Sulphur dioxide sensors

Worrell WL, Liu QG (1984) A new sulphur dioxide sensor using a novel two-phase solid-sulphate electrolyte. J Electroanal Chem 168 355-362... 

Figure 5.20 — Reversible flow-through optical waveguide gas sensors using a reagent immobilized on the inner walls of the tube for the determination of moisture (water) (A) and sulphur dioxide (B). For details, see text. (Reproduced from [64] and [65] with permission of the American Chemical Society and Elsevier Science Publishers, respectively).

Several combined electrodes have been developed to measure dissolved gases such as carbon dioxide (CO2), ammonia (NH3) and sulphur dioxide (S02). These sensor-like electrodes contain an internal solution that is isolated from the external solution by an impermeable membrane. The membrane forbids the passage of water or ions but is transparent to gas molecules dissolved in solution (Fig. 18.4). 

Poly(phenyl ester) dendrimers with six terminal platinum chelate complex units were used as highly selective sensors for sulphur dioxide, considered partly responsibly for the formation of smog and acid rain. In the presence of hydrogen peroxide or sunlight and ozone, S02 is oxidised to S03. The latter reacts spontaneously with water to form sulphuric acid. That is the reason why detection of minimal concentrations of sulphur dioxide with appropriate sensors is necessary. The arylplatinum(II) complexes attached to the molecular periphery of the dendrimers absorb sulphur dioxide with formation of a pentacoordi-... 

Nickel or cobalt proved useful candidates for providing the reference system (Imanaka et al. 1987a). The sensors, operating at 900-1000 K, were shown to respond to sulphur dioxide concentrations in the 30 ppm to 1% range. Such sensors have been developed further towards commercial application (Adachi and Imanaka 1991, Adachi and Imanaka 1995). 

Korotchenkov GS, Dmitriev SV, Brynzari VI (1999) Processes development for low cost and low power consuming SnOj thin film gas sensors (TFGS). Sens Actuators B 54 202-209 Lalauze R, Bui N, Pijolat C (1984) Interpretation of the electrical properties of SnO gas sensors after treatments with sulphur dioxide. Sens Actuators 6 119-125... 

Selectivities of BAW sensors differ according to their acceptor layer. Whereas palladium is highly selective for hydrogen, organic amines are only weakly selective for sulphur dioxide, and carbowaxes (well known as stationary phase in chromatography) interact with numerous non-polar gases, hence they are non-selective sensors for hydrocarbons. Response time also varies within a wide range. 

Numerous catalytic layers made by different immobiUzing techniques have been used to enhance the selectivity of amperometric sensors. One example chosen from a large variety was a platinum microelectrode coated with polyvinylpyridine carrying a layer of anodicaUy deposited paUadium/iridium oxides (Shi et aL 2001). Polyvinylpyridine is an electricaUy conducting polymer. The sensor has been used to determine sulphur dioxide in gaseous phase as weU as sulphite in solution. 

Applications for the lithium-sulphur dioxide reserve systems include underwater mine batteries and (active batteries) memory protection, manpack communicarions, life-support equipment, sonobuoys, space probes, missiles, mines, security systems, data buoys/stations, weather sondes and electronic counter measures. The non-reserve (active) systems are used for covert sensors, memory protection and weather sondes. 

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