Anal. Chem. 1995, 67, 2096-2102
Extraction of Organic Pollutants from Solid Samples Using Microwave Energy Vlorlca Lopez.Avila,* Richard Young, J a m Benedicto, Pauline no, and Robert Kim Midwest Research Institute, Califomia Operations, 625-8Clyde Avenue, Mountain View, Califomia 94043
Werner F. Beckert U.S. Environmental Protection Agency, Environmental Monitoring Systems Laboratory, 944 East Hamon Avenue, Las Vegas, Nevada 891 19
This study, which is part of an ongoing US. Environmental Protection Agency (EPA) research program, carried out by the Environmental Monitoring Systems Laboratory-Las Vegas, addresses new sample preparation techniques that (a) prevent or "izepollution in analytical laboratories, (b) improve target analyte recoveries, and (c) reduce sample preparation costs. We present here additional evaluation results of the microwaveassisted extraction (MAE) procedure (described previously in this journal) for 187 compounds and four Aroclors listed in the EPA Methods 8250,8081,and 8141k Our results demonstrate that most of these compounds can be recovered in good yields from the matrices investigated. For example, recoveries ranged from 80 to 120% for 79 of the 95 compounds listed in Method 8250,38 of the 45 organochlorine pesticides listed in Method 8081,and 34 of the 47 organophosphorus pesticides listed in Methd 8141A. When recoveries from freshly spiked soil samples were compared with those from aged samples, we found that recoveries usually decreased; as expected, there was more spread in recoveries with increased aging time. For 15 compounds in a reference soil, the recoveries of 14 compounds by MAE were equal to or better than recoveries obtained by Soxhlet extraction (naphthalene being the exception); for selected organochlorine pesticides, recoveries from spiked soil samples were at least 7% higher for MAE than for either Soxhlet or sonication extraction. we investigated a microwave-assisted In earlier extraction (MAE) technique for extracting polynuclear aromatic hydrocarbons and some base/neutral/acidic compounds, of interest to the US. Environmental Protection Agency @PA), from certified reference soils and marine sediments. These materials were subjected to MAE in a closed-vessel microwave system with hexane-acetone (1:l)as the extraction solvent at 80,115, or 145 'C for 5,10, or 20 min. For comparison, the same samples were (1) Beckert, W. F.; Lopez-Avila, V. Proceedings of the International Conference and Exhibition on Pollution Prevention in the Laboratory, Boston, MA, June 1993.
(2) Lopez-Avila, V.; Young, R; Beckert, W. F. Anal. Chem. 1994, 66, 10971106. (3) Lopez-Avila, V.; Young, R Application ofMicrowaue Energy to the &traction of Organic Compoundsfiom Solid Samples; EPA Report 600/R-94/031; US. Environmental Protection Agency, Environmental Monitoring Systems Laboratory: Las Vegas. NV, March 1994.
2096 Analytical Chemistry, Vol. 67, No. 13, July 1, 1995
subjected to (i) room temperature extraction by allowing the solvent mixture to stay in contact with the solid matrix the same amount of time as the microwaveextracted sample (icluding any cooling time) and (ii) simple heating with solvent in a closed container using a convection oven.3 Our results indicated that MAE compares favorably with Soxhlet/Soxtec and sonication extraction techniques. Moreover, MAE requires smaller volumes of organic solvents than the conventional techniques, and sample processing time is increased by shorter extraction times (10 min) and simultaneous extraction of up to 12 samples. In this study, which is part of an ongoing EPA program, carried out by the Environmental Monitoring Systems Laboratory &as Vegas, NV), to evaluate sample preparation techniques that (a) prevent or minimize pollution in analytical laboratories, (b) improve target analyte recoveries, and (c) reduce sample preparation costs, we have evaluated the extractability under MAE conditions of 95 compounds (icluding six surrogate compounds) listed in Method 8250,4 45 organochlorine pesticides (OCPs) and four Aroclors listed in Method 8081: and 47 organophosphorus pesticides (OPPs) listed in Method 814lA.'j Freshly spiked soil samples, spiked soil samples that were aged for 24 h, 14 days, or 21 days, and a few standard reference materials were extracted with hexane-acetone (1:l) at 115 OC for 10 min. The extracts were analyzed by gas chromatography/mass spectrometry (GC/ MS), gas chromatography with electron capture detection (GC/ ECD), or gas chromatography with nitrogen-phosphorus detection (GC/NPD), as specified in the respective EPA methods. We present here the recovery data for 187 compounds (including six surrogate compounds) and four Aroclors listed in Methods 8250,8081, and 814lA. These compounds were spiked into topsoil samples, and the samples were either extracted immediately or aged for 24 h, 14 days, or 21 days and then extracted by MAE. EXPERIMENTAL SECTION
