Approaching over 10 000-fold sensitivity increase in chiral capillary electrophoresis: Cation-selective exhaustive injection and sweeping cyclodextrin-modified micellar electrokinetic chromatography

A novel and simple method that combines an online concentration technique with an enantioseparation technique for capillary electrophoresis—namely, cation-selective exhaustive injection and sweeping cyclodextrin-modified micellar electrokinetic chromatography (CSEI-sweeping CD-modified MEKC)—realizes the effective enantioseparation of cationic analytes while keeping a significant increase of detection sensitivity. This technique consists of a slight modification of the basic CSEI-sweeping MEKC. The main idea is to simply add an anionic CD as a chiral selector into the micellar buffer including sodium dodecyl sulfate, but not to change any other buffers in order to preserve the online concentration mechanism. When applied to analysis of the street drug, methamphetamine, the method achieved not only a baseline enantioseparation but also limits of detection (LODs; S/N = 3) of 70–90 pg/mL (ppt) for each isomer. This translates to a more than 10 000-fold improvement compared to the LODs by the usual injection method. The present technique, which was made from a slight modification of CSEI-sweeping MEKC, would give an attractive approach that is applicable to almost any analytes for which CSEI-sweeping MEKC is applicable; all that is required is the selection of an appropriate anionic CD to be added to the micellar buffer.