determination of arsenic and antimony using selective hydride generation and gc pid

8/3/2019 Determination of Arsenic and Antimony Using Selective Hydride Generation and GC PID

1/6

1138 Anal. Chem. 1881, 63, 138-1142

(6) a) CaseMa, E. F. J. phys. chem. 971, 75, 275. (b) Casassa. E. F.

(7) Flory, P. J. M c @ ~ s f Polymer chemlsby; Cornell UniversityPress:

(8) Qrublsic, Z.; Rempp. R.; Benolt, H. J. pdvm. Scl.: Part B 1967, 5 .

(9) Potschka, M. Anal. Bkchem . 1987, 762, 47.(10) Cantor, P. R.; Schimrne i, P. R. Biophyslcel Chemlsby, Part I I . Tech-

niques for the S W f Bblc@cal Structure and Function; W. H. Free-man: New York, 1980: p 580.

(11) (a) Nozaki, Y.; Schechter, N. M.; Reynolds. J. A.; Tanford, C.BIochem&by 1976, 75, 3884. (b) Meredith, S. C.; Nathans, G. R.Anal. Blochem. 1982, 727, 234.

(12) Styrlq, M. G.: Davlson, C. J.; Wce, C.; Booth. C. J. J. Chem. Soc.,Farady Trans. 7 , 1984, 80 , 3051.

(13) (a) Holter, H.; Mailer, K.M. a p t / . Cell. Res. 1956, 75, 631. b) Lau-rent. T. C.; Granath, K. A. B M I m . B iophvs . Ac ta 1967, 738, 91.

(14) Halier, W.; Easedow, A. M.; Konig, 8. J. Chromalogr. 1977, 732,387.

(15) Poitevin, E.; Wahi. P. Blophys. Chem . 1988, 31 , 247.(16) Kato, T.; Katsuki, T.; Takahashi. A. Macromdecules 1964, 77. 1726.(17) Kawahara, K.; Ohta. K.; Mlyamoto,H.; Nakamura, S. Carbohydr. Po -

&m . 1984, 4 , 335.(18) Dubin, P. L.; Principi,J. M. J. Chromatogr. 1989, 479, 159.(19) Amu, T. C. Blophys. Che m. 1982, 76, 269.(20) A typographical error in re f 15 gives the exponent in eq 8 without the

negative sign.(21) Abramowk, M.;Stegun, 1. N?endbodcofMelhemabrcelFun&s; NBS

Applied Mathem atics Series; NBS: Washington, D.C., 1990; Voi. 55.(22) Dubin, P. L.; Kaplan, J. L.; Tian, E A . ; Mehta, M. J. C h r m t o g r .

1990, 575. 37.(23) Granath. K. Private communication.

J . m . I. , Part B 1967, 5 , 773.

Ithaca, NY, 1953; p 606.

753.

(24) Lavrenko, P. N.; Mtkryukbva,0. I.; D b n k o , S. A. pdym. Scl. U . S .S . R . 1986, 28 , 576 (translation of Vysokomol. S o d . 1986, A28,517.)

(25) Davldson, M. G.; Deen, W. M. Macrmh%ubs 1988, 27 , 3474. (b)Bohrer. M. P.; Patterson, G. D.; Canoii, P. J. M a c r m k u k s 1984,

(26) Luby-Phelps, K.; Castle, P. E.; Taylor. D. L.; Lanni. F. Proc. Net/.Aced. Scl. U . S . A . 1987. 8 4 . 4910.

(27) Dubin, P. L.; Wright, K. L.; Koontz,S. W. J . Polym. Sci., Pdym.Chem. Ed. 1977, 15, 2047.

(28) PhiiHes, 0 . D. J. Anal. Chem. 1990, 62, 1049A and references there-in.

(29) When the data re ed in ref 22 and 23 are superimposed, differentdependences of r o n Ma re no t swn; the different values of a re-ported

arisefrom the

sensittvityof

a to decisions involved in estabilsh-ing the best-fk line.(30) Hagei, L. in Aquews Slze Exdushm Chrometographv; Dubin, P. L.,

Ed.; Elsevier: Amsterdam, 1988; Chapter 5.(31) Frigon, R. P.; Ley poldt. J. K.; Uyeji, S.; Henderson. L. W. Anal. Chem.

(32) Dubln, P. L.; Principi, J. M. Macromolecules 1989, 22 , 1891.(33) Dubin, P. L.; Prlncipl,J. M.; Smith, B. A, ; Faiion, M. A. J. ColloM In -

terface Sci. 1989, 727, 558.

