Simultaneous determination of four synthesized metabolites of mequindox in urine samples using ultrasound-assisted dispersive liquid–liquid microextraction combined with high-performance liquid chromatography

A novel pretreatment method termed ultrasound-assisted dispersive liquid–liquid microextraction (UADLLME) coupled with high-performance liquid chromatography-ultraviolet detector (HPLC-UV) was applied for the detection of four synthesized metabolites of mequindox in pig urine samples. A total volume of 200 μL of methanol (dispersant) and 60 μL of 1,1,2,2-tetrachloroethane (extract) were injected into 5.0 mL of urine sample and then emulsified by ultrasound treatment for 4 min to form a cloudy solution. The effect of several factors on the recovery of each metabolite was investigated by a fitting derivation method for the first time. Under optimum conditions, the method yields a linear calibration curve in the concentration range from 0.5 to 500 μg/L and a limit of detection (LOD) of 0.16–0.28 μg/L for target analytes. The recoveries ranged from 72.0% to 91.3% with a relative standard deviation (RSD) of less than 5.2%. The enrichment factors for the four compounds ranged from 75 to 95. Two pig urine samples were successfully analyzed using the proposed method.