Chelates of Hf(IV) with eriochrome cyanine-R and pyrocatechol violet and their applications

Eriochrome cyanine-R(ECR) forms 1:1 and 2:1 (metal-ligand) chelates at pH 1.0 (520 nm) and 1.8 (560 nm) respectively. Pyrocatechol violet (PCV) also forms 1:1 and 2:1 chelates at pH 0.8(525 nm) and 2.0 (590 nm) respectively. The type of equilibria involved and reacting species of Hf(IV) participating in the reaction have been studied. The colour remains stable for 8 to 24 hr depending on the pH. Above pH 2.2, the complexes get precipitated due to the preferred hydrolysis of Hf(IV). Chelate formation constants, Beer's law range, molar absorptivity, sensitivity, effect of temperature and reagent concentration etc., have been evaluated. Certain masking reagents are suggested for eliminating the effects of some interfering cations like Th(IV), Zr(IV), Fe(II), Fe(II) and UO2(II). Suitable procedure for the determination of micro amounts of Hf(IV) is also described. (author)