APPLICATION OF PENTAFLUOROPHENYLDIMETHYLSILYL DERIVATIZATION FOR GAS-CHROMATOGRAPHY ELECTRON-CAPTURE DETECTION OF SUPERCRITICALLY EXTRACTEDSTEROLS

We report a convenient method of extracting and detecting sterols in e nvironmental water samples. Particle-associated sterols were extracted onto glass-fibre filters then the filters were supercritical fluid ex tracted (at 33 MPa, 80 degrees C for 30 min) followed by pentafluoroph enyldimethylsilyl (flophemesyl) derivatization for gas chromatographic -electron-capture detection (GC-ECD). Optimal derivatization of epicop rostanol, coprostanol, cholesterol, dihydrocholesterol, stigmasterol, beta-sitosterol and stigmastanol with neat flophemesyl chloride was ac hieved under mild conditions (i.e., room temperature, 15 min) without the need for added solvent. These sterols gave linear GC-ECD calibrati ons (r(2)greater than or equal to 0.99) while detection limits in the final solutions were 0.1-0.6 mu g/ml. Overall recoveries for the super critical extraction and derivatization steps were 80-110% (mean 92%). The procedure was applied to raw sewage and to river water samples and 0-55%-higher results were obtained over those achieved by modified Bl igh and Dyer extraction. Flophemesyl derivatization of sterols allows selective ECD, improved separation from other compounds such as polych lorinatedbiphenyls that may be found in environmental samples, and red uced clean-up requirements (e.g.. removing lipids by saponification wh ich may be needed when flame ionization detection is used). Characteri stic mass spectra if the flophemesyl derivatives are reported; these w ere obtained in order to distinguish between sterol classes and indivi dual sterols. (C) 1998 Elsevier Science B.V. All rights reserved.