Development and validation of a pressurised liquid extraction liquid chromatography-electrospray-tandem mass spectrometry method for beta-lactams and sulfonamides in animal feed.

This study presents the development and validation of a sensitive and fast (30 min extraction time and 10 min chromatographic run) method for the detection of penicillins, cephalosporins and sulfonamides in animal feed using pressurised liquid extraction and solid phase extraction as extraction and pre-concentration procedures, followed by liquid chromatography-quadrupole-linear ion-trap mass spectrometry. The developed method was validated showing limits of detection ranging from 0.12 (ampicillin) to 3.94 ng/g (amoxicillin), instrumental and analytical linearity coefficients above 0.99 in both standard and matrix-based solutions as well as relative recoveries ranging from 71% (cefoperazone) to 115% (cefazolin). Repeatability of the method was in the range of 1-9% (RSD %), whereas reproducibility ranged from 3% to 13% (RSD %). The developed and validated method was finally applied to the analysis of real feed samples. The results showed 10 out of 18 analytes to be present in at least one sample and all 14 samples to contain at least one analyte. Penicillin V, oxacillin, ceftiofur, cefoperazone, cefalexin, cefazolin, sulfamethoxypyridazine and sulfapyridine were not detected in any of the samples analysed. Considering the ban of antibacterials as growth promoters added in animal feed, this method is capable of detecting the low concentrations that could result from failure to comply with the regulations or on-site contamination.