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用EDTA络合滴定铜的缺点是选择性不高.利用一些螯合剂对铜有特别强的络合能力,例如三乙撑四胺、氨三乙酸和氮川三甲撑膦酸等,可以提高滴定铜的选择性.乙二胺四正丙酸(简称EDTP)的各级酸度常数及其与铜等九种金属离子的螯合物的稳定常数已经测定.据此,我们计算出ED-TP的酸效应系数α_Y(H)及其金属离子螯合物的表观稳定常数同列于表1.从表1可见,在pH4.5～7只有Cu—EDTP螫合物的K’大于10~8,而共余的则小得多,EDTP堪称为铜的高选择性螫合剂.Sanderson等曾以丽春红3R(Pnoceau 3R)为指示剂,在pH～9的氨性溶液中用EDTP滴定铜,Mg~(2+)、Ca~(2+)、
Titration with EDTA complexation is the lack of selectivity of copper. The use of some chelating agents have a particularly strong copper complexing ability, such as triethylenetetramine, nitrilotriacetic acid and nitrilotrimethylenephosphonic acid, etc., can increase the titration Copper selectivity. The acidity constants at all levels of ethylenediamine tetra-n-propionic acid (EDTP) and its stability constant with chelates of nine metal ions such as copper have been determined. Accordingly, we calculated the ED- The acid effect coefficient α_Y (H) and the apparent stability constant of the metal ion chelate are listed in Table 1. It can be seen from Table 1 that only K ’of the Cu-EDTP complex at pH 4.5-7 is greater than 10-8, While the rest is much smaller, EDTP is called copper highly selective mixture.Sanderson et al once used Plumoce 3R as an indicator, titrated copper with EDTP in pH ~ 9 ammonia solution , Mg ~ (2 +), Ca ~ (2+),