Anal. Chem. 1997, 69, 2171-2180
Comparison of ASE and SFE with Soxhlet, Sonication, and Methanolic Saponification Extractions for the Determination of Organic Micropollutants in Marine Particulate Matter Olaf P. Heemken,†,‡ Norbert Theobald,† and Bernd W. Wenclawiak‡
Bundesamt fu¨ r Seeschiffahrt und Hydrographie, Bernhard-Nocht-Strasse 78, 20305 Hamburg, Germany, and Analytische Chemie I, Universita¨ t-GH Siegen, Adolf-Reichwein-Strasse, 57068 Siegen, Germany
The methods of accelerated solvent extraction (ASE) and supercritical fluid extraction (SFE) of polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons, and chlorinated hydrocarbons from marine samples were investigated. The results of extractions of a certified sediment and four samples of suspended particulate matter (SPM) were compared to classical Soxhlet (SOX), ultrasonication (USE), and methanolic saponification extraction (MSE) methods. The recovery data, including precision and systematic deviations of each method, were evaluated statistically. It was found that recoveries and precision of ASE and SFE compared well with the other methods investigated. Using SFE, the average recoveries of PAHs in three different samples ranged from 96 to 105%, for ASE the recoveries were in the range of 97-108% compared to the reference methods. Compared to the certified values of sediment HS-6, the average recoveries of SFE and ASE were 87 and 88%, most compounds being within the limits of confidence. Also, for alkanes the average recoveries by SFE and ASE were equal to the results obtained by SOX, USE, and MSE. In the case of SFE, the recoveries were in the range 93-115%, and ASE achieved recoveries of 94-107% as compared to the other methods. For ASE and SFE, the influence of water on the extraction efficiency was examined. While the natural water content of the SPM sample (56 wt %) led to insufficient recoveries in ASE and SFE, quantitative extractions were achieved in SFE after addition of anhydrous sodium sulfate to the sample. Finally, ASE was applied to SPM-loaded filter candles whereby a mixture of n-hexane/acetone as extraction solvent allowed the simultaneous determination of PAHs, alkanes, and chlorinated hydrocarbons. Polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons are ubiquitous pollutants present in all compartments of the environment (atmosphere, soil, water). Due to the carcinogenic and mutagenic character of certain PAHs, their determination in environmental samples is of major concern. Single compound analysis of aliphatic hydrocarbons in aqueous media is an important tool in the identification of specific oil spills.1-3 A large number of different isolation procedures for † ‡
Bundesamt fu ¨ r Seeschiffahrt und Hydrographie. Universita¨t-GH Siegen.
S0003-2700(96)00695-6 CCC: $14.00
© 1997 American Chemical Society
PAHs and alkanes from several sample types have been described in the literature.4-6 Extractions are traditionally performed by means of Soxhlet or sonication. Unfortunately, these techniques are time-consuming and require large volumes of organic solvents, which often are toxic, and whose purchase and disposal are expensive. In the last few years, new extraction techniques have been established in order to reduce the volume of solvents required for extraction, improve the precision of analyte recoveries, and reduce extraction times and sample preparation costs. Such techniques include microwave extraction,7-9 supercritical fluid extraction10-12 and accelerated solvent extraction.13,14 Supercritical fluid extraction (SFE) using carbon dioxide has gained increasing attention in the extraction of pollutants from environmental samples because of its ability to shorten extraction time and reduce the amount of organic solvent required. On the other hand, method development for the extraction of real world samples is laborious because of a wide variety of parameters that can be modified and have to be optimized, such as extraction time, pressure, temperature, or choice of solvents/cosolvents. The strong matrix dependence of the extraction process15 precludes the transfer of SFE conditions gained in spike experiments to the extraction of real samples.11,16 Since several publications report various SFE conditions for the extraction of PAHs11,17-20 and (1) Dahlmann, G.; Timm, D.; Averbeck, C.; Camphuysen, C.; Skov, H.; Durinck, J. Mar. Pollut. Bull. 1994, 28, 305-310. (2) Rasmussen, D. V. Anal. Chem. 1976, 48, 1562-1566. (3) Hood, L. V. S.; Erikson, C. M. J. High Resolut. Chromatogr. Chromatogr. Commun. 1980, 3, 516-520. (4) Lipiatou, E.; Saliot, A. Mar. Pollut. Bull. 1991, 22, 297-304. (5) Bayona, J. M.; Grimalt, J.; Albaiges, J.; Walker, W.; de Lappe, B. W.; Risebrough, R. W. J. High Resolut. Chromatogr. Chromatogr. Commun. 1983, 6, 605-611. (6) Bjorseth, A. In Handbook of Polycyclic Aromatic Hydrocarbons; Ramdahl, T., Ed.; Marcel Dekker: New York, 1985. (7) Lopez-Avila, V.; Young, R.; Benedicto, J.; Ho, P.; Kim, R.; Beckert, W. F. Anal. Chem. 1995, 67, 2096-2102. (8) Dean, J. R.; Barnabas, I. J.; Fowlis, I. A. Anal. Proc. Incl. Anal. Commun. 1995, 32, 305-308. (9) Onuska, F. I.; Terry, K. A. J. High Resolut. Chromatogr. 1995, 18, 417421. (10) Paschke, T.; Hawthorne, S. B.; Miller, D. J.; Wenclawiak, B. J. Chromatogr. 1992, 609, 333-340. (11) Yang, Y.; Gharaibeh, A.; Hawthorne, S. B.; Miller, D. J. Anal. Chem. 1995, 67, 641-646. (12) Barnabas, I. J.; Dean, J. R.; Owen, S. P. Analyst 1994, 119, 2381-2394. (13) Ho ¨fler, F.; Ezzell, J.; Richter, B. Labor Praxis 1995, 3, 62-67. (14) Ho ¨fler, F.; Ezzell, J.; Richter, B. Labor Praxis 1995, 4. (15) Friedrich, C.; Cammann, K.; Kleibo ¨hmer, W. Fresenius J. Anal. Chem. 1995, 352, 730-734.
