Response sulfur dioxide sensors

Figure 9.45. Stable response of a Sn02sintered sensor that has been treated with sulfur dioxide. Sensor placed in a tunnelfor 1 month...

A new solid state chemical sensor for sulfur dioxide utilizing a sodium sulfate/rare earth sulfates/silicon dioxide electrolyte has been developed. The addition of rare earth sulfates and silicon dioxide to the sodium sulfate electrolyte was found to enhance the durability and electrical conductivity of the electrolyte. The electrolyte exhibits a Nernstian response in the range of SC gas concentrations from 30 ppm to 1 %. 

Figure 6. Characteristic patterns of response of an array of six sensors coated with different phthalocyanines to various vapor exposures. The maximum concentration was 100 ppm for ammonia, sulfur dioxide, and DMMP and 1000 ppm for water, ethanol, air and benzene. The central metal of each phthalocyanine is shown at the top.

Two disparate translation methods are investigated for the measurement of sulfur dioxide. Both involve interaction with an aqueous solution. In the first, collected S(IV) is translated by the enzyme sulfite oxidase to which is then measured by an enzymatic fluorometric method. The method is susceptible to interference from i CWg) efforts to minimize this interference is discussed. The second method involves the translation of SO2 into elemental Hg by reaction with aqueous mercurous nitrate at an air/liquid interface held in the pores of hydrophobic membrane tubes. The liberated mercury is measured by a conductometric gold film sensor. Both methods exhibit detection limits of 100 pptv with response times under two minutes. Ambient air measurements for air parcels containing sub-ppbv levels of SO2 show good correlation between the two methods. 

Target signatures used were taken from a commercially available database of laboratory-measured absorption spectra and were convolved with the spectral response of the sensor (as were the atmospheric contributions described previously). Target species were determined from the ground truth listing of potential releases provided with the dataset. Species in the target library used were methane, propane, butane, ethane, sulfur dioxide, ethylene, propylene, and benzene. 

Multimembrane systems are another type of potentiometric sensor based on ISEs, wherein the ISE response is modified by an additional membrane of a different function. To this group of sensors belong gas-sensitive electrodes, with a hydrophobic membrane isolating the analyte firom the complex sample medium. The chemical reaction of the gaseous analyte with a component of the solution surrounding the ISE membrane proper directly produces the species to be sensed by the electrode. In food analysis, electrodes used for sulfur dioxide or ammonia belong to this group of sensors. 

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