Abstract: The pHpotcntiometric titration was used to determine the dissociation constants of nitrilotri-acetic acid (NTA) in ethanol-water mixtures. The potassium nitrilotriacetate was titrated by a stan-dard solution of hydrochloric acid to increase the accuracy of the determination. In the method it was assumed that n is a mean number of dissociated proton in calculation of the acid dissociation constants. According to the characteristic of NTA, the values of K₁ and K₂ were obtained by treating the system as the first two-step proton dissociation equilibrium at a low pH, and K₃ as the last step at a higher pH. It is found that the values of K₁ and K₂ decrease with the increase of ethanol content in the solvent, but the value of K₃ is just contrary'to this result.

Key words: Nitrilotriacetic acid, Dissociation constant, Ethanol-water solvent