Divalent pairing ion for ion-interaction chromatography of sulphonates and carboxylates

An ion-interaction method for the simultaneous separation and UV detection of compounds with weak or strong ionic groups, using a divalent cationic ion pair reagent, namely hexamethonium bromide, has been studied and developed. The analytes considered were tartaric, fumaric, pyruvic, maleic, phthalic, benzoic, sorbic, 4-hydroxybenzoic, benzene and toluene-4-sulphonic acids, and they were chosen for their practical importance. The chromatographic optimization for their separation has been achieved by varying eluent composition (methanol, NaCl and hexamethonium concentrations) and studying the performance of different stationary phases (octyl- and octadecyl-silica based columns). The method developed has been successfully applied to benzoate and sorbate determination in orange juices.