Simple extraction method requiring no cleanup procedure for the detection of minocycline residues in porcine muscle and milk using triple quadrupole liquid chromatography-tandem mass spectrometry

A versatile analytical method was developed for simple detection of minocycline residues in porcine muscle and milk using liquid chromatography-triple quadrupole tandem mass spectrometry (LC/MS/MS) with electrospray ionization. Samples were extracted with a mixture of acetonitrile and ethyl acetate (2:1, v/v), and then defatted using n-hexane. No cleanup procedure was deemed necessary. Minocycline was separated on a reversed-phase analytical column using a combination of 0.1 % formic acid in water (A) and 0.1 % formic acid in acetonitrile (B) as the mobile phase. Matrix-matched calibration showed good linearity over a concentration range of 10-60 mu g/kg with a determination coefficient (R-2) of 0.9727. Fortified porcine and milk samples having concentrations equivalent to and double the limit of quantification (LOQ = 10 ng/g), respectively, yielded recovery ranges between 83.02 and 8.03 % and relative standard deviations <18 %. Samples collected from a large market located in Seoul, Korea, tested negative for minocycline residue. These results show that a combination of acetonitrile and ethyl acetate can effectively extract minocycline from porcine muscle and milk without solidphase extraction, a step usually required for cleanup before analysis. The developed method is simple, sensitive, and can be extrapolated to other food animal products that are rich in protein and fats.