Quantitative determination of pentazocine enantiomers in human serum using derivatized β-cyclodextrin-modified capillary electrophoresis and solid phase extraction

A high performance capillary electrophoresis (HPCE) assay for the quantitation of (-) and (+) pentazocine in human serum was developed. Resolution of the pentazocine enantiomers was achieved using 15mM methyl-beta-cyclodextrin (Me-beta-CD) in 100mM phosphate buffer pH 2.5. A 72cm uncoated fused-silica capillary at a constant voltage of 20kV was used for the analysis and 0.03mM hexadecyltrimethylammonium bromide (HTAB) was added to the buffer to decrease the adsorption of endogeneous substances onto the silica wall. The analytes of interest were extracted from serum using a solid phase extraction(SPE) procedure. The phenyl SPE cartridge gave good recoveries in excess of 90% for both (-) and (+) pentazocine, without any interferences. The detection limits were 25ng/mL and the limits of quantitation mere 35ng/mL for each enantiomer. The calibration curves were linear over a range 35-400ng/mL with nalorphine as the internal standard, and the coefficients of determination were greater than 0.999 (n=3). Precision and accuracy of the method were in the range 1.4-7.5% and 1.3-4.7%, respectively, for (-) pentazocine and 1.1-7.8% and 1.4-4.3%, respectively, for (+) pentazocine (n=3).