Negative-Ion Chemical Ionization Gas Chromatography–Mass Spectrometry Assay for Enantioselective Measurement of Amphetamines in Oral Fluid: Application to a Controlled Study with MDMA and Driving Under the Influence Cases

Abstract

Enantioselective analysis of amphetamine (AM), methamphetamine (MA), 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA), and 3,4-methylenedioxyethylamphetamine (MDEA) helps interpret toxicological results. Methods have been described for various matrices, but so far not for oral fluid, a matrix of increasing importance in testing for drugs of abuse, especially in the context of driving under the influence of drugs (DUID). After dilution with 200 microL carbonate buffer (pH 9), oral fluid samples (10-50 microL) were derivatized with S-heptafluorobutyrylprolyl chloride. The resulting diastereomers were extracted into 100 microL of cyclohexane, separated by gas chromatography (HP-5MS column), and detected by mass spectrometry in the negative-ion chemical ionization mode (GC-NICI-MS). The method was validated and applied to samples from a controlled study with MDMA and from authentic DUID cases. The derivatized AM, MA, MDA, MDMA, and MDEA enantiomers were well separated from each other. The method was linear from 5-250 microg/L per enantiomer of MDA and from 25-1250 microg/L per enantiomer of AM, MA, MDMA, and MDEA. With the exception of MDEA, analytical recoveries, repeatability, and intermediate precision were within required limits. The analyte concentrations and enantiomer ratios in the application samples correlated only weakly with corresponding published plasma data. This sensitive, reliable, and fast GC-NICI-MS assay enantioselectively measures AM, MA, MDA, and MDMA in oral fluid samples. Prediction of plasma concentrations and enantiomer ratios from respective oral fluid data is not possible.