Photometric determination of nickel by means of photochemically generated (Z)-2-thiophenaldehyde 2-pyridylhydrazone

Abstract

The photochemical isomerisation of 2-thiophenaldehyde 2-pyridylhydrazone (TAPH) in ethanolic solution was investigated and the E/Z ratio in the photostationary state was determined. (E)-TAPH scarcely reacted or did not react with metal ions whereas, after irradiation, (Z)-TAPH gave sensitive reactions with several metal ions. A photometric method was developed for the determination of nickel (0.017–0.9 µg ml^–1) in aqueous ethanolic medium (50%V/V) at pH 10.7 with a detection limit of 0.005 µg ml^–1 and a relative standard deviation of 1.03%. By considering the E/Z ratio in the photostationary state, the corrected stoicheiometry of the chelate was found to be 3:1 (ligand to metal). Applications of the method to the determination of nickel in special steels and environmental fume samples are described.