions from smelters could be assessed in an area within100 km from the source.

XRF was used as a tool for paleoenvironmental investigationsby Holynska et al.401 who characterized peat cores fromsouthern Poland by various XRF techniques after dating withthe naturally occurring isotope 210Pb. Strong time dependentvariations in concentrations of several trace elements weredetermined, and high concentrations of Pb and Zn indicated ananthropogenic origin.

9.5 Archaeological and forensic

Although a relatively specialized ®eld, the non-destructiveanalytical capabilities of XRF continue to make an importantcontribution in the analysis of archaeological and forensicsamples. The analysis of pottery, ceramic and porcelain is a casein point. Majolica ceramics from six provenances in Europewere analysed by LaBrecque et al.402 using a simple radio-isotope XRF instrument involving count times of 1000 s.These ceramics had previously been classi®ed stylistically, andby thermoluminescence and geographic origin, but theinvestigators used XRF determinations of Pb, Rb, Sr and

Zr and principal components analysis to con®rm theirprovenance. Conclusions were more consistent when Pbdata were omitted from the principal components analysis,probably because clay matrices may have been contaminatedwhen the Pb±Sn enamel was removed. Yu and Miao403 usedEDXRF to study the surface of 66 samples of Chineseporcelain for 13 elements. Principal components analysis wasundertaken on these data to study the clustering behaviour ofdata and discriminant analysis used to distinguish the periodand origin of the porcelains. Blue and white porcelain wasanalysed by Yu and Miao,404 using EDXRF to determineelements such as Mn and Co, which were characteristic of thecolorant. However, based on critical penetration depths,determinations of Rb, Sr, Y and Zr can originate from thebody of the porcelain so that the EDXRF technique is capableof providing data about the glaze, colorant and body for use inattributing samples to different periods and localities. Leunget al.405 used EDXRF to study ancient porcelain bodies from anewly discovered kiln site in China (Linjiang, Jiangxi) andconcluded that trace element measurement had considerablepotential for sensitive discrimination. Although not strictly anarchaeological application, Somogyi et al.406 investigated thedissolution of lead from the surface layer of glazed terracottapottery vessels using EDXRF and ICP-AES techniques. Theaim of this work was to measure the kinematics of lead releasefrom the pottery glaze by varying the pH and temperature ofthe liquid medium. Although affected by various parameters,the highest lead content was 500 mg ml21 after a 5000 minleach with dilute citric acid, a concentration that is of concernfor domestic use.

The authentication of paintings is another regular archae-ological application of XRF and Newman407 discussed the roleof X-ray radiography, X-ray diffraction and X-ray ¯uorescencein this ®eld (including paintings, sculptures and other objects ofart). In another authentication application, Diana et al.408

employed XRF to distinguish genuine works of the painterCaravaggio from replicas and copies from the 17th century.

XRF has also been used in a number of other archaeologicalapplications. Milazzo and Cicardi409 reported the analysis ofmetal alloys from the Corona Ferrea (Iron Crown) of Monzaas well as associated glasses and enamels, drawing attention tothe problem of quantifying measurements from irregularlyshaped objects by XRF. In a Chinese contribution, Maoet al.410 measured Cu, Fe, Pb, Sn and Zn in ancient Chinesebronzes using a dissolution technique in which a portion of thesample solution was spotted onto a ®lter-paper. In aninteresting application Torfs et al.411 investigated decayphenomena on the stonework of the Cathedral of Bari, Italy,using various analytical techniques, including EDXRF. Insidethe cathedral, weathering of stone appeared to be mainlyassociated with marine salts, whereas outside, deteriorationwas mainly related to pollution effects. Ancient Celtic glassesfound in excavation sites in Poland were analysed byBraziewicz et al.,412 who suggested that the measured ratioof Co to Mn may have some chronological signi®cance. Incontrast, Dietrich et al.413 analysed historical (17th century)ferrous ore and slag from the Sternmuehlenthal valley nearChemnitz, Germany, by several complementary techniques,including EDXRF, and found that the iron ore was processedlocally.

Goldmann et al.414 followed a popular forensic application inthe XRF analysis of glass fragments for classi®cation anddiscrimination. Micro-XRF has an important role to play inthis work. Rendle and Taylor415 discussed EDXRF methodsfor the determination of heavy elements in toxicologicalsamples including foodstuffs and urine samples. Finally, inthis section, Hida and Mitsui416 described the application ofmultivariate analysis to forensic science samples, including theclassi®cation of counterfeit coins based on XRF data.

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9.6 Industrial

Once again, the essential contribution made by XRF inindustrial laboratories is demonstrated by the wide range ofpublished papers available this year. Beginning with theanalysis of raw materials, Arikan et al.417 used EDXRFincorporating a 109Cd source for quality control in the iron oredressing process, samples being prepared as conventionalpowder pellets made by mixing the sample with cellulose. Asimilar procedure, based on WDXRF, was used to determineNb and Th in ore samples from a benefaction process by Changand Guan.418 Mzyk et al.419 used XRF to determine Ag and Cuin slags from re®ning and slimes from copper electro-re®ning.After dissolving the samples in nitric acid (ammonium acetatesolution for high Pb samples), XRF and ICP-AES were used todetermine Pb in the ®ltrate and XRF was used to analyse theresidue recovered after ®ltration. Combined XRF±XRDinstrumentation is often used in the cement industry,but extending the range of applications, Baumgartner andYellepeddi420 described its application for process and qualitycontrol in the heavy mineral sands industry, in particular in theanalysis of samples from the mineral separating plants,titanium slags, through to the ®nal product, rutile.

Turning now to iron and steel, Magallanes and Vazquez421

employed EDXRF for the automatic classi®cation of steelsbased on the determination of 12 relevant elements and using adata processing technique based on arti®cial neural networks.Unusually, for any branch of science, 100% accuracy inclassi®cation was claimed for this technique. Tano andcolleagues422 claimed a patent for a sampler designed tooffer a rapid analysis capability for steel slugs ¯oating overmolten steel. After removal of the sample from the molten steel,the slug was analysed by XRF. Ti and Mo were measured inspecial steels and alloys using WDXRF by Hasany et al.423 Amultivariable regression procedure was employed and thetechnique had the capability of determining Ti down to120 mg g21 and Mo down to 350 mg g21.

In the analysis of other metallurgical samples, copper alloyswere investigated by XRF (Luo et al.158). The authorsdetermined Cu, Fe, Pb and Mo and evaluated three partialleast-squares regression procedures for their ability to predictthe in¯uence of noise on the accuracy of results. The conclusionwas that partial least squares with single component predictiongave the best accuracy and stability in the analysis of copperalloys. Kitamura et al.,424 in a Japanese language publication,used a combination of XRF and XRD to characterizeinclusions in aluminium. A sample of aluminium was melted,then ®ltered through a porous aluminium ®lter. Metallicaluminium in the residue was dissolved in a bromine±methanolsolution and the inclusions retained on the membrane ®lter andanalysed. Corundum, a-quartz and a range of metallic elementsat ng g21 levels were all detected.

