Xylenol orange, the sodium salt of 3,3′-bis[N,N-di(carboxymethyl)-aminomethyl]-o-cresol-sulphonphthalein, forms a colored complex with zirconium that is decolorized by the presence of fluoride ions. This reaction is used for the spectrophotometric determination of fluoride. The reagent solution, Zr–xylenol orange was prepared by mixing the dye [0.01% (w/v) with depolymerized zirconium solution (0.04% (w/v)] in 20% (v/v) HCl medium [9]. At the time of analysis, 1 mL of reagent solution was added to 4 mL of sample solution (1:4). The resultant color of the mixture was monitored by measuring the absorbance at 550 nm.