This article was downloaded by: [University of Sherbrooke]On: 18 November 2014, At: 22:54Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Petroleum Science and TechnologyPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/lpet20

An Improved Method for theDetermination of PetroleumHydrocarbons From Soil Using a SimpleUltrasonic Extraction and FourierTransform Infrared SpectrophotometryM. N. Couto a b , J. R. Borges b , P. Guedes a b , R. Almeida a , E.Monteiro b , C. M. R. Almeida a , M. C. P. Basto a b & M. T. S. D.Vasconcelos aa CIMAR/CIIMAR—Centro Interdisciplinar de Investigação Marinha eAmbiental , Universidade do Porto , Porto , Portugalb Departamento de Química e Bioquímica , Faculdade de Ciências daUniversidade do Porto , Porto , PortugalPublished online: 23 Dec 2013.

To cite this article: M. N. Couto , J. R. Borges , P. Guedes , R. Almeida , E. Monteiro , C.M. R. Almeida , M. C. P. Basto & M. T. S. D. Vasconcelos (2014) An Improved Method for theDetermination of Petroleum Hydrocarbons From Soil Using a Simple Ultrasonic Extraction and FourierTransform Infrared Spectrophotometry, Petroleum Science and Technology, 32:4, 426-432, DOI:10.1080/10916466.2011.587383

To link to this article: http://dx.doi.org/10.1080/10916466.2011.587383

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Dow

nloa

ded

by [

Uni

vers

ity o

f Sh

erbr

ooke

] at

22:

54 1

8 N

ovem

ber

2014

Petroleum Science and Technology, 32:426–432, 2014Copyright C© Taylor & Francis Group, LLCISSN: 1091-6466 print / 1532-2459 onlineDOI: 10.1080/10916466.2011.587383

An Improved Method for the Determination of PetroleumHydrocarbons From Soil Using a Simple Ultrasonic

Extraction and Fourier Transform Infrared Spectrophotometry

M. N. Couto,1,2 J. R. Borges,2 P. Guedes,1,2 R. Almeida,1 E. Monteiro,2

C. M. R. Almeida,1 M. C. P. Basto,1,2 and M. T. S. D. Vasconcelos1

1CIMAR/CIIMAR—Centro Interdisciplinar de Investigacao Marinha e Ambiental, Universidade doPorto, Porto, Portugal

2Departamento de Quımica e Bioquımica, Faculdade de Ciencias da Universidade do Porto,Porto, Portugal

An environmentally friendly, cheap, and quick method for total petroleum hydrocarbons determinationin solid matrixes (soil and sediments) is described. The method involves a simple extraction process(ultrasonic bath) and requires reduced amounts of solvent and solid sample. The analysis is carried outby Fourier transform infrared spectrophotometry. Detection limits were 63 or 24 mg kg−1 depending onthe cell path length (10 or 40 mm, respectively). The method is suitable for application in weatheredcontaminated soils, which usually presents low availability of contaminants and seems to be a goodchoice, for instance, for monitoring evolution of soil or sediment recovering during a decontaminationprocess.

Keywords: FTIR, petroleum hydrocarbons, soil and sediment, tetrachloroethylene, ultrasonic extraction

1. INTRODUCTION

Soil contamination by petroleum hydrocarbons (PHC) is of environmental concern, as they cancause different kinds of stress on ecosystem and human health. Therefore, expeditious and reli-able methods for their determination in solid matrixes are useful, in order to provide either quickinformation on damaged extent or to monitor soil recovery rate after application of a remediationtechnology. In most cases, information on levels of total petroleum hydrocarbons (TPHC), withoutidentification/quantification of individual compounds, is enough for that purpose.

A bibliographic analysis of the available methods for TPHC determination revealed that the mostused ones have been gravimetry (EPA Method 9071 B, 1998), infrared (IR) spectrophotometry (U.S.Environmental Protection Agency, 1996), and gas chromatography with flame ionization detection(GC-FID; U.S. Environmental Protection Agency, 2000), the first two being cheaper and quickerthan the last one. In any case, a previous step for PHC extraction from the solid matrix is required.Available procedures include, among others, microwave assisted extraction (Shu and Lai, 2001),supercritical CO2 extraction (U.S. Environmental Protection Agency, 1996; Morselli et al., 1999),

