Study on the retention behavior of aromatic carboxylic and sulfonic acid on a new anion exchange column

摘要

Ion chromatography (IQ has gradually developed into a preferred method for the determination of inorganic anions. And in recent years some low molecular aliphatic acid can be also separated in the ion exchange column with the development of stationary phase. But for the determination of aromatic ionic compounds there are some problems. The aromatic anions show enhanced retention due to interaction with the pi electrons of the aromatic backbone. Although the addition of an organic modifier can alleviate the difficulty, it is not the ultimate solution. lonPac AS20 column was developed using a unique polymer bonding technology and its substrate coating is aliphatic backbone. The polymer is completely free of any pi electron-containing substituents in the AS20 column. In this paper, the retention behavior of aromatic carboxylic and sulfonic acid on two hydroxide-selective columns, lonPac AS11-HC, AS 16, and the new column AS20 was also studied. The result showed that the retentions of ten compounds on three columns were different with each other because of their different column characteristics. Among them 4-chlorobenzene sulfonic acid, 3,5-dihydric benzoic acid and salicylic acid obviously exhibited the weakest retention on the lonPac AS20. It was showed that pi-pi bond function between anion and stationary phases was weakened in AS20 column because its polymer was completely free of any pi electron-containing substituents. So in this paper the AS20 was selected as an analytical column to separate ten aromatic ionic compounds, fumaric acid with conjugate bond included. The retention behavior, separation of the ten compounds and effect of temperature on their retention in the anion-exchange column AS20 (2 mm) were studied. The result showed that those compounds could be separated with each other when running in gradient program and the organic modifier was unnecessary during the separation. So it is showed that AS20 column can be used as a separating column because its polymer is completely free of any pi electron-containing substituents. Finally, the effect of temperature on the retention behavior in AS20 column was studied and it was showed that the retention of nine compounds exhibited endothermic behavior.