Potentiometric pCO2 sensor using polyaniline-coated pH-sensitive electrodes

A very simple method of constructing a differential pCO(2) sensor device is described, using polyaniline-based pH electrodes in place of the pH-ISFET-based system employed previously. The polyaniline:film-coated Pt electrode. was shown to exhibit not only an enhanced potentiometric pH response but also a greatly reduced oxygen sensitivity compared with the uncoated Pt electrode. The proposed differential system employs two identical polyaniline electrodes to make a pCO(2) probe and a reference electrode. Both electrodes are made by coating the polyaniline surface with a gas-permeable silicone rubber membrane doped with valinomycin. The pCO(2) electrode is covered with a hydrogel-based recipient layer inside the gas-permeable membrane whereas the reference electrode does not have the hydrogel layer. In this sensor configuration, the emf differences between the pCO(2) and the reference electrodes serve as analytical signals and hence the ion responses caused by the two parts of the outer gas-permeable membranes cancel out. The polyaniline-based gas sensor system was shown to provide better emf stability than the uncoated Pt electrode-based counterpart.