Temperature dependence of the anion-exchange chromatographic behaviour of cyclic phosphate oligomers and their anion-exchange separation

Abstract

The temperature dependence of the chromatographic behaviour of a series of cyclic condensed phosphates with degree of polymerization from 3 to 8 on an anion-exchange column was investigated. The efficiency of Jandera's equation in predicting the elution behaviour was confirmed and the elution conditions for separating cyclic phosphates were established with the aid of computer simulations. An increase in column temperature resulted in a significant increase in the number of theoretical plates. Conditions for separating the six phosphates were not found at 30°C; however, the computer simulations suggested that suitable conditions for their separation existed at 70°C and this was confirmed experimentally. The enthalpy changes of the ion-exchange reaction of all phosphates were deterimed from the temperature dependences of their retention times and varied in proportion to their anionic charges.The ion-exchange reaction of these cyclic phosphates was governed by the dehydration of the anions and partial dissociation of ion pairs between cyclic phosphate anions and K + ions in the eluent.