Spectrophotometric and fluorometric determination of cobalt

The reaction of Co(II), pyridine-2-aldehyde-2-pyridyl hydrazone (PAPHY) and eosin at pH 5.6 produces the ternary complex Co(L)(HL)E2 (where HL represents the protonated form of the ligand and E represents the eosinate anion). This complex is extracted by a chloroform-acetone mixture to give a strongly coloured and highly fluorescent extract. Spectrophotometric and fluorometric methods for the determination of Co have been developed with detection limits of 0.017 and 0.008 ppm respectively. Cu(II), Ni, Fe(II), Pd(II) and Hg(II) interfere. The Spectrophotometric method has been successfully applied to the analysis of steels, following ion-exchange separation of Co.