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Monitoring of Polycyclic Aromatic Hydrocarbons in Water Using Headspace Solid-Phase Microextraction and Capillary Gas Chromatography
Microchemical Journal 63, 276 –284 (1999) Article ID mchj.1999.1791, available online at http://www.idealibrary.com on
Monitoring of Polycyclic Aromatic Hydrocarbons in Water Using Headspace Solid-Phase Microextraction and Capillary Gas Chromatography Dj. Djozan 1 and Y. Assadi Department of Analytical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran Accepted June 14, 1999 A laboratory-made fused silica fiber coated with a porous layer of activated charcoal (PLAC) was used as a new microsolid phase in solid-phase microextraction (SPME) mode for sampling of polycyclic aromatic hydrocarbons (PAHs) from the headspace of water samples. Effects of temperature, salt addition, stirring speed, and exposure time on extraction efficiency were investigated. Extraction at 80°C for 30 min in the presence of 12 g NaCl at constant stirring speed yields maximum efficiency. Using the proposed microsolid phase as an efficient sampling device and capillary gas chromatography with flame ionization detection, reliable determination of these compounds at sub-parts-per-billion concentrations was achieved. The calibration graphs were linear in the range 0.1–50 ng/ml and the detection limits were 0.03– 0.3 ng/ml. The proposed method was successfully applied to the determination of PAHs in environmental samples such as local municipal water. © 1999 Academic Press Key Words: activated charcoal; solid-phase microextraction; capillary gas chromatography; water pollutant analysis; polycyclic aromatic hydrocarbons.
INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) are widespread contaminants of the environment (1). A significant number of these compounds are either known or suspected carcinogens (2). Under the standards adopted by the European Community, the reference concentration in groundwater for the most dangerous PAH, benzo[a]pyrene, is 10 ng/liter; for fluoranthene and pyrene, 20 ng/liter; and for phenanthrene and anthracene, 100 ng/liter (3). Their identification and determination continue, therefore, to be an important analytical problem (4). The analysis of these compounds can be performed by various chromatographic and electrophoretic methods (5–7). The main problem with the monitoring of PAHs even by capillary GC is the very low concentration of the analytes and the complexity of the environmental matrices. Preconcentration and preseparation are therefore required to achieve the required sensitivity and selectivity. Various methods have been used for these purposes; however, they often require large volumes of solvents, are time consuming and more expensive, yield low concentration factors and have their own limitations (8 –10). Solid-phase microextraction (SPME), an extraction technique first introduced by Pawliszyn’s group (11, 12), offers solutions to many of the sampling problems. This technique represents a further important advance in the efficient extraction of various organic pollutants at trace levels from liquid (13–22), solid (23), and gas (24) samples. SPME has 1
To whom correspondence should be addressed. 276
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also been used for the sampling of volatile and semivolatile organic compounds from more complex samples such as soil and sludge (25–27). In addition, SPME has been successfully used as a device for sampling volatile organic compounds from biological samples and foodstuffs in chromatographic analysis (28 –33). Besides its chromatographic utility, SPME has been used for sampling in Raman spectroscopy (34), mass spectroscopy (18, 35), and ultraviolet adsorption spectroscopy (36, 37). SPME has also been used for the determination of PAHs in water and soil samples (17, 25, 38 – 41). On the basis of previous works (42, 43), we have studied the efficiency of new and homemade SPME fiber (fused silica fiber coated with a porous layer of activated charcoal) for the extraction and detemination of PAHs from the headspace of water samples. The extracts were monitored by capillary gas chromatography and flame ionization detection. EXPERIMENTAL Fiber preparation. The SPME device was constructed from the activated charcoalcoated fused silica optical fiber. A 10 cm-long fiber of outer diameter 100 mm was conditioned in 3 M HCl solution, dried at 60°C for 16 h, deactivated with trimethylchlorosilane, impregnated with a 5% (w/v) silicon OV1 solution in chloroform as a binder, and then coated with extrafine powdered activated charcoal to a total thickness of 55 mm. A 1.5-cm length of this fiber was mounted in the modified GC syringe as described in the literature (44). Fibers were conditioned and pretreated in an injection port of a gas chromatograph at 360°C for 1 h to remove fiber contamination. Reagents. Helium 99.999% was purchased from Air Products (Middle East Dubai, United Arab Emirates); naphthalene, biphenyl, acenaphthylene, fluorene, acenaphthene, phenanthrene, anthracene, 2-methyl anthracene, fluoranthene, pyrene, and benzo[a]fluorene were from Aldrich. Sodium chloride (P.A), methanol, activated charcoal (Part No. 21841), and other chemicals were from E. Merck, Darmstadt, Germany. The stock standard solution was prepared by dissolving 1 mg of each compound in 10 ml methanol. These solutions were used to prepare 50-ml model aqueous solutions containing the required amount of each analyte (0.1–50 ng/ml). Blank analyses were performed regularly to ensure that no PAHs were present in laboratory reagents, atmosphere, or fibers. Headspace SPME procedure. To a 70-ml vial containing a magnetic stirrer bar and 50 ml of water sample, 12 g NaCl was added. The vial was rapidly sealed with a silicon septum cap, and the fiber was exposed in the headspace of the vial. The vial was heated at 80°C with stirring for 30 min. The analytes were then thermally desorbed in the injector port of a gas chromatograph at 350°C for 2 min and analyzed. Gas chromatography. The GC apparatus consisted of a Shimadzu (Japan) GC-15A equipped with a flame ionization detector, a data processor Model C-R4A Chromatopac, hydrogen generator Model OPGU-1500 S, and split/splitless injector. A Shimadzu Hicap CBP-5 (SE-52, 54) capillary column (L 5 25 m, i.d. 5 0.33 mm, film thickness 5 0.5 mm) was used. The GC conditions were: column temperature program, 50°C with a 2-min hold, rising at 40°C/min to 140°C, then rising at 10°C/min to 280°C, 2-min hold. Carrier gas velocity was 30 cm/s, and makeup gas velocity, 30 ml/min. The analytes were injected in the splitless mode at 350°C; the splitter was opened after 2 min. Detector temperature was 350°C.
