Specific and sensitive spectrophotometric determination of cobalt with 3-(2′-thiazolylazo)-2,6-diaminotoluene

Abstract

Cobalt and 3-(2′-thiazolylazo)-2,6-diaminotoluene react in an acidic sodium acetate medium in the presence of vanadate to give several complexes. The soluble blue complex in a strong perchloric acid medium (H₀=–0.5) obeys Beer's law between 0.05 and 0.60 p.p.m., with a molar absorptivity of 9.74 × 10⁴ l mol^–1 cm^–1 at 590 nm, a Sandell sensitivity index of 0.60 ng cm^–2 and a relative error of 0.13%. The method is highly specific and has been applied to the spectrophotometric determination of cobalt in low-alloy steels, hydrofining catalysts and high-purity nickel salts.