Spectrophotometric determination of osmium: Anthranilic acid as a reagent

Abstract

Anthranilic acid has been found to be a highly sensitive reagent for the spectrophotometric determination of osmium(IV), osmium(VI) and osmium(VIII) at pH 6.0. In all three valence states the metal reacts with the reagent to form a dark-violet coloured compound, which shows maximum absorbance at 460 mμ. Osmium(IV) can be determined in the presence of diverse ions, if EDTA (disodium salt) is used as a masking agent. The optimun concentration range for the method is 2 to 6 p.p.m. of osmium(IV), where the % relative error per 1% absolute photometric error is only 2.8. By applying J ob's method of continuous variation, the molar ratio method and the slope ratio method, it was established that a 1 : 1 complex is formed between osmium(IV) and the reagent. The reaction of the reagent with osmium tetroxide or osmate indicates that the reagent is first oxidised and that then the reduced osmium(lV) forms a 1 : 1 complex with unoxidised excess reagent. The complex is stable in water and alcohol and has an average dissociation constant of 4.6 · 10 -5.