Effects of pH and organic solvent on chromatographic behavior in capillary electrochromatography

Abstract

Abstract. Electrochromatography is demonstrated using a 50 pm i.d. capillary column. The separation of solutes due to their different mobilities is obtained by the application of high voltage along the column. The elution times of solutes are dependent on the pH and composition of the eluent. Both electrophoretic and electroosmotic flow velocities are almost constant between 30 and 90% methanol in the eluent, and they increase with more than 90% methanol. The pH dependence of the electroosmotic flow velocity may be related to the dissociation of unreacted silanol groups on the surface of the ODs-silica particles.

Continuous-Bed Columns Containing Sol-Gel Bonded Packing Materials for Capillary Electrochromatography

“…As can be seen, the EOF for the ODS column increased significantly with an increase in buffer pH from 2.0 -7.5, and then remained nearly constant up to pH 9.0, while the mixed-mode ODS/SCX column exhibited nearly constant EOF over the whole pH range from 2 -9. As reported by Kitagawa and Tsuda, [36], the change in EOF with buffer pH for ODS columns is due to the pH dependent ionization of silanol groups. In the mixed-mode ODS/SCX column, there are two contributions to the double-layer, one from the ionization of residual silanol groups and another from the ionization of propylsulfonic acid groups.…”

Immobilized vancomycin as chiral stationary phase in packed capillary liquid chromatography

“…Thus, even if the carboxylic acid moiety of the selector is referred to as unimportant for chiral selectivity in CE, 8 the protonation of this carboxylic acid would still have to be considered to explain the retention maximum at pH around 4. One possible explanation for the reduced retention and selectivity at pH 3 might be that both the carboxylic acid moiety of the selector and the most acidic silanol groups (having pK a -values around 4.5 35 ) are becoming uncharged. This may lead to an increased attraction between the silica surface and the relatively freely moving vancomycin.…”

Electric Resistance Variation of Packing Materials in Capillary Electrochromatography by Using Fluorinated-Bonded Silica and Octadecylsilane Phases

“…The same instrument for pressurized flow driven electrochromatography as described in the former reports 3,4,7,8 was used with different types of columns. A high-voltage power supply (dc ± 30 kV, type HCZE-30P, Matsusada Precision, Kusano, Shiga) was used.…”

“…In pressurized flow driven electrochromatography, the electroosmotic velocity (Vosm) are given by 1,8 Vosm = L/(Rtn) -Vpres. L and R are the column length and the retardation factor 1/[1 + k]; k is the capacity factor, tn is the elution time of a neutral marker which was methanol.…”