Determination of aminoglycosides in milk by liquid chromatography with tandem mass spectrometry

A confirmatory method based on liquid chromatography with tandem mass spectrometry was developed for deter-mination of 12 aminoglycosides in milk. Extraction of aminoglycosides from milk was performed using by liquid extrac-tion using a 10 mM phosphate buffer containing 2% (w/v) trichloroacetic acid, followed by performance of a solid-phase clean-up procedure on a hydrophilic-lipophilic balance solid-phase extraction (HLB SPE). Ion-pair chromatography, using a mixture of 20 mM heptafluorobutyric acid (HFBA) in water and acetonitrile as the mobile phase, was used for retention of aminoglycosides on a reversed-phase C 18 column. Mass spectral acquisition was performed in the multiple reaction monitoring mode, selecting two precursor ion>product ion transitions for each target compound. Satisfied recoveries (70.1～109.6%) of all aminoglycosides were demonstrated in spiked milk at three levels from 50 ng/g to 200 ng/g. The coefficients of variation ranged from 3.2% to 14.0%. The limits of quantitation (LOQs) for aminoglycosides ranged from 2.5 ng/g to 40.3 ng/g.