Chromatographic separation of R-(−)/S-(+)-enantiomers of amphetamine and methamphetamine: differentiation between single methamphetamine consumption and co-consumption with amphetamine using enantioselective quantitative LC-MS/MS analysis

Abstract

The differentiation between single methamphetamine consumption and co-consumption with amphetamine is difficult, however possible by enantioselective analysis due to different preferred synthesis pathways of both substances. We quantified (R)-(−) and (S)-(+)-enantiomers of methamphetamine and amphetamine by a fast liquid chromatographic tandem-mass spectrometric method using a Lux® 3-μm AMP 150 × 3.0 mm analytical column after simple protein precipitation with methanol. Method validation for quantitative detection showed limits of quantification < 5 ng/mL, linearity in a range between 5 and 300 ng/mL and bias and imprecision data < 15%. Overall, 134 plasma samples of police cases from the German regions of Franconia and Northrhine-Westphalia were analyzed for the enantiomers of methamphetamine and amphetamine. In 28 cases, the intake of racemic illicit amphetamine could be demonstrated; (R)-(−) / (S)-(+)-amphetamine concentration ratios in these cases were between 1.38 and 4.50 with most of the ratios being < 2.0. These ratios were compared to a subgroup of 25 consumers with a co-consumption of (S)-(+)-methamphetamine and racemic amphetamine detected by the qualitative proof of (R)-(−)-amphetamine but also by (R)-(−) / (S)-(+)-amphetamine concentration ratios (< 1 in 11 of 25 cases). Within our collective of 106 plasma samples after methamphetamine use, 25 samples showed co-consumption with amphetamine which shows that co-consumption of both stimulants is not a rare scenario. Furthermore, we could show that if non-stereoselective methods are used and the concentration ratio of total methamphetamine/total amphetamine is determined, a reliable estimation of co-consumption is not possible.