Determination of stereoisomers of tramadol in pharmaceutical dosage forms by capillary zone electrophoresis

Abstract

The separation of the enantiomers of cis-and trans-tramadol was investigated by capillary zone electrophoresis employing neutral (beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin) and negatively charged (carboxymethyl-beta-cyclodextrin) cyclodextrins as chiral selectors. The baseline separation of these analytes was achieved with 8.5 mM carboxymethyl-beta-cyclodextrin in 65 mM phosphate buffer at pH 2.5, using a fused silica capillary (50 cm x 50 micrometre, i.d.), applied voltage of 18 kV and capillary temperature of 30 ํC. Validation of the optimum condition was performed on commercially available tramadol injection and capsule formulations. Validation of the method was assessed from the selectivity, linearity and range, precision, accuracy, limit of detection and quantification, stability of solution and system suitability. The linear ranges of 70-130 and 2.8-7.5 microgram/ml, respectively, were found for cis-and trans-tramadol. The intra-day and inter-day precision of each enantiomer calculated from the relative standard deviation was less than 1.5%. The limit of detection and limit of quantification of trans-tramadol were 0.48 and 1.46 microgram/ml, respectively. The proposed method was successfully applied to the direct determination of cis- and trans-tramadol in injection and capsule formulations without any sample clean-up procedures.