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alkanes,21-24 with different extraction yields, a more general SFE procedure for the simultaneous determination of these compound classes in marine matrices still has to be developed. Accelerated solvent extraction (ASE) is another new extraction technique, which allows faster extractions than classical methods. ASE requires only small volumes of solvents, which are recommended to be the same as those used in Soxhlet extractions. Extractions are performed at temperatures in the range of 50200 °C to enhance the speed of elution. Pressures of 5-200 atm are chosen to keep the solvents in liquid state. Extraction times range from 5 to 15 min. It has been reported that ASE of PAHs, polychlorinated biphenyls, basic, neutral, and acidic pollutants, pesticides, and herbicides achieved the same results as the abovementioned techniques.25 Similar to SFE, automation of ASE allows a sequential extraction of samples. Because of these advantages concerning speed, costs, and solvent quantities, SFE and ASE appear to be promising alternatives to classical extraction methods. In this study, suspended particulate matter (SPM) samples collected with different sampling techniques were investigated. These techniques included sampling of SPM by sedimentation, centrifugation, and filtration. Sedimentation traps are widely used in long-term monitoring because of the low velocity of the settling process and the time required to get sufficient amounts of SPM for analysis. Sampling of SPM by centrifugation is a rapid technique, but it requires expensive centrifuges. Filtration with filter candles of defined pore sizes is another commonly used method for the separation of SPM. In order to obtain sufficient amounts of SPM for analysis, large filter candles (depth filter) have to be used. Extraction of these SPM-loaded filters using classical ultrasonic requires high amounts of solvent (up to 1000 mL). For this reason it was important to find a different extraction technique, requiring less solvent. Based on the advantages provided by ASE, this method was applied for the extraction of SPM-loaded filter candles using commercially available 50 mL extraction vessels. The preparation of marine sediments and suspended particulate matter often includes drying of the samples. This is achieved by different techniques, such as air-drying, lyophilization, or thermal drying. All of these methods are time-consuming and involve the risk of contamination or loss of volatile analytes. Therefore, procedures allowing the extraction of moist samples are of special interest. Using methanolic saponification, the water content of a sample has no impact on the extraction efficiency of PAHs and alkanes. Also, ultrasonic extraction is not influenced by the moisture of the sample, if a suitable solvent, such as acetone or 2-propanol, is chosen.26 It has been reported that small amounts of water may act as a modifier during SFE, enhancing the (16) Burford, M. D.; Hawthorne, S. B.; Miller, D. J. Anal. Chem. 1993, 65, 14971505. (17) Meyer, A.; Kleibo ¨hmer, W. J. Chromatogr., A 1993, 657, 327-335. (18) Wenclawiak, B.; Rathmann, C.; Teuber, A. Fresenius J. Anal. Chem. 1992, 344, 497-500. (19) Lee, H. B.; Peart, T. E.; Hong-You, R. L.; Gere, D. R. J. Chromatogr., A 1993, 653, 83-91. (20) Hawthorne, S. B.; Miller, D. J. Anal. Chem. 1987, 59, 1705-1708. (21) Lopez-Avila, V.; Benedicto, J.; Dodhiwala, N. S.; Young, R.; Beckert, W. F. J. Chromatogr. Sci. 1992, 30, 335-343. (22) HP Peak 1993, 2, 2-4. (23) Hawthorne, S. B.; Krieger, M. S.; Miller, D. J. Anal. Chem. 1989, 61, 736740. (24) EPA Method 3560 Supercritical Fluid Extraction of Total Recoverable Hydrocarbons, 1995. (25) Ho ¨fler, F.; Jensen, D.; Ezzel, J.; Richter, B. Git Spezial 1995, 1, 68-71. (26) Heemken, O., Dissertation, Siegen, Germany, 1997.
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extraction rate.19 SFE of spiked samples with 20% moisture yielded quantitative recoveries of organophosphorus pesticides.27 The question was whether SPM and sediments with natural water contents (about 25-60 wt %) could be extracted by ASE and SFE without previous drying, which would reduce the time required for sample pretreatment and minimize the risk of contaminations or loss of analytes. In this study, conditions for the simultaneous determination of PAHs and alkanes in different matrices of marine particulate matter using SFE and ASE have been investigated and optimized. The results of these extractions were compared to results of classical ultrasonication, Soxhlet, and methanolic saponification extractions. The influence of water in marine samples on the extraction efficiency in SFE and ASE was examined. As a new application, the extraction of SPM-loaded filter candles using ASE was demonstrated. EXPERIMENTAL SECTION Samples. Sediment. The marine sediment used in this study was a certified reference material (HS-6) from the National Research Council of Canada (Promochem, Wesel, Germany). The sample contained 3 wt % water, as determined by thermal gravimetric analysis. Certified values were corrected for this content. This sediment was extracted 6-fold by ASE and SFE. Methanolic saponification, sonication, and Soxhlet extractions were performed in triplicate. SPM. SPM from the river Elbe was collected by means of sedimentation traps deployed at Hamburg from January to March 1994. For detailed sample characterization, see elsewhere.28 Extraction of the freeze-dried and homogenized SPM was performed by methanolic saponification extraction (MSE), SFE, and ASE (sample SPM I). An additional Soxhlet extraction (SOX) and determination of PAHs was carried out by ERGO Forschungsgesellschaft mbH (Hamburg, Germany). Samples from the river Weser were collected by a flow-through centrifuge (Model Z41, Plattberg GmbH, Lahr, Germany) during cruise GA 241 (RV Gauss) at a sampling depth of 3 m below the water surface with a flow rate of ∼1000 L/h. The sample was air-dried for four days at room temperature (water content 5.3 wt %) and extracted by SFE, MSE, and SOX in triplicate (sample SPM II). Aliquots of the undried SPM II (water content 56 wt %) were extracted by SFE, ASE, and MSE in triplicate. Filters. The filter candles used were fiberglass packages on stainless steel tubes (Voigt GmbH, Wernau, Germany). The pore size was 0.45 µm, dimensions of the filters were 85 mm length, 25 mm o.d., and 14 mm i.d. (of the stainless steel tube), so that they fitted in commercially available 50 mL extraction vessels (Suprex). The filters were cleaned by heating at 450 °C for 12 h prior to use. To load the filter candles, water samples were taken from the rivers Weser and Ems using 100 L glass bottles. While samples were being stirred, 2 × 50 L aliquots of water were filtrated to obtain two filters with the same amount of SPM for each station. After filtration, the filter candles were air-dried, transferred to glass bottles, and stored at -20 °C in the dark until extraction. One filter of each sampling station was extracted by USE, the other one by ASE. (27) Witter, B.; Francke, W.; Knauth, H. D. Fresenius J. Anal. Chem. 1995, 353, 107-109. (28) Stachel, B.; Elsholz, O.; Reincke, H. Fresenius J. Anal. Chem. 1995, 353, 21-27.
