Determination of anionic feed additives by two-dimensional capillary isotachophoresis

An isotachophoretic method was developed for the determination of organic and inorganic acids (benzoic, citric, formic, fumaric, lactic, malic, phosphoric and tartaric acid) in feed additive preparations. The resulting isotachophoretic measurements were carried out two-dimensionally in a column-coupling instrument equipped with contact conductivity (in both capillaries) and UV absorbance (in the analytical capillary) detectors, respectively. Preseparation was run in the first capillary at pH 6.1 of the leading electrolyte. The pH of the leading electrolyte of the second capillary was 2.5, with beta-cyclodextrin added to improve the separation selectivity for tartrate and fumarate. The terminating electrolyte was 5 mmol l(-1) caproic acid in all cases. The precision of the determinations including sample pretreatment, expressed as the relative standard deviation, varied between 3.3 and 7.9%, depending on the concentration levels of the analytes. The accuracy, determined by the recovery of analytes added, was typically in the order of 94 to 98%.