Protonated, hydroxo and mixed protonated-hydroxo complex equilibria of the rare earth ions with methyl thymol blue

Abstract

Complexation reactions of the rare earth ions, Y(III), La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III) and Lu(III) with 3,3′-bis[N,N′di(carboxymethyl)-aminomethyl]-thymolsulphonphthalein[methyl thymol blue, abbr. mtb] have been investigated potentiometrically at 30°C. Equilibria studied (at μ = 0.10) under three different situations, (i) considering the presence of metal hydroxo complex, (ii) ignoring the existence of M(OH) species and (iii) assuming 100% metal mtb association, indicate that the equilibrium constants obtained under these situations are highly close.