Extraction Conditions. SFE. Samples were extracted with a Suprex SFE 50 (Suprex GmbH, Duisburg, Germany). SFE conditions: 30 min static and 60 min dynamic mode at 80 °C and 400 atm. Carbon dioxide 5.5 grade (Messer/Griessheim, Duisburg, Germany) modified with 10 vol % methanol was used as fluid. Prior to use, the CO2 was purified by passing it through a cartridge filled with activated carbon. As a second modifier, 1.5 mL of toluene was added directly to the sample in the vessel. The flow rate was 1 mL/min (liquid), the total amount of fluid was 60 mL/extraction. About 0.3 g of sediment and 1.5 g of SPM was extracted using a 3 mL stainless steel vessel. To remove elemental sulfur, 200 mg of activated copper powder was placed at the outlet of the vessel; 3-5 mL of internal standard solution was added to the trapping solvent (5-3 mL of n-hexane) prior to extraction. Trapping was performed with a Dewar condenser as described in ref 29. ASE. Extractions were carried out using a Dionex ASE 200 (Dionex GmbH, Idstein, Germany) and a Suprex SFE 50 (Suprex GmbH, Duisburg, Germany) at a temperature of 100 °C and a pressure of 140 atm. A mixture of acetone/n-hexane (1:1 v/v) was used as extraction solvent in all cases. On the Dionex ASE 200, 0.3 g of sediment was extracted with stainless steel vessels of 11 mL volume and 3 g of undried SPM was extracted with 33 mL stainless steel vessels. The time for static extraction was 5 min, after a 5 min equilibration. Following static extraction, the outlet valve was opened and the vessel was rinsed with the same volume of solvent. As a final step, the vessel was purged with gaseous nitrogen. The total amount of extraction solvent was ∼20 mL for 11 mL vessels and 60 mL for 33 mL vessels; 3-5 mL of internal standard was added to the extracts after extraction. Certain modifications were necessary to be able to use the Suprex SFE 50 for ASE. The syringe pump was disconnected from the CO2 cylinder and filled with a mixture of acetone/nhexane (1:1 v/v). The restrictor was replaced by a stainless steel capillary tube (o.d. 1/16 in., i.d. 200 µm) leading into the trapping vial. An additional nitrogen pipe was installed at the inlet valve (four-position one-way switch valve) of the extraction vessel to perform a purge step after extraction. About 0.3 g of sediment and 1.5 g of SPM were extracted using vessels of 10 mL volume and ∼30 mL of solvent. Filter candles loaded with SPM were extracted in a 50 mL extraction vessel, using 90 mL of solvent. Due to thicker walls of these 10 and 50 mL extraction vessels, equilibration time was extended to 10 and 15 min, respectively. In all cases, 200 mg of copper was added to the sample prior to extraction. Trapping was performed as described in SFE. After extraction, 3-5 mL of internal standard was added to the extracts. Methanolic Saponification. Aliquots of 0.3 g of sediment and 3 g of SPM samples, to which 10 g of potassium hydroxide and 200 mg of copper had been added, were refluxed with a mixture of 100 mL of methanol/water (10:1 v/v) and 3-5 mL of internal standard for 2.5 h. After adding 100 mL of water, the solution was filtered and extracted with 100 mL of n-hexane. The extracts were dried over anhydrous sodium sulfate. Soxhlet. Aliquots of 0.3 g of sediments and 3 g of SPM were extracted with 150 mL of acetone/n-hexane (1:1 v/v) for 24 h. Prior to extraction, 200 mg of copper and 3-5 mL of internal standard were added to the extraction solvent. (29) Wenclawiak, B. W.; Heemken, O. P.; Sterzenbach, D.; Schipke, J.; Theobald, N.; Weigelt, V. Anal. Chem. 1995, 67, 4577-4580.
Ultrasonication Extraction (USE). Extractions were performed with a Bandelin, Sonarex Super RK 51434. Portions of 0.3 g of sediment were extracted three times with 40 mL of n-hexane/ acetone (1:1 v/v) for 30 min at room temperature; 5 mL of internal standard and 200 mg of copper were added to the solvent at the first extraction. Following each extraction, the outstanding solvent was decanted and the combined extracts were dried over anhydrous sodium sulfate. Sonication of filter candles containing SPM was performed using 3 × 200 mL of n-hexane/2-propanol (3:1 v/v) for 30 min at room temperature; 5 mL of internal standard and 200 mg of copper were added to the solvent at the first extraction. To remove the 2-propanol, the combined extracts were treated three times with 100 mL of water and the n-hexane was dried over anhydrous sodium sulfate. Cleanup and Analysis. HPLC. After concentrating the extracts to 100 µL, samples were fractionated by HPLC, consisting of a pump (L 6200, Merck/Hitachi, Darmstadt, Germany), an autosampler (HP Series 1050, Hewlett Packard), a fraction collector (L 5200, Merck/Hitachi, Darmstadt, Germany), a diode array detector (HP 1040 M Series II, Hewlett Packard), and a column oven (Techlab). The column was a Nucleosil 100-5 (Macherey/Nagel, Du¨ren, Germany). HPLC parameters were as follows: 2 min n-hexane/methylene chloride 40% (1 mL/min); in 6 min to 100% methylene chloride (1 mL/min); in 4 min to 100% methylene chloride (1 mL/min); in 5 min to 100% acetone (1.5 mL/min); in 10 min to n-hexane/methylene chloride 40% (1.5 mL/ min) for equilibration. The temperature was 20 °C. The fraction containing the analytes was collected from 1 to 3.5 min and reduced to 100 µL again. GC/MS. All extracts were analyzed with a gas chromatograph (Hewlett Packard 5890 Series II) and a mass-selective detector (MSD 5971 A). The GC system was equipped with a 5% phenylmethyl silicone capillary column, 0.25 m i.d., 0.5 µm film thickness, 25 m length (SE 52, Macherey/Nagel, Du¨ren, Germany), and helium was used as carrier gas. The GC oven temperature program was as follows: 40 °C, 5 °C/min to 310 °C, and 310 °C for 20 min. Parameters for the cold injection system KAS 3 (Gerstel GmbH, Mu¨lheim a.d. Ruhr, Germany) were as follows: 30 °C; 1 °C/s to 70 °C; 70 °C for 20 s; 12 °C/s to 320 °C; 320 °C for 120 s; splitless time 120 s; injection volume 2 µL. The mass spectrometer was operated in selected ion monitoring mode, detecting the following ion masses: m/z 66, 85, 128, 136, 142, 152, 154, 156, 164, 166, 178, 181, 183, 184, 188, 192, 202, 212, 228, 235, 240, 246, 252, 256, 264, 266, 276, 278, 284, 288, 292, 300, 312, 326, 360, and 396. Three calibration standard solutions were used to generate response factors for each compound relative to internal standards. The analytes in the samples were identified by matching the retention time of each compound with the retention times in calibration standards. Concentrations of analytes were calculated, based on recoveries of the internal standards. Standards and Chemicals. Standards. The internal standard contained -HCH, TCN, PCB 185 (Lab. Dr. Ehrenstorfer, Augsburg, Germany), and the perdeuterated compounds n-C-12, n-C16, n-C-20, n-C-30, Naph, Ace, Phen, Ant, Fluor, BaA, BeP, Per, BghiP, and Cor (MSD Isotops, Montreal, Canada). Concentrations were in the range of 80 ng/mL for aliphatic, 20 ng/mL for aromatic, and 10 ng/mL for chlorinated compounds. The calibration standards consisted of n-alkanes C-12 to C-30, Pri, Phy (Alltech Associations Inc., Unterhachingen, Germany), the PAHs listed in Analytical Chemistry, Vol. 69, No. 11, June 1, 1997
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Tables 1, 2, 5, and 6 (Aldrich Chemie GmbH, Steinheim, Germany and EGA Chemie, Steinheim, Germany), and the internal standard compounds. For the quantification of halogenated compounds, a second set of calibration standards containing the target analytes (Table 6) as well as -HCH, TCN, and PCB 185 was used. Concentrations in the calibration standard solutions were in the range from 2 to 20 ng/µL for alkanes, from 0.2 to 6 ng/µL for PAH, and from 10 to 100 pg/µL for halogenated compounds. All standard solutions were prepared in n-hexane. Abbreviations of compounds used. Pri, pristane; Phy, phytane; Naph, naphthalene; M2N, 2-methylnaphthalene; M1N, 1-methylnaphthalene; C2N2,6, 2,6-dimethylnaphthalene; Acy, acenaphthylene; Ace, acenapthene; Flu, fluorene; DBT, dibenzothiophene; Phen, phenanthrene; M1P, 1-methylphenanthrene; Ant, anthracene; Fluor, fluoranthene; Pyr, pyrene; BaA, benzo[a]anthracene; Chr/Tri, chrysene/triphenylene; BbF benzo[b]fluoranthene; BeP benzo[e]pyrene; BaP benzo[a]pyrene; Per, perylene; I123P, indeno[1,2,3-cd]pyrene; DBacA, dibenzo[a,c]anthracene; BghiP, benzo[ghi]perylene; Cor, coronene; HCH, hexachlorocyclhexane; TCN, tetrachloronaphthalene; PCB, polychlorinated biphenyls. Chemicals. Solvents used were acetone, toluene, n-hexane (Nanograde, Promochem, Wesel, Germany); methylene chloride, methanol, 2-propanol (Lichrosolv, Merck, Darmstadt, Germany); and water (HPLC, Baker). All solvents except water and 2-propanol were fractionally distilled before use. Copper powder (Baker) was activated with diluted nitric acid and consecutively rinsed with water, acetone, and n-hexane. The quality of Na2SO4 (Baker) was controlled by fluorescence of n-hexane extracts. RESULTS AND DISCUSSION Recovery Studies. The extraction yields of PAHs and alkanes from sediment HS-6 and SPM samples I and II are summarized in Tables 1-3 for the different extraction methods. To compare the mean recoveries obtained by the individual methods, the constant systematic error (bias) Drel was evaluated as a sum parameter for alkanes and for PAHs by30
Drel ) (X1 - X2)/X1 × 100%
(1)
where X1 and X2 are the extraction rates of alkanes or of PAHs for the methods concerned. The percentage bias values are given in Table 4, those for PAHs to the right and those for alkanes to the left side of the diagonal. A statistical evaluation of the bias showed that the mean recoveries of alkanes and PAHs obtained by the extraction methods investigated were not significantly different. In SFE of PAHs, the bias ranged from -3.8 to 4.7%, and in the extraction of alkanes, it was in the range of -6.9 to 15.1%, as compared to the other methods. A comparison of ASE with the other methods showed a bias from -3.2 to 8.3% in the extraction of PAHs and a bias in the range of -5.6 to 6.6% in the extraction of alkanes. SFE and ASE of both HS-6 and SPM I samples achieved equal results, with a bias of less than 3% in the extraction of alkanes and PAHs. Compared to certified values of HS-6, the bias of SFE and ASE was -13.5 and -11.9%., respectively, indicating average recoveries of 86 and 88%. Table 1 shows (30) Funk, W.; Dammann, V.; Vonderheit, C.; Oehlmann, G. Statistische Methoden in der Wasseranalytik; VCH: Weinheim, Germany, 1985.
