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

Abstract

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⁻¹ cm⁻¹, with a Sandell’s sensitivity of 3.9 × 10⁻³ μg cm⁻². The method follows Beer’s law up to 3.0 μg Th(IV)ml⁻¹. None of the common cations and anions tested interfere. The detection limit of the method is 0.04 μg 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.