TITRIMETRIC MICRODETERMINATIONS OF IRIDIUM (3) AND COBALT (3)

New titrimetric microdeterminations of iridium(III) and cobalt(III) with potassium ferrocyanide are described. For iridium(III), the reaction mixture containing iridium trichloride and potassium ferrocyanide is allowed to stand for 24 hours to effect reduction; whereas with cobalt(III) the reaction with potassium ferrocyanide is instantaneous. In both cases potassium ferrocyanide is added in excess and afterward the remaining excess is titrated against a standard solution of ceric sulfate using N-phenyl anthranilic acid as indicator. With iridium, a green colored complex, [Ir(I)Ir(III)-{Fe(CN)6}2]2-, is formed in the ratio of 1:1. Conductometric and potentiometric measurements show that cobalt (III) with potassium ferrocyanide forms a precipitation complex in the ratio of 1:1. It is peculiar in both cases that the complexes remain unaffected by ceric sulfate as long as potassium ferrocyanide is in excess. The interference due to various cations has been observed in both cases. Ranges in which iridium and cobalt have been estimated vary from 2.3 to 17 mg/liter and 0.42 to 2.14 mg/liter, respectively. For iridium, the method is time consuming but very simple. © 1969.