Screening assay of residual antibiotics in livestock samples by LC-MS/MS.

A LC-MS/MS screening assay of multi-class antibiotics was developed for 19 residual antibiotics in livestock samples. Sample preparation employed the QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) approach using 0.5% formic acid in acetonitrile-methanol (8 : 2), with salting-out using magnesium sulfate, trisodium citrate and sodium chloride. Recovery values from 5 different livestock samples ranged from 45.5 to 121.6%, and the RSDs were under 18% at two concentration levels. The limit of quantification values of 19 analytes were under 10 µg/kg in all livestock samples, and the procedure can detect almost all analytes under the MRL. Screening capability was confirmed by employing spiked samples. This new screening assay for residual antibiotics in livestock samples is expected to be useful for routine laboratory tests.