Process control in the cement industry regularly features inthis section and this year is no exception. Both Yellepeddi andBonvin425 and Uhlig et al.426 offered analytical overviews froma manufacturer's perspective and Yellepeddi and colleaguescontinued to promote the combined XRF/XRD analysis ofclinkers (containing about 1.6% m/m free lime), cement andsamples from the mining industry, the free-lime content ofclinker also being considered in another paper.427 Duer428

described a bench top EDXRF instrument incorporating a SiPIN detector designed for the analysis of the raw material feedof cement kilns and Potgieter and Horne429 evaluated thecapabilities of XRF, ordinary and potentiometric titrationsand ion selective electrodes for the determination of chloride incement, although since this paper was written in Afrikaans, itwas presumably aimed speci®cally at a South African audience.The reader's attention is also drawn to some interesting cementsampling and analysis developments listed in the on-linesection.

XRF also has an important role to play in the glass andceramic industries. Process and quality control in the glassindustry were considered in two publications,430,431 the latterdescribing the role of combined WD/EDXRF instrumentation.The challenging determination of light elements, speci®callyboron in glass, was discussed by Van Sprang and Bekkers,432

who compared the merits of two XRF-based techniques. Onemethod used the direct determination of B Ka with afundamental parameter quanti®cation. Calibration requiredsome care as the fundamental parameters depended on thechemical environment of B. The second method was based onthe use of the Compton scatter intensity to quantify theunanalysed light fraction in an otherwise quanti®ed matrix.Although no matrix-dependent calibration was required forthis method, it was not suf®ciently sensitive for samples below4% m/m B2O3. A systematic procedure for the preparation ofcalibration standards for the XRF analysis of ceramics wasdescribed by Ochandio-Cardo et al.155 The procedure wasdesigned to optimize the composition of a set of calibrationsamples, taking into account elements and concentrationranges, potential interference effects and the opportunity tomix metal oxides, salts and certi®ed reference materials.

Turning now to the coal, petroleum and nuclear industries, aEuropean Community report433 described the use of tenstandard wet chemical methods (principally national methods)for the determination of sulfate, pyrite and total sulfur and/ororganic sulfur in 7 coals and 2 cokes. Whereas all methods gavebroadly acceptable results, 2 XRF methods based on standardadditions proved to be unsatisfactory: a rare failure of the XRFtechnique? EDXRF was more successful in the analysis of coalsusing a standard additions procedure, as described byHeimburger et al.434 Lead in gasoline was measured byEDXRF in a Polish contribution from Jelen and Kraso-domski435 and the elements Ni, S and V were determined inpetroleum by Komine and Tomoike.436 Sulfur in fuels was alsoan application described by Daucik et al.,437 EDXRF beingused to advantage. Considering now the analysis of nuclearfuels, Mudher438 reviewed the use of X-ray methods for thedetermination of Pu and U. An interesting method for thedetermination of total U in solution was described byDewberry.439 The method involved exciting U by adding amCi quantity of 109Cd to the sample solution and measuring theU L-line ¯uorescence emission. The method was demonstratedon synthetic U samples over the concentration range 1±15 g l21

and a method for correcting sample self-absorption effects wasincluded. Morel and colleagues440 evaluated methods formeasurement of uranium enrichment by recording emissionsfrom 235U, 238U and X-ray ¯uorescence induced within thesample by radiation w100 keV. And ®nally, the role of severaltechniques, including XRF, in characterizing plutonium for thepurposes of international security, stock-pile stewardship andthe characterization of mixed oxide fuels were discussed in aconference presentation by Mahan et al.441

XRF has also contributed to an astonishing variety of otherindustrial applications including: the analysis of drugs;442

cigarettes widely smoked in Kenya and cigarette ash443 inwhich it was reported that signi®cant quantities of As, Ga andSe were ingested during smoking; beauty creams also sold inKenya,444 where concern was expressed about the Hg contentof some of the samples; anionic surfactants and other inorganicingredients of laundry detergent products,445 where the interestlay in determining alkylbenzene sulfonates, alkyl sulfonates,zeolite, phosphate, silicate and sulfate. XRF was also used inthe determination of Mn in a dye, FD&C Blue No 1,446

deposits of aluminium hydroxide and alum±sodium aluminatefound in the paper-making process,447 iodine in iodized salt448

and wear metals in lubricating oil.449

X-ray ¯uorescence was also applied in the jewellery industry.Marucco and Stankiewicz450 developed an XRF method forthe determination of gold in jewellery, the elements determined

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being Ag, Au, Cu, Ni, Pd and Zn. The technique, whichincorporated a mathematical matrix correction procedure, wascompared with other techniques and considered to offeradvantages in the range of jewellery grades that could beanalysed against a single calibration. Nguyen and Pham451

applied radioisotope XRF to an analysis of natural rubies fromVietnam and in addition to distinguishing sources, found acorrelation between colour of the gemstone and Cr content. Acouple of Chinese language publications452,453 described theapplication of XRF to the analysis of gold-plated jewellery andwhite carat gold jewellery, respectively.

A diverse range of reports has also appeared covering theapplication of XRF to various inorganic materials of industrialinterest. Takahashi and colleagues454 developed a new methodfor the determination of the REE in REE oxides and singlecrystals of REE hexaborides from the respective K-line spectra.Instrumentation was based on EDXRF. REE K-lines were alsomeasured by Yan et al.,455 using 241Am excitation and a high-purity germanium detector. The technique was applied to thedetermination of the REE in HCl solution from separationprocesses and also REE loaded organic phases. In a similarsolvent extraction application, Ravindra et al.456 used XRF todetermine Hf in Zr process stream samples. A particularconsideration was the choice of a Ge(111) crystal to avoidsecond order spectral interferences. Franca and colleagues457

determined La and Y in zirconium dioxide ceramic materialusing HPLC, XRF and INAA techniques, the XRF contribu-tion being the determination of Y. Bai et al.458 published anextensive Chinese language review of REE techniques and Kimet al.459 considered the development of reference materials forthe XRF analysis of lead titanate zirconate. In a conferencepresentation, Posey460 described the bene®ts of WDXRF in arange of applications in the semiconductor industry.

Turning now to the XRF analysis of organic-based materials,Van Dalen461 used WDXRF to measure P and S in edible oilsand fats. Samples were analysed in disposable liquid cells aftersolidi®cation with 15% stearic acid and the detection limit forboth these elements was reported to be 2 mg kg21. Smagunovaet al.462 reviewed the advantages and disadvantages of differentXRF methods for the elemental analysis of petroleum andpetrochemical products, organometallic and high molecularweight compounds and medicines. Particular attention waspaid to sample preparation techniques and methods ofcalibration. Bledzki and Kardasz463 discussed the role ofXRF, as well as X-ray absorption spectrometry and infraredtechniques, in the sorting of plastics for recycling of wastes.

