Development of transient trapping micellar electrokinetic chromatography coupled with mass spectrometry for steroids analysis.

An on-line sample preconcentration technique based on transient trapping (tr-trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr-trapping-UV) and electrospray ionization mass spectrometry detection (tr-trapping-ESI-MS). ESI-MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI-MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI-MS system, so its interference in ESI-MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr-trapping-ESI-MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr-trapping-ESI-MS protocol showed up to 540-fold enhancements of the peak intensity and 50-fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample.

Sensitive enantioseparation by transient trapping-cyclodextrin electrokinetic chromatography.

An on-line sample preconcentration based on transient trapping was applied to cyclodextrin electrokinetic chromatography (CDEKC) to realize a highly sensitive chiral analysis in capillary electrophoresis. The partial introduction of a micellar solution before the electrokinetic injection of a sample solution provided the effective preconcentration and enantioseparation of chiral compounds, resulting in the up to 240-fold enhancements of peak intensity and 100-fold improvements of limit of detection of (R),(S)-1-aminoindan as the model analyte. The demonstrated method could be applied to the other pharmaceutical compounds, which allowed five chiral analytes to be resolved with 40- to 160-fold sensitivity enhancements at once. The enantioseparation efficiency of the proposed method was slightly lower as compared to the conventional CDEKC, while the acceptable baseline separations of enantiomers were obtained in transient trapping-CDEKC relative to the undesirable resolution in the CDEKC with other preconcentration techniques. Additionally, it was clarified that transient trapping-CDEKC was also applicable to the analysis of enantiomeric excess, providing the sensitive detection of 43ppb of (R)-chlorpheniramine in 5ppm (S)-chlorpheniramine solution commercially available.

Highly sensitive chiral analysis in capillary electrophoresis with large-volume sample stacking with an electroosmotic flow pump.

To improve the sensitivity in chiral analysis by capillary electrophoresis without loss of optical resolution, application of large-volume sample stacking with an electroosmotic flow pump (LVSEP) was investigated. Effects of the addition of cyclodextrin (CD) into a running solution on the LVSEP preconcentration was theoretically studied, where the preconcentration efficiency and effective separation length would be slightly increased if the effective electrophoretic velocity (v(ep,eff,BGS)) of the analytes was decreased by interacting with CD. In LVSEP-CD-modified capillary zone electrophoresis (CDCZE) and LVSEP-CD electrokinetic chromatography with reduced v(ep,eff,BGS), up to 1000-fold sensitivity increases were achieved with almost no loss of resolution. In LVSEP-CD-modified micellar electrokinetic chromatography of amino acids with increased v(ep,eff,BGS), a 1300-fold sensitivity increase was achieved without much loss of resolution, indicating the versatile applicability of LVSEP to many separation modes. An enantio-excess (EE) assay was also carried out in LVSEP-CDCZE, resulting in successful analyses of up to 99.6% EE. Finally, we analyzed ibuprofen in urine by desalting with a C18 solid-phase extraction column. As a typical result, 250ppb ibuprofen was well concentrated and optically resolved with 84.0-86.6% recovery in LVSEP-CDCZE, indicating the applicability of LVSEP to real samples containing a large amount of unnecessary background salts.