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FIG. 1. Dependence of extraction efficiency on temperature. PAH concentration: 2 ng/ml of each; amount of NaCl: 12 g; speed of stirrer: 60% of maximum speed; exposure time: 30 min.
FIG. 2. Dependence of extraction efficiency on stirring speed. PAH concentration: 2 ng/ml of each; amount of NaCl: 12 g; exposure time: 30 min; exposure temperature: 80°C.
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FIG. 3. Dependence of extraction efficiency on amount of NaCl. PAH concentration: 2 ng/ml of each; exposure temperature: 80°C; stirring speed: 60% of maximum speed; exposure time: 30 min.
FIG. 4. Dependence of extraction efficiency on exposure time. PAH concentration: 2 ng/ml of each; exposure temperature: 80°C; stirring speed: 60% of maximum speed; amount of NaCl: 12 g.
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FIG. 5. Typical gas chromatogram of PAHs after extraction from model aqueous solution by headspace SPME. PAH concentration: 2 ng/ml of each; amount of NaCl: 12 g; stirring speed: 60% of maximum speed; exposure time: 30 min; exposure temperature: 80°C.
RESULTS AND DISCUSSION Effect of Extraction Temperature Extraction–temperature profiles were obtained for 50-ml model aqueous solutions by monitoring the recovery efficiency counts as a function of extraction temperature. As shown in Fig. 1, extraction efficiency always increases with temperature. It was observed that at 80°C, extraction efficiency was between 20 and 96% depending on the compound assayed. Apart from the low extraction recovery for the compounds with high boiling points, good sensitivity and precision were obtained for all the compounds studied (see Quantitative Analysis). Effect of Stirring Speed A potential influence on the headspace procedure is the establishment of equilibrium between liquid and headspace (gas) phases. The stirring speed of the aqueous solution can therefore be an important parameter. Extraction efficiencies of the studied compounds were measured from 50 ml of the model samples in the presence of 12 g NaCl and 30 min extraction time at 80°C at various stirring speeds. The results are shown in Fig. 2. From this figure, it is apparent that the extraction efficiency increases at a constant time with
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TABLE 1 Characteristic Parameters of Calibration Graphs and Analytical Features of the Determination of PAHs in Water Using Headspace SPME and Capillary Gas Chromatography with Flame Ionization Detection
Compound
Retention time (min) (n 5 5)
LOD a (ng/ml)
LDR b (ng/ml)
Correlation coefficient
RSD% c (n 5 5)
Naphthalene Biphenyl Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene 2-Methyl anthracene Fluoranthene Pyrene Benzo[a]fluorene
5.91 6 0.03 d 7.59 6 0.02 8.42 6 0.02 8.76 6 0.03 9.82 6 0.02 12.04 6 0.03 12.15 6 0.02 13.39 6 0.03 15.00 6 0.03 15.56 6 0.03 16.45 6 0.04
0.03 0.03 0.03 0.05 0.10 0.05 0.05 0.10 0.15 0.20 0.30
0.1–10 0.1–10 0.1–10 0.2–10 0.3–10 0.2–10 0.2–10 0.3–20 0.5–20 0.5–20 1.0–50
0.999 0.999 0.999 0.998 0.999 0.998 0.995 0.996 0.996 0.994 0.993
3.4 4.2 2.8 5.4 7.4 6.2 7.1 6.9 8.5 7.6 9.5
Limit of detection (S/N 5 3). Liner dynamic range. c Relative standard deviation (2 ng/ml). d Mean 6 SD. a b
