Analytical performance of an optical pH sensor for acid-base titration

Abstract The analytical performance of a reflectance optical fibre sensor is described for the determination of pH, particularly that of acid-base titration end-points. The sensor makes use of cresol red immobilized on the anion-exchange resin Dowex 1-X10, has a pH transition interval in the range 5.5–7.5 and uses a PTFE membrane as interface. The sensor r.s.d. is ca. 1% and the accuracy is excellent. It is useful for titrating strong and weak acids (such as HF) with bases and vice versa, and requires very small sample volumes. The sensor can titrate turbid and coloured solutions at different temperatures. The minimum response time necessary after each titrant addition is in the range 0.5–1 min.