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that the concentrations of most compounds were in the range of confidence (with the exception of Acy, Ace, Flu, and BaP). Since the bias values of all methods investigated are much closer to each other than to certified values, these results cannot be interpreted to low extraction yields. The error could probably originate from a wrong calibration in the GC/MS analysis. The precision of all extraction methods investigated, as expressed by the (mean) relative standard deviation (RSD) of the alkanes and PAH, was very good. As shown in Tables 1-3, the mean RSD of the different methods ranged from 2.9 to 3.7% for alkanes and from 3.2 to 5.2% for PAH in the extraction of HS6, from 3.4 to 5.0% for SPM I, and from 2.7 to 7.5% for SPM II. The overall methods RSD in the case of HS-6 averaged 11.5% for alkanes and 9.7% for PAH, for SPM I it amounted to 6.6% for alkanes and 6.9% for PAH, and for SPM II the overall methods RSD was 11.5% for alkanes and 6.3% for PAH. Considering the single compounds, high overall methods RSD (>20%) were found in HS-6 for C-12, C-15, C-28, C-30, M1N, M1P, and Cor. In SPM I, high overall methods RSD was found for Acy and Cor, in SPM II, for the alkanes C-13, C-14, and C-18 and for Acy. High overall methods RSD of low-boiling compounds (naphthalenes and C-12 to C-15) were probably not due to insufficient extraction rates of same methods but to evaporation losses during sample preparation and workup. For example, in USE, internal standard was added only in the first extraction, and vials were sealed only with aluminium foil during extraction, so that analyte losses in the second and third extractions were not quantified (therefore, naphthalenes in USE of HS-6 were treated as outliers and excluded from statistical evaluations). In Soxhlet extractions of HS-6, the elimination of sulfur was incomplete, so that interferences of M1P (m/z 192) with elemental sulfur (S6 fragment of the same mass) in the GC/MS analysis occurred. For coronene as a seven-ring PAH, SFE showed insufficient extraction efficiency from both sediment and SPM samples. To estimate proportional systematic errors, the different extraction methods were plotted vs the methods average, as shown in Figure 1. Linear regression analysis was performed by means of eq 2, whereby the proportional systematic error Frel was
Y ) A1X + A2
(2)
Frel ) |1 - A1| × 100%
(3)
calculated by equation.30 The values for A1 and the resulting errors Frel are shown in Table 5. In the extraction of PAHs from the three samples, the proportional error ranged from 1.3 to 8.0%, which indicates that no statistically significant difference exists between the methods. Higher differences were observed for the extraction of alkanes from HS-6, where the proportional error of SFE, ASE, MSE, and SOX was 15.0, 21.8, 15.9, and 18.9%, respectively. These findings are in accordance with high overall methods RSD for some alkanes in this sample. In SPM II the highest proportional error (10.3%) was found for MSE of alkanes. This was mainly due to poor recoveries of the compounds with the highest concentrations (C-29, C-27, C-25, C-23, C-17). It should be noted that a plot vs the overall methods average only allows a comparison of similarities/differences between the methods investigated. The accuracy of a method can only be determined by comparing it to certified values. In the case of HS-6, plots of
Table 1. Extraction of PAHs and Alkanes from a Certified Sediment HS-5 with SFE, ASE, MSE, SOX, and USEa SFE (n ) 6) compd C-12 C-13 C-14 C-15 C-16 C-17 C-18 Phy C-19 C-20 C-21 C-22 C-23 C-24 C-25 C-26 C-27 C-28 C-29 C-30
mean
RSD (%)
ASE (n ) 6) mean
RSD (%)
MSE (n ) 3) mean
RSD (%)
Soxhlet (n ) 3) mean
RSD (%)
USE (n ) 3) mean
RSD (%)
methods av mean
302 328 491 708 343 495 518 311 541 333 426 310 360 259 453 273 520 240 719 213
4.7 2.6 3.4 2.8 2.7 2.6 1.5 2.0 4.0 1.5 4.0 5.1 1.6 3.0 4.0 5.0 0.6 2.5 0.9 3.0
361 378 334 392 409 478 391 318 455 382 430 343 417 375 456 349 589 365 693 330
3.5 8.9 0.4 9.4 1.6 0.8 0.9 6.3 3.0 1.3 3.5 4.2 2.0 3.9 1.7 6.6 3.7 7.7 3.0 1.5
303 339 420 524 365 427 424 342 452 358 394 330 376 324 470 367 593 467 722 371
1.2 2.5 1.1 7.0 2.7 3.0 1.4 0.5 3.6 1.0 0.8 1.8 1.1 0.5 4.8 7.6 7.9 5.5 3.4 0.3
136 370 452 595 217 469 478 383 508 341 488 304 406 331 504 304 551 240 660 157
3.3 3.2 3.8 0.2 7.2 1.0 0.8 2.5 1.6 1.1 5.0 5.3 6.0 5.8 6.3 2.3 3.3 1.7 2.1 6.4
278 346 445 750 328 460 513 373 538 381 465 344 411 333 477 362 595 325 710 273
3.9 8.2 3.5 2.5 1.4 0.7 7.6 4.7 5.0 2.3 1.8 3.1 4.1 2.8 3.0 3.9 0.8 4.7 3.1 0.4
276 352 428 594 332 466 465 345 499 359 440 326 394 325 472 331 570 327 701 269
27.3 5.3 12.2 21.7 19.2 4.8 10.8 8.3 7.8 5.6 7.4 5.1 5.6 11.4 3.9 11.0 5.2 25.9 3.2 28.7
sum/av RSD (%)
8145
2.9
8243
3.7
8366
2.9
7894
3.4
8708
3.4
8271
11.5
Naph M2N M1N C2N2,6 Acy Ace Flu DBT Phen M1P Ant Fluor Pyr BaA Chr/Tri BbF BeP BaP Per I123P DBacA BghiP Cor
4445 3464 2055 1426 355 123 332 233 2895 363 801 3050 2357 1193 2049 1907 1528 1336 436 1732 485 1483 297
2.0 5.8 8.4 3.6 5.3 4.5 1.3 2.9 2.3 4.7 2.1 2.3 4.0 3.9 4.2 2.9 1.6 3.9 1.6 3.3 4.7 5.6 5.4
4256 2767 1314 1258 313 127 327 234 2908 353 822 3098 2328 1371 1755 2001 1444 1540 440 2067 658 1488 568
1.6 12.0 7.3 3.8 5.0 4.6 1.1 8.2 3.0 5.1 2.2 1.7 3.2 1.2 8.5 16.4 3.8 5.6 5.6 1.8 2.8 7.4 4.7
4507 3494 1933 1593 284 141 313 247 2994 608 754 2936 2295 1168 1852 1884 1340 1136 379 1541 440 1419 535
