Capillary electrochromatography: operating characteristics and enantiomeric separations

Abstract

Some fundamental aspects of capillary electrochromatography (CEC) (electroosmotic flow, capacity factor, plate height) were studied by carrying out the separation of some neutral compounds with capillaries packed with octadecylsilica particles (ODS). No loss of efficiency up to a linear electroosmotic velocity of 1.3 mm/s was observed for retained analytes (capacity factors varying from 0.7 to 2.5). The extra-column dispersions caused by the frit and the unpacked section separating the frit from the detection window were estimated. Chiral separations of the neutral enantiomers of chlorthalidone by packed capillary electrochromatography was successfully achieved using two approaches: (a) use of the chiral agent, hydroxypropyl-β-cyclodextrin (HPβCD) directly in the mobile phase with an achiral stationary phase (3 μm ODS); (b) use of a chiral stationary phase (5 μm HPβCD-bonded silica particles) with an achiral mobile phase. As with liquid chromatography, the second method achieves higher selectivity and resolution in a shorter analysis time.