Spectrophotometric titration of resorufin and resazurin with iron(II) in strong phosphoric acid medium and resorufin as a new redox indicator in the reductimetric titration of some metal ions

Spectrophotometric titration methods have been developed for the determination of micro-gram quantifies of resazurin and resorufin and the analysis of their binary mixture using iron(11) as a reductant in high concentration of orthophosphoric acid (10.5 M) medium. Both resazurin and resorufin are reduced to a blue-green semiquinone (lambda(max) 640 nm) with iron(II) in three electrons and one electron reduction steps respectively. Resorufin his been proposed as a new advantageous redox-indicator in the determination of V(V), V(IV), Mo(VI), Cr(VI), Cu(II), Sb(V), As(V), Os(VIII) and Ir(IV) in phosphoric acid medium using the same reductant.