Performance of Dicarboxylates for the Separation of Arsenic Species by Anion Exchange Chromatography

Abstract

This work presents a study of the chromatographic performance of several dicarboxylates as eluents in anion exchange chromatography for the separation of four As species. Retention factors, asymmetry factors and plate numbers were determined for arsenite, arsenate, dimethyl arsenate, and monomethyl arsonate. The eluents studied included the series of linear dicarboxylates from oxalate to adipate, three hydroxy-substituted dicarboxylates, and an aromatic dicarboxylate. The linear dicarboxylates showed a marked influence of the length of the aliphatic chain on the separation performance. The higher hydrophobicity of the longer chains increases their affinity to the stationary phase due to interactions with the polymeric support, resulting in shorter retention times, except for oxalate which has a high charge density and deviates from this trend. This hydrophobicity also affects the efficiency and asymmetry obtained for the different species. The hydroxy-substituted dicarboxylates showed a complex behavior and different interactions with the As species than their unsubstituted counterparts. On the other hand, the aromatic ring and high charge density of the phthalate ion resulted in very short retention times and high asymmetries for the inorganic species. In terms of overall performance, oxalate and malonate seem to be the most suitable choice for the separation of anionic arsenic species.