Cellulose based bulk pH optomembranes

The paper presents an efficient technique for the preparation of pH-sensitive bulk optomembranes for fiber optic chemical sensors (FOCS). The method is based on the physical entrapment of the reagent molecules in the bulk of cellulose acetate membranes. The durable immobilization of a pH indicator is achieved by the addition of an appropriate ion-balance reagent to the cellulose matrix. The composition and thickness of the pH-sensitive layer containing Congo red (basic pH chromoionophore) were optimized. The best performance (dynamic range, response time) were obtained for 10 mu m membranes containing 30% of a wetting agent and a hydrophilic plasticizer. The efficiency of this immobilization technique was also verified for unmodified acidic pH indicators: Bromothymol blue and Thymol blue. (C) 1998 Elsevier Science S.A. All rights reserved.