Micmwwe-AssistedJMractionprocedure. All MAEs were performed with a MESlOOO microwave sample extraction system (CEM Corp., Matthews, NC) described in ref 2. (4) Method 8250 (Revision 1, November 1992). In Test Methodsfor Eualuating Solid Wuste, 3rd ed.; SW-846, Proposed Update II; US. Environmental Protection Agency: Washington, DC, 1986. (5) Method 8081 (Revision 0, November 1992). In Test MethodsforEualuating Solid Waste, 3rd ed.; SW-846, Proposed Update II; US. Environmental Protection Agency: Washington, DC, 1986. (6) Method 814lA (Revision 1, November 1992). In TestMethods for Eualuah'ng Solid Waste, 3rd ed.; SW-846, Proposed Update 11; US. Environmental Protection Agency: Washington, DC, 1986. 0003-2700/95/0367-2096$9.00/0 0 1995 American Chemical Society
A 5-g portion of the spiked soil or the certitled material was accurately weighed into an aluminum dish and was transferred quantitatively to the Teflon-lined extraction vessel. For the wet samples, the calculated volume of water was added to the sample in the extraction vessel and allowed to equilibrate with the matrix for -10 min. A solution containing the surrogate compounds Q.e., 2-fluorobiphenyl, 2-fluorophenol, nitrobenzene& phenol-d5,terphenyl-du, and 2,4,&tribromophenol) was added to each sample immediately before the hexane-acetone (1:l) solvent (30 mL) was added. No surrogate compounds were used with the compounds listed in Methods 8081 and 814lA M e r ensuring that a new rupture membrane was in place, the extraction vessel was closed. Extractions were performed at 115 'C for 10 min at 100%power. After extraction, the vessels were allowed to cool to room temperature for -20 min before they were opened. The supernatant was filtered through glass wool prewashed with hexane-acetone and was then combined with the 2- to 3-mL hexane-acetone rinse of the extracted sample. The extract was concentrated to -5 mL using nitrogen blowdown evaporation and was centrifuged twice for 10 min at 2300 rpm to separate the fine particulates. The extract was concentrated to 1mL for GUMS, GC/ECD, or GC/NPD analysis. Spiking Procedure. Spiking of the topsoil samples with the target compounds was performed as follows. The sample was weighed into an aluminum cup, and 50-250 yL of a concentrated stock solution (prepared by compositing the various mixtures and diluting with methylene chloride) containing either the compounds listed in Method 8250, 8081, or 814lA, was added to the sample with a syringe, ensuring that the solution did not contact the aluminum cup. Polychlorinated biphenyls (PCBs) were spiked separately from the OCPs. The concentrations of the spiking solutions were 125 yg/mL for the compounds listed in Method 8250, 2-20 yg/mL for those listed in Method 8081 (OCPs), 5 yg/mL for PCBs, and 20-40 pg/mL (except thionazin and HMPA at 10 yg/mL) for the compounds listed in Method 814lA (OPPs). The individual spiking levels and results are given in the tables in the supporting information. The spiked samples were allowed to dry for -10 min and were then transferred to the MAE vessels. The topsoil samples identified as "aged samples were spiked as described above. Water (2 mL) was added to each sample after the spiked soil samples had been transferred to the extraction vessels. The vessels were capped and were stored in a refrigerator at 4 'C for 24 h, 14 days, or 21 days. The six surrogate compounds were added to the respective soil samples immediately prior to extraction. Analysis of Extracts. The analyses of the extracts containing the compounds listed in Method 8250 were performed on a Hewlett-Packard 5890 Series I1 gas chromatograph interfaced to a Hewlett-Packard 597lA mass spectrometer MSD/DOS Chemstation (Hewlett Packard, Palo Alto, CA) and equipped with a Hewlett-Packard 5973A autoinjector. The samples were intre i.d. x 0.25pm film thickness duced via a 30-m length x 0.25" DE5 fused-silica open-tubular column U&W Scientific, Folsom, CA) with helium as carrier gas at a flow rate of -1 mL/min. The column temperature was held at 40 "C for 4 min and then increased at 8 "C/min to a final temperature of 300 "C, where it was held for 10 min. The injection volume was 1 yL, and the injector temperature was 250 "C. The injector was set in the splitless mode for 1min after the injection. The electron energy
