Optimization of the separation and on-line sample concentration of phenethylamine designer drugs with capillary electrophoresis–fluorescence detection

Five 2C-series of phenethylamine designer drugs, including 2,5-dimethoxy-4-ethylthio-phenethylamine (2C-T-2), 2,5-dimethoxy-4-(n)-propylthiophenethylamine (2C-T-7), 4-chloro-2,5-dimethoxyphenethylamine (2C-C), 4-bromo-2,5-dimethoxy-phenethylamine (2C-B), 2,5-dimethoxy-4-iodo-phenethylamine (2C-I), were synthesized and standard GC/MS and fluorescence spectra are reported for them. A mixture of the five drugs was separated and detected by means of capillary electrophoresis (CE) with native fluorescence and light emitting diode (LED)-induced fluorescence (LIF) detection, respectively, for comparison. In the former case, exciting at a wavelength of 300 nm from a Xe lamp was used. The detection limits were found to be only in the range of ∼10−4 M by the micellar electrokinetic chromatography (MEKC) mode but were improved to ∼10−7 M when the sweeping-MEKC mode was used. For a highly sensitive analysis, LED-induced fluorescence detection was examined by derivatizing the compounds with a fluorescent dye, fluorescein isothiocyanate isomer I (FITC). A blue-LED (∼2 mW) was used as the fluorescence excitation source. The detection limits were improved to ∼10−7 and ∼10−8 M, respectively, when the MEKC and stacking-MEKC modes were applied. A mimic urine sample was obtained by spiking urine from a volunteer with the five standards, and after liquid–liquid extraction, the sample was examined by means of the MEKC–LIF mode. The extraction procedures used for the urine sample and the CE conditions for the separation were optimized.