Determination of carbadox and olaquindox metabolites in swine muscle by liquid chromatography/mass spectrometry

This paper presents LC–MS/MS method that was developed for the simultaneous determination and confirmation metabolites of carbadox (desoxycarbadox, quinoxaline-2-carboxylic) and olaquindox (3-methylquinoxaline-2-carboxylic acid) residues in pig muscle tissues at concentrations ≤3.0 μg kg−1. Pig muscle tissues were deproteinated with meta-phosphoric acid in methanol and then were extracted with ethyl acetate:dichloromethane (50:50, v/v). The whole extracts were evaporated to dryness in rotary evaporator at 45 °C, and dry residues were re-dissolved in 0.5% isopropanol in 1% acetic acid. The LC separation was performed on a C8 column with a gradient system consisting of isopropanol/water/acetic acid and methanol as the mobile phase. Additionally SelexION™ technology to reduce matrix effect was used. The decision limit (CCα) ranged from 1.04 μg kg−1 to 2.11 μg kg−1 and the detection capability (CCβ) ranged from 1.46 μg kg−1 to 2.89 μg kg−1. The total recoveries were from 99.8% to 101.2%. The results of validation fulfil the requirement of the confirmatory criteria according to the European Commission Decision 2002/657/EC.