The determination of cobalt in the water and waste water

Abstract

Two suitable alternative methods are described for the determination of cobalt in water or waste water. In the first method the cobalt is complexed with 3-methoxynitrosophenol and the absorbance of its chloroform extract measured at 410 mμ. Zinc, cadmium and lead do not interfere. Interference by nickel and copper is prevented using the procedure described. Using a slight modification, interference by iron is greatly reduced. Up to a certain limit Cr 6+ can be tolerated. The tolerance limit for Cr 3+ is higher than that of Cr 6+. With the second method the cobalt is complexed with ammonium thiocyanate, the complex extracted with methyl isobutyl ketone and the absorbance of the extract measured at 620 mμ. Zinc, lead, cadmium, nickel, chromium as Cr 3+ and Cr 6+ can be tolerated at high concentrations without causing interference. Interference caused by copper is prevented by reducing it to the cuprous state and then precipitating it as the iodide, while iron interference is prevented by the addition of chromate to precipitate the ferrous and ferric iron. The first method is suitable for cobalt concentrations of up to 3 mg/I. With the second method it is possible to use up to 10 mg of cobalt/l.