乙醇—水混合溶剂中次氮基三乙酸离解平衡的研究

次氮基三乙酸(NTA)在非水或混合溶剂中离解常数的测定尚未见报道,本文用电位法测定了乙醇-水混合溶剂中溶解度较小的NTA的离解常数,用标准盐酸溶液返滴定其钾盐可增加NTA浓度,提高测定准确度,测量系统防止CO_2装置和数据处理方法也比文献简单。

A Study of the Dissociation Equilibria of Nitdiotriacetic Acid in Ethanol-Water Mixtures

The pH potcntiometric 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.