A novel and simple LC-MS/MS quantitative method for dextromethorphan and dextrorphan in oral fluid.

To develop and validate a simple method using LC-MS/MS for determination of dextromethorphan (DXM) and dextrorphan (DT) in human oral fluid. Following protein precipitation, chromatographic separation used a phenyl column with isocratic elution (1 ml/min) of 10 mM ammonium-formate buffer and acetonitrile (65:35; v/v) with 0.1% formic acid. Retention times were 2.6 min for DT and 5 min for DXM. Total run time was 7 min. The intra- and inter-assay deviations (accuracy) for DT (1-100 ng/ml) and DXM (5-1000 ng/ml) ranged from -13.6 to 8.8% and -9.6 to 5.7%, respectively. Precision variations were ≤7.5%. Matrix effect was ≤11.8%. This method may prove helpful for quantification of DT and DXM in oral fluid for either clinical or toxicological purposes.