These and other industrial applications are also covered inthe companion comprehensive ASU review of industrialanalysis.464

9.7 Clinical and biological

During the last two decades, the in-vivo XRF determination oflead in bone has been extensively used for monitoring exposureto leaded gasoline, water, paint and industrial emissions.Skerfving et al.,465 related the accumulation of Pb in ®ngerbone to both time of exposure and blood lead. Similarly,Bergahl et al.466 compared occupational lead exposure in tibialand calcaneal bone with levels in blood plasma and wholeblood from active workers. Adolescents living in urban areaswere studied by Farias et al.467 Hernandez-Avila et al.468

reported on the contribution of lead mobilized in bone toplasma in environmentally exposed adults.

Akyuz et al.469 used radioisotope EDXRF analysis for thedetermination of other analytes in bone. Calcium, P and Srlevels in a control group were found to be higher than those intuberculous-arthritis patients, whereas the concentrations ofBa, Ce, La and Zn were no different. O'Meara et al.470 used a1 mCi 57Co source to excite U in bone. However, the estimateddetection minimum of 20 mg g21 may not be suf®ciently

sensitive for use in monitoring occupational exposures.Cadmium and Pb levels were measured by Gerhardsson etal.471 using in vivo XRF to assess kidney function in active andretired smelter workers.

Essential and toxic trace elements in teeth were estimated byZaichick and Ovchjarenko472 in an in vivo study of Ca, Pb, Srand Zn in frontal teeth enamel. Bloch et al.473 irradiated shedteeth with 122 and 136 keV gamma rays from a 5 mCi 57Cosource to assess the Pb levels in children living in Beijing andindustrial sites in the Urals, as compared with those childrenliving in urban locations in the USA.

Reiners et al.474 used 241Am to determine the thyroidaliodine content of women between the ages of 20 and 40 years.Other measurements on body tissues included Ali et al.475,476

working at the Swansea In Vivo Analysis and Cancer ResearchGroup, who used a plane polarized XRF con®guration for thein vivo determination of Pt in head and neck tumours. Aminimum detection limit of 5.6 mg g21 for Pt derived fromchemotherapeutic agents was reputed to be the most sensitivein vivo XRF system to date. Sam et al.477 used XRF todetermine traces of Ca, Cl, Co, Cr, Cu, Fe, K, Mn, Mo and Znin human milk. A calibration for the determination of Zn indry, ®nely divided hair was developed by Bolormaa et al.,478

based on measurements using synthetic reference samples.Laursen et al.479 reported the analysis of autopsy liver tissuesamples from the Greenland Inuit population in comparisonwith Danes. Part 1 of their work concerned the measurement ofBr, Cl, K and S, for which the Inuit data were on average lowerthan that of the Danes. A comparison between trace levels ofBr, Cu, Fe, Rb, Se and Zn in normal and cancer inoculatedmice by both XRF and PIXE was reported by Feldstein etal.480 The study was conducted on samples of blood, liver,kidney, colon and skin. Carvalho et al.481 collected humantissues of bone, hair, liver and kidney from 61 individuals (post-mortem) to study levels of As, Cu, Fe, Mn, Pb, Rb, Se, Sr andZn and apply the Pearson correlation matrix to investigate thecorrelation between the concentrations of these elements withrespect to age.

Zaichick482,483 compared three methods of estimating extra-cellular water by the determination of the `corrected brominespace'. The body ¯uids analysed included plasma from venousblood, ®nger blood and non-stimulated saliva. Olszowy et al.484

related the age, gender, weight, height and locality of donorsfrom measurements of Br in blood. Borjesson et al.485

published a review of in vivo studies using XRF with particularemphasis on the determination of Cd, Hg and Pb.

Monte Carlo computer simulation studies for in vivo XRFanalysis were reported by a number of workers during thisreview period. Lewis et al.486 from the Swansea Group used thetechnique to aid the design and optimization of their polarizedsource. O'Meara et al.487 applied the Monte Carlo simulationto measurements of Pb and U in bone. Two papers werepublished by Ao et al.488,489 on the application of the MonteCarlo code CEARXRF, again for the in vivo XRF analysis ofPb in bone. Hugtenburg et al.490 developed a program to modelthe measurement of cisplatin uptake by in vivo XRF for the`EGS4' Monte Carlo system with extensions to allow for linearpolarization and multiple element ¯uorescence.

Other biological applications included the work of Angeyo etal.,164 who published a semi-empirical method for improvedtrace multi-element determination in organic matrices based on109Cd radioisotope EDXRF. Akyruz et al.491 studied tracelevels of Ba, Br, Ca, Ce, Cu, Fe, I, La, Mn, Rb, Sr and Zn inrainbow trout. Nozaki and Makita99 reported on the detectionof various elements in major tissues of silky fowl. Cahill andcolleagues492 compared XRF and PIXE for the X-ray analysisof feathers. An investigation of inorganic contents of somediuretic pharmaceutical herbs growing in Turkey was reportedby Efe and Yilmaz,493 who used the XRF emission±transmis-sion technique. Vlachos et al.494 carried out a survey of

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concentrations of selected metals in seaweeds. The accumula-tion of Ca, Cu, Fe, K, Mn, Ni, Rb, Sr and Zn in the annualrings of Scots pine trees in the vicinity of a copper±nickelsmelter was determined by Larsson and Helmisaari.495 Stikanset al.496 reported on an improved technique for quantitativeEDXRF analysis of powdered plant materials. Gao et al.498

published a method for the determination of Cu, Fe, Sr and Znin liquorice by XRF.

9.8 Thin ®lms

Developments in both techniques and their applications arepresented in this review to emphasize the increasing use of XRFin the analysis of thin ®lms, multilayers and coatings. Cesareoet al.499 published some interesting studies in the use ofEDXRF for the analysis of thin and intermediate thicknessenvironmental samples. This study included the analysis ofalgae, microalgae and marine sediments prepared as thin ®lmsas well as the determination of the S concentration on a muralpainting in a church in Rome to provide an index ofdegradation. Lead was also monitored in urban air samplesto produce a map of its distribution. Thin layer samplepreparation techniques were described by Kyotani andIwatsuki500 in their method for simultaneous determinationof elements in vehicle exhaust particulates and atmosphericdusts.

Kaufmann et al.501 reported on attempts to extend thefundamental parameter approach to the analysis of single layer®lms made of carbon and silicon nitride, single layer ®lms ofcobalt plus oxygen matrices and complex multilayer structuresmade of C, Cu and Pd.

