IDENTIFICATION OF IRIDIUM WITH BENZIDINE AFTER SEPARATION BY SOLVENT-EXTRACTION

A new method is described for identification of 2.0 mug of Ir after separation from 1.0 mg Rh(III) and 0.50 mg of Pd(II), Pt(IV), Os(IV), Cu(II), Mn(II), Fe(III), Co(II), and Ni(II). The identification is made with benzidine, which is oxidized by Ir(IV) to a blue compound. Ir is very efficiently removed from solutions containing Rh(III) and a number of metal ions by extracting the triphenyl-n-propylphosphonium salt of the lr(IV) chlorocomplex into chloroform. Interference of Pd(II), Pt(IV), and Os(IV) is prevented by preliminary extraction into chloroform of the triphenyl-n-propylphosphonium salts of the corresponding chlorocomplexes, after reduction of lr(IV) to lr(III) by ascorbic acid. The lr(III) chlorocomplex is not extracted into chloroform and also does not react with phosphonium ions. lr(III) is oxidized to lr(IV) by chlorine water, reacted with phosphonium ions, and finally extracted into chloroform. This organic phase is shaken with perchlorate ions, which react with phosphonium ions, and the species is extracted into chloroform; the lr(IV) chlorocomplex is back-extracted into aqueous solution, free from interference. At this point benzidine is added and a blue color appears. (C) 1994 Academic Press, Inc.