0.8 4.0 5.0 5.8 3.9 1.7 3.0 1.4 6.5 0.4 1.4 3.9 2.0 3.7 3.6 5.1 2.1 5.5 3.8 5.2 4.2 3.4 8.6
4672 3460 1810 1446 302 133 311 228 2925 427 742 2856 2246 1138 1996 1819 1325 1150 406 1626 392 1397 526
9.5 4.1 5.0 5.2 10.9 3.5 4.2 2.6 2.9 2.5 0.9 2.8 2.4 3.6 1.5 4.3 1.8 2.6 2.2 1.9 1.2 3.9 16.6
2963 2073 1079 1059 310 121 284 204 2772 359 730 2967 2258 1244 2068 1834 1284 1135 377 1553 512 1349 513
5.4 4.2 3.8 7.4 4.4 3.8 3.6 1.6 1.7 3.3 2.2 2.6 2.1 7.6 0.7 1.7 1.4 2.3 2.9 1.2 1.1 3.8 6.8
4169 3052 1638 1357 313 129 313 229 2899 422 770 2982 2297 1223 1944 1889 1384 1260 408 1704 497 1427 488
14.8 18.4 23.0 13.5 7.5 5.7 5.4 6.1 2.5 23.0 4.6 2.9 1.8 6.7 6.2 3.4 6.4 12.7 6.6 11.4 18.1 3.7 19.9
34346 24059
3.7 3.4
33437 24401
5.1 4.5
33794 23225
3.7 3.6
33331 23312
4.2 3.9
29048 21587
3.3 3.1
32791 23317
9.7 6.4
sum/av RSD (%) sum* a
certified values
RSD (%)
3977 ( 1100
184 ( 50 223 ( 70 455 ( 120 2910 ( 600 1067 ( 400 3433 ( 650 2910 ( 600 1746 ( 300 1940 ( 300 2716 ( 600 2134 ( 400 1891 ( 580 1726 ( 720
27315
Certified values are corrected for water content. Concentration is nanograms per gram of dry mass (n, number of extractions).
the individual methods vs certified values gave proportional errors in the range of 1.4-5.4% for SFE, ASE, MSE, and SOX, while USE gave a proportional error of 17.3%, as shown by the values in parentheses in Table 5. Statistical tests showed that the extraction methods investigated gave equivalent results for the extraction of PAHs and alkanes from the three types of matrix. SFE showed a significantly lower extraction efficiency only for coronene as a seven-ring PAH both in sediment and in SPM. Other differences in extraction rates were found to be random errors. Influence of Water on Extraction Efficiency. To estimate the influence of water on extraction efficiency, an aliquot of undried SPM II, with a natural water content of 56 wt%, was extracted by SFE and ASE. The extraction results are shown in Table 6 as percentage recoveries of the methods average in Table 3. Additional extractions of the undried sample were performed using MSE, which gave results similar to that of extractions of
air-dried SPM. This experiment was performed to ensure that no losses of analytes or contamination of the sample occurred during drying. ASE and SFE of undried SPM showed decreased recoveries with high RSDs due to insufficient extractions. In SFE, the recovery of alkanes averaged 76% and the recovery of PAHs 60% compared to average extraction rates from air-dried SPM. In ASE, average recoveries were only 22% for alkanes and 45% for PAHs. In both cases, a slight decrease in recoveries was observed for PAHs, depending on their boiling points. Alkanes showed an alternating recovery pattern. In SFE, even-numbered alkanes, which originate mainly from anthropogenic sources, showed higher recoveries than odd-numbered alkanes including pristane and phythane. Odd-numbered alkanes are of biogenic origin, high amounts of long-chain alkanes (C-25, C-27, C-29) indicating input of terrestrial plants. It may be assumed that anthropogenic alkanes are adsorbed only to the surface of the SPM and thus Analytical Chemistry, Vol. 69, No. 11, June 1, 1997
2175
Table 2. Extraction of PAHs and Alkanes from SPM I (River Elbe) with SFE, ASE, MSE, and SOXa SFE (n ) 6) compd C-12 C-13 C-14 C-15 C-16 C-17 Pri C-18 Phy C-19 C-20 C-21 C-22 C-23 C-24 C-25 C-26 C-27 C-28 C-29 C-30 sum/av RSD (%) Naph M2N M1N C2N2,6 Acy Ace Flu DBT Phen M1P Ant Fluor Pyr BaA Chr/Tri BbF BeP BaP Per I123P DBacA BghiP Cor sum/av RSD (%) sumc
ASE (n ) 3)
MSE (n ) 3)
Soxhlet (n ) 1)
methods av
mean
RSD (%)
mean
RSD (%)
mean
RSD (%)
mean
RSD (%)
243 267 278 321 220 504 305 184 224 162 166 275 250 584 383 1327 597 2270 748 3083 702
1.6 8.0 2.4 3.6 3.1 4.7 4.7 3.1 3.8 3.9 3.9 3.3 4.4 3.3 3.3 3.9 3.3 3.6 4.1 5.5 4.4
253 251 238 278 236 437 293 211 231 205 193 302 282 547 397 1114 611 2345 752 3163 641
2.3 0.9 6.6 3.2 3.2 1.3 2.6 2.8 0.6 0.5 5.1 6.1 5.6 4.5 2.6 3.7 2.4 3.2 1.8 6.7 7.6
238 238 310 315 285 528 361 230 259 164 197 303 301 657 452 1598 625 2217 782 3089 684
10.3 4.7 10.4 4.3 12.6 1.6 2.6 13.2 3.7 4.5 6.2 2.3 3.5 1.5 0.8 3.1 2.3 4.3 4.0 4.4 5.5
245 252 276 305 247 490 320 208 238 177 185 293 277 596 411 1346 611 2277 761 3112 676
2.4 4.8 10.7 6.2 11.2 7.9 9.3 9.0 6.4 11.0 7.3 4.4 7.6 7.6 7.2 14.7 1.8 2.3 2.0 1.2 3.8
13097
3.9
12980
3.5
13831
5.0
13302
6.6
197 111 57 67 32 35 100 41 451 49 94 659 572 282 397 227 243 281 143 188 65 147 38
5.3 10.6 7.8 7.0 1.1 3.0 2.4 2.2 4.9 1.4 2.7 1.5 1.8 1.4 2.8 0.9 0.7 2.2 2.3 4.9 5.6 2.3 4.6
213 102 60 65 28 35 74 43 466 45 92 658 577 278 302 243 216 277 143 162 56 156 62
3.6 12.5 3.5 7.5 9.6 12.2 8.3 7.3 2.0 3.8 3.7 4.6 0.2 2.1 2.5 1.3 4.1 3.3 1.2 3.1 1.7 1.6 7.1
185 114 62 69 26 31 69 35 443 47 79 660 583 271 401 239 248 272 203 201 68 180 63
3.9 11.1 11.2 14.7 0.3 3.1 2.3 4.4 4.6 4.2 0.7 4.9 4.5 2.9 0.3 6.7 3.4 5.9 1.6 5.1 4.1 6.2 7.5
237 91 46 nq 18 39 84 nq 417 nq 91 618 487 257 322 261 226 245 nq 227 nq 207 34
198 109 60 67 29 34 81 39 453 47 88 659 577 277 367 237 236 277 163 184 63 161 54
5.7 4.6 3.4 2.1 8.8 6.6 16.9 9.3 2.1 2.7 7.2 0.1 0.8 1.6 12.4 2.9 5.9 1.3 17.3 8.9 8.5 8.8 21.4
4476 4412
3.4 3.4
4355 4003
4.6 4.7
4550 4129
4.9 4.7
3907
4461 4081
6.9 6.6
nqb
a Soxhlet extraction and quantification were performed by ERGO Forschungsgesellschaft mbH (Hamburg, Germany). Concentration is nanograms per gram of mass (n, number of extractions). b nq, not quantified. c Sum of compounds quantified in Soxhlet extraction.