77, 1170.

1983, 55, 1349.

RECEIVEDor review Decem ber 3,1990. Accepted February26, 1991. Th is work was supp orted by the donors of thePetroleum Research Fund administered by the AmericanChemical Society, and Gr ant CHE -9021484 from the Nation alScience Foundation.

Simultaneous Determination of Inorganic Arsenic and AntimonySpecies in Natural Waters Using Selective Hydride Generationwith Gas Chromatography/Photoionization Detection

Lynda S. Cutter, Gregory A. Cutter,* and Maria L. C. San Diego-McGloneDepartment of Oceanography, Old Dominion U niversity, Norfolk, Virginia23529-0276

Dissolved arsenic and antimony In natural waters can exlstIn the trivalent and pentavalent oxidation states, and thebkChemIca1and geochmnkal reactivities of these d . r m n t sare dependentupon their chemical forms. A method for thesimultaneous detmmhatkn of As(II1) + Sb(1II) and Ad111+V) + Sb(II1 +V) has been developed that uses selectivehydride generation, llquld nitrogen coded trapping, and gaschromatography/photoknlzatkn detectkn. The detection Hmttfor arsenk b 10 pmdn, WMlethat for anthrony b 3.3 pnoVL;precision (as relatlve standard devlatlon) for both elementsIs better than 3 % . The apparatus k, rugged and allows de-termlnatlons to be made In the field. I n addition to deter-

mlnlng dlssohred a r m lc and antlmony specks, an oxldatlvedlged has been developed to allow the rbnuitaneous deter-mlnatlon of the two elements In sedhnents and Mogenlcparticles. Numerous water and partlculate samples havebeen analyzed by using the described procedures.

INTRODUCTIONIn natu ral wa ters the metalloid elements (e.g.,As, Sb, Se)

can exist in a variety of oxidation states and chemical formswithin a given oxidation state(1-3). Thus, he determinationof the chem ical forms of metalloid elemen ts is an esse ntialpa rt of studying their biogeochemical cycles. Fur therm ore,

0003-2700/91/0363-1138$02.50/0

th e chemical forms of selenium an d arsenic have been usedto estim ate the redo x intensity in rain water (e.g., refs4, 5).Th e conventional method for speciating metalloids involvesselective hydride generation and atomic absorption detection.While this me thod has sufficiently low detection limits forconce ntrations found in na tural waters (i.e., nan o- to pico-molar), each element must be determined individually. Th esimultaneous determination of metalloid species thereforepresents a significant advantage.

Recently, Vien and Fry ( 6 )reported a m ethod for the si-multaneous determination of total arsenic, antimony, sele-nium, and tin using hydride generation, gas chromatographicseparation of the volatile hydrides, and detection by pho-toionization. U nfortun ately, the chemical cond itionsrequiredto selectively generate hydrides from t he d ifferent form s ofthese elements are mutually exclusive (Le., iodide must bepresent to quantitatively generate stibine (SbH3) from S b(V),but iodide interferes in the determination of selenium).However, the chemical conditions for selectively generatinghydrides from arsenic and a ntimony species are sufficientlysimilar o allow their simultaneous eterminations.This paperdescribesa meth od t ha t is specifically designedto determinethese elements in natural wa ters, with the required detectionlimits and analytical precision. Further, the appa ratus isrugged and canbe used for shipboard determinations. Sincethe chemical forms of arsenic and antimony are not stableduring c onventional sample storage (e.g., acidification), de-

0 1991 American Chem ical Society


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ANALYTICAL CHEMISTRY,VOL. 63, NO. 11, JUNE 1, 1991 1130

M and is stored in a glass reagent bottle untiluse. A 1-ml aliquotof this solution should ad just the pH of a 50-mL sample to 6.2.Potassium persulfate is 4% (w/v) and is made fresh daily.Distilled, deionized w ater (DD I)is used hroughout the procedurefor reagents and sample dilutions.

Th e following standa rd reference materials w ere employed:National Institute of Standard s and Technology (NIST ) BovineLiver (SRM 1577),River Sediment (SRM 1645),Estuarine Sed-iment (SRM 1646), and International Atomic Ene rgy Agency(IAEA) Copepod H omogenate (MA-A-1). Standards [loo0 ppmof As(V) and Sb(V)]were obtained from Baker. Ultrapu re'an-

timony trioxide (Sbz 03,Alfa) and arsenic trioxide (A% 03,MCB)were used to make Sb(II1) and As(II1) standar ds (lo00 pp m),respectively.

