IMPACT OF EXPERIMENTAL PARAMETERS ON THE RESOLUTION OF POSITIONAL ISOMERS OF AMINOBENZOIC ACID IN CAPILLARY ZONE ELECTROPHORESIS

The separation process in capillary zone electrophoresis is governed by many experimental parameters, such as the choice of the electrolyte, field strength, ionic strength, pH, temperature and additives (including organic modifiers). Positional isomers of substituted benzoic acids were used as model compounds in order to study the contributions of pH, electrolyte, ionic strength, addition of alcohols, the choice of the counter ion and the temperature to the electrophoretic separation and the magnitude of the electroosmotic flow. The results that obtained were compared critically with those of previous studies, in which only the modifier content had been varied. Obviously, pH was the most effective parameter in optimizing the resolution. However, thermostating of the capillary at elevated temperatures turned out to be a very effective additional feature; the resolution was increased and the analysis time was shortened considerably. Other options, such as the addition of alcohols or the choice of the counter ion, will also increase the resolution but also increase the analysis time. The improvement in the concentration sensitivity was studied using the technique of sample stacking. Volumes of up to 15 nl could be introduced in this way without serious separation problems, yielding a detection limit of 10(-6) M.