can be easily removed during extraction, even in the presence of water. Alkanes of biogenic origin are partly incorporated into plant cells. To extract such compounds, the solvents first have to diffuse into the matrix. This process seems to be impaired by high water contents. In ASE, the same effect was observed. While recoveries of even-numbered alkanes amounted nearly constantly to ∼30%, extraction of the biogenic odd-numbered n-alkanes C-23, C-25, C-27, and C-29 yielded only 16-29%. The results demonstrate that complete recovery of (biogenic) alkanes and PAHs from samples containing high water contents is not possible with SFE and ASE under such conditions. To be able to extract undried SPM without time-consuming drying processes, a homogeneous mixture of SPM II with ∼4 wt % portions anhydrous sodium sulfate was extracted by SFE. As shown in Table 6, quantitative average recoveries were achieved in these extractions for both alkanes and PAHs, compared to the 2176 Analytical Chemistry, Vol. 69, No. 11, June 1, 1997
extraction yields of air-dried samples (methods average). The mean percentage RSD was 9.0% for alkanes and 3.5% for PAHs. Although this technique allows fast sample preparation, the disadvantages of mixtures with sodium sulfate are a reduction of the sample volume and a risk of sample contamination. Extraction of Filter Candles with ASE and USE. As shown in the Experimental Section, extractions of the filter candles by USE required ∼600 mL of organic solvent/extraction. For that reason, extractions with ASE were performed in which the solvent quantity was reduced to 60 mL/extraction. Table 7 shows the results of filter extractions. Using ASE, the extraction of the river Ems filter gave an average recovery of 87% for alkanes and 101% for PAHs compared to USE. The smaller amount of alkanes in ASE is mainly attributable to the compounds C-17, C-18, and C-19, probably due to inhomogenity of the sample. Water samples were stirred during filtration, but homogenization nevertheless is much
Figure 1. Comparison of different extraction techniques for PAHs and alkanes by linear regression. Extraction rates of the methods investigated vs methods average are shown for sediment HS-6 (a), SPM I (b), and SPM II (c). For coefficients of linear regression, see Table 5.
more efficient with dried and milled samples. In samples from the river Weser, the recovery averaged 109% for alkanes and PAHs and 102% for chlorinated hydrocarbons. Considering the sum of each compound class, good conformity was achieved between the
extraction methods. Contrary to sediment extractions, USE also achieved comparable results for naphthalenes. During USE of the filters, the extraction bottles were closed, which minimized evaporation losses. Analytical Chemistry, Vol. 69, No. 11, June 1, 1997
2177
Table 3. Extraction of PAHs and Alkanes from SPM I (River Elbe) with SFE, ASE, MSE, and SOXa SFE (n ) 3) compd C-12 C-13 C-14 C-15 C-16 C-17 Pri C-18 Phy C-19 C-20 C-21 C-22 C-23 C-24 C-25 C-26 C-27 C-28 C-29 C-30
sum/av RSD (%)
Soxhlet (n ) 3)
mean
RSD (%)
mean
RSD (%)
mean
58 51 51 161 87 1224 126 212 89 278 152 427 381 1227 604 2062 689 2776 659 3104 596
5.8 13.4 17.1 4.7 7.1 6.8 11.3 11.2 13.3 9.9 8.0 4.0 7.1 1.4 5.5 0.2 8.9 2.6 9.2 2.5 6.7
76 96 94 154 105 934 124 132 60 184 134 364 320 1043 487 1828 593 2436 554 2541 492
4.9 6.3 1.5 10.2 2.8 2.9 1.3 1.3 1.5 5.4 1.7 1.8 0.9 2.6 2.4 3.0 0.8 0.8 0.3 1.4 1.8
58 48 50 142 85 1093 125 137 72 210 131 401 336 1233 541 1914 597 2790 567 3023 499
sum/av 15012 RSD (%) Naph M2N M1N C2N2,6 Acy Ace Flu DBT Phen M1P Ant Fluor Pyr BaA Chr/Tri BbF BeP BaP Per I123P DBacA BhiP Cor
MSE (n ) 6)
7.5 12752
113.4 5.1 117.7 4.3 56.8 5.4 86.0 4.7 20.8 5.8 19.7 1.2 64.8 1.3 21.0 3.0 167.8 2.7 26.5 1.9 37.4 2.5 268.9 2.7 226.9 4.7 121.6 2.8 193.2 2.4 181.7 4.4 170.0 2.8 163.3 1.6 266.6 7.3 156.5 3.4 45.3 4.1 122.5 1.2 50.3 20.3 2699
4.2
2.7 14051
113.7 0.8 116.4 4.3 61.0 10.6 82.1 14.7 11.5 4.0 17.0 1.1 39.8 2.1 18.4 0.9 151.8 0.9 24.8 1.2 29.9 2.4 256.9 1.1 207.0 0.7 113.7 2.0 184.0 1.2 179.4 2.7 166.7 3.0 149.7 2.8 279.0 2.3 170.9 3.1 48.7 3.1 127.2 0.1 66.7 1.8 2616
2.9
120.9 119.0 66.7 81.6 14.7 19.6 53.4 21.3 172.6 24.5 35.1 292.8 227.5 126.4 197.5 194.3 175.3 161.2 273.2 166.2 50.2 129.1 79.1 2802
methods av
RSD RSD (%) mean (%) 9.3 8.3 2.9 1.0 1.8 5.6 3.6 6.0 0.0 4.2 1.2 1.9 1.4 0.2 0.5 1.1 1.6 2.3 1.0 1.0 1.2
64 65 65 152 92 1083 125 160 74 224 139 397 346 1167 544 1935 627 2667 593 2889 529
13.6 33.6 31.6 5.3 9.6 11.0 0.8 23.0 15.8 17.6 6.7 6.4 7.4 7.6 8.8 5.0 7.1 6.1 7.9 8.6 9.0
Table 4. Constant Systematic Error (Bias) between the Individual Extraction Methods Investigateda method
SFE
SFE HS-6 SPM I SPM II ASE HS-6 SPM I SPM II MSE HS-6 SPM I SPM II SOX HS-6 SPM I SPM II USE HS-6* SPM 1 SPM II
ASE
MSE
SOX
USE
2.6 2.7 ni
1.6 -0.4 3.1
3.0 5.0 -3.8
4.7 nib ni
-1.1 -3.2 ni
0.3 2.4 ni
8.3 ni ni
1.4 5.4 -7.1
1.8 ni ni
1.2 -0.9 ni 2.6 5.6 -15.1
1.5 6.6 nuc
-3.1 ni -6.4
-4.2 ni nu
-5.6 ni 10.2
6.9 ni ni
5.6 ni ni
4.1 ni ni
Certif
-13.5
-11.9
-17.6
0.3 ni ni
-17.2
10.3 ni ni
-21.0
a Parameters for PAHs are given to the right, parameters for alkanes to the left side of the diagonal. b ni, not investigated. c nu, determination of bias for USE of HS-6 without naphthalanes.
