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recovered from the swabs were correspondingly increased. Because the filters are based on only two components they can be made up quickly and in bulk. After use they may be back-flushed, cleaned, and reused; but new ones can be made up much more quickly and, in any case, the use of new filters excludes the possibility of between-sample contamination. LITERATURE CITED (1) Benedetti-Pichler, A. A. “Identification of Materials”; Springer-Verlag: Wien, 1964; p 169.
(2) Giese, R. W. J. Chem. €due. 1973, 50, 81. (3) Davis, E. M.; Tsay, D. D.; Schlamowitz, M.; Walborg, E. F. Anal. Biochem. 1977, 80, 410-419. (4) Bratin, K.; Klssinger, P. T.; Briner, R. C.; Bruntlett, C. S. Anal. Chim. Acta 1981, 130, 295-311. (5) Lloyd, J. B. F. J . Chromtogr. 1983, 261, 391-406. (6) MacCrehan, W, A. Anal. Chem. 1982, 5 4 , 838-839. (7) Twibell, J. D;Wright, T.; Sanger, D.0.; Bramley, R. K.; Lloyd, J. B. F.; Downs, N. S. J. Forensic S d . 1984, 29, 277-283. (8) Shlh, Y.-T.; Carr, P. W. Talanta 1981, 28, 411-414.
RECEIVED for review March 14,1985. Accepted May 14,1985.
Solvent Thin Layer Separator for Microextraction of Water J6n Hriviilk Institute of Sanitary Engineering, Slovak Technical University, RadlinskSho 11, 813 68 Bratislava, Czechoslovakia Current and proposed environmental regulations require analyses of a wide variety of organic compounds in water by gas chromatography/mass spectrometry. Since the required detection limits are at the parts-per-billion level, an extraction/concentration step in the sample preparation is a necessity. Extraction of water by shaking with solvents is the simplest and the most rapid method. Currently, microextraction procedures for the analysis of organic contaminants in water are widely used and are becoming more popular because of their economy of solvents, easy extraction, and speed of analysis, Although extraction efficiencies are in the 40-60% range, consistent and reliable results are obtained (1-5). Microextraction of water samples with solvents that are lighter than water requires the separation of a thin layer of solvent which, after equilibration, floats on the water surface. When a separatory funnel is used, part of the solvent remains on the walls and a part is evaporated into the funnel; yields of the solvent are very low, or even none. For the microextraction a volumetric flask has been developed with a narrow neck, offering a relatively small water surface on which the solvent layer is formed (1). The time-consuming filling and emptying of the bottle with a narrow neck is eliminated by use of a flask with two necks. The top neck is a capillary for the solvent, and a side neck is used for addition of water (2). Figure 1 shows a simple extraction (volumetric) flask, equipped with a male joint 1,which is easy to handle; there are no problems in f i g or emptying it. After the completion of extraction and emulsion breaking, a separator, 2, of a thin layer of the solvent is connected to the flask, and through the side arm, 3, pure water is added until the solvent is transferred into the dry capillary, 4, to the height required. The added water first wets the ground glass joint and, thus, the loss of solvent due to wettability of the joint is avoided. In the case of heavy pollution the extract in capillary is suitable for gas chromatographic analysis. Any desired degree of concentration can be carried out in the case of less contaminated samples. The organic phase is transferred with a syringe into a 4 cm long and 2.5 mm wide glass tube with a conical bottom, evaporated down to the desired volume, and the residue is then injected for gas chromatographic analysis. During emulsion breaking it is recommended that the extraction flask be positioned with its bottom upward so as to avoid settling of the droplets of the solvent and bubbles on the walls. When centrifugation is needed, a cylindrical flask may be used instead of the volumetric one.
12 cm
Flgure 1. Solvent thin layer separator: (1) male joint of extraction flask, (2) separator, (3) side arm for water, (4) capillary for extract.
I
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io
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Figure 2. Chromatogram of water extract fortifled by gasoline, 0.02 mg
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A s an example, Figure 2 is a chromatogram of water fortzed by 0.02 mg L-l of gasoline and extracted with n-pentane. After
0003-2700/85/0357-2159$01.50/00 1985 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 11, SEPTEMBER 1985
980 mL of water was cooled to +5 "C, n-pentane (0.3 mL) was added and shaken for 5 min. The extract (2 pL) was chromatographed without preconcentration on a glass capillary column coated with silicone OV-101. Temperature programming from 25 to 125 "C at 2 O C / m i n after a lbmin initial hold at 25 "C and a splitless injection technique were used. Registry No. HzO, 7732-18-5.
LITERATURE CITED (1) &ob, K.; &ob, K., Jr.; Grob, G. J . Chromtogr. 1975, 706, 299. (2) Murray, D. A. J. J . ChrOmStogr. 1979, 777, 135. (3) Rhoades, J. W.; Nutton, C. P. J . Envlron. Sci. Health, Pari A 1980, 75, 467. (4) Thrun, K. E.; Simmons, K. E.; Oberholtzer, J. E. J . Envlron. Sci. Health, Pari A 1980, 75, 465. (5) Murray, D. A. J.; Lockhart, W. L. j . Chromatogr. 1981, 272, 305.
RECEIVED for review December 3,1984. Accepted May 6,1985.