Address correspondence to M. N. Couto/CIMAR/CIIMAR—Centro Interdisciplinar de Investigacao Marinha e Ambi-ental, Rua dos Bragas 289, 4050–123 Porto, Portugal and Faculdade de Ciencias, Universidade do Porto, Rua do CampoAlegre, 687 4169–007, Porto, Portugal. E-mail: maria.couto@fc.up.pt

426

Dow

nloa

ded

by [

Uni

vers

ity o

f Sh

erbr

ooke

] at

22:

54 1

8 N

ovem

ber

2014

DETERMINATION OF PETROLEUM HYDROCARBONS BY FTIR 427

ultrasonic (US) extraction (Liste and Felgentreu, 2006), as well as the more classic procedures suchas soxhlet extraction (Gallego et al., 2006). Among them, US extraction may offer some advantagessuch as lower cost, time consuming effectiveness or relatively low requirement of harmful solvents.For instance, soxhlet extraction requires relatively large volumes of organic solvents, which is anecological disadvantage. After the extraction step, TPHC determination by gravimetry requireselimination (by evaporation) of the solvent before analysis, which can imply loss of analyte orinclusion of compounds that contribute to the final weight but that are not the target contaminant(Villalobos et al., 2008). IR spectrophotometry analysis combined with US extraction may provide asimple, expeditious and economic methodology for TPHC determination in solid matrixes. However,to our knowledge, this methodology has been only used in a couple of studies (Liste and Felgentreu,2006; Idodo-Umeh and Ogbeibu, 2010).

For IR spectrophotometry determinations the solvent for the extraction step must be transparent inthe target wavelength interval and must have no C-H bonds. Otherwise it could cause false positiveresults. Reliable options on this point of view may be Freon 113 (Liste and Felgentreu, 2006),carbon tetrachloride (CCl4), or tetrachloroethylene (C2Cl4; Farmaki et al., 2007). Since Freon 113is considered one of the substances that may cause the depletion of the stratospheric ozone layer,its usage as solvent should be avoided. CCl4 is not also an advantageous alternative owing to itstoxicological effects (Farmaki et al., 2010). Therefore C2Cl4 seemed to be a better choice, despitenot being normally used for this purpose. Indeed, only two studies (Nascimento et al., 2008; Idodo-Umeh and Ogbeibu, 2010) that reported the use of C2Cl4 for TPHC extraction from solid matrixwere found.

The aim of this work was the optimization of an environmentally friend (requires a small volumeof solvent), cheap and quick method for TPHC determination in solid matrix (soils and sediments),characteristics which are not normally present in used conventional methods. The present methodinvolves US extraction with C2Cl4 and Fourier transform infrared (FTIR) spectrophotometry analy-sis, a combination only reported once (Idodo-Umeh and Ogbeibu, 2010). However, validation of themethod could not be found in the literature. In addition, relatively large volumes of solvent have beenused before (Liste and Felgentreu, 2006; Nascimento et al., 2008; Idodo-Umeh and Ogbeibu, 2010).

2. EXPERIMENTAL

2.1 Reagents and Material

Anhydrous sodium sulfate, p.a., and silica gel, 70–230 mesh, were obtained from Fluka andMacherey-Nagel, respectively. Silanized glass wool was obtained from Supelco. Tetrachloroethy-lene, ≥99% spectrophotometric grade, was obtained from Sigma-Aldrich. Isooctane, ≥99% ACSspectrophotometric grade, and hexadecane, 99%, both from Sigma-Aldrich, were used to preparestock standard solutions.

All glass material used in sample’s handling was firstly washed with Teepol and deionized waterand then soaked in 20% (v/v) HNO3 solution for at least 24 h. After being washed with deionizedwater, vials and septa were dried and maintained in the oven at 40◦C and the remaining requiredmaterial was dried at room temperature.

2.2 Samples

Certified reference material CRM 350-100, TPHC in Sandy Loam Soil (C6–C35), from ResourceTechnology Corporation, was used for quality control. The CRM was conserved at 4◦C in order toprevent loss of volatile compounds.

Dow

nloa

ded

by [

Uni

vers

ity o

f Sh

erbr

ooke

] at

22:

54 1

8 N

ovem

ber

2014

428 M. N. COUTO ET AL.

Soil samples were collected in a refinery plant and estuarine and sandy beach sediment sampleswere collected in Douro River estuary (North of Portugal) and in O Rostro beach (Galicia, Spain),respectively. All samples were dried at room temperature until constant weight, being afterwardssieved (2 mm) and conserved at –20◦C.

