CAPILLARY ELECTROPHORESIS, A FIRST CHOICE TECHNIQUE FOR THE CHIRAL ANALYSIS OF ILLICIT DRUGS. APPLICATION TO ANALYSIS OF AMPHETAMINE AND CONGENERS|
Tagliaro F., Manetto G., Bellini S.*, Pisi P., Scarcella D., Turrina S., Marigo M.
Institute of Forensic Medicine, University of Verona, Verona, Italy
* Glaxo Wellcome Medicines Research Centre, Verona, Italy
Capillary electrophoresis has proved to be a powerful technique in most analytical areas of forensic interest, including forensic toxicology and analysis of illicit and/or controlled substances. In this field, capillary electrophoresis was found particularly suitable for chiral analysis, and at present it represents a first choice method for the study of the enantiomeric composition of drugs in the pharmaceutical industry. The chiral analysis of amphetamine-related substances in both clandestine preparations and biological samples is widely recognized and, in this field, capillary electrophoresis was successfully applied, but only few reports concerned ring-substituted amphetamines, which represent the main components of "ecstasy". A simple but highly efficient method allowing the simultaneous chiral analysis of ephedrine, amphetamine, methamphetamine, 3,4-methylenedioxy-methamphetamine (MDMA), 3-4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxyethylamphetamine (MDE) is reported in the present work. I is based on capillary electrophoresis separation with native ß-cyclodextrin (15 mM) as the chiral selector. The optimized conditions were: pH 2.5 phosphate buffer, uncoated fused silica capillary (45 cm x 50 µm ID), applied potential 10 kV. Detection was by multi-wavelength (190-400 nm) UV absorbance. Under these conditions, good resolution was obtained for all the analytes, with excellent chiral selectivity and efficiency. The sensitivity for the individual enantiomers was better than 0.2 µg/ml. Analytical precision for migration times was characterized by intra-day relative standard deviation values <0.8% (< or equal 0.15% with internal standardization) and day-to-day <2.0% (< or equal 0.54% with internal standardization). Linearity, in the range 0.156-40 µg/ml, and accuracy were also satisfactory. After a simple liquid-liquid extraction, urine samples could be analyzed with a sensitivity well below the recommended NIDA cut-off of 500 ng/ml. For low concentration samples, such as hair, it was necessary to increase the sensitivity by applying a simple field-amplified sample stacking procedure (injection from 0.1 mM phosphoric acid), which allowed the chiral determination of MDA, MDMA and MDE at concentrations occurring in real ecstasy users, also with the possibility of recording UV spectra of the peaks.