stirring speed, and above 60% of maximum speed, the extraction–speed profiles of all compounds studied reach a plateau and remain constant. Effect of Salting Out For this investigation, we studied the effect of various amounts of sodium chloride (ranging from 0 to 20 g) on the efficiency of extraction of the analytes. Figure 3 plots the extraction efficiency versus amount of NaCl in model solutions. From the results obtained, for amounts of NaCl greater than 12 g, the extraction efficiencies of the compounds studied reach a plateau and remain constant. Effect of Exposure Time Extraction–time profiles were obtained for 50-ml model aqueous solutions by monitoring the recovery efficiency counts as a function of the duration of exposure to 12 g sodium chloride at 80°C at constant stirring time. As shown in Fig. 4, extraction efficiency increases with exposure time at constant temperature and reaches a plateau when a real equilibrium is established. For future quantitative analyses, an exposure time of 30 min is a reasonable compromise for good peak response at logical assay time. This is also a typical time for a GC run, and during the GC analysis, extraction of the next sample can be carried out. Quantitative Analysis Figure 5 shows a typical gas chromatogram for headspace-SPME extracts from 50-ml model aqueous solutions under the optimized extraction and chromatographic conditions. Quantitative analysis was carried out using 50-ml samples of standard solutions. Char-
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TABLE 2 Determination of PAHs in Real Water Samples Using Headspace SPME and Capillary Gas Chromatography with Flame Ionization Detection
Compound
Tap water a (ng/ml)
Municipal waste water a (ng/ml)
Rain water flowing asphalt a (ng/ml)
Naphthalene Biphenyl Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene 2-Methyl anthracene Fluoranthene Pyrene
ND b ND ND ND ND ND ND ND ND ND
0.132 6 0.007 ND ND ND ND ND ND ND ND ND
0.248 6 0.011 0.125 6 0.008 0.342 6 0.018 ND ND ND ND ND ND ND ND
Benzo[a]Fluorene
ND
ND
a b
Mean 6 SD, n 5 5. Not detected.
acteristic parameters of the quantitation for five replicate analyses including retention time reproducibility, detection limit, dynamic range, correlation coefficient of calibration graphs, and relative standard deviation are listed in Table 1. Limits of detection (LODs). The LODs obtained were lower than 0.05 ng/ml for naphthalene, biphenyl, acenaphthylene, acenaphthalene, phenanthrene, and anthracene, and over the range 0.1– 0.3 ng/ml for fluorene, 2-methyl anthracene, fluoranthene, pyrene, and benzo[a]fluorene. The detection limits obtained are remarkable, taking into account the rapid and simple sampling process without any serious practical difficulty. Comparison of these results with literature data using poly(dimethylsiloxane) fiber (41) shows that the proposed fiber has better absorption efficiency for the low-molecular-weight PAHs from the headspace of aqueous solutions. Linearity. The linearity of the calibration graphs was investigated for all compounds studied. The values for correlation coefficient (r) obtained are between 0.993 and 0.999, and show the acceptable linearity in the dynamic ranges represented in Table 1. Precision. The precision of the method for five replicate analyses of model aqueous solutions is summarized in Table 1. For the solution containing 2 ng/ml of each PAH, the coefficient of variation was between 3 and 9%. Taking into account the very low concentration level of the analytes, the precision is good. Application to Real Samples To evaluate the reliability of the proposed method, some local municipal water samples were analyzed. The analytical results are summarized in Table 2. These results show that gas chromatography after SPME using the proposed fiber is a powerful method for the monitoring of PAHs at very low concentrations in water samples.
