Quantitative Measurement of Dextromethorphan in Oral Fluid by ELISA and LC-MS-MS
Clothier, Morgan M.
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The development of a highly sensitive enzyme-linked immunosorbent assay (ELISA) followed by a liquid chromatography-tandem mass spectrometry (LC-MS-MS) confirmation method for the detection of dextromethorphan (DXM) and its metabolite, dextrorphan (DXO), in oral fluid is described. One of three ELISA plate vendors was chosen and validated based on cross-reactivity, precision, and limit of detection. For the screening assay, the Randox plate demonstrated zero interference from other drugs, and intra-day and inter-day precision less than 20%. Additionally, a specific limit of detection was determined for each individual plate. For the confirmation procedure, a LC-MS-MS method of testing DXM and DXO in oral fluid was validated based on guidelines required by the Scientific Working Group for Forensic Toxicology (SWGTOX). Experiments verified linearity of calibration standards, absence of carryover, accuracy and precision of ≤ 15%, calculated LOD, and no interference from other drugs. Further, the screening and confirmatory procedures were applied to sixty human subject samples to observe consistency between the two methods.