Determination of methamphetamine enantiomer composition in human hair by non-chiral liquid chromatography-tandem mass spectrometry method.

Abstract

Chiral separation is crucial for investigating methamphetamine positive cases. While (S)-(+)-enantiomer of methamphetamine (S-MAMP) is a schedule II controlled substance, (R)-(-)-enantiomer (R-MAMP) is an active ingredient of a few over-the-counter drugs in the United States. Among biological specimen types, hair provides greater detection window than blood, urine or oral fluid, and are therefore regarded with particular interest. Herein we describe a novel non-chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to directly determine methamphetamine enantiomeric composition (percentage) in hair specimens. Hair samples were washed once with acetone, powdered, incubated overnight at 53°C in 0.1M hydrochloric acid (HCl), and subjected to a solid phase extraction (SPE). The extracts were derivatized using Marfey's reagent at 53°C for 60min. The final mixture was analyzed by LC-MS/MS. Chromatographic separation was achieved using a C18 Kinetex analytical column and 60% (v/v) aqueous methanol as mobile phase (isocratic). Triple quadrupole mass spectrometer was equipped with an electro-spray ionization (ESI) source operating in negative mode and the chromatograms were acquired using a multiple-reaction monitoring (MRM) approach. The results were expressed as ratio of R- to S-MAMP and then derived to composition percentages without requiring quantitating each enantiomer. The method was precise and accurate across 0-100% S-composition at a range of 80-18,000pg/mg. The performance of the new method was compared with an (S)-(-)-N-trifluoroacetylprolyl chloride (S-TPC) derivatization and gas chromatography-mass spectrometry (GC-MS) method on authentic methamphetamine-positive hair samples. Not only the new Marfey's reagent approach presented satisfactory correlation with the S-TPC approach, but it also exhibited significantly improved quality (e.g., S/N) of the chromatograms. In summary, our protocol employs cost effective and minimally hazardous Marfey's reagent to derivatize trace amounts of methamphetamine extracted from hair samples and a non-chiral LC-MS/MS approach to separate and identify the two enantiomers. The method allows determination of the methamphetamine enantiomeric composition without requiring quantitation of each enantiomer and is therefore well suited for further investigate previously determined methamphetamine positive cases. This method represents a viable tool for evaluation of long-term drug exposure.