Interactions of uranium and thorium with arsenazo III in an aqueous medium

Complex formation of arsenazo III with U(IV), U(VI) and Th(IV) was examined using spectrophotometric techniques together with computational methods. U(VI) (added as UO22+) forms only a 1: 1 complex at pH 1.5, and in 6 M HCl and HClO4. Both U(IV) and Th(IV) form ML and ML2 complexes in 6 M HCl. The arsenazo III-U(IV) and Th(IV) system in 6 M HCl has isosbestic points, although there are more than two absorbing species in equilibrium.