Modelling of migration behaviour of inorganic anions in ion-exchange capillary electrochromatography

A theoretical model to explain the observed mobility of inorganic anions in capillary electrochromatography (CEC) using ion-exchange (IE) stationary p hases has been derived. The model divides contributions to the observed mob ility of an analyte ion into capillary electrophoretic (CE) and IE componen ts. The CE component includes the influence of varying the ionic strength o f the background electrolyte on the electrophoretic mobility of the analyte , while the IE component accounts for the variation in retention of the ana lyte ion caused by changing the composition of the background electrolyte. The model was verified using a mixture of UV-absorbing inorganic ions in el ectrolytes of differing eluotropic strength in both packed and open-tubular CEC systems, with excellent agreement (r(2) > 0.98) for both systems. Valu es of constants in the model equation determined by nonlinear regression we re used to estimate the relative strengths of the interactions of different analytes with the stationary phase and these were found to agree well with elution orders observed in conventional IE chromatography.