ABSORPTIOPHOTOMETRIC DETERMINATION OF MICRO AMOUNTS OF NICKEL WITH 5-(5-CHLORO-2-PYRIDYLAZO)-2,4-DIAMINOTOLUENE

In this paper, the optimum conditions of the color reaction of 5 (5 chloro 2 pyridylazo) 2,4 diaminotoluene (5 Cl PADAT) with Ni(Ⅱ) are reported. It is shown that 5 Cl PADAT reacts with Ni(Ⅱ) ion to form a stable purple colored (mole ratio 1∶2) complex in an HOAc NaOAc medium of pH 5.5～6.5. The absorption maxima of the complex is at 545nm in the presence of SDS. Its apparent molar absorptivity is 1.02×10 5L·mol -1 ·cm -1 . Beer′s law is obeyed in the concentration range of 0～4μg/10ml of Ni(Ⅱ). The selectivity of the reaction is improved by the addition of thiourea, NH 4F and Na 4P 2O 7 as masking agents. The proposed method has been applied to the determination of nickel in magnesium alloys, ores and steel with satisfactory results.