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CONCLUSION Laboratory-made SPME fiber (fused silica fiber coated with a porous layer of activated charcoal coated) has been shown to be a very convenient and powerful device for sampling trace amounts of PAHs dissolved in water and other aqueous samples. In comparison with other sampling techniques, it is simple, rapid, solvent free, and inexpensive. The preconcentration enhancement afforded by this fiber allows limits of detection at the sub-parts-per-billion level. REFERENCES 1. Wise, S. A.; Sander, L. C.; May, W. E. J. Chromatogr., 1993, 642, 329 –349. 2. International Agency for Research on Concer. IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man, Vol. 3: Certain Polycyclic Aromatic Hydrocarbons and Heterocyclic compounds. IARC, Lyon, 1973. 3. Moen, J. E. T.; Cornet, J. P.; Evers, C. W. A. In Contaminated Soil (J. W. Assink and W. J. Van den Brink, Eds.), p. 441. Martinus Nijhoff, Dordrecht, 1989. 4. Furton, K. G.; Jolly, E.; Pentzke, G. J. Chromatogr., 1993, 642, 33– 45. 5. Wise, S. A.; Sander, L. C.; May, W. E. J. Chromatogr., 1993, 642, 329 –349. 6. Terabe, S.; Miashita, Y.; Ishihama, Y.; Shibata, O. J. Chromatogr., 1993, 636, 47–57. 7. Otsuka, K.; Higashimori, M.; Koike, R.; Karuhaka, K.; Okada, Y.; Terabe, S. Electrophoresis, 1994, 15, 1280 –1283. 8. U.S. EPA method 624. Fed. Regist., 1984, 141, 49. 9. Novak, J.; Drozd, J. In Instrumentation in Analytical Chemistry (J. Zuka, Ed.), Vol. 1, Chap. 10. Ellis Horwood: West Sussex, 1991. 10. Suffet, I. H.; Malaiyandi, M. (Eds.) Advances in Chemistry, Vol. 214: Organic Pollutants in Water: Sampling, Analysis, and Toxicity Testing. Am. Chem. Soc., Washington, DC, 1981. 11. Belardi, R. G.; Pawliszyn, J. Water Pollut. Res. J. Can., 1989, 24, 179. 12. Arthur, C. L.; Pawliszyn, J. Anal. Chem., 1990, 62, 2145–2148. 13. Eisert, R.; Levsen, K. Fresenius J. Anal. Chem., 1995, 351, 555–562. 14. Potter. D. W.; Pawliszyn, J. J. Chromatogr., 1992, 625, 247–255. 15. Arthur, C. L.; Killam, L. M.; Motlagh, S.; Lim, M.; Potter, D. W.; Pawliszyn, J. Environ. Sci. Technol., 1992, 26, 979 –983. 16. Motlagh, S.; Pawliszyn, P. Anal. Chim. Acta, 1993, 284, 265–273. 17. Potter, D. W.; Pawliszyn, P. Environ. Sci. Technol., 1994, 28, 298 –305. 18. Cisper, M. E.; Earl, W. L.; Nogar, N. S.; Hemberger, P. H. Anal. Chem., 1994, 66, 1897–1901. 19. Buchholz, K. D.; Pawliszyn, J. Anal. Chem., 1994, 66, 160 –167. 20. Horng, J. Y.; Huang, S. D. J. Chromatogr., 1994, 678, 313–318. 21. Barnabas, I. J.; Dean, J. R.; Fowlis, I. A.; Owen, S. P. J. Chromatogr., 1995, 705, 305–312. 22. Boyd-Boland, A. A.; Pawliszyn, J. J. Chromatogr., 1995, 704, 163–172. 23. Santos, F. J.; Sarrion, M. N.; Galceran, M. T. J. Chromatogr. A, 1997, 771, 181–189. 24. Martos, P. A.; Pawliszyn, J. Anal. Chem., 1997, 69, 206 –215. 25. Zhang, Z.; Pawliszyn, J. Anal. Chem., 1993, 65, 1843–1852. 26. MacGillivary, B.; Pawliszyn, J.; Fowlie, P.; Sagara, C. J. Chromatogr. Sci., 1994, 32, 317–322. 27. Zhang, Z.; Pawliszyn, J. Anal. Chem., 1995, 67, 34 – 43. 28. Pelusio, F.; Nilsson, T.; Montanarella, L.; Tilio, R.; Larsen, B.; Facchetti, S.; Madsen, J. J. Agr. Food. Chem., 1995, 43, 2138 –2143. 29. Krogh, M.; Johansen, K.; Tonnesen, F.; Rasmussen, K. E. J. Chromatogr., 1995, 673, 299 –305. 30. Kumazawa, T.; Lee, X. P.; Tsai, M. C.; Seno, H.; Ishii, A.; Sato, K. Jpn. J. Forens. Toxicol., 1995, 1, 25–30. 31. Kumazawa, T.; Lee, X. P.; Sato, K.; Seno, H.; Ishii, A.; Suzuki, O. Jpn. J. Forens. Toxicol., 1995, 13, 182–188. 32. Yashiki, M.; Nagasawa, N.; Kojima, T.; Miyazaki, T.; Iwasaki, Y. Jpn. J. Forens. Toxicol., 1995, 13, 17–24. 33. Kumazawa, T.; Watanabe, K.; Sato, K.; Seno, H.; Ishii, A.; Suzuki, O. Jpn. J. Forens. Toxicol., 1995, 13, 207–210.
284 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44.
