Theoretical Calculation of Boron Isotopic Separation Factors in Ion-Exchange Chromatography

Abstract

N-Methylglucamine-modified polystyrene (NMG = N-methylglucamine) is a boron-specific resin widely used to remove boron from water by ion-exchange chromatography, which is reported to have the highest separation factor of boron isotopes (10B and 11B) up to date. In this paper, we calculated its boron isotopic separation factor (S) by quantum chemistry. Boric acid in the mobile phase is expected to interact with the functional group of the resin to form a monochelate complex. The polymer chain of the resin is proved to have little influence on S. HF/6-31G level of theory well meets the expectation of current calculations, while the higher level theories (B3LYP, M06-2X, and MP2) lead to larger errors. The inclusion of thermal scaling factors and explicit solvent molecules bring negligible improvement to S. The change of S with different pH values was obtained as well. Finally, S of various functional groups of chelating resins were calculated, among which phenols and carboxylic acids are found to have a dist...