was set at 70 eV and the electron multiplier voltage at 2160 V. Spectral data were acquired at a rate of 1s/scan (scanning range 35-500 amu). The instrument was tuned daily with DETPP introduced via the GC inlet. A 5-point internal standard calibration using standards at 5,10,25, 50, and 100 yg/mL was performed daily to establish the GC/MS linear range. The six internal standards specified below were spiked into every calibration standard and sample extract that was analyzed by GUMS. For quantification,we used the average relative response factors from the multilevel calibration. For OCP and PCB analyses, we used a Hewlett-Packard 5890 Series I1 gas chromatograph equipped with two ECDs and a Hewlett-Packard 5973A autoinjector. Samples were introduced via a splitless injector into a retention gap ( 2 k m length x 0.53mm i.d.) connected through a fused-silica Y-shaped inlet splitter to two 30-m length x 0.32" i.d. x 0.25-pm illm thickness fusedsilica open-tubular columns (a DE5 and a DB-1701) with helium as carrier gas at flow rates of 3.7 and 4.0 mL/min, respectively. For OCP analyses, the column temperature was increased at 5 "C/min from 80 to 275 "C (2-min hold); the injection volume was 1pL, and the injector temperature was 250 "C. A %pointexternal standard calibration using standards at 25, 50, and 100 ng/mL for the 20 pg/kg spike level and correspondingly higher concentrations for the higher spike levels was performed initially to establish the GC/ECD linear range. For PCB analyses, the column temperature was increased at 12 "C/min from 140 to 190 "C, held at 190 "C for 2 min and then increased at 4 "C/min to 275 "C; the injection volume was 1pL, and the injector temperature was 250 "C. A 4point external standard calibration using standards at 0.1, 0.25, 0.5, and 1yg/mL was performed for the Aroclors. For quantification,we used the average response factors from the multilevel calibration. For OPP analyses, we used a Hewlett-Packard 5890 Series I1 gas chromatograph equipped with two NPDs and a HewlettPackard 5973A autoinjector. Samples were introduced via a packedcolumn injector connected to a fused-silica retention gap ( 2 k m length x 0.5%" i.d.) and a fused-silica Y-shaped inlet splitter connected to two 30-m length x 0.32-mm i.d. x 0.25ym film fused-silica open-tubular columns (a DB-5 and a DB-1701) with helium as carrier gas at a flow rate of 3 mL/min. The column temperature was held at 120 "C for 3 min and then increased at 5 "C/min to 260 "C (hold 1 min). The injection volume was 1 pL, and the injector temperature was 250 "C. A 4point external standard calibration using standards at 1, 2.5, 5, and 10 yg/mL for the 1mg/kg spike level and half or twice these concentrations for the 0.5 and 2 mg/kg spike levels, respectively, was performed initially to establish the GC/NPD linear range. For quantification, we used the average response factors for the multilevel calibration. Solvents. All solvents used in this study were distilled-in-glass pesticide grade and were obtained from Baxter Scientific (McGaw Park, IL). Standards. Analytical reference standards of the 89 semivolatile compounds listed in Method 8250, 45 OCPs listed in Method 8081, and 47 compounds listed in Method 8141 were purchased as composite solutions in various solvents. The compounds listed in Method 8250 were purchased from Absolute Standards, Inc. (Camden, 0, as eight composite solutions in methylene chloride (mix 1 consisting of 14 ethers, phthalates, and nitrosamines; mix 2 of 14 compounds consisting mostly of chlorinated benzenes, nitrobenzene, and nitrotoluenes; Analytical Chemistry, Vol. 67, No. 73, July 1 , 1995
2097
Table I.MAE Method Performance for Selected Compounds Listed In Method 8250. compd 6 9 18 20 25 27 30 46 52 64 78 80 84 88
89
su-1
su-2 su-3 su-4 su-5 SU-6
compound name
ERA certified concn (mg/kg)b
typical recovery using EPA methodb
anthracene benzo[alanthracene bis(2ethylhexyl) phthalate butyl benzyl phthalate 2chlorophenol chrysene dibenzofuran 2,4dinitrotoluene fluorene naphthalene pentachlorophenol phenanthrene PYene 2,4,5trichlorophenol 2,4,Btrichlorophenol 2-fluorobiphenyl 2-fluorophenol nitrobenzene& phenol-ds terphenyl-d14 2,4,6tribromophenol
1.01 2.03 7.12 10.6 5.08 2.35 6.79 5.0 6.06 1.64 12.2 1.57 8.03 7.99 4.56 6.0 20.0 5.0 20.0 5.0 20.0
54.7 56.2 85.8 80.8 56.1 60.4 66.7 63.4 61.4 64.0 42.8 69.4 56.9 64.7 61.0
f f f f f f
average recove@ uncorrectedd correctede 60.6 91.1 125 109 52.3 99.8 75.6 80.6 60.2 43.3 81.8 95.8 95.3 86.4 63.6 82.3 63.5 61.6 70.4 127 96.7
68.6 103 150 128 76.2 114 88.8 83.0 72.1 64.3 85.0 110 110 96.9 71.1 102 99.5 87.4 96.0 142 94.8
RSD (%)
b1owdown evaporation recovery
4.7 6.7 11.2 10.8 15.7 8.5 1.9 4.2 1.0 15.7 6.8 6.8 12.8 1.3 4.7 8.8 14.1 15.8 13.1 8.4 3.9
88.3 88.3 83.5 84.8 68.6 87.9 85.1 97.1 83.5 67.3 96.2 87.1 86.7 89.2 89.4 80.8 63.8 70.5 73.3 89.6 102
Five compounds (i.e., 1,2- and 1,4dichlorobenzene, 2- and Cmethylphenol, and 1,2,4trichlorobenzene) are not listed because of questionable concentrations reported by ERA. AU recovery values are given in percent. Certified values reported by ERA are the true spiked concentrations; the “typicalrecoveries” values were reported by ERA. The number of determinations was four. Recoveries were not corrected for losses during blowdown evaporation. e Recoveries were corrected for losses during blowdown evaporation. f Data not available.