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Wittkamp, B. L.; Tilotta, D. C. Anal. Chem., 1995, 67, 600 – 605. Cai, Y.; Bayona, J. M. J. Chromatogr., 1995, 696, 113–122. Wittkamp, B. L.; Hawthorne, S. B. Anal. Chem., 1997, 69, 1197–1203. Wittkamp, B. L.; Hawthorne, S. B. Anal. Chem., 1997, 69, 1204 –1210. Liu, Y.; Lee, M. L.; Hageman, K. J.; Yang, Y.; Hawthorne, S. B. Anal. Chem., 1997, 69, 5001–5005. Hageman, K. J.; Mazeas, L.; Grabanski, C. B.; Miller, D. J.; Hawthorne, S. B. Anal. Chem., 1997, 69, 3892–3898. Daimon, H.; Pawliszyn, J. Anal. Commun., 1996, 33, 421– 424. Langenfeld, J. J.; Hawthorne, S. B.; Miller, D. J. Anal. Chem., 1996, 68, 144 –155. Djozan, Dj.; Assadi, Y. 21st International Symposium on Chromatography Stuttgart, 1996. Djozan, Dj.; Assadi, Y. Chromatographia, 1997, 45, 183–189. Hawthorne, S. B.; Miller, D. J.; Pawliszyn, J.; Arthur, C. L. J. Chromatogr., 1992, 603, 185–191.
Monitoring of Polycyclic Aromatic Hydrocarbons in Water Using Headspace Solid-Phase Microextraction and Capillary Gas Chromatography Dj. Djozan 1 and Y. Assadi Department of Analytical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran Accepted June 14, 1999 A laboratory-made fused silica fiber coated with a porous layer of activated charcoal (PLAC) was used as a new microsolid phase in solid-phase microextraction (SPME) mode for sampling of polycyclic aromatic hydrocarbons (PAHs) from the headspace of water samples. Effects of temperature, salt addition, stirring speed, and exposure time on extraction efficiency were investigated. Extraction at 80°C for 30 min in the presence of 12 g NaCl at constant stirring speed yields maximum efficiency. Using the proposed microsolid phase as an efficient sampling device and capillary gas chromatography with flame ionization detection, reliable determination of these compounds at sub-parts-per-billion concentrations was achieved. The calibration graphs were linear in the range 0.1–50 ng/ml and the detection limits were 0.03– 0.3 ng/ml. The proposed method was successfully applied to the determination of PAHs in environmental samples such as local municipal water. © 1999 Academic Press Key Words: activated charcoal; solid-phase microextraction; capillary gas chromatography; water pollutant analysis; polycyclic aromatic hydrocarbons.
INTRODUCTION Polycyclic aromatic hydrocarbons (PAHs) are widespread contaminants of the environment (1). A significant number of these compounds are either known or suspected carcinogens (2). Under the standards adopted by the European Community, the reference concentration in groundwater for the most dangerous PAH, benzo[a]pyrene, is 10 ng/liter; for fluoranthene and pyrene, 20 ng/liter; and for phenanthrene and anthracene, 100 ng/liter (3). Their identification and determination continue, therefore, to be an important analytical problem (4). The analysis of these compounds can be performed by various chromatographic and electrophoretic methods (5–7). The main problem with the monitoring of PAHs even by capillary GC is the very low concentration of the analytes and the complexity of the environmental matrices. Preconcentration and preseparation are therefore required to achieve the required sensitivity and selectivity. Various methods have been used for these purposes; however, they often require large volumes of solvents, are time consuming and more expensive, yield low concentration factors and have their own limitations (8 –10). Solid-phase microextraction (SPME), an extraction technique first introduced by Pawliszyn’s group (11, 12), offers solutions to many of the sampling problems. This technique represents a further important advance in the efficient extraction of various organic pollutants at trace levels from liquid (13–22), solid (23), and gas (24) samples. SPME has 1
To whom correspondence should be addressed. 276
0026-265X/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.
MONITORING OF PAHS IN WATER
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also been used for the sampling of volatile and semivolatile organic compounds from more complex samples such as soil and sludge (25–27). In addition, SPME has been successfully used as a device for sampling volatile organic compounds from biological samples and foodstuffs in chromatographic analysis (28 –33). Besides its chromatographic utility, SPME has been used for sampling in Raman spectroscopy (34), mass spectroscopy (18, 35), and ultraviolet adsorption spectroscopy (36, 37). SPME has also been used for the determination of PAHs in water and soil samples (17, 25, 38 – 41). On the basis of previous works (42, 43), we have studied the efficiency of new and homemade SPME fiber (fused silica fiber coated with a porous layer of activated charcoal) for the extraction and detemination of PAHs from the headspace of water samples. The extracts were monitored by