Procedures. Samp le Processing. Water samples tha t cannotbe analyzed w ithin approximately12 h of collection should beplaced in high-density polyethylene bottles (three-fourths full)and rapidly frozen by immersion in liquid nitrogen. Sedim entsand biogenic matte r should be kept frozen prior to processing.Particulate matteris dried at 40 OC, ground with an agate mortarand pestle, sieved through a 150-pm mesh polyethylene screen,and stored in a clean polyethylene bottle. Filtered particulatematerial is stored frozen in polyethylene vials until digested.Water samples are thawed by using a microwave oven (do notallow temperature to rise above 30 OC) just prior to analysis.

Determination of Aqueous As(ZZI)and Sb(ZZ4.Between 5 and50 milliliters (depending on con centration) of fresh or thawedsample is transferred t o the stripper bottom and th e volumebrought to 50 mL with DDI. A 1-mL aliquot of 2.5 M Tris-HC1is added (the pH at this point should be 6.2), the bottom isreattachedto the strippe r, and th e system is allowedto purge for2 min. After purging, the hydride tr ap is placedin liquid nitrogenan d 1.2 mL of 4% NaBH4 s injected into the stripper throughthe septum. After stripping for 7 min, the six-way valveis turnedto the colum n/inject position, and1 min later the tr ap is pulledfrom the liquid nitrogen; the integrator is started a t this time.After 45 s, the valve is returnedto the strip/trap positionso thathigh boiling point substances (e.g., water) do not enter the column.Arsenic has a retention time of approx imately 3 min, while th atof antimony is approximately 7 min, depending on exact columnlength, carrier flow rate, and oven temperature.

Determination of Aqueous As(ZZZ+ V) and Sb(ZZZ+ V). From1 o 50 mL of sample (fresh, thawed, or store d) is added to th estripper bottom and the volume adjustedto 50 mL with DDI. A2-ml aliquot of concentrated HCL an d 3 mL of KI solution areadded, and the stripper is assembled and purged for 3 min.NaBH4 solution (4 mL) is injected slowly over1 min, and thehydridesare collectedover a 7-min strip/trap time. Determinationof the hydrides then follows the procedure above. As(V) iscalculated to be th e difference between As(II1+ V) nd A s(II1)determinations, while Sb(V)is the difference between the Sb(1II+ V) and Sb(II1) determinations.

Particulate Digestion. Approximately 0.1 g of d ried and groundsediment is weighed in to an acid-cleaned, 50-mL beaker. Con-centrated nitric acid (5 mL) is added, th e beaker covered witha watch glass, and th e sam ple allowedto reflux gently on a warmhot plate for 6 h. The watch glass is then removed and t he nitricacid evaporated until the sample is completely dry(but notcharred). An &mL aliquot of 4% (w/v) potassium persulfate isadded, and th e sample isagain refluxed for 6 h. After the watch

glass is removed, the persulfate solutionis evaporatedto dryness;a white residue remains a t this point. A 10-mL aliquotof 6 MHCl is added and th e sample gently heated for1 h. If needed,sediment samplescan be filtered through 0.4-pm m embrane fdtersto remove any undigested mineral phases. Samples are storedin 30-mL high-density polyethylene bottles un til analysis.

Any amount of the digestcan be analyze d, but typically, 0.1-2.0-mL aliquota are d ilutedto 50 mL with DDI and analyzed byusing the As(II1+ V) and Sb(II1+ V) procedure.

RESULTS AND DISCUSSIONSample Processing and Storage. Aqueous Sam ples. The

conventional meansof storing water samples for trace elementanalyses uses polyethylene containers an d acidification toapH less than 2 in orderto prevent adsorption or precipitation( IO) . However, previous studies (9, II ) have shown that

Water vapor trap-50: C

Flgure 1. Appartus for the determinationof arsenic and antimonyspeck using selective hydride generation. Singlelines indlcate Teflontubing, while double iines represent glass tubing.

termina tions in the field are necessary. Th e method ha s beenapplied to the analysisof a variety of marine, fresh water, andrain water samples. In addition,a wet oxidative digest forsediments a nd biogenic materialshas been developedto allowthe simultaneous determination oftotal antimony an d arsenicin particulate matter. When sample size is limited (e.g.,fil-tered particles), this applicationof th e method is extremelyvaluable.

