Simultaneous determination of serotonin and creatinine in urine by combining two ultrasound-assisted emulsification microextractions with on-column stacking in capillary electrophoresis

This article describes the development of a rapid, simple, and sensitive analytical approach for the simultaneous determination of serotonin (5‐hydroxytryptamine) and creatinine in urine samples by combining two ultrasound‐assisted emulsification microextractions (USAEMEs) in series with on‐column stacking in CE. This serial USAEME procedure comprises analytes extraction from the donor solution (urine with K₂CO₃ additive) to an organic solvent followed by a back‐extraction from the organic phase into a small volume of hydrochloric acid. After 15 min of sample pretreatment, the acidic acceptor solution was analyzed directly on CE in the mode of capillary zone electrophoresis. The adoption of HCl as the acceptor phase not only provided effective back‐extraction but also facilitated pH‐mediated on‐column stacking in CE analysis. About 360‐fold sensitivity enhancement was achieved for serotonin detection. The limits of detection were 7.9 nM for serotonin and 13.3 μM for creatinine, respectively. Satisfactory results were obtained with respect to precision and recovery. The proposed method has been demonstrated to be convenient and effective for the analysis of real urine samples. We believe that two USAEMEs in series will find wide applications in simplified sample pretreatment prior to CE analysis.