capillary gas chromatography and flame ionization detection. EXPERIMENTAL Fiber preparation. The SPME device was constructed from the activated charcoalcoated fused silica optical fiber. A 10 cm-long fiber of outer diameter 100 mm was conditioned in 3 M HCl solution, dried at 60°C for 16 h, deactivated with trimethylchlorosilane, impregnated with a 5% (w/v) silicon OV1 solution in chloroform as a binder, and then coated with extrafine powdered activated charcoal to a total thickness of 55 mm. A 1.5-cm length of this fiber was mounted in the modified GC syringe as described in the literature (44). Fibers were conditioned and pretreated in an injection port of a gas chromatograph at 360°C for 1 h to remove fiber contamination. Reagents. Helium 99.999% was purchased from Air Products (Middle East Dubai, United Arab Emirates); naphthalene, biphenyl, acenaphthylene, fluorene, acenaphthene, phenanthrene, anthracene, 2-methyl anthracene, fluoranthene, pyrene, and benzo[a]fluorene were from Aldrich. Sodium chloride (P.A), methanol, activated charcoal (Part No. 21841), and other chemicals were from E. Merck, Darmstadt, Germany. The stock standard solution was prepared by dissolving 1 mg of each compound in 10 ml methanol. These solutions were used to prepare 50-ml model aqueous solutions containing the required amount of each analyte (0.1–50 ng/ml). Blank analyses were performed regularly to ensure that no PAHs were present in laboratory reagents, atmosphere, or fibers. Headspace SPME procedure. To a 70-ml vial containing a magnetic stirrer bar and 50 ml of water sample, 12 g NaCl was added. The vial was rapidly sealed with a silicon septum cap, and the fiber was exposed in the headspace of the vial. The vial was heated at 80°C with stirring for 30 min. The analytes were then thermally desorbed in the injector port of a gas chromatograph at 350°C for 2 min and analyzed. Gas chromatography. The GC apparatus consisted of a Shimadzu (Japan) GC-15A equipped with a flame ionization detector, a data processor Model C-R4A Chromatopac, hydrogen generator Model OPGU-1500 S, and split/splitless injector. A Shimadzu Hicap CBP-5 (SE-52, 54) capillary column (L 5 25 m, i.d. 5 0.33 mm, film thickness 5 0.5 mm) was used. The GC conditions were: column temperature program, 50°C with a 2-min hold, rising at 40°C/min to 140°C, then rising at 10°C/min to 280°C, 2-min hold. Carrier gas velocity was 30 cm/s, and makeup gas velocity, 30 ml/min. The analytes were injected in the splitless mode at 350°C; the splitter was opened after 2 min. Detector temperature was 350°C.
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FIG. 1. Dependence of extraction efficiency on temperature. PAH concentration: 2 ng/ml of each; amount of NaCl: 12 g; speed of stirrer: 60% of maximum speed; exposure time: 30 min.
FIG. 2. Dependence of extraction efficiency on stirring speed. PAH concentration: 2 ng/ml of each; amount of NaCl: 12 g; exposure time: 30 min; exposure temperature: 80°C.
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FIG. 3. Dependence of extraction efficiency on amount of NaCl. PAH concentration: 2 ng/ml of each; exposure temperature: 80°C; stirring speed: 60% of maximum speed; exposure time: 30 min.
FIG. 4. Dependence of extraction efficiency on exposure time. PAH concentration: 2 ng/ml of each; exposure temperature: 80°C; stirring speed: 60% of maximum speed; amount of NaCl: 12 g.
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FIG. 5. Typical gas chromatogram of PAHs after extraction from model aqueous solution by headspace SPME. PAH concentration: 2 ng/ml of each; amount of NaCl: 12 g; stirring speed: 60% of maximum speed; exposure time: 30 min; exposure temperature: 80°C.
RESULTS AND DISCUSSION Effect of Extraction Temperature Extraction–temperature profiles were obtained for 50-ml model aqueous solutions by monitoring the recovery efficiency counts as a function of extraction temperature. As shown in Fig. 1, extraction efficiency always increases with temperature. It was observed that at 80°C, extraction efficiency was between 20 and 96% depending on the compound assayed. Apart from the low extraction recovery for the compounds with high boiling points, good sensitivity and precision were obtained for all the compounds studied (see Quantitative Analysis). Effect of Stirring Speed A potential influence on the headspace procedure is the establishment of equilibrium between liquid and headspace (gas) phases. The stirring speed of the aqueous solution can therefore be an important parameter. Extraction efficiencies of the studied compounds were measured from 50 ml of the model samples in the presence of 12 g NaCl and 30 min extraction time at 80°C at various stirring speeds. The results are shown in Fig. 2. From this figure, it is apparent that the extraction efficiency increases at a constant time with
