Gas-sensing probes

Arnold M.A., Ostler T.J., Fiber optic ammonia gas sensing probe, Anal. Chem. 1986 58 1137. 

An electrode for the determination of L-aspaitate is constructed by chemical immobilization of L-aspartase on an ammonia gas-sensing probe. The electrode response is linear in the concentration range 0.7-20 mM with aslope of—59 mV/ decade. The biosensor is stable for more than 20 days (299). 

A gas-sensing probe is a galvanic cell whose potential is related to the concentration of a gas in a solution. Often, these devices are called gassensing electrodes in instrument brochures, which is a misnomer. 

Figure 21-17 illustrates the essential features of a potentiometric gas-sensing probe, which consists of a tube containing a reference electrode, a selective ion electrode, and an electrolyte solution. A thin, replaceable, gas-permeable membrane attached to one end of the tube serves as a barrier between the internal and analyte solutions. As can be seen from Figure 21-17, this device is a complete electrochemical cell and is more properly referred to as a probe rather than an electrode, a term that is frequently encountered in advertisements by instrument manufacturers. Gas-sensing probes have found widespread use in the determination of dissolved gases in water and other solvents. 

Although sold as gas-sensing electrodes, these devices are complete electrochemical cells and should be called gas-sensing probes. 

The only species that interfere are other dissolved gases that permeate the membrane and then affect the pH of the internal solution. The specificity of gas probes depends only on the permeability of the gas membrane. Gas-sensing probes for CO2, NO2, H2S, SO2, HF, HCN, and NH3 are now available from commercial sources. 

How does a gas-sensing probe differ from other membrane electrodes ... 

Gas-sensing probe An indicator/reference electrode system that is isolated from the analyte solution by a hydrophobic membrane. The membrane is permeable to a gas the potential is proportional to the gas content of the analyte solution. 

To conclude this section, it is intriguing to observe how developments in instrumental analysis have led to an increase of sensitivity and a dramatic decrease of analysis time required by procedures based on isothermal distillation. The method of Conway, developed more than 35 years ago [4.11], still in use in clinical and pharmaceutical laboratories, requires many hours to perform an assay of a volatile species. The samples are kept in small, enclosed chambers containing the donor and the acceptor liquid, respectively, and after the diffusion process has reached equilibrium, the acceptor liquid is titrated. Gas-sensing probes, which operate on the principles of ion-selective electrodes, separated from the... 

During the past three decades, several gas-sensing electrochemical devices have become available from commercial sources. In ihe manufacturer literature, I hose devices are often called gas-sensing "electrodes. figure 2.1-12 shows that these devices arc not, in fact, electrodes but instead are electrochemical cells made upof a specific-ion electrode and a reference electrode immersed in an internal solution retained by a thin gas-permeable membrane. Thus, gas-sensing probes is a more suitable name for ihese gas. sensor.s. 

FIGURE 23-12 Schematic of a gas-sensing probe for carbon dioxide. 

Table 2,5-5 lists representative gas-,sensing probes that are commercially available. An oxygen-sensitive probe is also on the market it, however, is based on a voliammetrie measurement and is discussed in Chapter 25,... 

Figure 11. Membrane phases involved in the response of the fiberoptic ammonia gas-sensing probe.

Figure 12. Glutamate response curve from the glutastate biosensor based on glutamate oxidase and the fiber-optic ammonia gas-sensing probe.

Solid-State Liquid Membrane Gas Sensing Probes Enzyme Electrodes Clinical Applications Food Applications Water Applications... 

See alsa Elemental Speclatlon Overview. lon-Selec-tive Electrodes Liquid Membrane Gas Sensing Probes. pH. Sensors Overview Amperometric Oxygen Sensors ... 

See also Enzymes Enzyme-Based Electrodes. Glasses. Ion-Selective Electrodes Overview Gas Sensing Probes Enzyme Electrodes. pH. Sensors Overview. 

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