2.7 13939 11.5 1.6 4.1 5.9 2.6 6.0 1.1 2.9 1.3 1.5 4.0 1.6 2.5 2.0 2.0 0.3 9.0 1.1 2.7 1.4 2.0 2.8 0.4 3.9 2.7
116 3.0 118 0.9 61 6.6 83 2.4 16 24.7 19 6.7 53 19.4 20 6.5 164 5.4 25 3.5 34 9.1 273 5.5 220 4.3 121 4.3 192 3.0 185 3.5 171 2.1 158 3.8 273 1.9 164 3.6 48 4.2 126 2.2 65 18.0 2706
HS-6 sample
alkanes
SPM I
SPM II
PAH
alkanes
PAH
alkanes
PAH
1.023 (0.974) 0.946 (0.962) 1.014 (0.982) 1.029 (0.985) 0.984 (0.827)
0.996 1.009 0.995 ni ni
1.029 1.014 1.033 0.920 ni
1.060 nib 0.897 1.044 ni
0.987 ni 0.980 1.033 ni
2.3 (2.6) 5.4 (3.8) 1.4 (1.8) 2.9 (1.5) 1.6 (17.3)
0.4 0.9 0.5 ni ni
2.9 1.4 3.3 8.0 ni
A1 SFE ASE MSE SOX USEc
1.150 0.792 0.841 1.189 1.038
F SFE ASE MSE SOX USEc
15.0 21.8 15.9 18.9 3.8
6.0 ni 10.3 4.4 ni
1.3 ni 2.0 3.3 ni
a Values in parentheses show comparison with certified values. b ni, not investigated. c Without naphthalenes.
6.3
a Concentration is nanograms per gram of dry mass (n, number of extractions).
Method Comparison by General Parameters. The extraction time of ASE was 15 min, SFE as well as USE took 1.5 h, MSE 2.5 h, and Soxhlet 24 h per extraction. Solvent consumption in SFE was 15 mL (modifier and trapping solvent), in ASE 20 mL, in USE 120 mL, in Soxhlet 150 mL, and in MSE 200 mL. On the other hand, method development for SFE is laborious, while classical extraction methods are well established for a wide range of compound classes. In ASE, the same solvents can be used as in Soxhlet extractions, only the extraction time and temperature have to be optimized. Automated devices for simultaneous or sequential extractions are available for ASE and some SFE devices (not in this study); simultaneous extractions can be performed with Soxhlet, sonication, and methanolic saponification, the 2178 Analytical Chemistry, Vol. 69, No. 11, June 1, 1997
Table 5. Coefficient A1 from Linear Regression (Eq 2) and Resulting Proportional Systematic Error Frel (Eq 3) for the Comparison of SFE, ASE, MSE, Soxhlet, and USE vs Methods Averagea
equipment cost of ASE and SFE being the highest. Wet samples can be extracted with MSE, but MSE may lead to chemical reactions with alkali-sensitive compounds (e.g., substitution of halogen in aromatic systems). SFE of wet samples required pretreatment with anhydrous sodium sulfate. CONCLUSIONS SFE and ASE have been proved to be successful techniques for extracting PAHs and alkanes from marine matrices. Statistical evaluations of accuracy and precision showed that equivalent results were achieved by ASE and SFE for the simultaneous extraction of alkanes and PAHs as compared to MSE, USE, and Soxhlet, with both sediment and SPM samples. Compared to the reference methods, average recoveries of PAHs in SFE of three different samples ranged from 96 to 105%. With ASE, recoveries ranged between 97 and 108%. Compared to the certified values
Table 6. Influence of Water on Extraction Efficiency of PAHs and Alkanes from Undried SPM II for Different Extraction Methodsa undried SPM II (water content 56 wt %) SFE (n ) 3) compd C-12 C-13 C-14 C-15 C-16 C-17 Pri C-18 Phy C-19 C-20 C-21 C-22 C-23 C-24 C-25 C-26 C-27 C-28 C-29 C-30
ASE (n ) 3)
SPM II + Na2SO4 MSE (n ) 3)
SFE (n ) 6)
mean RSD mean RSD mean RSD mean RSD (%) (%) (%) (%) (%) (%) (%) (%) 55 49 74 87 47 55 45 75 55 70 116 92 120 76 107 69 104 63 121 65 124
15.5 14.2 22.4 24.7 17.0 7.6 13.8 11.8 16.2 11.9 24.3 18.0 24.3 13.9 22.5 13.8 23.4 11.9 25.0 11.7 24.7
31 52 121 95 49 18 26 27 28 21 31 22 28 19 29 17 33 18 29 16 27
8.2 19.8 24.2 25.3 17.7 17.7 25.1 16.4 27.3 18.6 13.1 11.1 9.7 11.9 10.3 11.9 11.1 15.6 10.2 15.0 9.9
74 68 152 112 111 94 100 78 81 75 98 94 89 88 83 94 116 106 106 103 96
4.4 3.2 4.3 6.1 5.5 1.9 1.0 1.4 1.9 1.1 1.6 1.3 1.4 3.2 3.5 6.1 6.3 4.0 4.2 1.5 2.6
78 66 73 103 98 97 97 75 79 85 98 103 100 101 100 96 105 100 109 103 110
5.9 4.3 8.5 28.3 9.1 6.8 5.7 27.0 13.5 9.9 10.2 5.3 4.4 5.6 1.7 7.4 4.5 8.6 6.4 9.0 6.4
sum/av RSD (%)
76
17.6
22
15.7
99
3.2
100
9.0
Naph M2N M1N C2N2,6 Acy Ace Flu DBT Phen M1P Ant Fluor Pyr BaA Chr/Tri BbF BeP BaP Per I123P DBacA BghiP Cor
93 83 65 89 42 73 68 74 68 57 63 69 80 57 62 47 54 50 51 40 40 35 28
6.4 11.9 12.2 18.5 17.5 8.1 12.6 7.1 6.1 8.0 6.6 7.4 10.3 10.1 8.1 13.2 11.2 11.9 10.6 9.0 10.0 9.0 10.7
55 52 47 52 40 85 71 53 57 79 52 48 46 39 39 46 40 48 39 31 32 32 30
9.6 10.8 11.6 11.7 24.1 9.8 20.4 9.8 8.9 46.0 4.9 12.6 15.6 19.3 15.9 19.8 19.2 24.9 15.4 15.5 23.9 14.1 16.2
97 98 99 115 73 98 74 90 97 98 87 97 96 94 99 102 92 95 98 101 99 98 90
0.7 2.7 3.3 4.3 4.2 6.2 2.3 0.5 1.1 0.8 1.5 0.4 0.2 1.2 1.0 3.5 1.1 0.9 0.8 0.8 0.5 0.6 8.1
126 99 76 91 72 106 77 105 102 97 104 104 104 100 106 97 104 107 101 102 97 96 77
1.7 0.8 4.0 6.8 7.6 6.7 5.9 4.7 2.2 2.4 3.6 1.2 0.2 2.1 1.3 2.6 1.6 3.4 1.5 4.4 4.4 3.7 8.8
sum/av RSD (%)
60
10.3
45
16.5
97
2.0
101
3.5
a
Percentage recoveries are related to methods average in Table 3 (n, number of extractions).