mix 4 of three phenols and benzoic acid mix 5 of various anilines, dibenzofuran, benzyl alcohol, and 2-methyl naphthalene; mix 8 of 13 phenols; mix 9 of eight miscellaneous compounds; mix 10 of ethyl methanesulfonate and methyl methanesulfonate; and mix 11of 11nitrogencontaining compounds), one composite solution in methanol (mix 6 consisting of benzidine and 3,Ydichlorobenzidine), and one composite solution in methylene chloridebenzene (1:l) consisting of 17 polynuclear aromatic hydrocarbons. The individual concentrations of the compounds in these mixtures were 2 mg/mL. Dibenzo [ a f acridine was purchased from Chem Service (West Chester, PA) and 1,2diphenylhydrazine from Aldrich Chemical (Milwaukee, wr) . The six surrogate compounds listed in Table 1were purchased from Absolute Standards as two composite solutions; the acid surrogate standard contained Zfluorophenol, phenol-&, and 2,4,&tribromophenol at 2 mg/mL in methanol, and the baseheutral surrogate standard contained 2-fluorobiphenyl, terphenyldlr, and nitrobenzene& at 1 mg/mL in methylene chloride. The six internal standards listed in Method 8250 (i.e., 1,4-dichlorobenzene-d~,naphthalene&, acenaphthened10, phenanthrene&, chrysene-dlz, and perylene-dld were purchased from Supelco, Inc. (Bellefonte, PA) as a composite solution at 2 mg/mL in methylene chloride; their purities were stated to be 99%. An intermediate stock solution of the target compounds listed in Method 8250 at 125 pg/mL was prepared by combining the various composite solutions; the calibration standards at 5, 10, 15, and 50 pg/mL were prepared by serial dilution with methylene chloride of the 125 pg/mL composite solution. The six internal standards were spiked into every calibration standard and sample extract at 40 pg/mL. Analytical reference standards of the compounds listed in Method 8081 were purchased from Absolute Standards as one composite solution in toluene-hexane (1:l) containing 18 compounds (aldrin, the four BHCs, 4,4’-DDD, 4,4’-DDE, 4,4’-DDT, dieldrin, endosulfan I, endosulfan 11, endosulfan sulfate, endrin, endrin aldehyde, endrin ketone, heptachlor, heptachlor epoxide, 2098 Analytical Chemistry, Vol. 67, No. 13, July 1, 1995
and methoxychlor) at 2 mg/mL per compound; one composite solution from Absolute Standards in isooctane containing DBCP, etridiazole, chloroneb, propachlor, PCNB, chloropropylate, and chlorobenzilate at 100pg/mL per compound; and one composite solution from Absolute Standards in isooctane containing dichloran, chlorothalonil, DCPA, methoxychlor, and cis- and transpermethrin at 1 mg/mL per compound. Alachlor, hexachlorocyclopentadiene, and isodrin were purchased as individual solutions in methanol (concentration 5 mg/mL, except alachlor at 1 mg/mL) from NSI Environmental Solutions (Research Triangle Park, NC). The rest of the compounds listed in Method 8081 were obtained as neat materials from Chem Service, Ultra Scientific (North Kingstown, RT), or Aldrich Chemical. An intermediate stock solution of the compounds listed in Method 8081 at 2 pg/mL in acetone was prepared by combining the various composite stock solutions; this solution was used for spiking soil samples and for preparing the calibration standards. Aroclors 1016 and 1260 were purchased from Supelco, Inc., as solutions at 1mg/mL in isooctane, and Aroclors 1248 and 1254 were purchased as neat materials from C h e d Service. A composite solution of Aroclors 1016 and 1260 at 5 pg/mL in acetone was prepared by combining the two individual stock solutions at 1mg/mL; this solution was used for spiking soil samples and for preparing the calibration standards. Analytical reference standards of the compounds listed in Method 814l.A were purchased from Absolute Standards as individual solutions in either hexane or methanol, with the exceptions of aspon, azinphos ethyl, chlorofenvinphos, chlorpyrifos methyl, dichlorofenthion, ethion, and fonophos, which were obtained as neat materials from Ultra Scientific, Inc.; dicrotophos, leptophos, phosmet, trichlorfon, tri-o-cresylphosphate, and simazine, which were obtained as neat materials from Chem Service; famphur at 1 mg/mL in acetonitrile and atrazine at 1 mg/mL in methanol, which were obtained from NSI Environmental Solutions; and thionazin at 1mg/mL in methanol, which was obtained from
Supelco. An intermediate stock solution of the compounds listed in Method 814lA (in hexane-methanol-acetonitrile) at 20 pg/ mL was prepared by combining the various individual stock solutions; this solution was used for spiking soil samples and preparing the calibration standards. Soil and Sediment Materials. The topsoil (PH 7.5; cation exchange capacity 14.6 mequiv/100 g; organic carbon content 0.1%;water content 2.6%;sand 57.6%;silt 21.8% and clay 20.6%) used in this study was obtained from Sandoz Crop Protection (Gilroy, CA). The ERA soil (Lot 324) is a material spiked with selected semivolatile compounds and was purchased from Environmental Resource Associates (ERA, Arvada, CO). The other ERA soil (Lot 9801) was certified for PCBs. The certified values for these materials are included in Tables 1 and 3. The two reference sediments HS1 and HS2, certified for PCBs, are marine sediments collected from three harbors in Nova Scotia; these materials were purchased from the National Research Council of Canada, Atlantic Research Laboratory (Halifax, Canada). According to the certificate of analysis, these materials were freeze-dried, passed through a sieve (125pm mesh size), homogenized in a cement mixer, and then subsampled into 2Wg portions. Mormation on the physicochemical properties of these materials is not available. safety. The microwave unit, which incorporates several safety features described in ref 2, should be operated in accordance with CEM’s recommended operating safety instructions. A new rupture membrane per vessel should be used for each extraction. Should the membrane rupture due to increased pressure inside individual vessels, the solvent vapor is unlikely to leak into the cavity because all vessels are connected to a containment vessel via the solvent rupture vent tube. To prevent pressure buildup inside individual vessels, wet samples should not be extracted simultaneously with dry samples; when 12 samples are extracted simultaneously,they should be either all dry or all wet. Likewise, solvent blanks should not be heated together with samples that are to be extracted by MAE, because the former will heat faster than the latter. RESULTS AND DISCUSSION
