Confirmation of gentamicin and neomycin in milk by weak cation-exchange extraction and electrospray ionization/ion trap tandem mass spectrometry

A new procedure for the confirmation of two aminoglycoside antibiotics in m ilk was developed and validated. This work is among the early applications of ion trap mass spectrometry for regulatory methodology, and it incorporat es a novel weak cation-exchange extraction. The procedure was validated for the confirmation of both gentamicin and neomycin at 30 ng ml(-1) and above . Milk is first treated with acid and centrifuged. The supernate, excluding the fat layer, is buffered with sodium citrate to neutral pH, The extract is applied to a weak cation-exchange solid-phase extraction column. Aminogl ycosides are eluted with acidified methanol, Following separation by ion-pa ir liquid chromatography, analytes are ionized with an electrospray interfa ce, Protonated molecular ions are selectively stored in an ion trap mass sp ectrometer, then collisionally dissociated to yield unique product ion spec tra, Confirmation is based on matching spectral responses between samples a nd comparison standards consisting of a bona fide standard spiked into cont rol extracts. Method performance was demonstrated with replicate samples of control milk, fortified milk, and milk containing incurred residues of eac h compound, Copyright (C) 2000 John Wiley & Sons, Ltd.