Spectrophotometric studies of ruthenium(III)and rhodium(III)-oximidobenzotetronic acid complexes and the simultaneous determination of the two metals

Ruthenium(III) and rhodium(III) form stable coloured complexes in ethanolic solution with oximidobenzotetronic acid (OBTA). Ruthenium forms a purple-violet Ru(OBTA)(3) complex at pH 1.1-3.5, which is stable over the pH range 1.1-11.3. Rhodium(III) forms a yellowish-brown complex, RhCl(2)(OBTA)(2), at pH 2-8; at higher pH (11.5 and above) the complex is reddish-brown, but has the same Rh:OBTA ratio. A method for the simultaneous determination of these two metals is proposed, and the interference by commonly occurring ions has been investigated.