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

A gas chromatography–mass spectrometry method using negative-ion chemical ionization was developed to separately measure the left- and right-handed forms (enantiomers) of amphetamine, methamphetamine, MDA, MDMA, and MDEA in oral fluid. After adding a buffer and a derivatizing agent, the enantiomers were extracted and analyzed. The method was linear from 5–250 μg/L per enantiomer for MDA and from 25–1250 μg/L per enantiomer for the other drugs. Recoveries and precision were acceptable except for MDEA. When applied to samples from a controlled MDMA study and real driving-under-the-influence cases, the oral fluid concentrations and enantiomer ratios did not reliably predict plasma levels.

Study at a glance

Abstract

Abstract Background: 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). Methods: After dilution with 200 μL carbonate buffer (pH 9), oral fluid samples (10–50 μL) were derivatized with S-heptafluorobutyrylprolyl chloride. The resulting diastereomers were extracted into 100 μL 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. Results: The derivatized AM, MA, MDA, MDMA, and MDEA enantiomers were well separated from each other. The method was linear from 5–250 μg/L per enantiomer of MDA and from 25–1250 μg/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. Conclusions: 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.