Composition and thickness determination were the subjectsof work by Sammelselg and colleagues,502 who compareddifferent programmes and methods for thin oxide ®lms. Barreaet al.503 determined the absolute mass thickness of thin foilsand Belyaeva et al.504 assessed ion-plasma spray coatings.

Other applications included work by Jurczyk et al.505 on theanalysis of Cd, Cu, Cr, Ga, Ni, Se and Zn in mono- and poly-crystal microsamples by a thin layer method. The team at theUniversity of Sassari506 also published a method for forwardEDXRF analysis of thin and intermediate samples with threemain advantages identi®ed over normal XRF. Finally, scan-ning from a variable glancing angle with X-ray photons oraccelerated ions for excitation was used by Krasnolutskii andBlokhin507 in a study of sensitivity in thin ®lm analysis.

9.9 Chemical state analysis and speciation studies

A survey of novel X-ray analysis methods was published byKawai,508 whose research group at Kyoto University has used®ve instrument con®gurations to further their work onchemical state analysis. The Kyoto group509 used monochro-matized synchrotron radiation as primary excitation in thestudy of F Ka spectra of MnF2. A high-resolution X-raycrystal diffraction spectrometer was used by KuÈchler et al.510 tostudy the line width of Ka1,2 in the solid state 3d elements. Xiaoet al.511 reported on the possible use of EDXRF to discriminatedifferent chemical states by partitioning the measurement timeof the Si(Li) detector into many sub-divisions using a statisticaldata processing procedure.

Work in the soft energy X-ray region included several papersdevoted to the K spectrum of carbon. Okotrub andBulusheva512 studied fullerene compounds using the `PM3'method. Yamada et al.513 measured the C K spectra ofmechanically alloyed powders prepared from niobium, tung-sten and graphite using EPMA. Kaneyoshi et al.514 used themolecular orbital calculation method in the study of graphiteK-V X-ray emission spectra. Kim and colleagues515 calculatedthe anisotropic C K X-ray emission of carbon (graphite,diamond) and related materials.

Studies at Andhra University by Visakhapatnam generatedtwo papers related to satellite spectra for this review. Reddyet al.516 concentrated on the K X-ray satellite spectrum of Mg,whereas Rao et al.517 studied P Ka L1/Ka L0 ratios. Udaet al.518 reported on the theoretical intensity distribution of KX-ray satellite spectra emitted from K and Cr. Photons wereused by Murty et al.519 to excite the K X-ray satellite spectrumof Ca in a LiF(200) plane crystal spectrometer. Two paperswere published on the L emission spectra and satellites of W byworkers in the Institute for Chemical Research, KyotoUniversity;520,521 the ®t residuals of La and Lb spectraindicated the presence of satellites in the vicinity of eachspectrum which were generated from Coster±Kronig transi-tions.

Studies by Polasik and colleagues522 were carried out on all3d transition metals to explain the dependence of Kb to Ka X-ray intensity ratios on the changes in con®gurations of valenceelectrons. Holzer et al.523 concentrated on Ca, Cr, Cu, Fe, Mnand Ni using a single-crystal diffractometer optimized forminimal instrumental broadening. Buyukkasap524,525 reportedon the effect of alloying on the Ka and Kb XRF cross-sectionsin CrxNi12x and CrxAl12x alloys. Kb to Ka X-ray intensityratios of Cr, Fe, Ti and V were measured in pure metals andCrB, CrB2, FeB, TiC and VC by Raj et al.526 Using the multi-con®guration Dirac±Foch calculation, signi®cant changes werefound in the 3d electron population of Cr in CrB and CrB2 andTi in TiC from their pure metal values, whereas no change wasfound for Fe in FeB and V in VC. Raj and colleagues527 alsopublished similar work on Cu and Ni in various silicatecompounds. The nature of Mn oxidation states in photosystemII concentrated the minds of Bergmann and colleagues528 in astudy of the mechanism of oxygen evolution by photosynthesis.

Other applications included work by Leiro and Heinonen530

on Ka1.2 X-ray emission spectra of KCl as well as metallic Ca,Fe and K. A Doniach±Sunjic type line shape was used to ®ndLorentzian tails for the spectra. Chemical effects on La : Lbintensity ratios of Ba, Co and La were studied by Baydaset al.,531 with experimental values compared with theoreticalvalues of pure elements. To complete this paragraph, yourreviewer returned to another published work from the Kyotogroup,532 where extended ®ne structure in characteristic XRFwas demonstrated for Al. The radiative Auger effect K-LL lineat 1100±1400 eV with an oscillating structure between 1250 and1350 eV was used to calculate interatomic distance.

A timely introduction to speciation studies may be found in aGerman language paper by Floch et al.533 on the analyticaladvantages of XRF and soft X-ray spectrometry for speciationstudies. Three examples were offered: Zn in scrap from theautomotive industry containing Zn, ZnO and ZnFe2O4; thedetection of Al2O3 and AlN in low alloy steels and CrVI insolutions using Cr Lb1 and Cr La1,2 lines. Readers withparticular interest in the latter example can refer to Pappert'spaper,534 this time in English. Speciation and preconcentrationof CrIII and CrVI in waters by retention on ion exchange mediaand determination by EDXRF was presented by Menendez-Alonso et al.535 A partnership of EDXRF and ICP-AES wasused by Somogyi et al.394 to investigate speciation of elementsin lake sediments. The chemical compositions providedinformation on environmental processes which changed soiland vegetation during sediment accumulation. McDonaldet al.536 analysed PM2.5 emissions from residential woodcombustion and meat cooking to construct speci®c pro®les foruse in the chemical mass balance model for the apportionmentof ®ne particle sources. Vanadium speciation by EDXRF wasstudied by Kallithrakas-Kontos and Moshohoritou537 usingthe K-L2,3 and K-M2,3 lines.

In closing this year's review, we should like to acknowledgethe contribution made by Mike Holmes to previous reviews inthis series.

1790 J. Anal. At. Spectrom., 1999, 14, 1773±1799

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250 G. Li, T. Zhang, X. Huang, P. Yin and S. Fan, Yankuang Ceshi,1998, 17(2), 123.

251 X.-R. Wu, S.-H. Zeng, K. Liu, J.-Y. Wang and Y.-H. Tian,Gaodeng Xuexiao Huaxue Xuebao, 1999, 20(5), 39.

252 P. Wobrauschek, P. Kregsamer, W. Ladisich, R. Rieder, C. Streli,S. Garbe, M. Haller, A. Knochel and M. Radtke, Adv. X-RayAnal., 1997, 39, 755.

253 C. Streli, V. Bauer and P. Wobrauschek, Adv. X-Ray Anal., 1997,39, 771.

254 T. Fukuda, T. Shoji, M. Funabashi, T. Utaka, T. Arai,K. Miyazaki, A. Shimazaki and R. Wilson, Adv. X-Ray Anal.,1997, 39, 781.

