A Colorimetric Method for Trace Level Determination of Cobalt in Natural and Waste Water Samples

Abstract

Abstract A colorimetric method which can be used to determine concentrations of cobalt as low as 0.1 mg/L in natural and waste water samples is developed. This method involves the complexation of cobalt with 1-nitroso-2-naphthol-3,6, disulfonic acid disodium salt at the pH of 6.0, and the measurement of the absorbance of the colored complex at 520 nm. The interference by other metals as well as common anions was also investigated. Under the conditions employed, cobalt determination was found to be free of any interference by various metal ions and anions. The effect of digestion process using the E.P.A procedure 3030E was also investigated. On synthetic samples, the results on the determination of cobalt in digested and undigested samples were same within experimental error showing the digestion procedures did not hinder the applicability of the method to environmental samples. The method was then applied to actual waste water samples to determine the concentration of cobalt. Greater than 98% recovery of cobalt was obtained using the method developed, and better than 96% agreement between the concentrations of cobalt determined using this method and the atomic absorption spectroscopy was obtained. The method is applicable for the detection of cobalt at concentrations in environmental samples as low as 0.1 mg/L with greater than 95% accuracy, and is proposed to be used as a standard method for a rapid on-site analysis of cobalt in water and waste water samples.