Determination of Nalidixic Acid Using Dispersive Liquid-Liquid Microextraction Followed by HPLC-UV

A fast, simple, and sensitive sample preparation procedure based on dispersive liquid-liquid microextraction (DLLME) followed by high-performance liquid chromatography and ultraviolet (HPLC-UV) detection was developed for the determination of nalidixic acid in a human urine sample. A mixture of extraction solvent (35 mu L carbon tetrachloride) and disperser solvent (1.0 mL acetonitrile) were rapidly injected into an aqueous sample (5.0 mL) for the formation of cloudy solution; the analyte in the sample was extracted into the fine droplets of carbon tetrachloride. After extraction, phase separation was performed by centrifugation and the enriched analyte in the sedimented phase was determined by HPLC-UV. The influence of several important parameters on extraction efficiency of nalidixic acid was evaluated. Under optimized experimental conditions, the calibration graph was linear in the concentration range of 1-800 mu g L-1 with the coefficient of determination being 0.9994. The limits of detection and quantification were 0.2 and 0.7 mu g L-1, respectively. The relative standard deviations (RSDs) and accuracies were in the range of 1.1-8.7% and 92.7-104.9%, respectively. This procedure was successfully applied to the determination of nalidixic acid in spiked urine samples with satisfactory results. The relative recoveries of urine samples ranged from 103.1% to 105.1%, with RSDs varying from 0.8% to 2.4%.