试验了用光度显色剂2-(5-硝基-2-吡啶偶氮)-5-二甲氨基苯胺(5-NO2-PADMA)作为螯合滴定铜的指示剂.在pH 4.5的乙酸盐缓冲介质中,5-NO2-PADMA与铜(Ⅱ)生成紫红色螯合物,其吸收峰在550 nm波长处,在无铜(Ⅱ)存在时,该试剂本身的吸收峰在450 nm处,对比度达100 nm.在相同缓冲介质中用EDTA标准溶液滴定铜(Ⅱ)时,滴定终点时溶液由紫红色突变为黄绿色(铜量大于5 mg时接近绿色),终点敏锐可辨.方法中采用指示剂溶液浓度为1 g·L-1溶剂为N,N-二甲基甲酰胺,滴定时加入5~10滴指示剂较为适宜.用此方法测定了化学试剂硝酸铜及铝合金中铜量.

The chromogenic reagent,2-(5-nitro-2-pyridylazo)-5-dimethylaminoaniline (abbreviated as 5-NO2-PADMA),was tested for its use as an indicator in chelatometric titration of copper.In an acetate buffer medium of pH 4.5,a reddish violet chelate was formed by 5-NO2-PADMA with Cu(Ⅱ),having its absorption maxima at the wavelength of 550 nm,while in the absence of Cu(Ⅱ),an absorption maxima at 450 nm was observed due to 5-NO2-PADMA itself,giving the value of Δλ 100 nm.In the course of titration of Cu(Ⅱ) with EDTA standard solution as titrant in the same buffer medium,a color change from reddish violet to greenish yellow color (or to green color when more than 5 mg of copper was present) was observed indicating the end point of titration.The color change could be distinguished sharply.A 1 g·L-1 5-NO2-PADMA solution in N,N-dimethylformamide was used and 5-10 drops of the solution were the suitable amount used for end point indication.The proposed method has been used in the determination of copper in samples of chemical reagent and aluminum alloy.