PRINCIPLE:

The procedure for the determination of Fluoride is based on a process of discoloration carried out by fluoride ions, when they react with zirconium, forming a "colorlesscomplex" (ZrF6²^- ) more stable than the "colored complex" formed by the reaction of zirconium with SPADNS. Therefore, the presence of fluoride in the sample, proportionally decreases the intensity of the red staining (Zr / SPADNS complex ) which is read at 570 nm