Detection of cefquinome in milk by liquid chromatography and screening methods Original Research Article

A liquid chromatography method for the determination of the cephalosporin cefquinome (CEF) in milk was developed/modified on the basis of published papers. Mean recovery rates for CEF and for the internal standard sulfamethizole (SMZ) were in the same range (92.9 and 92.5%, respectively). Limits of detection (≤2 μg CEF kg−1) and quantification (≤3 μg CEF kg−1) are far below the EU maximum residue level (MRL) of 20 μg kg−1. Lyophilized CEF samples can be used for internal control of the analysis as the concentration is not influenced by the lyophilization process and by subsequent storage at 6 °C. The detection limits of microbial inhibitor tests are far greater than the EU MRL and vary widely from Delvo SP as the most sensitive (≤100 μg kg−1) to BR-AS special as the least sensitive (≈2000 μg kg−1). The detection limits were slightly lower when determined with incurred rather than with spiked test samples. If an identification of the residue by β-lactamases is needed, great care has to be taken as CEF is stable against several commercially available β-lactamases. By the receptor assay, Beta star CEF can be detected in spiked as well as in incurred samples at a level of 10–15 μg CEF kg−1.