A new type of solid state electrodes sensitive to pH changes is described, in which the chemical-sensitive layer consists of Pt microparticles deposited on a conducting polymer (polyaniline, polypyrrole) blend containing 22.7% w/w zeohte. These sensors are stable in aqueous electrolyte solutions of low pH value at temperatures up to 45 degrees C with response time in seconds. At 25 degrees C, sensor sensitivity was -310 +/- 40 mV/pH and -1300 +/- 100 mV/pH for polyaniline and polypyrrole blends, respectively. Interferences appear to be acceptably small. (c) 2006 Wiley Periodicals, Inc.