A simple and rapid assay based on hot water extraction and liquid chromatography-tandem mass spectrometry for monitoring quinolone residues in bovine milk

A rapid, specific and sensitive procedure for determining residues of eight widespread used quinolone antimicrobials in bovine milk is presented. The method is based on the matrix solid-phase dispersion technique with hot water as extractant followed by LC/MS/MS. The entire sample treatment did not take more than 40 min. Hot water appeared to be an efficient extracting medium, since absolute recoveries of the analytes in milk were 77-90%. The method proved to be robust as matrix effects did not affect significantly the accuracy of the method, as evidenced by analyzing six different batches of milk. Using norfloxacin as surrogate analyte, the accuracy of the method at three different spike levels of the analytes in milk was 93-110% with RSDs not larger than 10%. On the basis of a S/N of 10, estimated LOQs of this method range from 0.3 to 1.5 ng/ml, well below the tolerance levels of quinolones in milk set by the European Union.