EXPERIMENTAL SECTIONApparatus. Th e app aratus used to generate and collect the

hydrides from aqueous solutions is shownin Figure 1. Th e glassstripping vessel and water trap (glass U-tube immersed in 2-propanol a t-50 OC by using an immersion cooler) are exactly thesame as those described by C utter(7,8). For sam ples of anoxicwater, a 5 cm long, 6-mm (0.d.) glass tube t ha t is loosely packedwith g lass wool soaked in1 M zinc acetate is placed between thestripper and w ater trap t o remove hydrogen sulfide. The gen-erated arsine (ASH,) and stibine are collected in a glass U-tube(16 cm long, 6 mm 0.d.) packed with glass wool treated withdimethyldichlorosilane. T his tra p is interfacedto the gas chro-matograph/photoionization detector (HN U Model 321 with a10.2-eV lamp; a ttenua tion X10) byusing a six-way, stainless steelchromatographic valve (Whitey). Th e valve is plumbedso thatthere are two positions; strip/tr ap and column/inject. In thestrip /tra p position, the effluent from the stripping app aratuspasses through the hydride trap and is then vented to the at-mosphere; carriergas passes directly into the GC column. In thecolumn/injsct position, the carrier gas passea through the hydridetra p and into the GC colum n, while the stripping gas is venteddirectly to the atmosphere. All glass surfaces are trea ted withdimethyldichlorosilane,and all connections are made with TeflonSwagelok connectors and Teflon tubing.

Th e gas chromatographic column consists of a 4-m , l/s-in.Teflon (TF E) tube packed with Carbopack B H T 100 (40/60mesh, Supelco). T he followinggas flow rates and column con-ditions are used: stripping gas, 100 mL/min helium; carrier gas,30 mL/min helium; column temperature , 30 OC (70 "C when notin use); detector temperature, 125 OC.An integrator/plotter (HP3392A) s used o record chromatogramsand determinepeak meas.

Reagents and Standards. Reagents for the hydride deter-mination are exactlyas described by Andreae et al.(9). Allreagents and acids are reagent grade (Baker) with th e exceptionof Baker 'Instra-analyzed" nitric acid. Zero grade helium is usedfor both stripp ing and carrier gas with additional in-line oxygenand activated charcoal traps. Th e hydrochloric acid is bubbledwith a stream of helium(30 mL /min) for 3 h (for a 2.4-L bottle)to remove free chlorine gas. It is subsequ ently passed through10 mL of A Gl x8 resin (100/200 mesh, Bio-Rad; washed with 4M HCl) held in a chromatographic column (Econo-column,Biu-Rad) to remove any arsenic and antimo ny contamination andstored in a glass bottle until dispensed. Potassium iodide(1 M)and 4 % (w/v) sodium tetrahydridobora te (Alfa) are made freshevery 4 h, since they are not stable with storage. Tris-HC1 is 2.5


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1140 ANALYTICALCHEMISTRY,VOL. 63, NO. 11, JUNE 1, 1991

Table I. Storage Results for Oxic and Anoxic SeawaterSamples Taken in the Black Sea (43O04N, 4O00E) n June1988 (All Concentrations in nmol/L)

shipboard storeddepth, m As(II1 + V) Sb(II1 + V) As(II1 + V) Sb(II1 + V)

Oxic Water Column5 3.72 f 0.02 1.36 f 0.05 3.62 i .14 0.93 f 0.06

30 5.17 f 0.36 0.83 f 0.12 5.22 f 0.20 0.75 i .0490 36.1 f 0.05 0.33 f 0.02 36.2 f 0.3 0.37 f 0.04

500 11.4 f 0.1 0.61 i 0.02 32.8 i 0.2 0.40 i .01800 10.4 f 0.2 0.92 f 0.02 31.3 f 0.4 0.34 f 0.04

1500 7.01 f 0.41 0.55 f 0.05 27.0 f 0.2 0.28 i 0.01

All determinations made intriplicate.

Anoxic Water Column

trivalent forms of arsenic an d antimony will oxidize duringsuch storage. Thus, th e samples must either be analyzedimmediately after collection (e.g., on board ship) or stored ina manne r t ha t does not compromise the chemical forms ofarsenic and antimony. Rapid freezing a t liquid nitrogentemp eratur es and subse quen t storag e below -40 OC have beenshown to preserve th e original chemical forms(I). Rapidfreezing is particularly impo rtant for saline waters since theionic strength of brines formed during slow freezing canpromote changes.

