Validation of a liquid chromatography–mass spectrometry multi-residue method for the simultaneous determination of sulfonamides, tetracyclines, and pyrimethamine in milk

A multiresidue method suitable for confirmation and determination of six sulfonamides (SAs), three tetracyclines (TCs), and pyrimethamine (PYR) in cow milk was validated. Milk samples were extracted using copolymer Oasis HLB solid-phase extraction (SPE) and analyzed by liquid chromatography–electrospray mass spectrometry with positive ion mode. Estimated method detection limits (MDL) and method quantitation limits (MQL) ranged from 0.48 to 2.64 and 0.61 to 8.64 ng/mL, respectively. These values are far lower than the maximum residue limits (MRLs) established by several control authorities. Excellent linear dynamic range was observed from the method quantitation limits to 300 ng/mL with correlation coefficients better than 0.9900 for all compounds. The method was accurate with recoveries ranging from 72.01 to 97.39%. Good intra-precision and intermediate precision were obtained with RSD better than 11.08%. The method is fairly robust with sample pH being the only critical control point.