Electromembrane extraction combined with cyclodextrin-modified capillary electrophoresis for the quantification of trimipramine enantiomers

A sensitive, simple and reproducible method was developed for preconcentration and determination of trimipramine (TPM) enantiomers in biological samples using electromembrane extraction combined with cyclodextrin-modified capillary electrophoresis (CE). During the extraction, TPM enantiomers migrated from a 5mL sample solution through a thin layer of 2-nitrophenyl octyl ether NPOE immobilized in the pores of a hollow fiber, and into a 20 mu L acidic aqueous acceptor phase presented inside the lumen of the fiber. A BoxBehnken design and the response surface methodology (RSM) were used for the optimization of different variables on extraction efficiency. Optimized extraction conditions were: NPOE as supported liquid membrane, inter-electrode distance of 5mm, stirring rate of 1000rpm, 51V potential difference, 34min as the extraction time, acceptor phase pH 1.0 and donor phase pH 4.5. Then, the extract was analyzed using optimized cyclodextrin (CD)-modified CE method for the separation of TPM enantiomers. Best results were achieved using 100mM phosphate running buffer (pH 2.0) containing 10mM a-CD as the chiral selector, applied voltage of 18kV and 20 degrees C. The range of quantitation for both enantiomers was 20500ng/mL. The method was very reproducible so that intra- and interday RSDs (n=6) were <6%. The limits of quantitation and detection for both enantiomers were 20 and 7ng/mL, respectively. Finally, this method was successfully applied to determine the concentration of TPM enantiomers in plasma and urine samples without any pre-treatment.