Direct and derivative spectrophotometric determination of thorium with 2,4-dihydroxybenzaldehyde isonicotinoyl hydrazone

A simple and sensitive spectrophotometric method is developed for the deter mination 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 mu g/ml of thorium(IV). The molar absorptivity and t he Sandell's sensitivity of the method are 2.20.10(4) l.mol(-1).cm(-1) and 0.0106 mu g/cm(2), respectively. The interference of various ions was studi ed. 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 maxim um amplitude at 415 nm. Thus a sensitive derivative spectrophotometric meth od for the determination of Th(IV) is proposed.