零电流示波电位滴定的研究 Ⅰ.非配偶型铂电极上的螯合滴定:EDTA滴定金属离子

STUDIES ON ZERO-CURRENT OSCILLO-POTENTIOMETRIC TITRATIONS Ⅰ.CHELOMETRIC TITRATION ON UNCOUPLED PLATINUM ELECTRODE:TITRATION OF METAL IONS WITH EDTA

(一)前言螯合电位滴定是电位滴定的一个主要组成部分,文献极为丰富。这些滴定主要是在金属电极和离子选择电极上进行的。金属电极分为两类:配偶型和非配偶型。配偶型电极如Pt/Fe^(3+);Fe^(2+)、Hg/Hg^(2+);HgY^(2-);MY^(n-4)M^(n+),其“电极/溶液”界面上总有一对决定电位的电对。非配偶型电极的界面上则不存在明显的电对,如铂电极上EDTA滴定Ca^(2+),溶液中不外加高价的铂离子;滴定Fe^(3+),也不外加Fe^(2+)。关于非配偶型电极上的螯合滴定。

Classical chelometric potentiometric titration on metal indicator electrodes are usually carried out on coupled electrodes. In the interface between an coupled electrode and solution there is always a redox couple present for determining the potential of the electrode. The metal electrode is called uncoupled when there is no such a redox couple present in the electrode-solution interface. EDTA titration of Ca, Sr, Ba, Zn, Cd, Pb and La ions on uncoupled Pt electrodes are reported using the sudden position shift of a fluorescent spot on the screen of a simple cathode-ray oscillopolarograph to indicate the end-point of titration.The end-point indication is directly visual and sensitive. Accurate results are obtained.