An extractive-spectrophotometric method for determination of fluoride ions in natural waters based on its bleaching effect on the iron (III)-thiocyanate complex

An extractive-spectrophotometric method based on the bleaching effect of F- ions on the iron (III)-thiocyanate complex extracted into methyl iso-butyl keton (MIBK) is proposed for the determination of fluoride ions in natural waters. This method is a simple and rapid method and there is no need for special and expensive reagents. The experimental conditions such as SCN- concentration, pH and kind of solvent were optimized, and we found that 0.15 M SCN-, pH = 5 and MIBK are the best selections. Limit of detection is 0.1 mg F-/L with a linear dynamic range 0.5-7 mg/L which covers optimum concentration of F ions in drinking water (0.7-1.2 mg/L). Interference of Fe3+ and Al3+ ions was easily eliminated by the extractive procedure using a solution of oxine in chloroform. Finally, the proposed method was used in determination of fluoride content of some real water samples and the obtained results compared with those obtained from the standard method. No significant differences were observed between them.