Assessment of silica-based reversed-phase materials for the analysis of a range of basic analytes by capillary electrochromatography

Abstract

A range of C18 bonded silica stationary phases, two specifically designed for capillary electrochromatography (CEC) use, have been evaluated for their performance in the CEC analysis of basic analytes of differing physico-chemical properties. The performance of the phases towards basic analytes will be discussed in terms of various CEC parameters and by Principal Component Analysis (PCA) of five LC chromatographic parameters – hydrophobic and steric selectivity, hydrogen bonding and ion-exchange capacities at pH 7.6 and 2.7. The CEC phases, which the PCA highlighted as possessing high non-acidic silanol activity, were shown to give substantially enhanced EOF at pH 7.8 and did not exhibit the phenomenon of “drying-out” at pH values below 6.1 which was pronounced with hydrophobic LC phases. The Hypersil CEC Basic C18 phase was found to provide superior performance in analysing the basic analytes compared to the Hypersil CEC C18 phase, this was attributed by PCA to its non-acidic base silica. Through the use of experimentally derived electrophoretic mobility values, LC retention factor, and electrosmotic flow values in CEC, it was possible to predict the CEC retention behaviour of ten basic analytes to an accuracy of ± 6%.