Extraction and enrichment of pesticides for analysis using binary supercritical fluid mixtures

To improve the extraction selectivity in analytical supercritical fluid extraction (SFE), binary mixtures of supercritical fluids have been used to selectively produce lipid-free extracts of trace pesticide residues for chromatographic analysis. Mixtures of nitrogen and HC-134a have been used in conjunction with carbon dioxide to selectively extract both fortified and incurred residues from a variety of fatty foods using both experimental and commercially-available extraction instrumentation. Extraction of fortified pesticides in butter fat showed high recoveries for both organo-chlorine and -phosphorus pesticides with recoveries declining for specific pesticide moieties at the 1 ppb spiking level for CO2/N-2 mixtures. For CO2 and HC-134a mixtures, there was poor and little improvement in analyte recovery relative to using neat SC-CO2 for fortified organochlorine pesticides in butter fat at the 0.5-5.0 ppm level. However using a CO2/HC-134a mixture for organophosphorus pesticides in butter fat improved recoveries (> 90%) of the analytes at the 1-3.5 ppm level relative to using neat SC-CO2 . Excellent recoveries were obtained for incurred organochlorine and -phosphorus pesticides from a variety of food products at ppb levels using either CO2/N-2 or CO2/HC-134 mixtures. Results from these and additional experiments suggest that binary fluid mixtures can significantly reduce the need for additional sample cleanup prior to chromatographic analysis, allowing in some cases, direct injection of the extract after dilution into the gas chromatograph.