An enantioselective CE-based determination of methorphan and its main metabolites in blood is described. Enantiomeric separations were carried out in 50cm×50μm (ID) uncoated fused silica capillaries, using a background electrolyte composed of 150mM sodium phosphate pH 4.4 added with 5mM 2-(hydroxypropyl)-β-cyclodextrin and methanol 20% (v/v), at a constant voltage of 25kV. Sample injections were performed under field amplified sample stacking conditions. Detection was by recording UV absorbance at the wavelength of 200nm. Linearity of response was assessed within a concentration range from 25 to 500ng/mL for dextrometorhan, levomethorphan and their main metabolites (namely dextrorphan and levorphanol, respectively). Folcodine was used as internal standard. Under these conditions, the limit of quantification resulted 25ng/mL for each one of the analytes. The intra-day and inter-day precision, in terms of coefficient of variation (CV) were below 3.7% and 14.9 % for migration times and peak areas, respectively. The present method was successfully applied to the analysis of post-mortem blood samples from ten subjects died for heroin overdoses. Among the samples "positive" for methorphan (n=4), the d-enantiomer was found in concentrations ranging from 214 to 1282ng/mL. The concentration of its main metabolite dextrorphan in the same samples ranged from 49 to 389ng/mL.
Keywords: Capillary electrophoresis; Chiral analysis; Dextromethorphan; Levomethorphan; Opiate overdose.
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