Enantiomeric separation of some common controlled stimulants by capillary electrophoresis with contactless conductivity detection.

Abstract

CE methods with capacitively coupled contactless conductivity detection (C4D) were developed for the enantiomeric separation of the following stimulants: amphetamine (AP), methamphetamine (MA), ephedrine (EP), pseudoephedrine (PE), norephedrine (NE) and norpseudoephedrine (NPE). Acetic acid (pH 2.5 and 2.8) was found to be the optimal background electrolyte for the CEâ C4D system. The chiral selectors, carboxymethylâ βâ cyclodextrin (CMBCD), heptakis(2,6â diâ Oâ methyl)â βâ cyclodextrin (DMBCD) and chiral crown ether (+)â (18â crownâ 6)â 2,3,11,12â tetracarboxylic acid (18C6H4), were investigated for their enantioseparation properties in the BGE. The use of either a single or a combination of two chiral selectors was chosen to obtain optimal condition of enantiomeric selectivity. Enantiomeric separation of AP and MA was achieved using the single chiral selector CMBCD and (hydroxypropyl)methyl cellulose (HPMC) as the modifier. A combination of the two chiral selectors, CMBCD and DMBCD and HPMC as the modifier, was required for enantiomeric separation of EP and PE. In addition, a combination of DMBCD and 18C6H4 was successfully applied for the enantiomeric separation of NE and NPE. The detection limits of the enantiomers were found to be in the range of 2.3â 5.7â μmol/L. Good precisions of migration time and peak area were obtained. The developed CEâ C4D method was successfully applied to urine samples of athletes for the identification of enantiomers of the detected stimulants.