[Study on the retention behaviour and mechanism of organic acids on an anion exchanger]

The retention behaviour and mechanism of organic acids on an anion exchange column Shim-pack IC-A1 (Shimadzu, Japan) have been studied. The retention valences (x) of organic acids on the anion exchanger were measured based on the following equation: logk' = -(x/y)log[Eluent] + constant By using the linearity of logk' vs log[Eluent] and the retention valences, the retention mechanisms of organic acids can be predicted. Acetic acid eluted as the non-dissociated form by a non ion exchange mechanism, because its retention valence was only 0.21. In this work, the multi-peak for one organic acid was observed. The chromatograms of citric acid obtained using PyA eluent with different concentration were showed. Two peaks were observed. As eluent concentration decreased, the detection sensitivity (peak area) was increased due to the decrease of the background conductivity. The multiple peaks of citric acid were also observed when the mixture of phthalic acid(PhA) and trihydroxymethylaminomethane (TRIS) was used as eluent. The multi-peaks for one organic acid result from the fact that different forms of the organic acid can be separated each other on anion exchanger by ion-exchange mechanism. The two peaks of citric acid were caused by separation of mono- and divalent citrate anion.