Optical-fibre sensing of fluoride ions in a flow-stream.

The Alizarin Fluorine Blue method for the determination of fluoride has been adapted for use with optical fibres. The reagent was immobilized on a polymer matrix, Amberlite XAD-2, and the reflectance of this reagent phase was measured as a function of fluoride concentration by use of a flow-cell assembly and a bifurcated fibre-optic system. A linear response was obtained for 0.16-0.95mM fluoride at a pH of 4.1, with a response time of approximately 12 min.