Evaluation of Designer Amphetamine Interference in GC–MS Amine Confirmation Procedures

In recent years, a class of new designer drugs commonly referred to as 'bath salts' have made their way to the illicit drug market. The most common drugs encountered are designer amphetamines and cathinones. Many analytical methods for analysis and identification of bath salts have been published, but there has been little reported on their impact on existing gas chromatography-mass spectrometry (GC-MS) amine confirmation methods. Due to structural similarities, the potential exists that designer amphetamines may interfere with methods used for analysis of sympathomimetic amines. Methiopropamine, 4-fluoroamphetamine, 4-fluoromethamphetamine (4-FMA) and 4-methylamphetamine were examined for potential interference with immunoassays and GC-MS confirmation analysis utilizing three derivatization procedures: R(-)-α-methoxy-α-trifluoromethylphenylacetyl chloride (R-MTPAC), heptafluorobutyric anhydride (HFBA) and chlorodifluoroacetic anhydride (ClF(2)AA). Significant cross-reactivity was observed with all the four compounds on the Syva Emit(®) II Plus Amphetamines and Roche KIMS Amphetamines II immunoassays. Laboratories utilizing GC-MS selected-ion-monitoring confirmation methods with R-MTPAC, HFBA or ClF(2)AA derivatives could experience potential chromatographic and mass spectral interferences from 4-fluroamphetamine, 4-FMA and methiopropamine in the form of ion ratio and quantitative failures. Careful ion selection, proper selectivity and specificity studies during method validation and rigid chromatographic and spectral acceptance criteria are required to assure the robustness and accuracy of GC-MS methods.