1038 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Anal. Chem. 1993, 65, 1038-1042 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ Solventless Collection of Analytes by Rapid Depressurization after Static Supercritical Fluid Extraction zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML David J. Miller' and Steven B. Hawthorne zyxwvut Energy and Environmental Research Center, University zyxwvut of North Dakota, Box 9018, University Station, Grand Forks, North Dakota 58202-9018 Mary Ellen P. McNally E.I. du Pont de Nemours and Company, Du Pont Agricultural Products Experiment Station, Wilmington, Delaware 19880-0402 A method has been developed to collect analytes from supercrltkal fMd extraction(SFE) that utHlzw no fbw re$trlctor and an empty colkc#on vial. Followingd a t k SFE, the analytcw are coUectd by rapldly (3-30 8) depressurklng the CO, zyxwvut etlluent through a 178-lun 1.d. stainless steel tube Into a cappedscrew- top vlal. Collection efficiencies of analytes as volatile as mheptaneare quantitatlve (>95 %), and wet samples showed no evldence of restrictor plugglng In contrast to the plugglng associated with the SFE of wd samples when small 1.d. flow restrictom are used. Solventless collection of PCBs, PAHs, gasoline, and diesel fuel by SFE generally showed high (>90 % ) collection efflclencles, and recoveries normally exceed those obtained using dynamlc SFE with collection In a llquld solvent. INTRODUCTION zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Supercritical fluid extraction (SFE) has become an at- tractive alternative to conventional solvent methods for the removal of analytes from solid samplesbecause of the reduced time needed for extraction and less liquid solvents required. In order to obtain quantitative results, good collection efficiencies are necessary as well as good SFE extraction efficiencies. A wide variety of methods for trapping analytes have been reported including collection in liquid solvent,1-3 collection on sorbent resin traps,@ collection on cryogenically cooled surfaces,' and collection directly into chromatographic columns via on-column or split/splitless injection ports.a11 All of these methods have one thing in common, i.e., they rely on a depressurization step which utilizes a flow restrictor (small i.d. linear restrictor or some type of variable restrictor) at the outlet of the SFE cell. An inherent problem with linear * Corresponding author. (1) Hawthorne, S. B.; Miller, D. J. Anal. Chem. 1987,59, 1705-1708. (2) Campbell, R. M.; Lee, M. L. J. Anal. Chem. 1986,58,2247-2251. (3) Lopez-Avila, V.; Dodhiwala, N. S.; Beckert, W. F. J. Chromatogr. (4) Hedrick, J. L.; Taylor L. T. J. High Resolut. Chromatogr. 1990,13, (5) Miller Schantz, M.; Cheder, S. M. zyxwvutsr J. Chromatogr. 1986,363,397- (6) Schneiderman, M. A.; Sharma, A. K.; Locke, D. C. J. Chromatogr. (7) Wright, B. W.; Wright, C. W.; Gale, R. W.; Smith, R. D. Anal. (8) Hawthorne, S. B.; Miller, D. J.; Langenfeld, J. J. J. Chromatogr. (9) Levy, J. M.; Cavalier, R. A.; Bosch, T. N.; Rynaski, A. F.; Huhak, (10) Hawthorne, S. B.; Krieger, M. S.; Miller D. J. Anal. Chem. 1988, (11) Xie, Q. L.; Markides, K. E.; Lee, M. L. J. Chromatogr. Sci. 1989, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Sci. 1990, 28, 468-476. 312-316. 401. 1987,409, 343. Chem. 1987,59, 38-44. Sei. 1990, 28, 2-8. W. E. J. Chromatogr. Sci. 1989,27, 341-346. 60, 472-477. 27, 365-370. restrictors is the possibility of reduced flow due to plugging which occurs when the sample matrix contains high concen- trations of extractable material or water. Several methods have been used to eliminate plugging problems including heating the restridor7J2-15 or maintaining the collection solvent at constant temperature (e.g., 5 "C) during the collection step.16 McNally, Deardorff, and Fahmy have reported the devel- opment of a multivesselextractor that first statically extracts analytes and then utilizes a rapid depressurization step to remove extracted analytss from the system. A unique property of their design is the elimination of the use of a flow restrictor, which allows the extraction effluent to be trans- ferred rapidly for collection. With this apparatus, excellent collection efficiencies of nonvolatile analytes such as Diuron (a phenylmethylurea pesticide) spiked on soil (97.3 f 6.6% ) were achieved.17 Since solventless collection into an empty vial has only been reported for nonvolatile analytes, the application of this technique to more volatile species was investigated. Determiningcollection efficiencies (rather then extraction efficiencies) was the primary goal of this study; therefore, analytes added to a relatively inert matrix were used to test the collection system. Even though the use of spikes is not always avalid indication of extraction efficiency,18 spike recoveries are an excellent method to determine collection efficiency after SFE. The effects of different trapping parameters on collection efficiencies including vial configuration, exit tube inside diameter (which controls venting rate), extraction temperature, analyte volatility, and collection time were investigated. Collection efficiencies for alkanes (c6430), PAHs, PCBs, gasoline, and diesel fuel are presented. EXPERIMENTAL SECTION All extractions, except where noted, were performed in triplicate with an ISCO Model SFX 2-10 extractor and a 2.5-mL cell. Approximately 2 g of seaaand (FisherScientific,Fair Lawn, NJ) was loaded into the cell and spiked with the test solutions. The cell was then pressurized to 400 atm with SFC-grade COz (12) Burford, M. D.; Hawthorne, S. B.; Miller, D. J.; Braggins, T. J. Chromatogr. 1992,609, 331-342. (13) Wong, J. M.; Kado, N. Y.; Kuzmicky, P. A.; Ning, H. S.; Woodrow, D. P.; Hsieh, D. P. H.; Seiber, J. N. Anal. Chem. 1991, 63, 1644-1650. (14) McNair, H. M.; Frazier, J. 0. Am. Lab. 1991, 23, 24D-I. (15) Campbell, R. C.; Meunier, D. M.; Cortes, H. J. J. Microcolumn Sep. 1989, 1 (6), 302-308. (16) Langenfeld, J. J.; Burford, M. D.; Hawthorne, S. B.; Miller, D. J. J. Chromatogr. 1992,459,297-307. (17) McNally, M. E.P.;Deardorff, C. M.; Fahmy,T. M. In Supercritical Fluid Technology: Theoretical and Applied Approaches in Analytical Chemistry;Bright, F. V., McNally, M. E. P., Eds.;ACS Symposium Series 488; American Chemical Society: Washington, DC, 1992; Chapter 12. (18) Burford, M. D.; Hawthorne, S. B.; Miller, D. J. Anal. Chem. In press. 0003-2700/93/0365-1038$04.00/0 Q 1993 American Chemical Soclety