DETERMINATION OF ZIRCONIUM AND MOLYBDENUM WITH 4,5-DIHYDROXYBENZENE-1,3-DISULFONIC ACID DISODIUM SALT BY ION-PAIR REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

An analytical process based on reversed-phase high-performance liquid chromatography, with ultraviolet/visible detection at 315 nm, was stud ied. 4,5-Dihydroxybenzene-1,3-disulfonic acid disodium salt (Tiron) wa s used as chelating agent. Optimum conditions for the determination of zirconium and molybdenum ions, including the concentration of the buf fer, the pH of the chelating medium and the mobile phase, the concentr ation of Tiron, the time of colour development and the composition of the mobile phase, were investigated. Tiron chelates were eluted within 15 min, with methanol-water (63 + 37) as the mobile phase, which cont ained acetate buffer (1.5 x 10(-3) mol l-1, pH 4.0), Tiron (1.5 x 10(- 3) mol l-1) and tetrabutylammonium bromide (3 X 10(-2) mol l-1). The s eparation was performed with a C18 reversed-phase column. The proposed method was applied to the determination of Zr(IV) and Mo(VI) in a rel atively complex substance, nickel-base alloy. The precision and accura cy of the method were evaluated. The experimental values obtained from the calibration graphs and by the standard additions method were comp ared with the certified values. There was good agreement between these values. With five consecutive injections of 100 mul of sample solutio n, containing 200 ng each of Zr(IV) and Mo(VI), the recoveries obtaine d for Zr and Mo were 97 and 106%, respectively. The detection limits ( signal-to-noise ratio = 3) were 9.0 and 3.6 ppb for Zr(IV)-Tiron and M o(VI)-Tiron, respectively.