Drug Testing in Blood: Validated Negative-Ion Chemical Ionization Gas Chromatographic–Mass Spectrometric Assay for Determination of Amphetamine and Methamphetamine Enantiomers and Its Application to Toxicology Cases

Abstract

Abstract Background: Enantioselective analysis of amphetamine (AM) or methamphetamine (MA) in urine is already a well-established tool for differentiation of illicit from therapeutic ingestion of AM or MA derivatives. However, because of the increasing importance of plasma or serum in analytical toxicology, a method for enantioselective analysis of AM and MA in these matrices is needed. Methods: AM and/or MA were extracted from 0.2 mL of blood plasma or serum by mixed-mode solid-phase extraction. After derivatization with S-(−)-heptafluorobutyrylprolyl chloride, the resulting diastereomers were separated by gas chromatography on a HP-5MS column during a 15-min program and detected by mass spectrometry in the negative-ion chemical ionization mode (NICI-GC-MS). The method was fully validated and applied to >50 samples from authentic toxicology cases. Results: The derivatized AM and MA enantiomers were well separated and sensitively detected. The method was linear from 5 to 250 μg/L per enantiomer with analytical recoveries, accuracy, and within- and between-run precision well within required limits. Extraction yields were 88.9–98.6%. Implications of concentrations and enantiomeric composition of AM and MA in the authentic samples were considered. Conclusions: This sensitive, reliable, rapid NICI-GC-MS assay is suitable for enantioselective determination of AM and MA in blood plasma or serum samples.