Microdetermination of fluoride in water by ion-exchange spectrophotometry

A method for the determination of microgram per litre levels of fluoride has been developed, based on ion-exchange spectrophotometry (IES). The fluoride reacts with slightly polymerised zirconium and xylenol orange and the reaction product is sorbed on Dowex 1-X8 resin. The absorbance of the resin phase at 580 and 750 nm is measured directly. The calibration graph is linear in the concentration range 2–20 µg l–1 and the RSD is 1.8%. The determination limit with 500 ml of sample is 1.1 µg l–1; the sensitivity can be enhanced by increasing the sample volume. The method has been applied to the determination of fluoride in tap and raw water using 500 ml of sample.