Differential pulse-polarographic determination of cobalt after extraction as 1-nitroso-2-naphtholate

The differential pulse-polarographic determination of cobalt in the ppb-region after extraction of cobalt(III)-1-nitroso-2-naphthol chelate from citrate buffer solution (pH 5) into benzene is described. The cobalt(III) chelate is determined in a electrolysis solution composed of a 1∶1 mixture of the extract and acetonitrile solution containing 8 mmol/l perchloric acid and 0.2 mol/l sodium perchlorate. A well-developed reduction wave of the ligand in the cobalt(III) chelate is obtained. The limit of determination is in the range of 1–2 ppb of cobalt.