Capillary electrophoretic analysis of anions in a multi-anion background electrolyte: Interference of system peaks

This study deals with the simultaneous analysis of UV-transparent anions by capillary electrophoresis with indirect UV-detection. With a background el ectrolyte (BGE) based on UV-absorbing chromate and UV-transparent berate, t he interference of system peaks with those of sample anions (chloride, sulf ate, citrate, phosphate) is shown. The existence of such system peaks, and their position in relation to the peaks of the sample anions, are explained on the basis of the eigenpeak theory proposed by Poppe [1]. With this BGE the system peaks were manifested as a negative peak followed by a positive peak. Their shapes depended on the relative mobilities of the analyte and BGE anions and their areas depended on the amount of sample. T he mobility of the system peak depends on the borate/boric acid mobility, w hich was adjusted by slight variation of the pH close to its pK(a) - pH is the key factor governing system-peak mobility. When the locations of the sy stem peaks are optimized, the quantification of citrate can be achieved; th is was successfully used for determination of anions in milk.