2.3 Analytical Procedures

2.3.1 Extraction step

About 1 g of solid sample (soil or sediment) was mixed with anhydrous sodium sulfate (1:1 (w/w))for chemically drying the sample. A suitable amount of C2Cl4 [1:10 (msample/vsolvent)] was added andUS extraction (Elma, Transsonic 460/H model) was performed for 30 min. The obtained suspensionwas then centrifuged (Selecta Unitronic) at 1500 rotations per minute for 2 min. The obtained extractwas decanted and mixed with 0.3 g of silica gel [deactivated with 2% of water (wwater/wdry silica gel)],in order to remove non–mineral oil contaminants as animal greases and vegetable oils (U.S. Envi-ronmental Protection Agency, 1996). The mixture of extract and silica gel was well homogenized(Unitronic) for 10 min and filtered through silanized glass wool into a disposable pipette. The filteredextract was refrigerated at 4◦C until FTIR spectrophotometry analysis (within 1 h).

2.3.2 Determination

TPHC analysis of the sample extracts was performed by FTIR spectrophotometry (Jasco FT/IR-460 Plus model), using pure solvent for background spectra and scanning the range 2700–3200 cm−1,the absorbance (Abs) being measured as peak height, near 2926 cm−1, after baseline correction. Twoquartz cells (of 10 and of 40 mm path length [Infrasil I, Starna Scientific]), were used dependingon the TPHC concentrations in the samples. Cells were washed with clean solvent in an US bath(Sonorex TK 30, Bandelin) for 3 min.

TPHC were quantified by direct comparison with the calibration curve. For this purpose, cali-bration curves were carried out using standards solutions that were prepared in C2Cl4, from a stockstandard solution containing equal volumes of isooctane and hexadecane (Farmaki et al., 2007). Con-centration ranges tested for 10 mm and 40 mm path length cells were 13–234 mg L-1 and 1.2–38.4mg L-1, respectively. Concentration intervals generally used for 10 mm and 40 mm path length cellswere 21–140 mg L−1 (210–1400 mg kg−1) and 2–23 mg L−1 (20–230 mg kg−1), respectively.

The quality control of the method was carried out by (a) analyzing the CRM, (b) analyzingextracts of solid samples (soil or sediment) spiked with known amount of hydrocarbons, and (c)comparing the obtained results with those provided by an external laboratory for the same sample(only soil).

3. RESULTS AND DISCUSSION

In a first step, acceptable conditions for FTIR spectrophotometry determination were established.Normally, IR spectra of solutions containing hydrocarbons present characteristic bands of C-Hbonds: 2853 cm−1 and 2926 cm−1 (C-H stretch of CH2), 2962 cm−1 (C-H stretch of CH3), and3040 cm−1 (stretching vibration of C-H aromatic bonds). Therefore, the 2700 - 3200 cm−1 intervalwas used in the measurements. In a preliminary step, measurements of the bands were carried out interms of both area (between 2700 and 3200 cm−1 or between 2922 and 2970 cm−1) and height of thehighest peak in the interval 2922–2970 cm−1. Both alternatives have been used to quantify oil andgrease in water (Daghbouche et al., 1997) but maximum peak height has been the most used, even

Dow

nloa

ded

by [

Uni

vers

ity o

f Sh

erbr

ooke

] at

22:

54 1

8 N

ovem

ber

2014

DETERMINATION OF PETROLEUM HYDROCARBONS BY FTIR 429

TABLE 1Characteristics of the analytical procedurea

Cell path length, mm 10 40

Linear range, mg L−1 (mg kg−1) 13–234 (130–2340) 1.2–38.4 (12–384)LOD, mg L−1 (mg kg−1) 6.3 (63) 2.4 (24)LOQ, mg L−1 (mg kg−1) 21 (210) 8.1 (81)Repeatability, % 11 2.1Reproducibility, % 14 9.3

Note. LOD = limit of detection; LOQ = limit of quantification.aCorresponding concentration values expressed as mg kg−1

soil are presented in brackets.

in standard procedures (EPA Method 8440, 1996; Farmaki et al., 2007). Although, in theory, peakarea could provide more accurate data than peak height, in the present work it was observed thatdata obtained by using areas (by automatic integration) were not reproducible (results not shown).Therefore, further measurements were carried out in terms of height of the highest peak, around2926 cm−1.