255 L. Ortega, F. Comin, V. Formoso and A. Stierle, J. SynchrotronRadiat., 1998, 5(3), 1064.

256 F. Comin, P. Mangiagalli, G. Apostolo, M. Navizet andL. Vincze, Presented at 7th Conference on TXRF and RelatedMethods, Austin, TX, USA, September 1998.

257 S. Brennan, P. Pianetta, S. Ghosh, N. Takaura, C. Wiemer,A. Fischer-Colbrie, S. Laderman, A. Shimazaki, A. Waldhauerand M. A. Zaitz, Mater. Res. Soc. Symp. Proc., 1998,524(Applications of Synchrotron Radiation Techniques toMaterials Science IV), 245.

258 P. Pianetta, S. Brennan, S. Ghosh, N. Takaura, C. Wiemer,A. Fisher-Colbrie, S. Ladermann, A. Shimazaki andA. Waldhauer, (Stanford Synchrotron Radiation Lab., Stanford,CA 94309, USA). Presented at 7th Conference on TXRF andRelated Methods, Austin, TX, USA, September 1998.

259 Y. L. Soo, S. Huang, Y. H. Kao and A. D. Compaan, J. Appl.Phys., 1998, 83(8), 4173.

260 Y. Wu, J. Pan, L. Zhao, G. Li and Y. Huang, Guangpu Shiyanshi,1998, 15(3), 12.

261 J. Pan, G. Li, L. Zhao, Y. Huang, L. Yuan and J. Chen, Hejishu,1997, 20(3), 164.

262 R. S. Hockett, Adv. X-Ray Anal., 1997, 39, 767.263 S. De Gendt, I. Rink, K. Kenis, T. Wortelboer, P. Mertens,

W. Berneike, V. Erdmann, M. Horn, B. Kolbesen, C. Neumann,S. Metz, S. Pahlke and P. Postam-Khani, (IMEC vzw, Leuven,Belgium). Presented at 7th Conference on TXRF and RelatedMethods, Austin, TX, USA, September 1998.

264 L. Fabry, S. Pahlke, L. Kotz, P. Wobrauschek and C. Streli,Fresenius' J. Anal. Chem., 1998, 363(1), 98.

265 S. Pahlke, L. Kotz, T. Ehmann, P. Eichinger and A. Huber,Proc.ÐElectrochem. Soc, 1998, 1(Silicon Materials Science andTechnology, Vol. 2), 1524.

266 R. Klockenkaemper and A. von Bohlen, Anal. Commun., 1999,36(2), 27.

267 W. Frank, A. Schindler and H.-J. Thomas, Fresenius' J. Anal.Chem., 1998, 361(6±7), 625.

268 W. L. Wu and W. E. Wallace, J. Vac. Sci. Technol., B, 1998,16(4), 1958.

269 H. Schwenke, J. Knoth, L. Fabry, S. Pahlke, R. Scholz andL. Frey, J. Electrochem. Soc., 1997, 144(11), 3979.

270 F. Schroder-Oeynhausen, B. Burkhardt, T. Fladung, F. Kotter,A. Schneiders, L. Wiedmann and A. Benninghoven, J. Vac. Sci.Technol., B, 1998, 16(3), 1002.

271 K. Iltgen, C. Weiss, A. Ghatak-Roy, T. Hossain, E. Zschechand A. Benninghoven, (AMD, Saxony Manufacturing GmbH,01139 Dresden, Germany). Presented at 7th Conference onTXRF and Related Methods, Austin, TX, USA, September1998.

272 P. K. De Bokx, S. J. Kidd, G. Wiener, H. P. Urbach, S. DeGendt, P. W. Mertens and M. M. Heyns, Proc.ÐElectrochem.

Soc., 1998, 98-1(Silicon Materials Science and Technology, Vol.2), 1511.

273 G. Wiener, S. J. Kidd, C. A. Mutasers, R. A. M. Wolters andP. K. de Bokx, Appl. Surf. Sci., 1998, 125(2), 129.

274 B. Holynska, M. Olko, B. Ostachowicz, J. Ostachowicz,D. Wegrzynek, M. Claes, R. Van Grieken, P. De Bokx,P. Kump and M. Necemer, Fresenius' J. Anal. Chem., 1998,362(3), 294.

275 R. Klockenkaemper and A. von Bohlen, J. Anal. At. Spectrom.,1999, 14(4), 571.

276 S. D. Lofthouse, G. M. Greenway and S. C. Stephen, J. Anal. At.Spectrom., 1998, 13(12), 1333.

277 G. Zaray, K. Barkacs, M. Ovari, A. Varga, E. Krakovska (Ed.)and S. Ruzcikova (Ed.), Total re¯ection X-ray ¯uorescencespectrometry in environmental research. Proc.ÐSemin. At.Spectrochem., 14th, Stroffek Publishing, Kosice, Slovakia,1998, 174±178.

278 H. M. Ortner, P. Hoffmann, S. Weinbruch, F. J. Stadermann andM. Wentzel, Analyst (Cambridge, U.K.), 1998, 123(5), 833.

279 R. E. Neuhauser, U. Panne and R. Niessner, (Inst. Hydrochem.,Tech. Univ. Munich, Munich, Germany). Presented at 25thFACSS, Austin, TX, USA, October 11±15, 1998.

280 R. P. Pettersson, Spectrochim. Acta, Part B, 1998, 53, 101.281 R. P. Pettersson and M. Olsson, J. Anal. At. Spectrom., 1998,

13(7), 609.282 I. Varga, E. Rierpl and A. Tusai, J. Anal. At. Spectrom., 1999,

14(5), 881.283 K. Barkacs, A. Varga, K. Gal-Solymos and G. Zaray, J. Anal. At.

Spectrom., 1999, 14(4), 577.284 R. Zahlbruckner, Ch. Krapfenbauer and F. Vojir, Curr. Status

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285 M. Xie, Fortschr.-Ber. VDI, Reihe 17, 1997, 160, 1.286 M. Xie, A. von Bohlen, R. Klockenkaemper, X. Jian and

K. Guenther, Z. Lebensm.-Unters. Forsch., 1998, 207(1), 31.287 M.-Y. Xie, H.-L. Wen, A. von Bohlen and K. Guenther, Gaodeng

Xuexiao Huaxue Xuebao, 1999, 20(5), 85.288 J. A. Liendo, A. C. Gonzalez, C. Castelli, J. Gomez, J. Jimenez,

L. Marco, L. Sajo-Bohus, E. D. Greaves, N. R. Fletcher andS. Bauman, X-Ray Spectrom., 1999, 28(1), 3.

289 I. Savage and S. J. Haswell, J. Anal. At. Spectrom., 1998, 13(10),1119.

290 M. Gonzalez, L. Tapia, M. Alvarado, J. D. Tornero andR. Fernandez, J. Anal. At. Spectrom., 1999, 14(5), 885.

291 U. Majerska, J. Braziewicz, D. Banas, A. Kubala-Kukus andA. Urbaniak, Biol. Trace Elem. Res., 1997, 60(1±2), 91.

292 P. Trabuc, Ph. Llug and Ph. Bienvenu, J. Phys. IV, 1998, 8(PR5,Rayons X et Matiere), Pr5/351.

293 V. P. Krasnolutskii, A. A. Bakirov, G. I. Poluyanova,I. N. Zakharchenko and V. P. Dudkevich, Zavod. Lab., 1997,63(12), 24.

