An electrokinetic supercharging approach for the enantiodetermination of cathinones in urine samples by capillary electrophoresis

Abstract

This paper presents a strategy based on electrokinetic supercharging (EKS) in combination with capillary electrophoresis (CE) for the enantiodetermination of a group of cathinones in urine samples after sample pretreatment with liquid–liquid extraction (LLE). The background electrolyte (BGE) consisted of an aqueous solution of 70 mM of monosodium phosphate at pH 2.5 containing 8 mM 2-hydroxypropyl β-cyclodextrin (β-CD) and 5 mM β-CD, which acted as chiral selectors. To solve capillary electrophoresis’s lack of sensitivity, we used EKS as the preconcentration strategy. We also tested several parameters affecting this strategy, i.e. the choice of suitable leading and terminating electrolytes, their injected volumes, and the sample injection times and voltages. The highest response enhancement was achieved by electrokinetically injecting the sample (10 kV, 120 s) between a leading electrolyte (LE) of 25 mM HCl and a terminating electrolyte (TE) of 75 mM tetrabutylammonium bromide, both of which were hydrodynamically injected at 50 mbar for 40 s. The method was validated by analysing spiked urine samples. The linear range went from 15 to 250 ng/mL, limits of detection (LODs) were between 4 and 8 ng/mL, and RSDs were below 11% in terms of intra-day and inter-day repeatability. This is therefore an efficient method for the enantiodetermination of cathinones in urine samples by forensic laboratories.