Direct and Derivative Spectrophotometric Determination of Thorium with 2,4-dihydroxybenzaldehyde Isonicotinoyl Hydrazone

A simple and sensitive spectrophotometric method is developed for the determination of throium in aqueous medium. The metal ion forms yellow coloured complex with 2,4-dihydroxybenzaldehyde isonicotinoyl hydrazone (2,4-DHBINH) in the pH range 2.0–8.0. The complex shows an absorption maximum at 390 nm. The absorbance of the complex is maximum at pH 5.5 Beer's law is obeyed in the range 0.30–7.00 μg/ml of thorium(IV). The molar absorptivity and the Sandell's sensitivity of the method are 2.20· 104 l·mol−1·cm−1 and 0.0106 μg/cm−2, respectively. The interference of various ions was studied. The composition of the complex is 1:1 {Th(IV) : 2,4-DHBINH}. The first derivative spectrum of the complex shows a zero cross at 391.2 nm and maximum amplitude at 415 nm. Thus a sensitive derivative spectrophotometric method for the determination of Th(IV) is proposed.