Spectrophotometric determination of thorium in standard samples and monazite sands based on the floated complex of thorium with N-hydroxy-N,N'-diphenylbenzamidine and thorin

A selective and sensitive spectrophotometric method for the determination of Th(IV) has been based on the reaction with thorin and subsequent extraction of the red-orange coloured complex with N-hydroxy-N,N-diphenylbenzamidine (HDPBA) in benzene as floated complex at pH 2.2. The complex in ethanol exhibits a maximum absorbance at 495 nm, with a molar absorptivity of 6.0×10⁴ lmol^-1cm^-1, with a Sandells sensitivity of 3.9×10^-3 gcm^-2. The method follows Beers law up to 3.0 g Th(IV) ml^-1. None of the common cations and anions tested interfere. The detection limit of the method is 0.04 g Th(IV) ml^-1, the RSD (n=10) is 1.4%. The method has been successfully employed for the determination of thorium in various standard and monazite samples.