Optimization of background electrolytes for capillary electrophoresis I. Mathematical and computational model

A mathematical and computational model is introduced for optimization of ba ckground electrolyte systems for capillary zone electrophoresis of anions. The model takes into account mono- or di- or trivalent ions and allows also for modeling of highly acidic or alkaline electrolytes, where a presence o f hydrogen and hydroxide ions is significant. At maximum, the electrolyte c an contain two co-anions and two counter-cations. The mathematical relation s of the model are formulated to enable an easy algorithmization and progra mming in a computer language. The model assesses the composition of the bac kground electrolyte in the analyte zone, which enables prediction of the pa rameters of the system that are experimentally available, like the transfer ratio, which is a measure of the sensitivity in the indirect photometric d etection or the molar conductivity detection response, which expresses the sensitivity of the conductivity detection. Furthermore, the model also enab les the evaluation of a tendency of the analyte to undergo electromigration dispersion and allows the optimization of the composition of the backgroun d electrolyte to reach a good sensitivity of detection while still having t he dispersion properties in the acceptable range. Although the model presen ted is aimed towards the separation of anions, it can be straightforwardly rearranged to serve for simulation of electromigration of cationic analytes . The suitability of the model is checked by inspecting the behavior of a p hosphate buffer for analysis of anions. It is shown that parameters of the phosphate buffer when used at neutral and alkaline pH values possess singul arities that indicate a possible occurrence of system peaks. Moreover, if t he mobility of any analyte of the sample is close to the mobilities of the system peaks, the indirect detector signals following the background electr olyte properties will be heavily amplified and distorted. When a specific d etector sensitive on presence of the analyte were used, the signal would be almost lost due to the excessive dispersion of the peak. (C) 2001 Publishe d by Elsevier Science B.V.