A rapid spectrophotometric method for determination of fluoride in silicates with the zirconyl-xylenol orange complex

A critical study has been made of the effect of acid concentration and of polymerized and depolymerized zirconyl ions on the formation of ZrO-XO complexes and their stabilities. At an optimum acidity of 0.5-0.6M hydrochloric acid, most of the common cations occurring in silicates do not interfere. Maximum colour development is almost instantaneous for the depolymerized ZrO-XO complex, but takes a few hours for the polymerized complex; the colour is stable for several hours. The absorbance is highest for the depolymerized ZrO-XO complex and decreases with an increase in polymerization of the zirconyl ions. Dissolved oxides of nitrogen affect the stability of the ZrO-XO complex but can be eliminated with urea. A simple, rapid and sensitive spectrophotometric method has been worked out for use of this complex in determination of fluoride in silicates, without separation, after fusion of the sample with sodium hydroxide at 450-550 degrees.