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TABLE 1 Characteristic Parameters of Calibration Graphs and Analytical Features of the Determination of PAHs in Water Using Headspace SPME and Capillary Gas Chromatography with Flame Ionization Detection
Compound
Retention time (min) (n 5 5)
LOD a (ng/ml)
LDR b (ng/ml)
Correlation coefficient
RSD% c (n 5 5)
Naphthalene Biphenyl Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene 2-Methyl anthracene Fluoranthene Pyrene Benzo[a]fluorene
5.91 6 0.03 d 7.59 6 0.02 8.42 6 0.02 8.76 6 0.03 9.82 6 0.02 12.04 6 0.03 12.15 6 0.02 13.39 6 0.03 15.00 6 0.03 15.56 6 0.03 16.45 6 0.04
0.03 0.03 0.03 0.05 0.10 0.05 0.05 0.10 0.15 0.20 0.30
0.1–10 0.1–10 0.1–10 0.2–10 0.3–10 0.2–10 0.2–10 0.3–20 0.5–20 0.5–20 1.0–50
0.999 0.999 0.999 0.998 0.999 0.998 0.995 0.996 0.996 0.994 0.993
3.4 4.2 2.8 5.4 7.4 6.2 7.1 6.9 8.5 7.6 9.5
Limit of detection (S/N 5 3). Liner dynamic range. c Relative standard deviation (2 ng/ml). d Mean 6 SD. a b
stirring speed, and above 60% of maximum speed, the extraction–speed profiles of all compounds studied reach a plateau and remain constant. Effect of Salting Out For this investigation, we studied the effect of various amounts of sodium chloride (ranging from 0 to 20 g) on the efficiency of extraction of the analytes. Figure 3 plots the extraction efficiency versus amount of NaCl in model solutions. From the results obtained, for amounts of NaCl greater than 12 g, the extraction efficiencies of the compounds studied reach a plateau and remain constant. Effect of Exposure Time Extraction–time profiles were obtained for 50-ml model aqueous solutions by monitoring the recovery efficiency counts as a function of the duration of exposure to 12 g sodium chloride at 80°C at constant stirring time. As shown in Fig. 4, extraction efficiency increases with exposure time at constant temperature and reaches a plateau when a real equilibrium is established. For future quantitative analyses, an exposure time of 30 min is a reasonable compromise for good peak response at logical assay time. This is also a typical time for a GC run, and during the GC analysis, extraction of the next sample can be carried out. Quantitative Analysis Figure 5 shows a typical gas chromatogram for headspace-SPME extracts from 50-ml model aqueous solutions under the optimized extraction and chromatographic conditions. Quantitative analysis was carried out using 50-ml samples of standard solutions. Char-
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TABLE 2 Determination of PAHs in Real Water Samples Using Headspace SPME and Capillary Gas Chromatography with Flame Ionization Detection
Compound
Tap water a (ng/ml)
Municipal waste water a (ng/ml)
Rain water flowing asphalt a (ng/ml)
Naphthalene Biphenyl Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene 2-Methyl anthracene Fluoranthene Pyrene
ND b ND ND ND ND ND ND ND ND ND
0.132 6 0.007 ND ND ND ND ND ND ND ND ND
0.248 6 0.011 0.125 6 0.008 0.342 6 0.018 ND ND ND ND ND ND ND ND
Benzo[a]Fluorene
ND
ND
a b
Mean 6 SD, n 5 5. Not detected.
acteristic parameters of the quantitation for five replicate analyses including retention time reproducibility, detection limit, dynamic range, correlation coefficient of calibration graphs, and relative standard deviation are listed in Table 1. Limits of detection (LODs). The LODs obtained were lower than 0.05 ng/ml for naphthalene, biphenyl, acenaphthylene, acenaphthalene, phenanthrene, and anthracene, and over the range 0.1– 0.3 ng/ml for fluorene, 2-methyl anthracene, fluoranthene, pyrene, and benzo[a]fluorene. The detection limits obtained are remarkable, taking into account the rapid and simple sampling process without any serious practical difficulty. Comparison of these results with literature data using poly(dimethylsiloxane) fiber (41) shows that the proposed fiber has better absorption efficiency for the low-molecular-weight PAHs from the headspace of aqueous solutions. Linearity. The linearity of the calibration graphs was investigated for all compounds studied. The values for correlation coefficient (r) obtained are between 0.993 and 0.999, and show the acceptable linearity in the dynamic ranges represented in Table 1. Precision. The precision of the method for five replicate analyses of model aqueous solutions is summarized in Table 1. For the solution containing 2 ng/ml of each PAH, the coefficient of variation was between 3 and 9%. Taking into account the very low concentration level of the analytes, the precision is good. Application to Real Samples To evaluate the reliability of the proposed method, some local municipal water samples were analyzed. The analytical results are summarized in Table 2. These results show that gas chromatography after SPME using the proposed fiber is a powerful method for the monitoring of PAHs at very low concentrations in water samples.
