Study of physically absorbed stationary phases for open tubullar capillary electrochromatography

A novel method based on the adsorption of positively charged compounds on the wall of a fused-silica capillary was applied to prepare stationary phases for open tubular capillary electrochromatography (OTCEC). The positively charged substances including cationic surfactant such as cetyltrimethylammonium bromide (CTAB) and basic chiral selectors such as protein, peptide and amino acid were physically adsorbed onto the capillary wall under specially selected conditions. The adsorbed stationary phase of CTAB was used to separate neutral compounds, while the others were used for chiral separations. The run-to-run reproducibility of retention time was rather good with relative standard deviation (RSD) values of less than 2.3%. The separation efficiency was excellent with the highest theoretical plate number of up to 590000/m and the average one above 250000/m. Stored at 2-8 degrees C in the refrigerator, the adsorbed stationary phase can last at least one month. It was observed that the UV spectra for the enantiomers are significantly different due to the diastereomeric interactions of enantiomers with the chiral stationary phase in the detection window. With the use of the same capillary, the same instrument, and the same mobile phase, the superiority of OTCEC over open tubular liquid chromatography (OTLC) and capillary zone electrophoresis (CZE) was illustrated.