The Direct Spectrophotometric Determination of Fluoride Ion

A direct method for the determination of fluoride ion in the parts per million range is described. The color reaction of fluoride ion and lanthanum chelate of 3-aminomethylalizarin- N,N-diacetic acid forms the basis for the spectrophotometric method. The intense blue fluoride complex in a mixed solvent system of 16% dimethylformamide- 84% water is stable and independent of pH in the range of 4.6-5.6. Other halogens and common anions do not interfere in the measurements. Interfering ions are removed through ion exchange separations. Results on the determination of fluorine in selected samples are presented