Discrimination of dimethylamphetamine and methamphetamine use: simultaneous determination of dimethylamphetamine-N-oxide and other metabolites in urine by high-performance liquid chromatography-electrospray ionization mass spectrometry.

A simple and sensitive method by high-performance liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) has been investigated for the simultaneous determination of dimethylamphetamine (DMA), its specific yet labile main metabolite dimethylamphetamine-N-oxide (DMAO), and other metabolites, methamphetamine (MA) and amphetamine (AP), in urine. A combination of Bond Elut SCX columns for the solid-phase extraction of urine and a semi-micro SCX column for LC separations provided satisfactory results. The use of acetonitrile/5mM ammonium acetate buffer adjusted to pH 4 (65:35, v/v) as the mobile phase at a flow rate of 0.2 mL/min was found to be the most effective. The detection limits were 5 ng/mL for DMAO, 10 ng/mL for DMA and MA, and 50 ng/mL for AP in the SIM mode.