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CONCLUSION Laboratory-made SPME fiber (fused silica fiber coated with a porous layer of activated charcoal coated) has been shown to be a very convenient and powerful device for sampling trace amounts of PAHs dissolved in water and other aqueous samples. In comparison with other sampling techniques, it is simple, rapid, solvent free, and inexpensive. The preconcentration enhancement afforded by this fiber allows limits of detection at the sub-parts-per-billion level. REFERENCES 1. Wise, S. A.; Sander, L. C.; May, W. E. J. Chromatogr., 1993, 642, 329 –349. 2. International Agency for Research on Concer. IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man, Vol. 3: Certain Polycyclic Aromatic Hydrocarbons and Heterocyclic compounds. IARC, Lyon, 1973. 3. Moen, J. E. T.; Cornet, J. P.; Evers, C. W. A. In Contaminated Soil (J. W. Assink and W. J. Van den Brink, Eds.), p. 441. Martinus Nijhoff, Dordrecht, 1989. 4. Furton, K. G.; Jolly, E.; Pentzke, G. J. Chromatogr., 1993, 642, 33– 45. 5. Wise, S. A.; Sander, L. C.; May, W. E. J. Chromatogr., 1993, 642, 329 –349. 6. Terabe, S.; Miashita, Y.; Ishihama, Y.; Shibata, O. J. Chromatogr., 1993, 636, 47–57. 7. Otsuka, K.; Higashimori, M.; Koike, R.; Karuhaka, K.; Okada, Y.; Terabe, S. Electrophoresis, 1994, 15, 1280 –1283. 8. U.S. EPA method 624. Fed. Regist., 1984, 141, 49. 9. Novak, J.; Drozd, J. In Instrumentation in Analytical Chemistry (J. Zuka, Ed.), Vol. 1, Chap. 10. Ellis Horwood: West Sussex, 1991. 10. Suffet, I. H.; Malaiyandi, M. (Eds.) Advances in Chemistry, Vol. 214: Organic Pollutants in Water: Sampling, Analysis, and Toxicity Testing. Am. Chem. Soc., Washington, DC, 1981. 11. Belardi, R. G.; Pawliszyn, J. Water Pollut. Res. J. Can., 1989, 24, 179. 12. Arthur, C. L.; Pawliszyn, J. Anal. Chem., 1990, 62, 2145–2148. 13. Eisert, R.; Levsen, K. Fresenius J. Anal. Chem., 1995, 351, 555–562. 14. Potter. D. W.; Pawliszyn, J. J. Chromatogr., 1992, 625, 247–255. 15. Arthur, C. L.; Killam, L. M.; Motlagh, S.; Lim, M.; Potter, D. W.; Pawliszyn, J. Environ. Sci. Technol., 1992, 26, 979 –983. 16. Motlagh, S.; Pawliszyn, P. Anal. Chim. Acta, 1993, 284, 265–273. 17. Potter, D. W.; Pawliszyn, P. Environ. Sci. Technol., 1994, 28, 298 –305. 18. Cisper, M. E.; Earl, W. L.; Nogar, N. S.; Hemberger, P. H. Anal. Chem., 1994, 66, 1897–1901. 19. Buchholz, K. D.; Pawliszyn, J. Anal. Chem., 1994, 66, 160 –167. 20. Horng, J. Y.; Huang, S. D. J. Chromatogr., 1994, 678, 313–318. 21. Barnabas, I. J.; Dean, J. R.; Fowlis, I. A.; Owen, S. P. J. Chromatogr., 1995, 705, 305–312. 22. Boyd-Boland, A. A.; Pawliszyn, J. J. Chromatogr., 1995, 704, 163–172. 23. Santos, F. J.; Sarrion, M. N.; Galceran, M. T. J. Chromatogr. A, 1997, 771, 181–189. 24. Martos, P. A.; Pawliszyn, J. Anal. Chem., 1997, 69, 206 –215. 25. Zhang, Z.; Pawliszyn, J. Anal. Chem., 1993, 65, 1843–1852. 26. MacGillivary, B.; Pawliszyn, J.; Fowlie, P.; Sagara, C. J. Chromatogr. Sci., 1994, 32, 317–322. 27. Zhang, Z.; Pawliszyn, J. Anal. Chem., 1995, 67, 34 – 43. 28. Pelusio, F.; Nilsson, T.; Montanarella, L.; Tilio, R.; Larsen, B.; Facchetti, S.; Madsen, J. J. Agr. Food. Chem., 1995, 43, 2138 –2143. 29. Krogh, M.; Johansen, K.; Tonnesen, F.; Rasmussen, K. E. J. Chromatogr., 1995, 673, 299 –305. 30. Kumazawa, T.; Lee, X. P.; Tsai, M. C.; Seno, H.; Ishii, A.; Sato, K. Jpn. J. Forens. Toxicol., 1995, 1, 25–30. 31. Kumazawa, T.; Lee, X. P.; Sato, K.; Seno, H.; Ishii, A.; Suzuki, O. Jpn. J. Forens. Toxicol., 1995, 13, 182–188. 32. Yashiki, M.; Nagasawa, N.; Kojima, T.; Miyazaki, T.; Iwasaki, Y. Jpn. J. Forens. Toxicol., 1995, 13, 17–24. 33. Kumazawa, T.; Watanabe, K.; Sato, K.; Seno, H.; Ishii, A.; Suzuki, O. Jpn. J. Forens. Toxicol., 1995, 13, 207–210.
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