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 thorium 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 x 104 l x mol-1 x 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. (author)