SPECTROPHOTOMETRIC INVESTIGATION OF THE COMPLEXATION EQUILIBRIA OF ZIRCONIUM(IV) WITH LAWSONE AND DETERMINATION OF ZIRCONIUM

The complexation equilibria of zirconium(IV) with lawsone (2-hydroxy-1 ,4-naphthoquinone) have been studied spectrophotometrically in 40% (v/ v) ethanol at 20 degrees C and at an ionic strength of 0.1 M (NaClO4). A complete picture of the solution equilibria in the pH range 1.5-4.0 is presented. The absorbance vs. pH graphs were analysed to character ize the complexation equilibria in solution. A simple, rapid, selectiv e, and sensitive method for the spectrophotometric determination of zi rconium is proposed based on the formation of Zr(lawsone)(2) at pH 3.3 (lambda(max) = 450nm, epsilon = 1.13 x 10(4) 1 . mol(-1) . cm(-1)). Th e interference caused by a number of ions can be masked by the additio n of cyanide. The method has been applied to the determination of zirc onium in some synthetic samples.