POLYMER-MEMBRANE pH ELECTRODES AS INTERNAL ELEMENTS FOR POTENTIOMETRIC GAS-SENSING SYSTEMS

The use of polymer-membrane pH electrodes as internal sensing elements for the fabrication of inexpensive ammonia and carbon dioxide gas sensing systems is reported. The pH-responsive polymer membranes are prepared by incorporating tridodecylamine as the neutral carrier in plasticized poly(viny1 chloride) membranes. Both static and continuous-flow gas-sensing arrangements are described. For miniature static gas sensors, the internal polymer pH electrode can be made with or without an internal reference solution. In the latter case, the polymeric membrane is coated directly onto a graphite substrate. The polymer pH electrode can also be prepared in tubular form and used in conjunction with a gas dialysis chamber for automated continuous-flow determinations of carbon dioxide and ammonia. Slopes, response times, and reproducibility of these new gas-sensing systems are evaluated using optimized internal electrolytes, flow rates, and gas-permeable membrane materials. When appropriate reagents and materials are used, the static sensors exhibit slopes in the range 48-62 mV/decade with potentials reproducible to less than +1.5 mV at gas concentrations greater than lo3 M.