Determination of small anions by capillary electrophoresis using indirect UV detection with sulphonated nitrosonaphthol dyes

A capillary zone electrophoretic method was developed for routine separation of non-UV-absorbing inorganic anions, phosphonic compounds and organic acids. The background electrolyte solutions were prepared from three new dye reagents normally used for the complexation of metals, namely, the sodium salts of 1-nitroso-2-naphthol-3,6-disulphonic acid (Nitroso-R salt), 1-nitroso-2-naphthol-6-sulphonic acid (126NNS) and 2-nitroso-1-naphthol-6-sulphonic acid (216NNS). The optimized separations were carried out in 0.5 mM dye solution at pH 8.00, with UV detection of the analytes at 254 nm. All analytes in the sample mixtures were separated from each other within 20 min. The currents under the optimized separation conditions were only 1.5 mu A, 0.9 CLA and 0.9 CLA in Nitroso-R, 126NNS and 216NNS, respectively. The detection limits of the compounds injected from vials were 1 mu g/ml at 254 nm. The method performed well for the analysis of inorganic anions and for screening of by-products in the production of clodronate. It was also promising for the screening of organic acids in fluids formed in the production of sugar. The repeatability of the analyses was evaluated in experiments involving nine replicate injections, replenishment of the background electrolyte solution after each run and temperature control at 25 degrees C. The standard deviations of the absolute migration times of the compounds were from 0.1 to 2%, but also up to 9% when slowly moving analytes with broad sample zones were analysed.