2-(5-硝基-4-甲基-2-吡啶偶氮)-5-二甲氨基苯胺的合成及其与钴(Ⅱ)显色反应的探讨

Discussion on the synthesis of 2-(5-nitro-4-methyl-2-pyridylazo)-5-dimethylaniline and its color reaction with cobalt(Ⅱ)

合成了新显色剂2-（5-Jg基-4-甲基-2-吡啶偶氮）-5-二甲氨基苯胺（缩写为：5-NOz-4-Me—PADMA），并研究了其与钴（Ⅱ）的显色反应。结果表明，在pH4．0～7．0的HAc—NaAc缓冲溶液中，钴（Ⅱ）与5-NO2-4-Me—PADMA反应形成紫红色络合物，其最大吸收峰位于568nm处；钴络合物形成后非常稳定，当以无机酸酸化，由于质子化作用，可转化成另-种具有较高吸收特性绿蓝色的稳定双质子化型体，其吸收峰红移至620nm，灵敏度提高3倍。以1．8mol／LH2SO4作测量介质，钴（Ⅱ）的浓度在0～1．0μg／mL范围内符合比尔定律，表观摩尔吸光系数为6．02×10^4L·mol^-1·cm。方法应用于矿样中微量钴的测定，结果与火焰原子吸收光谱法测定结果相-致，相对标准偏差（n-6）小于2％。

A new chromogenic reagent 2- （5-nitro-4-methyl-2-pyridylazo）-5-dimethylaniline （ 5-NO2-4- Me-PADMA） was synthesized and its color reaction with cobalt（Ⅱ） was also investigated. It showed that, in HAc-NaAe buffer solution at pH 4.0-7.0,Co（H） reacted with 5-NO274-Me-PADMA to form a violet-red complex, whose maximal absorption peak appeared at 568 nm. Cobalt complex kept very stable after formation. When it was acidified with inorganic acid, it was converted into greenish blue double-proton body with high absorption characteristics under the effect of protonation. Its absorption peaks shifted to 620 nm, and its sensitivity was tripled. In the medium of l. 8 mol/L H2SO4, the con- centration of CO （Ⅱ） obeyed Beer＇s law in the range of 0-1.0 μg/mL. The apparent molar absorptivity was 6.02 ×10^4L·mol^-1·cm^-1. The proposed method was applied to the determination of micro co- balt in ores, whose results were consistent with flame atomic absorption spectrometry. The relative standard deviation （n=6） was less than 2 %.