Practically linear responses (correlation coefficient R > 0.998; n = 5) were observed all over theconcentrations range tested (sum of the concentrations of isooctane and hexadecane): 13–234 mgL−1 for 10 mm cell path length and 1.2–38.4 mg L−1 for 40 mm cell path length.

From the calibration curve, limit of detection (LOD) and limit of quantification (LOQ) werecalculated according to IUPAC guide (Thompson et al., 2002; Table 1). Repeatability and repro-ducibility of the analysis (Thompson et al., 2002; two different days, three or five samples per day)were relatively low (≤14%; Table 1).

For the TPHC extraction from the sample, a published procedure (Liste and Felgentreu, 2006;10 g of soil; 30 g of anhydrous sodium sulfate; 110 mL of Freon 113 as solvent; 60 min of sonication;and neutral aluminum oxide powder to clean the sample) was used as starting point. Several changeswere introduced: the masses of both sample and anhydrous sodium sulfate were reduced to 1 g each,only 10 mL of C2Cl4 were used as solvent (U.S. Environmental Protection Agency, 1996; Farmakiet al., 2007) and the extraction time was reduced to 30 min. With this procedure a 5- (Idodo-Umehand Ogbeibu, 2010) or 10-fold (Liste and Felgentreu, 2006) decrease in soil mass; a 3- (Idodo-Umehand Ogbeibu, 2010) to 5- (Nascimento et al., 2008) or 11-fold (Liste and Felgentreu, 2006) decreasein the solvent volume and a 2-fold (Liste and Felgentreu, 2006) to decrease in extraction time wereachieved.

The described extraction procedure followed by TPHC analysis by FTIR spectrophotometryprovided method LODs of 63 mg kg−1 or 24 mg kg−1, depending on the cell path length used(Table 1). These LODs were similar to those reported in literature (Nascimento et al., 2008) wherea much more time consuming extraction (agitation for 4 h plus 30 min) had been used. The presentLODs were higher than that reported in EPA Method 8440 (Villalobos et al., 2008; 10 mg kg−1),but this methodology requires more expensive and much less common equipment for extraction(supercritical fluid of carbon dioxide for extraction).

The optimized procedure was applied to the certified material CRM 350-100. First, assays ofrepeatability and reproducibility of the signal observed for diluted 1:10 or 1:50 CRM extractsdepending on the cell path length (10 and 40 mm, respectively) were performed according to IUPACguide (Thompson et al., 2002; Table 2). Relative standard deviations (RSD) lower than 17% wereobserved and, as expected, with better repeatability than reproducibility. Both were lower than 14%,being similar to the results obtained for simple standard solutions.

Dow

nloa

ded

by [

Uni

vers

ity o

f Sh

erbr

ooke

] at

22:

54 1

8 N

ovem

ber

2014

430 M. N. COUTO ET AL.

TABLE 2Characteristics of the Signal Observed for Diluted 1:10 or 1:50 Extracts of Certified Reference Material CRM

350–100 for 10 and 40 mm Cell Path Length, Respectively

Cell path length/mm 10 40

Repeatability, % (n = 3) 8.6 13Reproducibility, % (n = 3) 13 14RSDa, % 15 17

aRSD was calculated as stot = (srepeatibility2/n + sreproducibilty

2)1/2.

For the CRM material a recovery around 70% (Table 3) was observed, with the experimentalvalue still inside the prediction interval (Table 3). This recovery yield may be a result of the presenceof a volatile fraction that evaporated during the handling of the sample.

Another possibility for the observed CRM recovery may result from the incomplete extraction ofPHC from the solid sample, similarly to what had been reported in literature (Nadim et al., 2002),in which extraction solvent (Freon 113) could not fully extract some ranges of hydrocarbons, forinstance, heavier molecules. In fact, other works reported the use of, at least, two extraction steps(Nascimento et al., 2008; Idodo-Umeh and Ogbeibu, 2010) for obtaining quantitative recoveries ofhydrocarbons. However, in the present case, an increased number of extraction steps substantiallydecreased recovery of CRM (results not shown).

A possible degradation of organic compounds by oxidative mechanisms caused by US, resultinginto oxygen derived compounds that could be eliminated in the silica purification step, was alsoconsidered. For this purpose, the same extraction procedure was applied to a standard solution ofPHC and ca. 13% of PHC concentration loss was observed. However, when only the last part of theprocedure (silica gel addition, agitation for 10 min, and filtration, without the previous US step) wasapplied to the standard solution of PHC a similar loss was observed.