While previous investigators have reported th at acidifiedstorge for total inorganic (i.e.,(111 +V)) arsenic and antimonyis acceptable(9, II), the results in Table I indicate tha t theremay be storage artifacts when anoxic water samples are keptin this manner. In particular, As(II1+ V) concentrationsdetermined on sam ples stored via acidification are an averageof 225% higher than those determ ined immediately at sea;shipboard and stored concentrations in th e oxic water columnare identical. In contrast, Sb(I I1+ V) in the anoxic watersamples tha t were stored are a n average of49% lower tha nthose determ ined at sea. Again, the oxic samples did not showthis tren d. All of the sam ples were filtered through 0.4-kmfilters, and possible explanations for the be havior of arsenicinclude the oxidation of organic arsenic species not de tectedby the inorganic methods or the oxidation of an inorganic,colloidal form th at passed thro ugh the filter (e.g.,w 3 ) .heloss of antimon y during storage may be dueto adsorption. Inany case, these da ta argue for the determination of arsenican d antimo ny species in the field.

Particulate Samples. The handling and storage of samp lesmust n ot alter the concentration of particulate arsenic andantimony. For biogenic materials and sediments, changes inconcentration may occur via bacterial degradation duringstorage. In order to prevent this, samples are placed inacid-cleaned polyethylene vials or bags and frozen imme di-ately. Samples are dried slowly at40 OC to prevent potentiallosses from volatilization. T o ensure homogene ity, samples

are sieved through a polyethylene mesh afte r grinding withan agate mortar a nd pestle. Dried and ground samples arestored in clean polyethylene bottles.

Hydride Generation and Chromatographic Separation.Chromatographc Separation . The operation of the pho-toionization detector (PID) is based on the absorption ofultraviolet rad iation causing molecules in th e de tector chamberto ionize (if their ionization potentials are less than that ofthe UV source,10.2 eV). Thus, the PID is capable of detedingarsine (I P of 10.03 eV) and stibine ( IPof 9.58 eV), but as anonspecific detector, these hydrides must be chromato-graphically separated from other coeluting compounds.Among the known compounds produced by the hydridegeneration conditions used here are c arbon dioxide, diborane,an d hydrogen sulfide, as well as methylated arsine(11) and

I I 1 I I I I 1 I

0 2 4 6 8Time (min.)

Figwe 2. Typical chromatogramshowkrg the separationof arsine (ca.

5 ng) and stibine (ca.2 ng) in a seawater sample.

stibine (9). CarbopackB H T 100 (Supelco)was chosen as th echromatographic packing because of its ability to sep aratemost volatile sulfur compounds an d because of the similarities(e.g., boiling points) between these compounds and the in-organic hydrides. An example chroma togram is shown inFigure 2, where arsine has a retention time of ca. 3 min an dthat of stibine is ca. 7 min. Me thylated arsine and stibine (e.g.,CH3AsH2, (CH3)&3bH) do not elute from the Carbopackcolumn at 30 C. This eliminates any interference from themeth ylated species, bu t it also precludes their simultane ousdetermination with the inorganic species.

Hydrogen sulfide elutes before arsin e (i.e., with th e un re-solved peaks preceding arsine; Figure2), and since the PI Dis an e xtreme ly sensitive dete ctor for H 2S (e.g., ref12), thissulfur gas can interfere with th e determ ination of arsenic inanoxic waters (Le., the arsine peak is only a shoulder on thelarger H@ peak). In orderto remove this interference an H atra p, consisting of a sm all tube filled with glass wool th at issoaked in zinc acetate, is placed in-line between the stripperand th e water trap. This tra p efficiently removes hydrogensulfide concentrations up to2.0 mmol of S/L. Analyses ofarsenic and antimony standards with and without the sulfidetra p show identical peak areas. Thu s, the zinc acetate tra peliminates hydrogen sulfide interference without affecting thedeterminations of arsenic and antimony.

The only other chromatographic interferents are highboiling point compounds (e.g., wa ter) tha t have retention times

longer tha n 10 min and elute during subsequen t chromato-grams. These compoundscan be eliminated by returning thesix-way valve to the str ipltr ap position45 s after pulling thehydride trap from the liquid nitrogen. Within this time span,arsine and stibine are revolatilized, but higher boiling pointsu bta ne s remain in the trap. If the valve is not switched backto the str ip/t rap posit ion, at least1 h is required to elute al lof these substances.

