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偶氮基邻位为氨基的杂环偶氮试剂对钴(Ⅱ)、钯(Ⅱ)等金属离子具有优良的分析性能。作者新合成的2-(5-溴-2-吡啶偶氮)-5-二甲氨基苯胺(简写5-Br-PADMA)属这类试剂,该试剂的合成及其应用尚未见报道。本文研究了钴(Ⅱ)与5-Br-PADMA的显色反应。结果表明,在pH 4.7～9.2范围内,钴(Ⅱ)与5-Br-PADMA形成1:2的红色配合物。配合物一旦形成,即非常稳定,加入强酸可使其转化为另一种青蓝色具有较高摩尔吸光系数的双质子化型体,选择性也相应提高。配合物存0.25～3.5mol·L~(-1)盐酸溶液中的最大吸收峰位于563和610nm,表观摩尔吸光系
Heterocyclic azo reagents whose ortho-azo groups are amino groups have good analytical properties for metal ions such as cobalt (II) and palladium (II). The newly synthesized 2- (5-bromo-2-pyridylazo) -5-dimethylaminoaniline (abbreviation 5-Br-PADMA) belongs to this class of reagents. The synthesis and application of this reagent have not been reported yet. In this paper, the color reaction of cobalt (Ⅱ) with 5-Br-PADMA was studied. The results show that cobalt (Ⅱ) forms a 1: 2 red complex with 5-Br-PADMA in the pH range of 4.7 ~ 9.2. Once the complex is formed, it is very stable. Addition of a strong acid converts it to another proton-blue dual protonated species with a higher molar extinction coefficient, with a corresponding increase in selectivity. The maximum absorption peak in 0.25 ~ 3.5 mol·L ~ (-1) HCl solution of the complex was located at 563 and 610 nm, and the apparent molar absorptivity