OPTICAL SENSOR FOR THE PH 10-13 RANGE USING A NEW SUPPORT MATERIAL

A pH-sensitive membrane has been developed consisting of a polyester support covered with a thin layer of cellulose onto which a pH-indicator is covalently immobilized. The sensor membrane is completely transparent and shows a pH-induced colour change that makes it capable of measuring pH in the 10-13 range. Its performance was studied with respect to relative signal change, reproducibility, and long-term use. The response time for 90% of the total signal change to occur was 1 min. The material has a response that is stable over hours of operation at high pHs. This is in contrast to conventional glass electrodes which tend to become unstable at high pH, but also suffer from interferences due to the so-called alkali error. Hence, this optrode sensor presents an attractive alternative for measuring the pH of highly alkaline solutions as occurring in chemical industry, scrubbers, and waste water treatment plants. The immobilization scheme is of general interest in that it allows immobilization of vinylsulfonyl dyes with a broad variety of pk(a)-values, thereby allowing the design of a variety of pH (and other) sensors possessing the same mechanical support.