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Development of an optical pH sensor based on sol- gel immobilization

The aim of paper was to prepare optical sol-gel sensor for pH determination during acid-base titrations. The sol-gel technology is being increasingly used in optical chemical sensors development. Sol-gels are prepared from two precursor molecules, tetraetoxysilane (TEOS) and propyltrimethoxysilane (pTriMOS) in ethanol as a solvent and HCl solution as a catalyst. The selected pH dye molecules Bromocresol purple and Bromocresol green and their combinations were immobilized inside the gel structure. The immobilization of the sensing layer was proceeded by spin-coating technique. Two types of sensor layer carriers were used, microscope cover slip and PVC foil. Immobilized pH dyes showed almost the same properties as “free” pH dyes in the solution. The influence of the amount of the pH indicator dyes on the UV-Vis absorbance was investigated. The leaching effect in water was observed on all sensor layers. The sensing layer was attached to the bifurcated “Y type” optical fiber to measure the UV-Vis absorbance change during the pH titration, and to determinate the equivalence point of the acid-base titration.

Keywords: sol-gel pH sensor immobilization

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