Semivolatile Compounds (Method 8250). There are presently 118 semivolatile compounds listed in EPA Method 8250 (Revision 1,November 1992). We initially selected 92 compounds for our experimental work; the other 26 compounds were OCPs and PCBs, which we investigated separately with the compounds listed in Method 8081. From the 92 semivolatile compounds, we are reporting data for only 89 compounds. Benzo[blfluoranthene (compound 10) and benzo[klfluoranthene (compound 11) could not be resolved on the DB-5 column, and therefore we are reporting only one set of numbers for both compounds. We deleted N-nitrosodimethylamine,which was difficult to separate from the solvent under the gas chromatographic conditions used in this study, and N-nitrosodiphenylamine,which decomposed in the gas chromatographic inlet to diphenylamine; thus, the latter two compounds could not be reliably quantified by Method 8250 without conducting separate experiments for each compound. We also spiked the samples with six surrogate compounds; thus, the total number of compounds for which we are reporting MAE recoveries is 95. When topsoil samples were spiked with the 95 compounds and extracted immediately by MAE, the recoveries of 79 compounds ranged from 80 to 120%the recoveries of 14 compounds were
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40 82
45
50
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55
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90
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130
spiked topsdl
Figure 1. Distribution of recoveries for the compounds listed in Method 8250 that were spiked into topsoil samples (freshly spiked soil vs spiked soil aged for 24 h).
below 80%, and the recovery of 7,12-dimethylbenz[alanthracene (compound 40) was above 120% F i r e 1). From the 14 compounds with recoveries below 80%, five compounds had recoveries below 20%. The nine compounds with recoveries ranging from 80 to 20% were Caminobiphenyl (41, aniline (5), benzoic acid (S),4,Minitro-2-methylphenol(44), methyl and ethyl methanesulfonates (60 and 50, respectively), hexachlorocyclopentadiene (55), and 1- and 2-naphthylamines (65 and 66, respectively). Of the five compounds with recoveries below 20%, benzidine (7) could not be recovered at all, the recovery of a,adimethylphenethylamine (41) was 7.0%,the recovery of 2-picoline (82) was 7.7%, the recovery of dibenzo[ajlacridine (28) was 10.6%, and the recovery of 2,4dinitrophenol (45) was 17.2%). When topsoil samples were spiked with the 95 compounds, aged for 24 h at 4 “C (water was added to the spiked soil to ensure good mixing of the target compounds with the matrix), and then extracted by MAE, only 46 compounds had recoveries between 80 and 120%; the recoveries of 47 compounds were below 80%, and the recovery of benzoic acid (8)was above 120%. As shown in Figure 1,there is a downward trend in recovery on going from freshly spiked soil samples to the aged samples as more recoveries fall below the line of equality. Recoveries of six compounds were higher when they were extracted from the wet, aged matrix. For example, the recoveries of benzoic acid (8)increased from 42 to 123%dibenzo[ajlacridine (28) from 11to 97%;2,4dmitrophenol (45) from 17 to 69%; and 2-picoline (82) from 8 to 66%. Water appears to have a beneficial effect in this case, possibly displacing the analyte from the soil matrix into the organic solvent. When the MAE technique was used to extract the ERA soil sample and the recoveries (Table 1) were calculated on the basis of the concentrations certified by ERA (ERA reported the true spikes as the certified concentrations), we found that recoveries obtained by MAE were higher for 11of the 15 compounds known to be present in this matrix, as compared to recoveries reported by ERA The recoveries of three compounds were almost identical for both techniques, and only the recoveries of naphthalene were significantly lower when MAE was used r a b l e 1). When comparing the MAE and “typical recovery using EPA method” data, as reported by ERA, we used the uncorrected recovery values for MAE since the values reported by ERA were also not corrected for evaporation losses from blowdown. The lower recoveries for Analytical Chemistty, Vol. 67,No. 13,Jub 1, 1995
2099
C
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110
1
100
I 70
D
!
c. z
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60 50
lI
7 30
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splkod tDpBdl
50
I
60
io
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80
X Recomy--h..hty
do
I
1w
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i
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iio
.piW tapmoil
Figure 2. Distribution of recoveries for the compounds listed in Method 8081 that were spiked into topsoil samples (freshly spiked vs spiked soil aged for 24 h).
