Spectrophotometric and analogue derivative spectrophotometric determination of cobalt with 2,2′-dipyridyl-2-benzothiazolylhydrazone

Abstract

2,2′-Dipyridyl-2-benzothiazolylhydrazone (DPBH) reacts with cobalt(II) to form a 1:3 (metal:ligand) complex having an absorption maximum at 530 nm in weakly acidic to alkaline media. The complex, once formed; remains stable even when its solution is acidified by addition of hydrochloric acid. The complex is extractable into chloroform, benzene and 4-methylpentan-2-one. The chloroform extract has an absorption maximum at 504 nm and gives a constant absorbance in the pH range 2.0–9.3. Apparent molar absorptivities and sensitivities for an absorbance of 0.001 in the proposed procedures without and with extraction are 2.50 × 10⁴ l mol^–1 cm^–1, 2.35 ng cm^–2 and 3.43 × 10⁴ l mol^–1 cm^–1, 1.72 ng cm^–2, respectively. Both proposed methods are selective for cobalt and especially in the method without extraction none of the other ions usually encountered interfere in the cobalt determination. Application of one of the proposed methods to the determination of cobalt in standard iron and steel samples and further sensitisation of the methods by employing analogue derivative spectrophotometry are also described.