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偶氮肿Ⅲ(Arsenazo Ⅲ)作为显色剂,已被广泛的应用。至于在酸性介质中用作络合滴定指示剂,直至目前为止,在国内外仍未见过报导。基于偶氮肿Ⅲ与稀土元素能形成稳定的绿色络合物,本文选择了稀土元素中与EDTA络合稳定常数较小的La~(3+),配成La-EDTA等当量溶液,预先加入滴定溶液中,由于被测的金属离子与EDTA所形成的络合物更稳定,从而能快速地置换出La~(3+)。这样,借La~(3+)与偶氮肿Ⅲ所形成的绿色络合物来判断终点。用此在pH5～6分别
Arsenazo Ⅲ (Arsenazo Ⅲ) as a developer, has been widely used. As for complexation in acidic medium titration indicator, so far, at home and abroad have not yet been reported. Based on azo complex Ⅲ and rare earth elements can form a stable green complex, rare earth elements selected in this complex with EDTA stability constant small La ~ (3 +), dubbed La-EDTA equivalent solution, pre-added In the titration solution, La ~ (3+) can be quickly displaced due to the more stable interaction between the metal ion and the complex formed by EDTA. In this way, La ~ (3+) and azo complex formed by the green complex to determine the end point. Use this at pH5 ~ 6 respectively