CHELATOMETRIC MICRO-DETERMINATION OF THALLIUM

In this paper,the use of 4-(2-Pyridylazo)-resorcinol (PAR), 2-(2-Thiazolylazo)-5-diethylaminop henol (TAE), 4-(2-Pyridylazo)-2-naphthol (PAN), Xylenol Orange (XO), 2-(2-Benzothiazo lylazo)-5-diethylaminophenol (BAE), Methylthymol Blue(MTB), 4-(2-Thiazolylazo)-resorcinol (TAR), and 1- (2-Thiazolylazo)-2-naphthol (TAN) as indicators for the direct chelatometric micro-determination of thallium(Ⅲ) are compared. The results are summarized as follows: Indicator optimum acidity in PH Titratable range in mg Tl Relative error % E. P. Colour change PAR 2.7-5.8 4-504 -2.2 to 2.5 Red to yellow TAE 3.4-6.0 4-504 -4.0 to 1.5 Blue- violet to pink PAN 3.7-6.1 4-504 -2.9 to 1.2 Red to orange XO 3.5-5.7 4-504 -2.5 to 2.8 Purple to Yellow BAE 3.3-5.7 10-504 +0.1 to 3.3 Blue-violet to pink MTB 3.8-5.8 10-504 -1.5 to 0.2 Blue to yellow TAR 4.3-6.2 10-504 -1.5 to 2.2 Red to yellow TAN 4.8-6.0 50-504 -3.6 to 0.6 Violet to Brown Among the metallochromic indicators studied,PAR,TAE,PAN and XO are preferred for the direct chelatometric microdetermination of thallium. 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 the direct chelatometric micro- determination of thallium(Ⅲ) with PAR XO and TAE as indicators and the elimination of some interfere ions are also reported. Besides, with PAR as indicator, the thallium in the lake water and the waste water is determinated and consecutive micro-determination of thallium (Ⅰ ) and thallium (Ⅲ) are also reported.