Reversible Indicators For Alkali Metal Ion Optical Sensors

An indicator system that responds reversibly to alkali metal ion concentrations has been developed. The components of the indicator system include the Cu(II) complex of aqueous polyethylenimine, an anionic fluorophor, and a neutral ionophore immobilized by adsorption on silica particles. In the absence of alkali metal ion, the anionic fluorophor binds to the Cu(II)-polyethylenimine complex where the presence of the paramagnetic Cu(II) ion causes quenching. When an alkali metal ion is present, it complexes with the ionophore forming a hydrophobic cation which binds to some of the anionic fluorophor rendering it fluorescent. The fluorescence of the indicator can be measured through optical fiber resulting in a reversible sensor for alkali metal ions.