ABSTRACT
In 1957, R. W. Stow et al. first described the concept of determining the partial pressure of gas dissolved in a sample by measuring the pH of a thin film of solution separated from the sample by a hydrophobic, gas-permeable membrane. In 1973 J. W. Ross et al. described several gas-sensing probes and their mode of operation and suggested several others which might be feasible. Gas-sensing probes without membranes, otherwise known as "air-gap electrodes", do not differ significantly in principle from gas-sensing membrane probes. Although only gas-sensing probes incorporating glass pH electrodes have so far been considered, in fact it is possible to use other ion-selective electrodes as the basis of practical sensors. The synthetic polymeric materials commonly used to form a gas-permeable, hydrophobic membrane can be divided into two distinct groups, microporous and homogeneous. Like ion-selective electrodes, gas-sensing probes exhibit faster response at high determinant concentrations, becoming more and more sluggish as the limit of detection is approached.
