pH Controlled Condition for Selective Simultaneous Determination of Nickel and Cobalt in Alloys by First Derivative Spectrophotometry



1-(2-Pyridylazo)-2-naphthol (PAN) has been used for the simultaneous determination of nickel and cobalt at trace levels. PAN complexes of nickel and cobalt in the pH 1.89 form red and green colored complexes, respectively which are soluble in aqueous Tween 80 micellar media. Under optimum conditions, calibration graphs for simultaneous determination by first derivative spectrophotometry were obtained. Zero crossing first derivative spectrophotometry at 641 and 580 nm was used for the simultaneous determination. The method is able to determine cobalt to nickel ratio 15:1 to 1:6 (Wt/Wt), accurately. Accuracy and reproducibility of the determination method on the known various amounts of cobalt and nickel in their binary mixtures were tested. Effects of diverse ions on the determination of cobalt and nickel to investigate selectivity of the method were also studied. The recommended procedure was applied to various nickel-cobalt alloys.