A Spectrophotometric Study of the Chelates of Ammonium Aurintricarboxylate with Scandium, Yttrium, and Lanthanum

The formation of a pink colour produced by the interaction of ammonium aurintricarboxylate (Aluminon) and scandium, yttrium, or lanthanum has been studied to determine the composition, stability and other characteristics of the chelates formed. The absorbance curves of the complexes show maxima at 535 mμ all the etiolates. The compositions of the chelates have been established by three different methods. The apparent stability constants of the etiolates are estimated as 104^-4-104^.9 for scandium, 104^.4-104^.6 for yttrium, and 10^4-1 -104^.5 for lanthanum at pH 5.5 and at 25^°. The chelates are stable over a wide range of pH (i.e. 4.5 to 8.5). The maximum colour formation is attained a pH 5.5 when the mixtures contain greater than 4-fold excess of the reagent with respect to the metal solution and the colour intensity remains unaltered even after keeping the mixture for 12 hours at the room temperature. A tentative suggestion has been made for the position of the chelate ring in the chelates.