铜离子选择电极络合滴定法分步滴定锌和镁

Continuous Determination of Mg^(2+) and Zn^(2+) with Complexometric Titration by Ion-Selective Electrode

以EDTA为滴定剂,Cu-EDTA为置换剂,铜离子选择电极为指示电极,通过控制氨的用量调节αZn(NH3),采用电位滴定法可对Zn2+、Mg2+进行分步滴定.研究表明:Cu-EDTA可增大Zn2+、Mg2+的滴定突跃,其适宜浓度为0.005 mol/L,体系游离氨的浓度为0.01 mol/L时,lgK′ZnY lgK′MgY,能首先滴定Zn2+.然后加氨水调节体系至pH=10.4,可对Mg2+准确滴定.但重金属离子Pb2+、Hg2+、Cu2+等产生干扰,少量的Fe3+、Al3+可加入三乙醇胺进行掩蔽.

A method of continuous determination of Mg^2＋ and Zn^2＋ by copper ion-selective electrode was investigated. In this study, Mg^2＋ and Zn^2＋ were titrated with EDTA with Cu-EDTA as the displacer, and Zn （NH3） eontrolled by the amount of ammonia water. The results showed that the presence of 0. 005 mol/L Cu- EDTA increased the titration-jump of Mg^2＋ and Zn^2＋. At the same time,lgK＇ZnY lgwas much lager than lgK＇MgY in the presence of 0. 01mol/L free NHs, Under this condition, Zn^2＋ was titrated first. Then, Mg^2＋ can be accurate titrated at a pH of 10. 4 by adding ammonia. Some heavy metal ions, such as Pb^2＋, Hg^2＋, Cu^2＋ eaused interference with the titration, while addition of small amounts of Fe^3＋ or Al^3＋ in triethanolamine eould mask the interference.