Multi-residue analysis of avermectins and moxidectin by ion-trap LC-MSn

A multi-residue method was developed and validated for the quantitation and confirmation of avermectins and moxidectin residues in bovine liver. Targe t analytes were extracted from liver homogenate using C8 solid phase cartri dges, chromatographed under basic pH conditions in order to promote the for mation of analyte anions, and detected by ion-trap mass spectrometry (MS) i n negative ion mode using an atmospheric pressure chemical ionization inter face (APCI). The method provided detection capabilities (CCbeta, where beta = 0.05) for eprinomectin, abamectin, doramectin, moxidectin and ivermectin of 3.1, 3.2, 2.2, 4.0 and 3.2 ng g(-1) liver respectively, well below thei r respective maximum residue limits (MRLs). The critical concentrations for MRL compliance (CC alpha, where alpha = 0.01) were 840, 28, 130, 130 and 1 30 ng g(-1) respectively. Analysis of liver fortified at the appropriate MR Ls gave recoveries (% +/- RSD) of 70.9 +/- 11.6 (n = 14), 69.1 +/- 3.9 (n = 13), 65.9 +/- 6.4 (n = 19), 69.7 +/- 9.3 (n = 19) and 73.2 +/- 10.5 (n = 1 9), respectively, for each analyte. Calibration curves fitted a second orde r polynomial function (R-2 greater than or equal to 0.9978) over a wide ran ge of concentrations (0 to 10000 ng ml(-1)). The detection of two daughter- ions for each analyte allowed for quantitation and the confirmation of iden tity. The method is suitable for application in European Union statutory ve terinary drug residue surveillance programmes, since it fulfils appropriate analytical criteria, and has the particular advantage of enabling high thr oughput multi-residue quantitation and confirmation of the target analytes.