Critical comparison of retention models for optimisation of the separationof anions in ion chromatography III. Anion chromatography using hydroxide eluents on a Dionex AS11 stationary phase

Three ion chromatography (IC) retention models, namely the linear solvent s trength model (LSSM), empirical end points model (EEPM) and three-point cur ve fitting using DryLab from LC Resources were evaluated in terms of their ability to predict retention factors for inorganic anions separated on a Di onex AS11 column using electrolytically generated hydroxide eluents. Extens ive experimental retention data were gathered for 21 anions (fluoride, acet ate, formate, bromate, chloride, nitrite, methanesulfonate, bromide, chlora te, nitrate, iodide, thiocyanate, succinate, sulfate, tartrate, oxalate, tu ngstate, phthalate, chromate, thiosulfate and phosphate) using hydroxide el uents of varying concentration. Although the purely theoretical LSSM was fo und to give adequate performance, the EEPM (in which a linear relationship is assumed between the logarithm of retention factor and the logarithm of e luent strength, but the slope is determined empirically) and DryLab perform ed better, with DryLab giving the best accuracy and precision of the three models. The EEPM and DryLab were also shown to have advantages in terms of their low knowledge requirements and ease of solution. Compared with IC usi ng dual eluent species, the retention behaviour in IC using single eluent s pecies was found to be easier to model by both theoretical and empirical ap proaches. (C) 1999 Elsevier Science B.V. All rights reserved.