Use of 2-(5-Nitro-2-Pyridylazo)-5-Dimethylaminoaniline as Indicator in Chelatometric Titration of Copper

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.