The influence of the formation of metal-indicator complexes of the M2I species on the accuracy of complexometric micro titrations with photometric end-point determination

Abstract

When micromolar amounts of tervalent and quadrivalent metals such as bismuth, thorium and iron are bound to triphenylmethane dyes and titrated complexometrically, large systematic deviations are found.

There are reasons to suppose that M₂I type complexes are formed. It is shown that if M₂I predominates in solution, the large systematic deviations can be accounted for theoretically. The use of azo-type indicators, such as PAR, TAR and TAN, gives more accurate results.