| A single multiresidue sample extraction and cleanup procedure, including acetonitrile for extraction, the combination of two solid phase extraction (SPE) cartridges, a graphitized nonporous carbon cartridge and an aminopropyl cartridge, as well as a "salting out" process for cleanup, was developed. The extract obtained from this procedure can be used for both gas chromatography/chemical ionization/ion trap/mass spectrometry (GC/CI/IT/MS) and liquid chromatography/atmospheric pressure chemical ionization/mass spectrometry (LC/APCI/MS) pesticide analysis in food.;The pesticides were extracted from lettuce, tomatoes and celery with the sample extraction and cleanup procedure developed. Recovery and sensitivity studies were performed for 106 pesticides and pesticide metabolites by GC/CI/IT/MS and for 13 pesticides by LC/APCI/MS. Of the one hundred six GC/CI/IT/MS determined pesticides and pesticide metabolites studied, ninety percent were recovered between 70--130% in all three crops spiked at the 0.075 ppm level with coefficient of variation values between 1 and 20%. Over 75% of the pesticides and pesticide metabolites could be detected at less than 10 ppb, and approximately 25% could be detected at 1 ppb or less. As a group, organophosphates were very sensitive. The vast majority of the organophosphates could be detected at level below 10 parts per billion and half could be detected in parts per trillion concentrations. Recoveries were between 70 and 113% for the thirteen LC/APCI/MS analyzed pesticides in all three crops spiked at the 0.050 ppm level, except diuron in celery and thiodicarb in tomatoes and celery. Limits of detection (LOD) were in the range of 1 ppb to 10 ppb except thiodicarb in tomatoes and celery that had LOD 500 ppb and 25 ppb, respectively. Coefficients of variation (C.V.) were between 1 to 17% except thiodicarb in tomatoes with a C.V. 34%. Thiram and thiophanate methyl were also studied, but could not be recovered from all three crops. |