294 M. Shimoyama, T. Nakanishi, Y. Hamanaga, T. Ninomiya andY. Ozaki, J. Trace Microprobe Tech., 1998, 16(2), 175.

295 P. Vandenabeele, B. Wehling, L. Moens, B. Dekeyzer, B. Cardon,A. von Bohlen and R. Klockenkaemper, Analyst (Cambridge,U.K.), 1999, 124(2), 169.

296 G. Van Hooydonk, M. De Reu, L. Moens, J. Van Aelst andL. Milis, Eur. J. Inorg. Chem., 1998(5), 639.

297 A. Rammler, H. Gallinger, J. Flachowsky and J. Gottlieb (Ed.),On-site analysis by mobile X-ray ¯uorescence. Field ScreeningEur., Proc. Int. Conf. Strategies Tech. Invest. Monit. Contam.Sites, 1st, Kluwer, Dordrecht, The Netherlands, 1997, 335±338.

298 A. Muller, J. Pelzer and J. Gottlieb (Ed.), Heavy metal screeningusing an XRF ®eld spectrometer. Field Screening Eur., Proc. Int.Conf. Strategies Tech. Invest. Monit. Contam. Sites, 1st, Kluwer,Dordrecht, The Netherlands, 1997, 313±318.

299 T. M. Spittler, NATO ASI Ser., Ser. 2: Environ., 1998, 1998,40(Air Pollution in the Ural Mountains), 115.

300 J. F. Schneider, Am. Environ. Lab., 1998, 10(3), 20.301 R. Henderson, L. DeGeorge, G. Little and K. McDade, Contam.

Soils, 1998, 3, 401.302 M. K. Waligora, Chemical analysis of chromium in soil using X-

ray ¯uorescence spectroscopy supporting ®eld remediationoperations. Field Anal. Methods Hazard. Wastes Toxic Chem.,Proc. Spec. Conf., Air and Waste Management Association,Pittsburgh, PA, USA, 1997, 815±821.

303 W. T. Elam and J. V. Gilfrich, Adv. X-Ray Anal., 1997, 39, 861.304 W. T. Elam, J. W. Adams, K. R. Hudson, B. McDonald and

J. V. Gilfrich, Field Anal. Chem. Technol., 1998, 2(2), 97.305 W. T. Elam, J. Adams, K. R. Hudson, B. McDonald, D. Eng,

G. Robitaille and I. Aggarwal, Field demonstration of the

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SCAPS XRF metals sensor. Field Anal. Methods Hazard. WastesToxic Chem., Proc. Spec. Conf., Air and Waste ManagementAssoc., Pittsburgh, PA, USA, 1997, 681±689.

306 S. Shefsky, Comparing ®eld portable X-ray ¯uorescence (XRF)to laboratory analysis of heavy metals in soil. Field Anal. MethodsHazard. Wastes Toxic Chem., Proc. Spec. Conf., Air and WasteManagement Assoc., Pittsburgh, PA, USA, 1997, 195±205.

307 V. J. Kirtay, J. H. Kellum and S. E. Apitz, Water Sci. Technol.,1998, 37(6±7), 141.

308 V. J. Kirtay, J. H. Kellum and S. E. Apitz, The validation of ®eld-portable X-ray ¯uorescence spectrometry for the analysis ofmetals in marine sediments. Field Anal. Methods Hazard. WastesToxic Chem., Proc. Spec. Conf., Air and Waste ManagementAssoc., Pittsburgh, PA, USA, 1997, 822±837.

309 S. Afshari, V. Nagarkar and M. R. Squillante, Appl. Radiat. Isot.,1997, 48(10±12), 1425.

310 S. Afshari, V. Nagarkar and M. R. Squillante, Appl. Radiat. Isot.,1997, 48(10), 1425.

311 A. V. Derbin, V. V. Ivanov, V. G. Muratov, O. P. Polytsya andA. Kh. Khusainov, Ekol. Khim., 1998, 7(1), 38.

312 G. E. Gigante and R. Cesareo, Radiat. Phys. Chem., 1998,51(4±6), 689.

313 A. Longoni, C. Fiorini, P. Leutenegger, S. Sciuti, G. Fronterotta,L. Struder and P. Lechner, Nucl. Instrum. Methods Phys. Res.,Sect. A, 1998, 409(1±3), 407.

314 M. R. Keinbusch, D. Sackett, J. Bass and S. Manchester, Proc.Annu. Meet.ÐAir Waste Manage. Assoc., 1996, 89th, ta3006/1.

315 B. Allen, D. Sackett, C. Parsons and S. Shefsky, On-site analysisof metals in liquids using portable X-ray ¯uorescence. Field Anal.Methods Hazard. Wastes Toxic Chem., Proc. Spec. Conf., Air andWaste Management Assoc., Pittsburgh, PA, USA, 1997, 838±841.

316 S. Piorek and J. Gottlib (Ed.), On-site, in-situ characterization ofcontaminated soil and liquid hazardous waste with ®eld portableX-ray analyzer. A cost effective approach. Field Screening Eur.,Proc. Int. Conf. Strategies Tech. Invest. Monit. Contam. Sites, 1st,Kluwer, Dordrecht, The Netherlands, 1997, 329±333.

317 S. Piorek, E. Piorek and G. Johnson, Characterization of liquidhazardous waste with a ®eld portable energy-dispersive X-rayanalyzer, Air and Waste Management Assoc., Pittsburgh, PA,USA, 1997, 842±847.

318 W. K. Warburton, D. A. Darknell and B. Hubbard, J. Radioanal.Nucl. Chem., 1998, 233(1±2), 233.

319 W. K. Warburton, D. A. Darknell and B. Hubbard-Nelson,Mater. Res. Soc. Symp. Proc., 1998, 487(Semiconductors forRoom-Temperature Radiation Detector Applications II), 559.

