Capillary electrophoresis with laser-induced fluorescence and pre-column derivatization for the analysis of illicit drugs

In the current paper, we report the development of a new capillary electrophoresis method using pre-column derivatization and laser-induced fluorescence detection for the determination of ephedrine and amphetamine drugs. Our new method allows for the identification and quantification of six commonly used illicit drugs namely pseudoephedrine, ephedrine, amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, and 3,4-methylenedioxymethylamphetamine, respectively, as well as propafenone (internal standard). Following derivatization with fluorescein isothiocyanate, a total of six amphetamine drugs and the internal standard could readily be separated using a fused-silica 75 μm ID × 60 cm length (effective length: 50.2 cm) capillary column. The mobile phase consisted of buffer containing 20 mM borate (pH 12, adjusted with sodium hydroxide). Samples were injected in pressure mode with the capillary being operated at 25 kV/25 °C, and the detection of the derivatized compounds was sought using a laser-induced fluorescence (LIF) detector (λex = 488 nm and λem = 520 nm), with a run-time of 20 min. The current method was validated with regard to precision (relative standard deviation, RSD), accuracy, sensitivity, linear range, limit of detection (LOD) and limit of quantification (LOQ). In human blood and urine samples, detection limits were 0.2 ng mL−1, and the linear range of the calibration curves was 0.5–100 ng mL−1. The intra-day and inter-day precisions were both less than 13.22%.