Colorimetric detection of fluoride in an aqueous solution using Zr(IV)–EDTA complex and a novel hemicyanine dye

A new highly sensitive and selective colorimetric method for fluoride determination in water is described. The novel reagent used is a hemicyanine dye (HC), which forms a stable complex with Zr–EDTA, the fluoride-binding site, through the hydroxyl groups. The hemicyanine-chelating Zr–EDTA complex (HC–Zr–EDTA) is ready to react with fluoride ion to release HC. This result in remarkable color change of the sensing solutions from red (λmax = 513 nm) to yellow (λmax = 427 nm) at pH 4.40. When applied to the colorimetric determination of fluoride ions, a linear range from 3.0 × 10−6 to 5.0 × 10−5 mol/L and a detection limit of 2.8 × 10−6 mol/L with a correlation coefficient of 0.9993 can be achieved under the optimized conditions. Because of the specific affinity of fluorides for the [Zr–EDTA], there is little interference by other ions. This method has been successfully applied to the determination of fluorides in toothpaste samples.