Surfactant-assisted dispersive liquid-liquid microextraction combined with field-amplified sample stacking in capillary electrophoresis for the determination of mexiletine and lidocaine

A sensitive method for the determination of mexiletine and lidocaine using surfactant-assisted dispersive liquid-liquid microextraction coupled with capillary electrophoresis was developed. Triton X-100 and dichloromethane were used as the dispersive agent and extraction solvent, respectively. After the extraction, mexiletine and lidocaine were analyzed using capillary electrophoresis with ultraviolet detection. The detection sensitivity was further enhanced through the use of field-amplified sample stacking. Under optimal extraction and stacking conditions, the calibration curves were linear over a concentration range of 0.05-1.00 mu M for mexiletine and 0.03-1.00 mu M for lidocaine. The limits of detection (signal-to-noise ratio of 3) were 0.01 and 0.01 mu M for mexiletine and lidocaine, respectively. An approximately 1141- to 1250-fold improvement in sensitivity was observed for the two analytes compared with the injection of a standard solution without the surfactant-assisted dispersive liquid-liquid microextraction and field-amplified sample stacking procedures. This developed method was successfully applied to the determination of mexiletine and lidocaine in human urine and serum samples. Both precision and accuracy for urine and serum samples were less than 8.7 and 6.7%, respectively. The recoveries of the two analytes from urine and serum samples were 54.7-64.9% and 16.1-56.5%, respectively.