Selective Hydride Generation. In order to determine theconcentrationof inorganic arsenic and antim ony species, arsineand stibine must be generated from their trivalent stateswithout affecting the pentava lent forms. Subsequently,As(II1+ V) and Sb(I1I+V) must be reduced qu antitativelyto theirrespective hydrides and the concentrationsof h(V) nd Sb(V)calculated by difference. Exam ination of the published


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ANALYTICAL CHEMISTRY,VOL. 63 , NO. 11, JUNE 1, lQS1 1141

Table 11. Recoveriesof Total Arsenic an d Antimonyfo r Various W et Oxidative Digestsn,*

dieest recovery

material

N I S T River Sed imentSR M 1645 As: 66'S b 5 lC

NIST Estuarine SedimentSR M 1646 As: 11.6f 1.3Sb: 0.4'

N I S T Bovine Liver SRM 1577 As: 0.047 *0.006S b 0.003'IAEA Copepod HomogenateMA-A-1 As: 7.6 f 0.7

S b 0.08 f 0.04

57.6 f 3.044.4 f 2.38.59 f 0.43ND

0.014 *0.001NDee

59.5 *2.9 48.3 f .1 41.7 f .16.76 f .34 NDd 35.5 *1.77.99 f 0.36 9.24 f .28 5.16 f .170.20 f 0.02 ND 0.06 f 0.01

e e 0.050 f .003e e ND6.90 f 0.28 6.59 f 0.26 0.18 k 0.01ND ND 0.049 f .001

65.5 f .848.9 k 2.911.2 f .60.49 k 0.05

0.042f

0.0020.003 f .0017.51 f .540.069 f .004

Concentrationsin micrograms As or Sb pe r gram. bAll digests performed at least in triplicate. Only noncertified value is available.dNon-detectable. eDigestwa s no t tested.

method s of Andreae (11) for arsenic and Andreae et al. forantimony (9) revealed t ha t conditions for hydride generationfrom the trivalent ions [As(III) and Sb(III)] are nearly iden-tical, while those for Sb (II1+ V) are more rigorous (Le., re-quiring higher acid concentration and the addition of KI)thanthose or As(III + V). Thus, e initially selected the a ntimo nyprocedure for the simultaneous determination of both ele-ments.

Standards of As(V) and Sb(V) subjected to the Sb(II1)method showed no detectable recoveries, indicating th at theSb(II1) method is specific for the trivalen t forms. Moreov er,the recoveries ofAs(II1) and As(1II +V) using the Sb(II I) andSb(II1 +V) meth ods are identical with those obta ined byusingthe arsenic-only methods. Thus, th e recommended conditionsare c apable of selectively volatilizing the triv alen t and p en-tavalent forms of both arsenic and antimony. Th e only otherparameter t ha t req uired evaluation was the rea ction/strippingtime t o ensure q uantitative recoveries of the h ydrides withour apparatus. In Figure3 it can be seen th at th e recoveriesof arsine and stibine are essentially c omp lete by7 min; thistime is similar to the 6-min str ip/ tra p time used by A ndreaeet al. (9).

Several modifications to t he A ndreae e t al.(9) techniquewere developed, primarily to reduce reagent blanks a nd in-tereferences. First, it was found tha t Sb(II1+ V) could notbe quantitatively recovered by using certain batches of hy-drochloric acid. However, after bubbling helium through th eacid for 3 h, full recovery was regained. Since the interfere ntappea rs to be volatile, we speculate tha t it is free chlorine gasin the hydrochloric acid. In add ition to purging with helium,the HCl is passed through th e anion-exchange resin AGlX8to eliminate the large arsenic and antimony blanks associatedwith the acid ( 13 ) . This blank varies considerably from lotto lot, and ranges from


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1142 ANALYTICAL CHEMISTRY,VOL. 63, NO. 11, JUNE 1, l Q Q l

Table 111. Amounts of Arsenic and Antimony in Natural Waters and Particulate Materialsa

A. Water Samples (nmol/L)

Type, ocation As(II1) AsW)

mid-Chesapeake Bay,4 m, 6/14/88sediment porewater, mid-Chesapeake Bay,6/15/88Sacramento River, CA,9/24/86 0.07 f 0.01 11.5 f 0.3rain water, Bermuda,1/25/89


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GC321 (no longer in production) GC322 (replacement for GC321)

The work in this report was done with an HNU GC311 shown above. The replacement instrumentdescribed in this report is a GC322 manufactured b y:

PID Analyers,LLC,

2 Washington Circle,

Sandwich, MA 02563 T 1 774 413 5281 F 1 774 413 5298

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determination of arsenic and antimony using selective hydride generation and gc pid

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