Low recoveries of the CRM may also be related to the quantification procedure, that is, thecalibration curve used. In fact, calibration curve was carried out with a mixture of only two standards,as had been used before (Farmaki et al., 2007). Nevertheless, the shape of the spectra of standardsolutions and CRM extract were identical.

These results confirmed that evaporative losses may be the main mechanism responsible forthe low recovery yield observed for CRM, which contains very volatile and volatile PHC, namelythose in the range between C5–C10. Such problems have been observed before in water matrixes(Romero and Ferrer, 1999). For instance, it has been reported that low boiling point constituents(gasoline and other volatile fractions) can be lost by evaporation during manipulative transfers(sample preparation). However, the losses due to manipulative transfers in IR methods may be much

TABLE 3Results Obtained (mg kg−1) for Certified Reference Material CRM 350–100

Experimental Valuesa

CRM 350-100Cell path length/mm 10 40

Reference Value ± SDa 8300 ± 870 6249 ± 1036 5774 ± 1355Confidence Interval (95%) 7380–9200Prediction Interval 4240–12300

aMean and SD (n = 8).

Dow

nloa

ded

by [

Uni

vers

ity o

f Sh

erbr

ooke

] at

22:

54 1

8 N

ovem

ber

2014

DETERMINATION OF PETROLEUM HYDROCARBONS BY FTIR 431

lower than those experienced during gravimetric procedures, which require solvent evaporationbefore residue is weighed (Romero and Ferrer, 1999).

Therefore, the optimized procedure seems to be a good choice for estimation of levels of PHCcontamination in solid matrixes and for monitoring evolution of solid matrixes recovering duringdecontamination processes. Although PHC recoveries from soils may be below 100%, this procedurehas the advantage of reducing time and solvent consumption.

The method was applied to a soil from a refinery and sediments from two different origins, onefrom an estuarine area and another one from a sandy beach, for evaluating the respective TPHCcontents. For the spiked extracts, mean recoveries of 102 ± 9% (n = 4), 92 ± 11% (n = 3), and116 ± 18% (n = 3) were observed for soil and for estuarine and sandy beach sediments, respectively.

The soil sample was also analyzed in an external laboratory, which quantified mineral oil contentbetween C10 and C40 using a different method (ISO, 2004). The differences between results wereabout 11% (1800 mg kg−1 using this method vs. 1600 mg kg−1 from external laboratory) and,therefore, of similar magnitude to experimental errors associated to the method (Table 3). In addition,in a study carried out, in parallel, aiming to survey suitable conditions for biological remediationof soil from a petrol refinery, similar percentages of TPHC removal were obtained by FTIR and byGC-FID between C10 and C40 hydrocarbons (Couto et al., 2012). However, as previous mentioned,the last one is more expensive and time consuming than FTIR.

4. CONCLUSIONS

The present method is simpler, more expeditious and ecological, and requires only equipmentavailable in most laboratories comparatively to other developed methods for determination of TPHC.Despite TPHC determination in soils by IR spectrophotometry preceded by US extraction or theuse of C2Cl4 as the extraction solvent having been reported on a few previous papers, severalimprovements were achieved in this work such as: a 5- or 10-fold decrease in soil mass; a 3- or11-fold decrease in the solvent volume and a 2 times decrease in extraction time.

The method seems to be a good choice for estimation of levels of PHC contamination in solidmatrixes, even when weathered contamination is present, and for monitoring evolution of soil orsediment recovering during a decontamination process.

FUNDING

The authors thank “Fundacao para a Ciencia e a Tecnologia” for the PhD scholarship of N. Couto(SFRH/31816/2006), cofinanced by POPH/FSE and for BII scholarships (CIIMAR/2008/BII/01–25)of P. Guedes and R. Almeida (in project ERA-AMPERA/0003/2007), and Refinaria do Porto (GALPEnergia) for financial and logistical (C. Santos) support.

REFERENCES

Couto, M. N. P. F., Pinto, D., Basto, M. C. P., and Vasconcelos, M. T. S. D. (2012). Role of natural attenuation, phytoremediationand hybrid technologies in the remediation of a refinery soil with old/recent petroleum hydrocartbons contamination.Environ. Technol. 33: 2097–2104.

