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Column liquid chromatography Tramadol and O-demethyl tramadol in plasma Pharmacokinetics SummaryA sensitive liquid chromatographic assay for the quantitative determination of the opioid analgesic tramadol and its active metabolite is described. Fluconazole was used as internal standard. The assay involved a single tert-butyl methyl ether extraction and LC analysis with fluorescence detection. Chromatography was at 30 ~ pumping an isocratic mobile phase of acetonitrile-water (19:81, v/v) containing 0.06 M NaHzPO4 and 0.05 M triethylamine, adjusted to pH 7.90, at 1 mL min -1 through a reversed-phase, 250 • 4 mm base-stable column. The limit of quantitation of tramadol and its active metabolite was 1 ng mL -1, only 0.5 mL plasma sample was required for the determination. The calibration curve was linear from 1-1000 ng mL -1. Intra and inter-day precision (C.V.) did not exceed 10 %. Mean recoveries of 96.38 % for tramadol and 96.62 % for O-demethyltramadol with CVs of 0.43 % and 1.46 % were obtained. Applicability of the method was demonstrated by a pharmacokinetic study on normal volunteers who received 100 mg tramadol intravenously.

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