Capillary electrokinetic chromatography with charged linear polymers as a nonmicellar pseudostationary phase: determination of capacity factors and characterization by solvation parameters.

Abstract

A permanent polycation, polydiallyldimethylammonium (PDADMA), is applied as a linear, polymeric, replaceable, and nonmicellar pseudostationary phase for the separation of neutral analytes by capillary electrokinetic chromatography. It is shown that this polymer used in the background electrolyte is able to separate the analytes even if it does not form micelles under the given conditions. The most favorable aspect for practical use lays in the simple replacement of the separation media after each run, thus generating highly reproducible conditions. To determine the capacity factors of the analytes, a new method, based on an isotachophoretic regime, has been introduced for the measurement of the electrophoretic mobility of the polymeric pseudo-stationary phase. The capacity factors in the separation system, derived from the mobilities of the polymer, the electroosmotic flow, and the mobilities of 15 individual aromatic analytes, range between 0.3 and 1.2 for the given separation media (aqueous solution of acetate buffer, pH 5.2, with 4% w/w PDADMA). The type of interaction in the pseudochromatographic system was clarified from solvation parameters based on the linear free energy relationship model. It was found that pi and n electron interactions and hydrogen-bond basicity of the polymer, as compared with the aqueous bulk phase, are the main cause of retention of the analytes.