Colour reaction of thorium(IV) with bromophosphonazo -mB and tetradecylpyridinium bromide in ethanol-aqueous solution and its analytical application

The colour reaction of thorium( IV) with bromophosphonazo-mB (BPAmB) was studied. It was found that BPAmB reacts with thorium(IV) to form a blue binary complex in pH 1 similar to 2 acidic media, the apparent molar absorptivity was 8.27 x 10(4)L.mol(-1).cm(-1) at 686 nm. In 0.50 similar to 1.00 mol/L hydrochloric acid solution containing a suitable amount of ethanol, a ternary micell complex of Th(IV)-BPAmB-tetradecylpyridinium bromide (TPB) with apparent molar absorptivity up to epsilon = 1.41 x 10(5)L.mol(-1).cm(-1) at 695 nm was formed which can be used for the spectrophotometric determination of thorium (IV). Beer's law is obeyed in the range of 0 similar to 800 mu g/L for Th(IV). This method has good selectivity and high sensitivity, It has been applied to the determination of trace thorium in rock standard samples with satisfactory results.