Determination of levamisole and tetramisole in seized cocaine samples by enantioselective high-performance liquid chromatography and circular dichroism detection

• Levamisole and tetramisole are used as adulterants of street cocaine samples.
• An enantioselective HPLC method was validated to quantify tetramisole enantiomers.
• CD detection directly identifies levamisole and dexamisole in seized cocaine samples.
• Levamisole and dexamisole determination may shed light on acute intoxication cases.

Levamisole, an anthelmintic drug, has been increasingly employed as an adulterant of illicit street cocaine over the last decade; recently, the use of tetramisole, the racemic mixture of levamisole and its enantiomer dexamisole, was also occasionally observed. A new enantioselective high-performance liquid chromatography (HPLC) method, performed on cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phases in normal-phase mode, was validated to determine the enantiomeric composition of tetramisole enantiomers in seized cocaine samples. Furthermore, the hyphenation of the validated HPLC method with a circular dichroism (CD) detection system allowed the direct determination of elution order and a selective monitoring of levamisole and dexamisole in the presence of possible interferences. The method was applied to the identification and quantitation of the two enantiomers of tetramisole in seized street cocaine samples.