The tin oxide electrochemical sensor is the active component in the personal breathalyzer used for ethanol detection. The sensor works by ethanol vapor reacting with oxygen species adsorbed to the SnO2 surface, then releasing trapped electrons back into the conduction band which changes the output voltage. However, to the best of our knowledge, the analytical characterization of this sensor for other volatile organic compounds has not been explored. This sensor, about 1.6 cm in diameter and length, with a hard-wired resistor, is commercially available for less than $10. Only a 5 volt power supply and a voltmeter for readout are required to complete the instrument. Reproducible headspace in 12 mL glass vials was optimized using a plastic test tube cap with a small hole to insulate heating of the solution by the sensor. Response time for detection of concentrated alcohol solutions to a consistent mV plateau value was about 120 sec. Application to following the proof during the distillation of ethanol or percent isopropanol in rubbing alcohol products appears feasible. Determination of ethanol in beer, wine, and rum has compared favorably to such analysis done by indirect HPLC. Amines such as tetramethylethylenediamine as well as other oxygenated organic compounds such as ketones, ethers, and esters are detected easily by this sensor at low percentages. Freshness of chicken, shrimp, and salmon as small samples in a plastic microwell plate were monitored in close proximity by the sensor for about 10-14 days. A maximum response at about 50-75 hr was observed for the room temperature chicken and shrimp samples indicating spoilage. These samples stored in the refrigerator showed a significantly lower quite stable response. Both room temperature and refrigerated salmon showed similar response curves as a function of time to a maximum of 250-300 hr. The spiciness of various curry seasonings have also been correlated to the label description using microwell detection.
Author: Ruyu Yan
Advisor: Dr. Neil D. Danielson, Department of Chemistry and Biochemistry
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