Single‐run chemo‐ and enantio‐selective high‐performance liquid chromatography separation of tramadol and its principal metabolite, O‐desmethyltramadol, using a chlorinated immobilized amylose‐based chiral stationary phase under multimodal elution conditions

A direct enantio‐ and chemo‐selective high‐performance liquid chromatography method was developed for separating the enantiomers of the pain medicine tramadol and its O‐desmethyl active metabolite in a single run. The simultaneous separation was achieved on the immobilized‐type amylose tris(3‐chloro‐5‐methylphenylcarbamate) chiral stationary phase. The method was optimized in normal‐phase and reversed‐phase using ethanol as an organic modifier. It was demonstrated that ethanol is a valid alternative to the predominant high‐performance liquid chromatography solvents in use for the preparation of reversed‐phase eluents such as methanol and acetonitrile. With the green mobile phase ethanol‐water‐diethylamine, 80:20:0.1 (v/v/v) the limits of quantification for the (+)/(‐)‐enantiomers of tramadol and its O‐desmethyl active metabolite were 1.14/1.16 and 1.33/1.40 μg mL–1, respectively. [ABSTRACT FROM AUTHOR]