Determination of dextromethorphan and levomethorphan in seized heroin samples by enantioselective HPLC and electronic CD

Accepted Manuscript version. The Published Journal Article is available on the Journal of Pharmaceutical and Biomedical Analysis, Volume 81-82, pages 76-79 (DOI: https://doi.org/10.1016/j.jpba.2013.03.024). Supplementary Material available free of charge on the article webpage.
© 2013. This Manuscript version is made available under the CC-BY-NC-ND 4.0 license. https://creativecommons.org/licenses/by-nc-nd/4.0/

ABSTRACT

A new enantioselective HPLC method was developed for the resolution and determination of the enantiomers of methorphan, dextromethorphan (DXM) and levomethorphan (LVM), on a Chiralcel® OJ column (250mm×4.6mm I.D.). The resolution of DXM and LVM was obtained using a mobile phase consisting of (n-hexane)-(2-propanol)-diethylamine (70:30:0.1, v/v/v) at a flow rate of 0.5 mL/min. The enantioselective method was found to be selective (α=1.92) and sensitive (LOD=2.8 μg/mL for both DXM and LVM). The method was coupled with electronic circular dichroism (CD), allowing the determination of the elution order based on the sign of CD signals of the single enantiomers at 285nm (positive for DXM, negative for LVM). Under the optimized conditions, the validated method was applied to the identification and quantitation of the enantiomers of methorphan in samples of different sources of illicit drugs of abuse (heroin). DXM was found in eight seized samples of street heroin; two of these samples, for which the DXM content was found to be over 5% (w/w) and exceeding a 10% (w/w) ratio with respect to diacetylmorphine, were the cause of two deaths for overdose due to acute narcotism.