配位滴定法连续测定铜和锌的新指示剂

对2-（3，5-二氨-2-吡啶偶氮）-5-二甲基苯胺（3，5-diCl-PADMAB）作指示剂络合滴定铜和锌进行了研究。在pH5．0的乙酸-乙酸钠介质中，以3，5-diCl-PADAMAB作指示剂，EDTA为滴定剂连续测定铜和锌，滴定终点颜色变化敏锐，准确度高，铜和锌量各在0～20mg范围内与EDTA量成正比。方法用于合金中铜和锌的测定，分析结果的相对标准偏差为〈0．1％和〈0．4％。

A NEW INDICATOR USED IN SUCCESSIVE CHELATOMETRIC TITRATION OF COPPER AND ZINC

The reagent, 2-(3, 5-dichloro-2-pyridylazo)-5-dimethylarninobenzene (abbreviated as 3, 5-diCl-PADMAB hereafter) was studied for use as a new indicator in chelatometry. In an acetate buffer of pH 5. 0, Zn( II ) in the presence of Cu( II) which was masked with thiourea and ascorbic acid previously, was titrated with EDTA standard solution until the 3,5-diCl-PADMAB indicator turned its color from reddish violet to bright yellow. Then the Cu( II ) was demasked from its thiourea complex, and continued the titration of free Cu( II ) ion with EDTA solution until the indicator changed its color from bluish violet to yellowish green. Both of the color changes at the end point of titration were very sharp and distinct. RSD's of the results obtained in analyzing two known samples of brass were found to be <0.1 % for Cu and <0. 4 % for Zn.