Analytical aspects of some azo dyes from chromotropic acid

Summary Nitroso-SNADNS-4, itself a yellow coloured dye in acid medium forms a reddish-pink colouration with thorium in weakly acid solution. The colour is stable for about 24 hours and to a temperature up to 50C. The thorium complex shows maximum absorbance at the wave length 520 m, while that of the dye occurs at 430 m. The maximum intensity of colour of the thorium complex is shown at aph 2.5. The colour system conforms to Beer's law in a wide range of concentration of thorium and presents a reliable method for the spectrophotometric determination of the metal even in presence of a large number of common ions, the ions interfering are: tin, iron, nickel, cobalt, cerium(IV), zirconium, gold, phosphate and fluoride. The average percentage of deviation of the absorbance index in the determination of thorium is 1.14.Part VI: See Z. analyt. Chem. 167, 105 (1959)