Effect of Column Temperature on the Retention of Inorganic Anions and Organic Acids in Non-Suppressed Anion-Exchange IC

An investigation has been conducted into the effect of column temperature on the retention of inorganic anions and organic acids in non-suppressed ion chromatography on an anion-exchange column. Potassium biphthalate and p-hydroxybenzoic acid–tris–boric acid were used as mobile phases. The column temperature was from 25 to 50 °C. Endothermic and exothermic retention of inorganic anions were both observed when potassium biphthalate was used as mobile phase. When p-hydroxybenzoic acid–tris–boric acid was used as mobile phase, however, endothermic behavior only was observed. Moreover, for the two mobile phases, variation of the retention time of the system peaks with changing temperature was reversed. For retention of the organic acids, only endothermic behavior was observed with the two mobile phases. Variation of retention time was greater when p-hydroxybenzoic acid–tris–boric acid was used as mobile phase than when potassium biphthalate was used. These results indicated the exchange reaction in anion-exchange chromatography could be either endothermic or exothermic, depending on the solute and mobile phase ions involved. Different relative changes of retention time were observed for individual inorganic anions and organic acids with increasing column temperature. In general, variation of retention time with increasing temperature was greater for strongly retained inorganic anions and organic acids than for weakly retained species. Van’t Hoff plots for inorganic anions, organic acids, and system peaks were linear. Selectivity variation of the retention of inorganic anions and organic acids was achieved by changing the temperature. In achieving optimum separation of inorganic anions and organic acids, temperature was a valuable tool. To reduce the retention times of the ions and avoid interference from system peaks in non-suppressed anion-exchange ion chromatography with the two mobile phases, a low column temperature, for example, 35 °C, was best.