Abstract
Supercritical fluid extraction (SFE) of fruits and vegetables poses unique sample preparation considerations because the sample size is small (1–3 g) and the analyte is distributed in a moist solid matrix. The goal of this research was to develop practical sample preparation procedures for SFE of pesticide residues in produce so that acceptable accuracy and precision are maintained. In this study, 130 extractions of potato, fortified with up to 40 pesticides, were performed with 2 commercial SFE instruments. Extracts were analyzed by gas chromatography with ion trap mass spectrometry or electron capture detection. Four sample preparation procedures were tested and Hydromatrix was used to control the amount of water in the sample. The highest recoveries and lowest standard deviations were obtained when 20–50 g samples were blended with an equal amount of Hydromatrix and dry ice was added to keep the samples frozen. The dry ice helped produce a homogeneous flowable powder and greatly reduced the degradation or vaporization of several pesticides. Recoveries of most pesticides from subsamples of <4 g with this procedure were 90–105%, with relative standard deviations of 1–6%. Only diphenylamine and disulfo-ton gave reduced recoveries with this procedure. When samples were extracted sequentially with an autosampler, certain pesticides were degraded in the extraction vessels over a period 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 analyzed with the method, and results were comparable with those from traditional analyses.
Speciation of uranium and organic compounds on solid matrix studied by supercritical fluid extraction
