A fiber optic pH sensor using acid-base indicators covalently bound on controlled pore glasses

This paper describes an extensive spectrophotometric study on several acid-base indicators immobilized on controlled pore glass by means of a silylation process. The spectrophotometric properties of the immobilized indicators are at variance with those of the free indicators as far as pH dependence and ranges are concerned. The differing of the spectrophotometric properties of the indicators, when the latter are immobilized on solid supports, can be justified from the point of view of steric hindrance and of the reactivity of the indicators. Particular attention was paid to the pH-sensitive bands and their position. The effect of ionic strength is also investigated. Early tests performed with optical fibers are described.