Spectrophotometric determination of nickel with 2-(5-nitro-2-pyridylazo)-1-naphthol and nonionic surfactant

Abstract

A sensitive and selective spectrophotometric method was developed for the determination of nickel based upon the reaction with 2-(5-nitro-2-pyridylazo)-1-naphthol (5N-α-PAN) at pH 8.5 in the presence of Triton X-100. Interference from foreign ions can be avoided by the use of masking agents and EDTA. Iron does not interfere if oxidized to Fe (III). Mn (II) and Cu (II) are masked with tartrate and 1, 2-diaminopropane (1, 2-DAP) respectively. The 5N-α-PAN chelates of Zn (II), Cd (II) and Pb (II) are completely decomposed by the addition of EDTA after the color development of the Ni chelate. Interference from Co (II) (<50μg) are eliminated by the combined use of 1, 2-DAP and EDTA. When larger amounts of Co (II) (<450μg) are present, the influence can be corrected by measurement of the absorbances at 595nm and 632nm. A recommended procedure is as follows : An aliquot of sample solution containing up to 35μg of nickel is transfered to 50ml volumetric flask and a few mg of ammonium persulphate, 2.0ml of 20 (w/w)% Triton X-100, 2.0ml of 0.1M tartrate and 1.0ml of 0.1M 1, 2-DAP are added successively. After the addition of 2.0ml of 0.05 (w/w)% 5N-α-PAN in dioxane, the solution is adjusted to pH 8.5 with boric acid buffer (pH 8.5) and allowed to stand for 30 minutes. Then 1.0ml of 0.05 M EDTA is added and the resultant solution is diluted to the mark with water. After 20 minutes, the absorbance at 632nm is measured against a reagent blank. Beer's law is obeyed over the concentration range (535)μg Ni/50ml and the molar absorptivity is 7.4×10⁴l mol^-1cm^-1. For the determination of 26μg of Ni, the following amounts of foreign ions are tolerated : Co (II) 50μg (450μg by correction method), Zn (II) 60μg, Cd (II) 110μg, Cu (II) 400μg, Mn(II) 480μg, Pb(II) 2mg, Fe(III) 14mg, Al(III) 13.5mg, Mg(II) 12mg, Ca(II) 20mg.