Determination of Quinoxalines and Their Two Main Metabolites in Environmental Water Samples by Liquid Chromatography–Tandem Mass Spectrometry

Abstract

A sensitive high performance liquid chromatography–tandem mass spectrometry method was developed for the determination of residues of carbadox, mequindox, olaquindox, quinocetone, cyadox, quinoxaline-2-carboxylic acid, and 3-methylquinoxaline-2-carboxylic acid in environmental water samples. The samples were freeze-dried at −80°C, re-dissolved in 1.0 mL methanol-water (5:95), then purified with N-propyl ethylenediamine. The separation of the analytes was performed on a column (150 × 2.1 mm i.d., 5.0 µm) using acetonitrile and 0.1% formic acid as mobile phases. The target compounds were confirmed and quantified by tandem mass spectrometry in multiple reaction monitoring mode. The results showed that there were linear relationships between peak area and concentrations of these compounds with correlation coefficients exceeding 0.99. The average recoveries at the spiked levels of 0.25, 0.5, 1.0, and 2.0 µ g L−1 ranged from 68.7% to 109% with relative standard deviations less than 14% except cyadox. The limits of detection of the analytes were between 2.0 and 6.0 ng L−1. This method meets the requirements for the determination of drug residues in environmental water samples.