Determination of mequindox and its metabolites in mariculture water by liquid chromatography-tandem mass spectrometry

【Objective】To establish an accurate and rapid method for the detection of mequindox（MEQ）and its metabolites in mariculture water，provide a reference for the actual detection in mariculture environment.【Method】Ultrasonic assisted dispersive liquid-liquid microextraction（UA-DLLME）was used to enrich MEQ and its metabolites in seawater samples. Liquid chromatography-tandem mass spectrometry（LC-MS/MS）was used to determine the concentration of veterinary drug residue. The single factor optimization and response surface optimization were used to optimize the microextraction conditions affecting the recovery rate to obtain the maximum recovery rate，and the optimal conditions were applied to the determination of actual samples.【Result】Tetrachloroethane and methanol were selected as extractant and disperser by single factor optimization test. The optimal extraction parameters were determined by response surface optimization test as extractant volume 80 μL，disperser volume 175 μL，ultrasound time 5.2 min. Three factors，extractant dosage and disperser dosage，extractant dosage and ultrasonic time had significant effects on the recovery rate（P<0.05）. No residue of MEQ was detected in actual samples，and the average recoveries of positive control experiments were 53.0%- 93.0%，the relative standard deviations were 2.8%-12.7%. The linearities of MEQ and its metabolites were good in the range of 1.0-500.0 μg/L，and the correlation coefficient R²≥0.99500. The limit of detections were 0.022-0.170 µg/L. The limit of quantitations were 0.073-0.567 µg/L.【Conclusion】UA-DLLME combined with LC-MS/MS has the characteristics of simple operation，high sensitivity and environmental friendliness，which can be used for the rapid detection of veterinary drug residues of MEQ and its metabolites in mariculture water.