Determination of 8 Species of Banned Drugs in Bovine Milk by Using QuEChERS Cleanup Approach and Liquid Chromatography-Tandem Mass Spectrometry

Abstract

A method was developed for determination of 8 species of unauthorized drugs in bovine milk by liquid chromatography-tandem mass spectrometry(LC-MS/MS).All target drugs covered 5 nitroimidazoles,7 β-agonists,9 androgens,7 glucocorticoids,3 estrogens,2 sedatives,1 chloramphenicol and 6 resorcylic acid lactones.After homogenization,the sample was mixed with β-glucuronidase/arylsulfatase for enzymatic reaction in ammonia acetate buffer and followed by extraction with basic and then acidic acetonitrile solutions.Cleanup of the extracts was processed by a modified dispersive solid phase extration(QuEChERS).The analystes were then separated by a C18column(150 mm×2.1 mm i.d.,3.0μ) utilising gradient elution with methanol/water(containing 0.1% formic acid) and acetontrile/water,and finally detected by tandem mass spectrometry in positive/negative ESI mode.Identification and quantification were achieved by LC-MS/MS with multi-reaction monitoring.Isotope internal standards for 7 compounds and matrix-matched calibrations were respectively used to quantify the residue contents.Good linearity in response was obtained in the concentration range of 0.02-0.40 μg/kg for chloramphenicol and 0.20-10.0 μg/kg for the other 39 analytes,with correlation coefficients larger than 0.99.The limits of quantification(S/N=10) was around 0.07-0.93 μg/kg.Method validation was carried out at half minimum required performance limits(MRPL),MRPL and double MRPL level of each substance,and the recoveries were in the range of 60.3%-119.3% with relative standard deviations(RSD) smaller than 18.9%.