Figum 3. Distribution of recoveries for the compounds listed in Method 8081 that were spiked into topsoil samples (freshly spiked vs spiked soil aged for 14 days).
naphthalene were most probably due to losses during blowdown evaporation since in separate experiments we found that 33%of the amount of naphthalene in hexane-acetone, subjected to blowdown evaporation, was lost. In summary, the MAE technique performed adequately for the semivolatile compounds listed in Method 8250 (the data shown in Figure 1 are also included in Table 1 of the supporting information). The RSDs for the freshly spiked topsoil were < 10% for 64 of the 95 compounds given in Table 1 of the supporting information, 10-20% for 25 compounds, and 28-39% for four compounds. We are not reporting the RSDs for benzidine (0% recovery), and we report only a combined RSD value for benze [blfluoranthene and benzo[klfluoranthene since these two compounds could not be resolved on the DE5 column. Organochlorine Pesticides and PCBs. In our previous publication' on the MAE technique, we reported recoveries ranging from 83 to 117%when hexane-acetone (1:l) alone spiked with 20 OCPs was heated at 115 "C using microwave energy, and slightly lower but still good recoveries (above 80%, except for ychlordane at 74%)when the experiments were carried out in the presence of soil. In the present study, we expanded the list of OCP compounds to 45, and we evaluated the MAE technique with soil freshly spiked with the target compounds, spiked soil aged for 24 h at 4 OC, and spiked soil aged for 14 days at 4 "C. Table 2 of the supporting information summarizesthe recovery data for the compounds listed in Method 8081, and Figures 2 and 3 illustrate the distribution of these recoveries. From the 45 compounds that were extracted by MAE from the freshly spiked soil, 38 compounds had recoveries between 80 and 120%, six compounds had recoveries between 50 and 80%,and the recovery of captafol (7) was above 120% (Figure 2). For the spiked soil samples aged for 24 h (Figure 2), 28 compounds had recoveries between 80 and 120%,12 compounds had recoveries between 50 and 80%,three compounds [captafol(7), captan (8), and dichlone (21)]were poorly recovered and chioroneb (12) and 4,4'-DDT (19)had recoveries above 120%. For the spiked soil samples aged for 14 days (Figure 3), 14 compounds had recoveries between 80 and 120%,24 compounds had recoveries between 50 and 80%, and seven compounds had recoveries below 50%. The seven compounds with recoveries below 50% were alachlor (1), captafol(7),
captan (8), diallate (21), etridiazole (30), hexachlorocyclopentadiene (34), and propachlor (41). A decrease in recovery with increased aging time (Figures 2 and 3) is also evident in the case of OCPs. This is especially apparent for captafol(7), captan (8), and dichlone (21) when the recoveries from freshly spiked vs spiked soil aged for 24 h are compared (i.e., the recovery of captafol dropped from 122 to 36%, the recovery of captan dropped from 105 to 21%,and the recovery of dichlone dropped from 78 to 10%). The recoveries of etridiazole (30) and hexachlorocyclopentadiene(34) were almost identical from the freshly spiked and the spiked soil aged for 24 h (Figure 2), but they dropped to 50%for the spiked soil aged for 14 days (Figure 3). The recoveries of other compounds, such as chlorothalonil(l4) and propachlor (41), also decreased with increased aging time (e.g., the recovery of chlorothalonil dropped from 83% for freshly spiked soil to 63%for the spiked soil aged for 24 h to 56%for the spiked soil aged for 14 days, and the recovery of propachlor dropped from 92%for freshly spiked soil to 63%for the spiked soil aged for 24 h to 43%for the spiked soil aged for 14 days). Despite these few occurrences in which recoveries were lower from the spiked soil aged for 24 h and the spiked soil aged for 14 days (we suspect that microbial degradation may at least partially account for the loss of compounds), the recoveries obtained by MAE are comparable to or higher than those achieved by the conventional extraction techniques. When we compared recoveries obtained by MAE with those we reported earlier7 for the sonication and Soxhlet extraction techniques Vable 2) for topsoil samples spiked with selected OCPs at 50 pg/kg (except hexachlorobenzene at 200 pg/kg and hexachlorocyclopentadiene at 100 pg/kg), we found that the recoveries were at least 7%higher for MAE than those for either the Soxhlet or the sonication technique [except for 4,4'-DDT, where the recoveries were above 100%for all three techniques, and for dieldrin, where the Soxhlet recoveries were 1% higher than the MAE or sonication recoveries Fable 2)]. Hexachlorocyclopentadieneexhibited the largest increase in recovery by MAE
2100 Analytical Chemistry, Vol. 67, No. 13, July 1, 1995
(7) Lopez-Anla, V. Sonication and Soxhlet &traction in Environmental Analysis: Methods Comparison. EPA Report 600/X-93/010;US. Environmental Protection Agency: Environmental Monitoring Systems Laboratory: JAS Vegas, NV, February 1993.
