Analysis of josamycin in three kinds of feed using ultra-high performance liquid chromatography with tandem mass spectrometry

In this study, a new and accurate method based on ultra-high performance liquid chromatography (UHPLC) with electrospray ionisation tandem triple quadrupole mass spectrometry (MS/MS) was developed and validated for the determination of josamycin in three kinds of feeds (compound, concentrated and premix feeds). The optimised sample pretreatment procedure included extracting from the matrix with a mixture of methanol and acetonitrile (1:1, v/v) followed by drying under nitrogen and redissolving in phosphate buffer solution (pH = 8, 0.1 mol/L) followed by purifying using HLB cartridges. Validation of the method was carried out in three different matrices (compound, concentrated and premix feed) by recovery experiments, using samples spiked at concentration levels of 20, 100 and 200 g/kg. Satisfactory recoveries from 82.4% to 93.0%, with RSDs lower than 17.4% under intermediate precision conditions were obtained in all feed matrices tested. The developed method was applied to commercially samples and josamycin was found frequently in feed containing kitasamycin.