[Multiresidue method for pesticides and veterinary drugs in bovine milk using GC/MS and LC/MS/MS]

A simple, sensitive and selective method with gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) has been developed to detect 342 pesticides and veterinary drugs contaminating bovine milk at the maximum residue limits (MRLs) defined in the "positive list system". Sample preparation was performed by extracting the analytes with acetonitrile, followed by salting-out with sodium chloride. For some pesticides, the extract was further cleaned up by n-hexane partitioning and PSA cartridge column chromatography. GC/MS-EI or -NCI was used to determine pesticide residues, while LC/MS/MS-ESI was applicable to the determination of pesticide and veterinary drug residues. The variation of the recoveries of these drugs at MRL was relatively wide; however the relative standard deviations of the recovery of each drug were within 28%, suggesting that the present method is good enough for use as a screening test for contaminants at the MRLs. These results show that this method is useful for multiresidue analysis of numerous pesticides and veterinary drugs in bovine milk.