Extraction–Spectrophotometric Method for Determination of Fluoride in the Range of Microgram per Liter in Natural Waters

Abstract.

 In this study a new extraction–spectrophotometric method for the determination of fluoride ion in natural waters has been presented by use of octyl chemically bonded solid phase extraction (SPE) cartridge. In this method at first aluminium–oxinate chelate is adsorbed on SPE cartridge, then the water sample (containing fluoride ion) is passed through the SPE device. The excess of oxine on the sorbent is washed with acetate buffer and finally the residual of aluminium–oxinate chelate on the sorbent is eluted by ethanol and its absorbance is read at 375 nm. The decrease of adsorbed aluminium–oxinate chelate on sorbent is proportional to the fluoride ion concentration in the water samples. The detection limit of this method is 80 ng/ml and the linear dynamic range is between 0.1–2 µg/ml. Sensitivity of the method is excellent and absorbance variation for each µg/ml fluoride ion is 0.6 (approximately equal to Eriochrome cyanine R-zirconium standard method and ten times better than the Alizarin complexon standard method). Results of this method have good agreement with the Eriochrome cyanine R-zirconium standard method. Also this method has less interferences as compared with SPADNS standard method.