Application of dispersive liquid-liquid microextraction and CE with UV detection for the chiral separation and determination of the multiple illicit drugs on forensic samples

A new method was developed for pre-concentration, chiral separation and determination of multiple illicit drugs on forensic samples using dispersive liquid-liquid microextraction (DLLME) and capillary electrophoresis (CE) with Ultra Violet (UV) detection. The method was based on the formation of tiny droplets of an organic extractant in the prepared sample solution using water-immiscible organic solvent (chloroform) dissolved in water-miscible organic dispersive solvent (isopropyl alcohol). The organic phase, which extracted heroin, DL-methamphetamine, DL-3, 4-methylenedioxymethamphetamine and dl-ketamine from the prepared sample solution, was separated by centrifuging. The sedimented phase was transferred into a small volume CE auto-sampler vial with 10 μL of 1% HCl methanol solution and evaporated to dryness. The residue was reconstituted in lidocaine hydrochloride aqueous solution (internal standard) and introduced by electrokinetic injection into CE. Parameters affecting extraction efficiency were investigated and optimized. Under optimum conditions, linearity of the method was 0.15-6500 μg/L for all target analytes. The LODs (S/N=3) were 0.05-0.20 μg/L. Excellent repeatability (RSD ≤ 4.4%, n=5) was achieved. The feasibility of this method was demonstrated by analyzing spiked forensic samples. To our knowledge, it is the first time to combine DLLME with CE for chiral separation and determining illicit drugs on forensic samples.