Simultaneous Determination of Cobalt(II) and Nickel(II) in Co-Ni Alloy Plating Solution by Dual-Wavelength Standard Addition Spectrophotometry

A new dual-wavelength standard addition spectrophotometry for simultaneous determination of cobalt(Ⅱ) and nickel(Ⅱ)was established based on the reaction of cobalt(Ⅱ) and nickel(Ⅱ) with PAN to form stable complexes in pH 5.0 HAc-NaAc buffer medium and in the presence of polyvinyl alcohol.The maximum absorptions of the two complexes are located at 612nm and 578nm.A couple of wavelengths of cobalt complex,580nm and 626nm,were accurately selected as the measuring wavelengths,and nickel(Ⅱ)as standard-addition component.Beer's law is obeyed in the range of 0-15μg/25mL for Ni 2+ and 0-10μg/25mL for Co 2+ ,respectively.The method is simple,rapid and sensitive,and was used in simultaneous determination of Ni 2+ and Co 2+ in plating solution with relative standard deviations of less than 1.2% for Co 2+ and 0.82% for Ni 2+ .