320 P. Sarrazin, D. Blake, D. Bish, D. Vaniman and S. Collins,J. Phys. IV, 1998, 8(PR5, Rayons X et Matiere), pR5/465.

321 F. Paglietti, P. Plescia and B. Mishra (Ed.), Applications ofSEXI. EPD Congr. 1998, Proc. Sess. Symp., Minerals, Metalsand Materials Soc., Warrendale, PA, USA, 1998, 888±899.

322 A. Russell, T. Feldmann and J. Gottlib (Ed.), The use of `Joule-Thomson' type cooled detectors for ®eld transportable energydispersive X-ray ¯uorescence spectrometers. Field Screening Eur.,Proc. Int. Conf. Strategies Tech. Invest. Monit. Contam. Sites, 1st,Kluwer, Dordrecht, The Netherlands, 1997, 339±342.

323 M. Hirai, T. Utaka, Y. Sako, A. Nisawa, S. Nomura andK. Taniguchi, X-sen Bunseki no Shinpo, 1998, 29, 93.

324 R. G. Helmer, R. J. Gehrke and M. V. Carpenter, Nucl. Instrum.Methods Phys. Res., Sect. A, 1999, 422(1±3), 826.

325 R. J. Gehrke, E. W. Killian, L. V. East, J. M. Hoggan,S. G. Goodwin and G. D. McLaughlin, J. Radioanal. Nucl.Chem., 1998, 233(1±2), 225.

326 L. Ge, Y. Zhang, Y. Chen and W. Lai, Appl. Radiat. Isot., 1998,49(12), 1713.

327 P. J. Potts, P. C. Webb and O. Williams-Thorpe, J. Anal. At.Spectrom., 1997, 12, 769.

328 S. Tokkesdal Pedersen and M. S. Finney, Cim., Betons, Platres,Chaux, 1998, 833, 262.

329 S. T. Pedersen and M. S. Finney, World Cem., 1998, 29(6), 30.330 Y. Miyoshi, Jpn. Kokai Tokkyo Koho JP 10 197,460 [98 197,460]

(Cl. G01N23/223), 31 Jul 1998, Appl. 97/864, 7 Jan 1997; 4 pp.331 W. Li, G. Ascenzo, R. Curini, G. M. Gasparini, M. Casarci,

B. Mattia, D. M. Traverso and F. Bellisario, Anal. Chim. Acta,1998, 362, 253.

332 M. Casarci, F. Bellisario, G. M. Gasparini, L. W. Li, B. Mattia,D. M. Traverso, D. C Shallcross (Ed.), R. Paimin (Ed.) andL. M. Prvcic (Ed.), Value Adding Solvent Extr., [Pap. ISEC'96],1996, 2, 1121.

333 D. J. Connolly, R. W. Dye, N. J. Mravich, C. C. Stauffer and

B. A. Stuchell, U.S. US 5,818,899 (Cl. 375-45; G01N23/223), 6Oct 1998, Appl. 832,425, 2 Apr 1997; 7 pp.

334 M. C. Ringo, M. S. Huhta, G. Shea-McCarthy, J. E. Penner-Hahn and C. E. Evans, Nucl. Instrum. Methods Phys. Res., Sect.B, 1999, 149(1±2), 177.

335 Y. Shacham-Diamand, B. Yokhin, I. Mazor, A. Kepten,R. Shaviv and A. Gabai, Proc. SPIE-Int. Soc. Opt. Eng., 1998,3509(In-Line Characterization Techniques for Performanceand Yield Enhancement in Microelectronic Manufacturing),3509.

336 D. Connolly and C. Walker, Ultrapure Water, 1998, 15(3), 53.337 V. E. Buhrke (Ed.), R. Jenkins (Ed.) and D.K. Smith (Ed.), A

practical guide for the preparation of specimens for X-ray¯uorescence and X-ray diffraction analysis, Wiley, New York,NY, USA, 1998, 0 471 19458 1, 333 pp.

338 S. Hogopian-Babikian, R. F. Hamilton, S. S. Iyengar, R. Jenkins,J. Renault, V. E. Buhrke (Ed.), R. Jenkins (Ed.) and D. K. Smith(Ed.), A practical guide for the preparation of specimens for X-ray ¯uorescence and X-ray diffraction analysis. Pract. GuidePrep. Specimens X-ray Fluoresc. X-ray Diffr. Anal, Wiley-VCH,New York, NY, USA, 1998, 1±33.

339 V. E. Buhrke, R. F. Hamilton, R. Jenkins, D. K. Smith,J. E. Taggart Jr., V. E. Buhrke (Ed.), R. Jenkins (Ed.) andD. K. Smith (Ed.), Specimen preparation equipment. Pract.Guide Prep. Specimens X-ray Fluoresc. X-ray Diffr. Anal, Wiley-VCH, New York, NY, USA, 1998, 265±283.

340 F. Feret, R. Jenkins, V. E. Buhrke (Ed.), R. Jenkins (Ed.) andD. K. Smith (Ed.), Specimen preparation procedures in X-ray¯uorescence analysis. Pract. Guide Prep. Specimens X-rayFluoresc. X-ray Diffr. Anal, Wiley-VCH, New York, NY,USA, 1998, 35±37.

341 V. E. Buhrke, L. E. Creasy, J. F. Croke, F. Feret, R. Jenkins,H. M. Kanare, V. Kocman, V. E. Buhrke (Ed.), R. Jenkins (Ed.)and D. K. Smith (Ed.), Specimen preparation in X-ray¯uorescence. Pract. Guide Prep. Specimens X-ray Fluoresc. X-ray Diffr. Anal, Wiley-VCH, New York, NY, USA, 1998, 59±122.

342 A. B. Blank and L. P. Eksperiandova, X-Ray Spectrom., 1998,27(3), 147.

343 M. A. Allen, Anal. Commun., 1998, 35(2), 75.344 J. D. de V. Louw and S. T. Pedersen, Symp. Ser.ÐS. Afr. Inst.

Min. Metall., 1997, S17(Heavy Minerals 1997), 179.345 J. Malmqvist, X-Ray Spectrom., 1998, 27(3), 183.346 J. Shannon, Symp. Ser.ÐS. Afr. Inst. Min. Metall., 1997,

S17(Heavy Minerals 1997), 175.347 F. Claisse, J. Phys. IV, 1998, 8(PR5, Rayons X et Matiere), Pr5/

379.348 R. K. W. Merkle, M. Loubser and S. M. C. Verryn, (Dept. Geol.,

Univ. Pretoria, Pretoria 0002, South Africa). Presented atAnalitika '98, Midrand, Gauteng, South Africa, October 12±14, 1998.

349 A. J. Nielson, D. C. Turner, A. Wilson, D. C. Wherry andR. Wong, Adv. X-Ray Anal., 1997, 39, 799.

350 J. Wolska and B. Vrebos, Am. Environ. Lab., 1998, 10(5), 24.351 E. Menendez-Alonso, S. J. Hill, M. E. Foulkes and J. S. Crighton,

(Anal. Chem. Res. Unit, Dept. Environ. Sci., Univ. Plymouth,Plymouth, UK PL4 8AA). Presented at Ninth Biennial NationalAtomic Spectroscopy Symposium, Bath, UK, July 8±10, 1998.

