Abstract: The intrinsic protonation constants of three steps of chelating ion exchange resin D751 containing iminodiacetic groups in water and ethanol-water mixtures have been deter-mined at 25 ℃ by potentoimetric titration and by means of the extrapolation procedure without the assumption on the activity coefficients of charged species in the resin phase. The changes in the acid-base properties of the chelating resin D751 in the water and the ethanol-water mixtures have been obse-rved, and the observed effects are explained. The variation of apparent protonation constants with the degree of neutralizaton has been demonstrated.

Key words: Chelating ion exchange resin, Apparent protonation constant, Intrinsic protonation conatant, Ethanol-water mixture solvent