Simultaneous Multiresidue Analysis of (β-Lactam Antibiotics in Bovine Milk by Liquid Chromatography with Ultraviolet Detection and Confirmation by Electrospray Mass Spectrometry

Abstract

A multiresidue analytical method was developed for the simultaneous determination of amoxicillin, cephapirin, procaine penicillin G, ampicil-lin, cloxacillin, and ceftiofur in bovine milk. The method involved ultrafiltration of milk diluted with an equal volume of 50% acetonitrile through a 10 000 dalton molecular mass cutoff filter. Separation of these β-lactam antibiotics from other milk components was performed by ion-paired (octane- and dodecanesulfonate) liquid chromatography using a phenyl column eluted with acetonitrile-water solution. Ultraviolet ab-sorbance of the column effluent was monitored in the 200-350 nm range of a photodiode-array detector. For quantitation, the chromatograms were acquired at λ210 nm for penicillin G, am-picillin, and cloxacillin; λ230 nm for amoxicillin; and λ290 for cephapirin, procaine, and ceftiofur. The limit of detection for the simultaneous determination of these antibiotics was estimated to be 100 ppb. Liquid chromatography/electrospray mass spectrometry could be used to confirm these antibiotics for quantities down to 100 pg entering the mass spectrometer.