of sediment HS-6, average recoveries of SFE and ASE were 86 and 88%, respectively, most compounds being in the limits of confidence. Also, the average recoveries of alkanes by SFE and ASE were equal to the results obtained by SOX, USE, and MSE. In the case of SFE, recoveries were in the range 93-115%, while ASE achieved recoveries of 94-107%. Relative standard deviations of ASE and SFE were in the range of 2.9-7.5% for alkanes and PAHs. The overall methods RSD was 6.6% for alkanes and PAH in SPM I and II and 11.5% for alkanes and 6.4% for PAH in HS-6. Taking into account general criteria such as solvent consumption, extraction time, and practical conditions of the different
Table 7. ASE and USE of SPM-Loaded Filter Candlesa filter with SPM from river Ems compd
river Weser
USE
ASE
% of USE
C-12 C-13 C-14 C-15 C-16 C-17 Pri C-18 Phy C-19 C-20 C-21 C-22 C-23 C-24 C-25 C-26 C-27 C-28 C-29 C-30
2.8 2.1 3.4 9.8 4.7 115.8 6.3 16.5 4.2 29.0 6.2 13.3 10.6 31.2 14.3 41.0 16.5 60.5 14.0 62.4 10.5
3.1 3.7 3.2 6.3 4.9 36.5 4.1 6.3 3.0 12.1 5.7 13.0 12.1 33.0 15.9 51.3 16.4 76.4 17.0 77.1 12.5
109 176 95 64 104 32 65 38 72 42 92 98 114 106 111 125 99 126 121 124 120
4.3 5.6 4.7 8.6 4.9 48.4 7.2 5.7 4.3 8.0 6.7 16.3 14.1 43.6 25.4 89.4 30.2 140.3 32.2 147.3 26.2
4.3 5.3 4.5 12.7 5.7 52.7 8.0 6.9 5.3 9.0 8.3 19.6 17.6 50.3 23.9 92.4 26.5 166.9 29.9 147.8 21.5
99 94 96 147 118 109 112 121 124 112 124 120 125 115 94 103 88 119 93 100 82
sum
475.3
413.6
87
673.2
719.0
109
Naph M2N M1N C2N2,6 Acy Ace Flu DBT Phen M1P Ant Fluor Pyr BaA Chr/Tri BbFb BeP BaP Per I123P DBacA BghiP Cor sum
USE
ASE
% of USE
1.86 1.52 0.88 2.50 0.31 0.48 0.89 0.36 3.39 0.44 0.66 6.80 5.51 3.13 4.94 4.10 3.98 4.31 6.48 3.90 1.19 2.90 1.19
1.86 1.48 0.81 1.35 0.33 0.42 0.78 0.54 3.61 0.58 0.84 6.64 5.24 3.08 4.45 5.41 4.07 4.17 5.99 4.82 1.14 2.86 1.60
100 97 92 54 106 87 87 151 106 130 128 98 95 98 90 132 102 97 92 123 96 99 135
1.69 1.83 0.86 1.53 0.59 0.37 0.64 0.56 3.90 0.60 0.95 9.88 8.45 5.27 7.71 14.19 6.31 7.28 7.70 5.47 1.62 5.04 4.28
1.71 1.51 0.94 1.56 0.52 0.42 0.87 0.66 4.70 0.87 1.14 10.35 8.96 5.44 7.63 14.62 6.22 7.34 8.56 7.26 1.81 5.10 3.50
101 83 109 102 88 114 136 118 120 144 120 105 106 103 99 103 98 101 111 133 112 101 82
61.73
62.07
101
96.72
101.69
108
R-HCH γ-HCH HCB DDE DDD DDT PCB 28 PCB 52 PCB 101 PCB 118 PCB 153 PCB 105 PCB 138 PCB 156 PCB 180
0.269 nd 0.012 0.061 0.127 nd 0.066 nd 0.057 0.042 0.165 0.057 0.175 0.066 0.078
0.187 ndc 0.008 0.119 0.253 nd 0.046 0.311 0.101 0.073 0.483 0.071 0.608 0.171 0.203
0.261 nd 0.011 0.117 0.315 0.186 0.053 0.229 0.108 0.053 0.466 0.075 0.545 0.083 0.255
140
sum
1.17
2.63
2.76
102
133 98 125 116 74 106 73 97 106 90 48 126
a Concentration is in nanograms per liter. The SPM content was 69.2 mg/L in the river Weser and 39.6 mg/L in the river Ems. b For the Weser sum of BbF and BkF. c nd, not detected.
methods, SFE and ASE are the preferable techniques. The major advantage of the ASE is extraction time (15 min). Solvent Analytical Chemistry, Vol. 69, No. 11, June 1, 1997
2179
consumption in SFE was only 15 mL including modifier and trapping solvent, in ASE 20 mL. Because of the small amount of solvent necessary in these extraction techniques, the concentration step is much shorter (or in some cases not required) and the risk of analyte losses is greatly reduced. The extraction of filter candles showed a new application for ASE, where the amount of organic solvent was reduced from 600 to 60 mL, as compared to traditional USE. Use of n-hexane/acetone in ASE allowed the simultaneous determination of alkanes, PAHs, and chlorinated compounds.
2180
Analytical Chemistry, Vol. 69, No. 11, June 1, 1997
ACKNOWLEDGMENT We thank B. Stachel from ARGE Elbe for providing the SPM sample of the river Elbe and the results of Soxhlet extraction, and also F. Ho¨fler from Dionex GmbH, who enabled extractions on a Dionex ASE 200. Received for review July 18, 1996. Accepted March 3, 1997.X AC960695F X
Abstract published in Advance ACS Abstracts, April 15, 1997.
