DEVELOPMENT OF A SAMPLE PREPARATION TECHNIQUE FOR SUPERCRITICAL-FLUIDEXTRACTION FOR MULTIRESIDUE ANALYSIS OF PESTICIDES IN PRODUCE

Supercritical fluid extraction (SFE) of fruits and vegetables poses un ique sample preparation considerations because the sample size is smal l (1-3 g) and the analyte is distributed in a moist solid matrix, The goal of this research was to develop practical sample preparation proc edures for SFE of pesticide residues in produce so that acceptable acc uracy and precision are maintained, In this study, 130 extractions of potato, fortified with up to 40 pesticides, were performed with 2 comm ercial SFE instruments, Extracts were analyzed by gas chromatography w ith ion trap mass spectrometry or electron capture detection, four sam ple preparation procedures were tested and Hydromatrix was used to con trol the amount of water in the sample, The highest recoveries and low est standard deviations were obtained when 20-50 g samples were blende d with an equal amount of Hydromatrix and dry ice was added to keep th e samples frozen, The dry ice helped produce a homogeneous flowable po wder and greatly reduced the degradation or vaporization of several pe sticides. Recoveries of most pesticides from subsamples of <4 g with t his procedure were 90-105%, with relative standard deviations of 1-6%, Only diphenylamine and disulfoton gave reduced recoveries with this p rocedure, When samples were extracted sequentially with an autosampler , certain pesticides were degraded in the extraction vessels over a pe riod of several hours, To avoid losses of these pesticides, the sample in the extraction vessel was either purged with CO2 to remove oxygen or kept frozen until extracted, Peach and orange check samples were an alyzed with the method, and results were comparable with those from tr aditional analyses.