Doping control analysis of methoxyphenamine using liquid chromatography-tandem mass spectrometry

Methoxyphenamine (o-methoxy-N,alpha-dimethylphenethylamine, Orthoxine) used in earlier times as a bronchodilator is prohibited in sports according to the regulations of the World Anti-Doping Agency (WADA). The drug and several of its metabolites are commonly analysed in doping control screening assays using gas chromatography-mass spectrometry requiring extraction from urine specimens. A complementary method employing liquid chromatography-atmospheric pressure chemical ionisation-tandem mass spectrometry and direct injection of urine aliquots was developed, which provided a fast and sensitive alternative to confirm the presence of the prohibited compound and degradation products in sports drug testing samples. In particular, the chromatographic separation of the active drug from isomeric compounds such as the designer drug p-methoxymetamphetamine (PMMA) was of particular interest to unambiguously identify the applied substance and was accomplished using a C6-phenyl reverse-phase column with isocratic elution. The established procedure was validated for methoxyphenamine with regard to specificity, limit of detection (0.7 ng mL(-1)), intraday- and interday precision (2.5-5.8% and 10.8-16.2%, respectively) and its applicability was demonstrated with an authentic doping control sample which tested positive for the prohibited compound early in 2008.