~
~~
Table 2. Comparison of MAE with Sonication and Soxhiet ExtractionTechniques
compd no. 2 3 6 19 23 24 25 27 31 32 33 34
sonicationu average recovery (%) RSD (%)
compound name
66.2 70.2
aldrin a-BHC
6-BHC
SoxhleP average recovery (%) RSD (%) 77.9 69.7 68.2 128 96.4 69.1 58.2 62.9 85.0 69.7 73.6 21.9
5.2 6.2
C
4,4'-DDT
108 79.3 68.4 63.3 62.1 68.6 60.9 65.7 44.8
dieldrin endosulfan I endosulfan I1 endrin heptachlor heptachlor epoxide hexachlorobenzene hexachlorocyclopentadiene
5.7 4.4 3.9 5.3 6.4 5.2 4.9 5.6 11
MAE*
average recovery (%)
RSD (%)
87 94.4 96.9 116 85.9 86.8 71.9 97.4 110 95.3 80.8 107
2.1 4.1 2.8 5.6 3.8 3.1 6.3 1.9 1.4 2.7 1.6 12
3.7 4.7 1.7 3.6 2.7 3.3 8.3 2.7 6.7 2.9 7.2 96
0 The spike level was 50 ,ug/kg for the sonication and Soxhlet extraction experiments. The number of determinations was three. These data were taken from ref 4. The number of determinations was three. The spike levels are listed in Table 2 of the supporting information. Data not available.
Table 3. MAE Method Performancefor PCBs
matrix H S 1 marine sediment HS2 marine sediment ERA soil (Lot 9801) freshly spiked topsoil
spiked topsoil aged for 24 h at 4 'C superfund site sample 1 superfund site sample 2 superfund site sample 3 superfund site sample 4
certified value or spike level (mg/kg)
Aroclor type
uncorrectedn
0.022c 0.112c 394' 0.1009
1254 1254 1260 1016 1260 1016 1260 1248 1248 1248 1248
93.2d 76.7e 82.8d 73.7e 76.P 79.6c 81.6e 102e 157e 86Ae 75.3e
0.1009 469 1.13h 0.033* 6.7*
average
(%)
correctedb 89.9 85.9 82.5 92.8 88.6
RSD (%) 8.1 6.0 2.6 5.6 4.2 14 10 3.5 6.3 35 17
blowdown evaporation recovery (%) 92.1 85.8 92.1 85.8 92.1
Recoveries were not corrected for losses during blowdown evaporation. Recoveries were corrected for losses during blowdown evaporation. Certified by the National Research Council of Canada. The number of determinations was four. e The number of determinations was three. /Certified by ERA 8 Spiked in our laboratory. * Reported by an independent laboratory that used Soxhlet extraction and GC/ECD.
as compared with the other two techniques. Method precisions (RSDs) were comparable for the three techniques, with the exception of the very high RSDs for the Soxhlet extraction of hexachlorocyclopentadiene. The results for the performance of the method for four Aroclors are presented in Table 3. Samples of two standard reference marine sediments (HS1 and HS2), a standard reference soil, a freshly spiked topsoil, a spiked and aged topsoil, and four soils from a Superfund site were extracted by MAE. The recoveries of Aroclor 1016 and 1260 (corrected for blowdown evaporation losses) were in the range of 82-93% the recoveries of Aroclor 1248 i d 1254 ranged from 75-157% over a concentration range of 0.022-465 mg/kg. Organophosphorus Pesticides. Of the 51 compounds presently listed in the Method 814% 47 are OPPs, two are industrial chemicals, and two are triazine herbicides. In our study, we spiked 47 of the 51 compounds into soil samples. Carbophenothion, diazinon, parathion methyl, and terbufos were not spiked, because we could not quantify them under the gas chromatographic conditions we used. Carbophenothion coelutes with famphur on the DE5 column and with Bolstar on the DE210 column; diazinon coelutes with disulfoton on the DE5 column and with sulfotepp on the DB-210 column; parathion methyl coelutes with chlorpyrifos methyl on the DB-5 column and with
malathion on the DE210 column; and terbufos coelutes with fonophos on the DE5 column and with naled on the DE210 column. Table 3 of the supporting information summarizes recovery data for the compounds listed in Method 814lA, and Figures 4 and 5 show the distributions of the recoveries. Of the 47 compounds listed in Method 814% which were extracted by MAE from the freshly spiked soil, 35 compounds had recoveries between 80 and 120%,four compounds [dichlorofenthion (12), dichlorvos (13), fensulfothion (23),and mevinphos (29)l had recoveries between 50 and 80%,six compounds [monochrotophos (30), naled (31), phosphamidon (35), TEPP (39), trichlorfon (42), and HMPA (44)l had recoveries below 20%,and azinphos ethyl (3) and simazine (47) had recoveries above 120%. For the spiked soil samples aged for 24 h (Figure 4), 37 compounds had recoveries between 80 and 120%,three compounds [demeton-S (1l),naled (311,and trichlorfon (42)l had recoveries between 50 and 80%, two compounds [monochrotophos (30) and TEPP (39)l had recoveries below 50%, and five compounds had recoveries above 120%. For the spiked topsoil samples aged for 21 days ( F i r e 5), 35 compounds had recoveries between 80 and 120%, three compounds [dioxathion (16),phorate (33),and thionazin (40)l had recoveries between 50 and 80%, seven compounds [demeton-0 (lo),demeton-S (1l),monochrotophos Analytical Chemistry, Vol. 67,No. 13, July 1, 1995
