Enantiomeric identification of chiral drugs, adulterants and impurities by capillary electrophoresis-ESI-mass spectrometry (CE-ESI-MS)

Most of the illicit drugs and some adulterants occur as optical isomers with different psychotropic activities. Especially for illicit methamphetamine and Ephedra alkaloid samples not only the enantioselective determination of the active substance but also the enantioselective determination of the chiral impurities is important for intelligence purposes with respect to the discrimination of different production batches. Capillary electrophoresis is often used for chiral analysis because high enantiomeric resolution is achieved by simply adding polar cyclodextrins to the running buffer. To obtain higher sensitivity and selectivity, capillary electrophoresis coupled to mass spectrometry was applied in this work for the chiral separation and unambiguous identification of drugs and adulterants belonging to different families of compounds. To overcome the problem of contaminating the mass spectrometer with non-volatile cyclodextrins and to avoid ion suppression, mixtures of chiral selectors were employed only at low concentrations. The running buffer consisted of 1 mol/l formic acid containing 1 mmol/l 2,3-diacetyl-6sulfato-beta-cyclodextrin and 10 mmol/l 2-hydroxypropyl-beta-cyclodextrin. Dry nitrogen gas was delivered at 4 l/min at 250°C. The pressure of nebulizing nitrogen gas was set at 4 psi. The sheath liquid was isopropanol/water (50/50, v/v) at a flow rate of 3 μl/min. Enantiomeric separation of the most important beta-phenylethylamines, methadone and tetramisole was achieved at 20°C within 30 minutes using a high voltage of +25 kV. The developed CE-ESI-MS method allows the chiral identification of a wide range of drugs and adulterants. It was also possible to discriminate between different batches of illicit methamphetamine samples by comparing their chiral impurities.