Study of physically adsorbed stationary phases for open tubular capillary electrochromatography

A novel method based on the adsorption of positively charged compounds on t he wall of a fused-silica capillary was applied to prepare stationary phase s for open tubular capillary electrochromatography (OTCEC). The positively charged substances including cationic surfactant such as cetyltrimethylammo nium bromide (CTAB) and basic chiral selectors such as protein, peptide and amino acid were physically adsorbed onto the capillary wall under speciall y selected conditions. The adsorbed stationary phase of CTAB was used to se parate neutral compounds, while the others were used for chiral separations . The run-to-run reproducibility of retention time was rather good with rel ative standard deviation (RSD) values of less than 2.3%. The separation eff iciency was excellent with the highest theoretical plate number of up to 59 0 000/m and the average one above 250 000/m. Stored at 2-8 degrees C in the refrigerator, the adsorbed stationary phase can last at least one month. I t was observed that the UV spectra for the enantiomers are significantly di fferent due to the diastereomeric interactions of enantiomers with the chir al stationary phase in the detection window. With the use of the same capil lary, the same instrument, and the same mobile phase, the superiority of OT CEC over open tubular liquid chromatography (OTLC) and capillary zone elect rophoresis (CZE) was illustrated.