2101
t
x P -r
i:
2 0
160
130 120 110 100
-
-
c
60 50 4030
Y K
3s
70 80
I
15
w -
d
5
I
13
44
--
31 42
-
Id0
CONCLUSIONS
2oL I / 10
O
i
T 10
O
1
SO
io
I do 701
30
X Rwwry--hhly
do
I
ti0
90
I
110
140
I
130
'
rplW topadl
Figure 4. Distribution of recoveries for the compounds listed in Method 8141A that were spiked into topsoil samples (freshly spiked vs spiked soil aged for 24.h).
- . . .. - . . . -... ... _......- . .. . -
.. ....
13
a 2 P
120 110
-
90 80 70 -
loo
60
from 5.6 to 84.7%. The recoveries decreased, however, for the spiked soil aged for 21 days (Figure 5). We attributed the decreases mainly to microbial degradation of target compounds, although chemical transformations, such as debromination for naled and dehydrochlorination for trichlorfon, are also possible. The latter two compounds are known to be converted to dichlorvos,6 and this may explain the very high recoveries of dichlorvos (13). Microwave-assisted extraction of organic compounds from solid samples, including extraction of pollutants of environmental concern from soil and sediment samples, is a viable technique for sample preparation. We demonstrated in this study that many of the compounds of interest to the EPA can be extracted from spiked and spiked/aged soil sampleswith a relatively small volume of organic solvent (30 mL in MAE vs 300 mL in Soxhlet extraction) in 10 min. Repeated extractions with fresh solvent portions were not required, since separate experiments showed that the amounts of analytes recovered in the second fraction were insigniicant. Safety issues associated with the handling of flammable solvents in a microwave system have been adequately addressed by at least one manufacturer, and work is in progress now to validate the f i s t MAE method, proposed for the EPA, in a multilaboratory evaluation study. ACKNOWLEWMENT
34 10
30 11
710
20
I
30
40
I
SO
eo
X R.cwy--huhly
I
70
80
I
W
100
1
110
120
I
130
a @ k d topaOrl
Figure 5. Distribution of recoveries for the compounds listed in Method 8141A that were spiked into topsoil samples (freshly spiked vs spiked soil aged for 21 days).
(30), naled (31), phosmet (34), trichlorfon (42), and HMPA (a)] had recoveries below 50%, and dichlorvos (13) and simazine (47) had recoveries above 120%.
The six compounds that exhibited recoveries below 20%from naled (31), freshly spiked soil samples were monocrotophos (30), phosphamidon (35), TEPP (38),trichlorfon (42), and HMPA (44).We found significant improvement in their recoveries when we extracted them from aged topsoil samples and ath.ibuted this to the presence of water in the matrix. For example, the average recoveries increased for monocrotophosfrom 9.4 to 39%, for naled from 9.4 to 62.3%,for phosphamidon from 16.6 to 98.1%,for TEPP from 5.4 to 34%,for trichlorfon from 7.8 to 54.0%, and for HMPA
2102 Analytical Chemistry, Vol. 67, No. 73,July 7, 7995
The authors thank the CEM Corp. for the loan of the microwave unit used in this study to Midwest Research Institute. The US.EPA, through its Office of Research and Development (ORD) ,partially funded and collaborated in the research described here. It has been subjected to the Agency's review and has been approved as an EPA publication. Readers should note the existence of a patent describing the microwave-assisted extraction of biological materials. Neither the EPA nor ORD endorses or recommends any trade names or commercial products mentioned in this article; they are noted solely for the purpose of description and clarification. The US. Government has a nonexclusive royalty-free license in and to any copyright covering this article. SUPPORTINQ INFORMATION AVAILABLE
Tables listing spike levels and MAE performance data for the compounds listed in Methods 8250,8081, and 814lA (12 pages). Ordering information is given on any current masthead page. Received for review November 4 , 1994. Accepted March 30, 1995.@ AC9410732 @Abstractpublished in Advance ACS Abstracts, May 15, 1995.
