CHELATOMETRIC MICRO-DETERMINATION OF ZIRCONIUM

In this communication, the use of Methylthymol Blue, Xylenol Orange, 4-(4′-nitrophenylazo)catechol, Eriochrome Black T and 2-hydroxyl-4-sulfonaphthalene-azo-resorcinol as indicators for the chelatometric micro-determination of zirconium has been studied.The results are summarized as follows:■ Among the metallochromic indicators studied, Methylthymol Blue and Xylenol Orange may be regarded as the best ones for the chelatometric micro-determination of zirconium, because they can be used over a wider acidity range and titratable range, and possess very sharp end-point. The effect of diverse ions for chelatometric micro-determination of zirconium with Methylthymol Blue and Xylenol Orange as indicators is also reported. The interference of iron(Ⅲ) can be eliminated by hydroxylamine. Thorium(Ⅳ) and titanium(Ⅳ) do not interfere even up to 10 mg. The tolerable amounts for some ions in the titration are Sn(Ⅳ), 0.2; V(Ⅴ), 2.7; W(Ⅵ), 0.3; Cu(Ⅱ), Mn(Ⅱ), AI(Ⅲ), RE(Ⅲ), Bi(Ⅲ),Cr(Ⅵ), Mo(Ⅵ) and U(Ⅵ), 5.0 mg. Large amounts of nitrate, sulfate, tartrate, and citrate ions exert no effect, while microgram amounts of fluoride, oxalate, phosphate and ascorbate ions, as well as hydrogen peroxide, interfere seriously and must be removed before titration. Besides, eight further indicators, namely Acid Chrome Blue K, Alizarin S-methylene blue, Chrome Azurol S, 2,4-dinitrophenylazocatechol, Eriochrome Cyanine R, gallocyanine, haematoxylin and Stilbazo, have been tested and found to be inferior to the above mentioned ones for this very purpose.