Solid-liquid Separation after Liquid-liquid Extraction: Spectrophotometric Determination of Cobalt by Extraction of its 2-Methoxyethyl Xanthate in Molten Naphthalene

A selective spectrophotometric method has been developed for the determination of cobalt after extraction of its 2-methoxyethyl xanthate complex into molten naphthalene. Cobalt reacts with this xanthate in the ratio of 1 : 2 (metal : ligand ratio) in a pH range of 3.5-9.2 and over an acid range of 2.5-7.0 M. It absorbs strongly at 355 nm. Beer's law is obeyed over the concentration range of 2.5-46.0 ~ig of cobalt in 10 ml of the final solution. The molar absorptivity and sensitivity in terms of Sandell's definition are calculated to be 1.287 x 104 1 mo1-1 cm-1 and 0.0046 μg /cm2 respectively. Ten replicate determinations of sample solution containing 25 μg of cobalt gives a mean absorbance of 0.546 with a standard deviation of ± 0.0037 and a relative standard deviation of ± 0.670/o. Interference by various ions has been studied and the conditions developed for the determination of cobalt in complex materials such as alloys.