352 L. P. Eksperiandova, A. B. Blank and I. I. Fokina, Fresenius'J. Anal. Chem., 1998, 361(3), 287.

353 L. P. Eksperiandova, A. B. Blank and Y. N. Makarovskaya,X-Ray Spectrom., 1999, 28(1), 24.

354 N. Echi, Jpn. Kokai Tokkyo Koho JP 10 19,811 [98 19,811] (Cl.G01N23/223), 23 Jan 1998, Appl. 96/188,432, 28 Jun 1996; 5 pp.

355 C. Neelmeijer, J. Hueller, M. Maeder and B. Borchers, Ger.Offen. DE 19,728,930 (Cl. G01T1/36), 14 Jan 1999, Appl.19,728,930, 7 Jul 1997; 6 pp.

356 M. S. Carvalho, M. de Lourdes F. Domingues, J. L. Mantovanoand E. Q. S. Filho, Spectrochim. Acta, Part B, 1998, 53, 1945.

357 L. P. Eksperiandova, Y. N. Makarovska and A. B. Blank, Anal.Chim. Acta, 1998, 371(1), 105.

358 M. Necemer and P. Kump, Spectrochim. Acta, Part B, 1999, 54,621.

359 L. Cornejo-Ponce, P. Peralta-Zamora and M. I. Maretti S. Bueno,Talanta, 1998, 46, 1371.

360 P. J. Potts, Geostand. Newsl., 1998, 22(1), 57.361 C. Pirola, (R&D Application Lab., Milestone Srl, 24010 Sorisole,

Italy). Presented at European Winter Conference on PlasmaSpectrochemistry, Pau, France, January 10±15, 1999.

362 J. Bacso, A. Pazsit, A. Somogyi, A. Vertes (Ed.), S. Nagy (Ed.)and K. Suvegh (Ed.), Energy dispersive X-ray ¯uorescence

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363 V. Y. Borkhodoev, J. Trace Microprobe Tech., 1998, 16(3), 341.364 S. Puri, J. S. Shahi, B. Chand, M. L. Garg, N. Singh, P. N. Trehan

and N. Nath, X-Ray Spectrom., 1998, 27, 105.365 K. H. Angeyo, J. P. Patel, J. M. Mangala and D. G. S. Narayana,

Appl. Radiat. Isot., 1998, 49(7), 885.366 K. R. S. Devan, D. P. Winkoun and V. R. K. Murty, Appl.

Radiat. Isot., 1997, 48, 1397.367 A. Majchrak, B. Pencakova, E. Krakovska (Ed.) and

S. Ruzickova (Ed.), Determination of some elements in streamsediments by ED XRF method. Proc.ÐSemin. At. Spectrochem.,14th, Stroffek Publishing, Kosice, Slovakia, 1998, 283±287.

368 A. Somogyi, M. Braun and J. Posta, Spectrochim. Acta, Part B,1997, 52(13), 2011.

369 M. Bounakhla, A. Sabir, M. Labraimi, A. A. Haddou, A. ElHamdaoui, M. Bahlouli, M. El Maghraoui and P. Kump,Elemental analysis of Moroccan marine sediments using INAAand XRF. Harmonization Health Relat. Environ. Meas. UsingNucl. Isot. Tech., Proc. Int. Symp. 1996, International AtomicEnergy Agency, Vienna, Austria, 1997, 571±580.

370 J. H. F. Jansen, S. J. Van der Gaast, B. Koster and A. J. Vaars,Mar. Geol., 1998, 151(1±4), 143.

371 R. Rieder, T. Economou, H. Wanke, A. Turkevich, J. Crisp,J. Bruckner, G. Dreibus and H. Y. McSween Jr., Science(Washington, D. C.), 1997, 278(5344), 1771.

372 D. Mihajlovic and T. Sta®lov, X-Ray Spectrom., 1998, 27(6), 397.373 M. J. Adams and J. R. Allen, Analyst (Cambridge, U.K.), 1998,

123(4), 537.374 Y. Wang, D. Lui, Y. Gao, H. Song, J. Li, W. Chen, Y. Teng and

S. Zhou, Geostand. Newsl., 1998, 22(2), 247.375 J. Kucera, V. Sychra and J. Koubek, Fresenius' J. Anal. Chem.,

1998, 360(3±4), 402.376 N. Blagojevic, (Australian Nuclear Sci. Technol. Org., Menai,

NSW 2234, Australia). Presented at 1998 Winter Conference onPlasma Spectrochemistry, Scottsdale, AZ, USA, January 5±10,1998.

377 M. Odegard, S. H. Dundas, B. Flem and A. Grimstvedt,(Geological Survey Norway, 7040 Trondheim, Norway). Pre-sented at 1998 Winter Conference on Plasma Spectrochemistry,Scottsdale, AZ, USA, January 5±10, 1998.

378 T. H. Nguyen, J. Boman and M. Leermakers, X-Ray Spectrom.,1998, 27(4), 265.

379 T. H. Nguyen, J. Boman, M. Leermakers and W. Baeyens, X-RaySpectrom., 1998, 27(4), 277.

380 G. M. B. Marcazzan, X-Ray Spectrom., 1998, 27(4), 247.381 E. Cortes, P. Toro and P. Artaxo, Chemical characterization and

source identi®cation of airborne particulate matter in Santiago,Chile. Harmonization Health Relat. Environ. Meas. Using Nucl.Isot. Tech., Proc. Int. Symp. 1996, International Atomic EnergyAgency, Vienna, Austria, 1997, 487±497.

382 C. D. Alonso, M. H. R. B. Martins, J. Romano and R. Godinho,J. Air Waste Manage. Assoc., 1997, 47(12), 1297.

383 A. Malanca, A. Mainardi and B. Zani, J. Radioanal. Nucl. Chem.,1998, 230(1±2), 115.

384 Z. Nejedly, J. L. Campbell, W. J. Teesdale, J. F. Dlouhy,T. F. Dann, R. M. Hoff, J. R. Brook and H. A. Wiebe, J. AirWaste Manage. Assoc., 1998, 48(5), 386.

385 O. V. Shuvayeva, K. P. Koutzenogii, V. B. Baryshev,V. I. Rezchikov, A. I. Smirnova, L. D. Ivanova andF. V. Sukchorukov, Atmos. Res., 1998, 46(3±4), 349.

386 S. M. Talebi, Pollut. Res., 1997, 16(4), 203.387 N. Kallithrakas-Kontos, K. Zoumi, S. Nikolakaki and

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