Analysis of amphetamine, methamphetamine and methylenedioxy-methamphetamine by micellar capillary electrophoresis using cation-selective exhaustive injection.

Cation-selective exhaustive injection (CSEI) is used as an on-line concentration method for the high-sensitivity analysis of illicit amphetamines using CE. Optimum conditions for the determination of amphetamine, methamphetamine and methylenedioxy-methamphetamine were investigated. Sodium dodecyl sulfate (25 mM) in 100 mM phosphate buffer (pH 2.9) with 20% methanol as organic additive was used as the background electrolyte for CE separation. The LOD, based on an S/N of 3:1, was about 0.01 microg/mL using normal capillary micellar electrokinetic chromatography, while by using CSEI in combination with micellar sweeping the sensitivity increased up to 1000-fold with the LOD lower than 50 pg/mL. The reproducibility of CSEI combined with micellar sweeping for analyzing amphetamines was satisfactory (relative standard deviation around 10% by using area ratios against an internal standard). This method is highly sensitive and can be used to analyze trace amount amphetamines in human hair.