Complex-forming equilibria in isotachophoresis : VII. Evaluation of the ion-pair formation constants of phosphorus oxo acids with histidine and assessment of their separability

Abstract

The qualitative indices ( R E) of six phosphorus oxo acids (phosphorous, orthophosphoric, pyrophosphoric, triphosphoric, trimetaphosphoric and tetrametaphosphoric acids) were observed using histidine-buffered electrolyte systems. The ion-pair formation constants of the phosphorus oxo acids with histidine (1:1) were evaluated by the least-squares method utilizing a simulation of the isotachophoretic steady state. The separability of the six oxo acids and hypophosphorous acid was assessed using the evaluated constants. The separation of the seven oxo acids with a histidine-buffered electrolyte system as reported by Yagi et al. could be elucidated as the result of the decrease in the effective mobilities accompanied by ion-pair formation.