The use of supercritical fluid extraction (SFE) to recover pesticides from environmental matrices was investigated using chlorpyrifos methyl spiked on a wheat kernel substrate. Volume-based extraction recovery profiles were generated to determine the pressure, temperature, and fluid composition that yielded the maximum analyte recovery and minimum extraction time. On-line coupled microcolumn liquid chromatography-gas chromatography (LC-GC) with electron capture detection was used to effect cleanup of the extracts and to determine the recoveries of chlorpyrifos methyl.
With unmodified CO, as the extraction solvent, we obtained only 65% recovery of chlorpyrifos methyl spiked at the 50 parts per billion (ppb) level on the wheat. The use of CO, mixed with 2% methanol, however, yielded recoveries averaging 97.8%, with a relative standard deviation of 4.0%. Extraction times were 10 min or less for a 1-g sample size. The use of PEEK sealing material in the extraction vessels and in the ferrules of the finger-tight fittings in the SFE system permitted rapid cycling between multiple samples and reliable, leak-free operation. This approach could significantly shorten the sample preparation time associated with pesticide residue analysis.