Design of background electrolytes for indirect detection of anions by capillary electrophoresis

In capillary electrophoresis of inorganic and other low molecular weight anions using indirect photometric detection, the correct design of the background electrolyte can considerably reduce the time needed for method development and can increase the quality of the separation achieved. This article discusses the basic steps for development of suitable electrolytes, based on fundamental knowledge of the nature of the analytes and the proposed background electrolyte. Consideration is given to the choice of the absorbing probe used for indirect detection, based on the relative mobilities of the probe and the analytes, and the desired limits of detection. Choice of the electro-osmotic flow modifier and correct buffering protocols are also discussed. Finally, strategies to increase the useful mobility range of the background electrolyte are given, based on matching the mobilities of multiple electrolyte probes with the mobilities of the analytes.