LC–MS–MS Quantification of Four Quinoxaline-1,4-Dioxides in Swine Feed

A sensitive and reliable method by liquid chromatography–tandem mass spectrometry was developed for the simultaneous determination of carbadox, mequindox, olaquindox and quinocetone in swine feed. The analytes were extracted from swine feed with acetonitrile/water (60:40, v/v), and then further purified by solid-phase extraction using Oasis HLB cartridges. The mean recovery values ranged from 83–108%, and intra-day and inter-day variation were <10.8 and 9.6%, respectively. The limits of quantification for the four compounds were <20 μg kg^?1. This procedure is applicable for detecting the four quinoxaline-1,4-dioxides in swine feed.