Spectrophotometric determination of cobalt with isonitrosodimedon

An extraction procedure with iso-amylalcohol for the determination of traces of cobalt was developed using isonitrosodimedon. At 374mμ, the wavelength of maximal absorption, the molar extinction coefficient is as high as 19.680, allowing cobalt determination as low as 0.5μg/ml in the organic phase. The extraction is quantitative between pH 4 and 7. The most common ions in a 100-fold excess do not disturb the determination, though Fe⁺³, Cu⁺², Cr⁺³ and Ni⁺² should be absent.