Daghbouche, Y., Garrigues, S., Morales-Rubio, A., and de la Guardia, M. (1997). Evaluation of extraction alternatives forFourier transform infrared spectrometric determination of oil and greases in water. Anal. Chim. Acta 345:161–171.

Farmaki, E., Kaloudis, T., Dimitrou, K., Thanasoulias, N., Kousouris, L., and Tzoumerkas, F. (2007). Validation of a FT-IRmethod for the determination of oils and grease in water using tetrachloroethylene as the extraction solvent. Desalination210:52–60.

Dow

nloa

ded

by [

Uni

vers

ity o

f Sh

erbr

ooke

] at

22:

54 1

8 N

ovem

ber

2014

432 M. N. COUTO ET AL.

Gallego, J. R., Gonzalez-Rojas, E., Pelaez, A. I., Sanchez, J., Garcıa-Martınez, M. J., Ortiz, J. E., Torres, T., and Llamas,J. F. (2006). Natural attenuation and bioremediation of Prestige fuel oil along the Atlantic coast of Galicia (Spain). Org.Geochem. 37:1869–1884.

Idodo-Umeh, G., and Ogbeibu, A. E. (2010). Bioaccumultaion by the heavy metals in Cassava tubers and plantain fruitsgrown in soils impacted with petroleum and non-petroleum activities. Res. J. Environ. Sci. 4:33–41.

ISO. (2004). Soil quality: Determination of content of hydrocarbon in the range C10 to C40 by gas chromatography. ISO/DISMethod 16703:2004. Geneva, Switzerland: ISO.

Liste, H.-H., and Felgentreu, D. (2006). Crop growth, culturable bacteria, and degradation of petrol hydrocarbons (PHCs) ina long-term contaminated field soil. Appl. Soil. Ecol. 31:43–52.

Morselli, L., Setti, L., Iannuccilli, A., Maly, S., Dinelli, G., and Quattroni, G. (1999). Supercritical fluid extraction for thedetermination of petroleum hydrocarbons in soil. J. Chromatogr. A 845:357–363.

Nadim, F., Liu, S., Hoag, G. E., Chen, J., Carley, R. J., and Zack, P. (2002). A comparison of spectrophotometric and gaschromatographic measurements of heavy petroleum products in soil samples. Water Air Soil Pollut. 134:97–109.

Nascimento, A. R., Ziolli, R. L., Ararun, J. T., Pires, C. S., and Silva, T. B. (2008). Validation of method for the determinationof TPH (total petroleum hydrocarbon) by infrared detection. Ecletica Quımica 33:35–42.

Romero, M. T., and Ferrer, N. (1999). Determination of oil and grease by solid phase extraction and infrared spectroscopy.Anal. Chim. Acta 395:77–84.

Shu, Y. Y., and Lai, T. L. (2001). Effect of moisture on the extraction efficiency of polycyclic aromatic hydrocarbons fromsoils under atmospheric pressure by focused microwave-assisted extraction. J. Chromatogr. A 927:131–141.

Thompson, M., Ellison, S. L. R., and Wood, R. (2002). Harmonized guidelines for single laboratory validation of methodsof analysis. Pure Appl. Chem. 74:835–855.

U.S. Environmental Protection Agency. (1996). Total recoverable petroleum hydrocarbon by infrared spectrophotometry.United States Environmental Protection Agency, SW-846 Manual. EPA Method 8440. Washington, DC: US GovernmentPrinting Office.

U.S. Environmental Protection Agency. (1998). n-Hexane extractable material (HEM) for sludge, sediment, and solidsamples. United States Environmental Protection Agency, SW-846 Manual. EPA Method 9071 B.Washington, DC: USGovernment Printing Office.

U.S. Environmental Protection Agency. (2000). Nonhalogenated Organics using GC/FID. United States EnvironmentalProtection Agency, SW-846 Manual. EPA Method 8015 C. Washington, DC: U.S. Government Printing Office.

Villalobos, M., Avila-Forcada, A. P., and Gutierrez-Ruiz, M. E. (2008). An improved gravimetric method to determine totalpetroleum hydrocarbons in contaminated soils. Water Air Soil Pollut. 194:151–161.

Dow

nloa

ded

by [

Uni

vers

ity o

f Sh

erbr

ooke

] at

22:

54 1

8 N

ovem

ber

2014