New technologies are needed for detection and identification of gaseous species in near-real time. Voltammetry, applied to cermet electrochemical cell microsensors, was shown in this study to be promising in its ability to discern and quantify gases. The miniature cermet cells were fabricated from ceramic, metallic, and metal oxide components, and reacted uniquely with gases and mixtures in the atmosphere. Neural net chemometrics algorithms were used to interpret the waveforms to extract information about the presence and concentration of constituent gases. Results to date have shown that these sensors can correctly identify more than thirty electroactive gases while showing a high tolerance for interferents. A single element sensor can determine gas concentrations from the part per million level to the percentage level while arrays provide even better detection and discrimination. This work focuses on four constituents of diesel exhaust: benzene, 1,3-butadiene, acrolein, and acetaldehyde. Voltammetric sensors demonstrated reproducible responses to four concentrations of each constituent spiked into diesel exhaust.
12 Gaseous photo-induced oxidations of a variety of organic compounds by titanium dioxide (TiO2) have been studied extensively in the literature. The response of the organic to photochemical reactions with TiO2 and the extent of organic oxidation are typically measured by monitoring the initial concentration of organic and the oxidation by- products using gas chromatography. In this study, TiO2 sensors are produced by coating and drying films of Degussa P25 TiO2 onto Al2O3 substrates. Tests are conducted at ambient temperatures in a controlled atmospheric cell. Electrical responses from the TiO2 sensors are monitored as the sensors are exposed to a variety of organic compounds in the presence of ultraviolet light. Unique voltammetric `signatures' are obtained from the sensors as they react with specific gaseous organics. These signatures can be used to distinguish and identify gaseous constituents.
KEYWORDS: Sensors, Chemical analysis, Microsensors, Signal processing, Prototyping, Gases, Neural networks, Signal attenuation, Electrodes, Feedback control
Many industrial and environmental processes, including bioremediation, would benefit from the feedback and control information provided by a local multi-analyte chemical sensor. For most processes, such a sensor would need to be rugged enough to be placed in situ for long-term remote monitoring, and inexpensive enough to be fielded in useful numbers. The multi-analyte capability is difficult to obtain from common passive sensors, but can be provided by an active device that produces a spectrum-type response. Such new active gas microsensor technology has been developed at Argonne National Laboratory. The technology couples an electrocatalytic ceramic-metallic (cermet) microsensor with a voltammetric measurement technique and advanced neural signal processing. It has been demonstrated to be flexible, rugged, and very economical to produce and deploy. Both narrow interest detectors and wide spectrum instruments have been developed around this technology. Much of this technology's strength lies in the active measurement technique employed. The technique involves applying voltammetry to a miniature electrocatalytic cell to produce unique chemical 'signatures' from the analytes. These signatures are processed with neural pattern recognition algorithms to identify and quantify the components in the analyte. The neural signal processing allows for innovative sampling and analysis strategies to be employed with the microsensor. In most situations, the whole response signature from the voltammogram can be used to identify, classify, and quantify an analyte, without dissecting it into component parts. This allows an instrument to be calibrated once for a specific gas or mixture of gases by simple exposure to a multi-component standard rather than by a series of individual gases. The sampled unknown analytes can vary in composition or in concentration; the calibration, sensing, and processing methods of these active voltammetric microsensors can detect, recognize, and quantify different signatures and support subsequent analyses. The instrument can be trained to recognize and report expected analyte components (within some tolerance), but also can alarm when unexpected components are detected. Unknowns can be repeat-sampled to build a reference library for later post processing and verification.
Conference Committee Involvement (4)
Chemical and Biological Sensors for Industrial and Environmental Monitoring III
12 September 2007 | Boston, MA, United States
Chemical and Biological Sensors for Industrial and Environmental Monitoring II
3 October 2006 | Boston, Massachusetts, United States
Chemical and Biological Sensors for Industrial and Environmental Security
25 October 2005 | Boston, MA, United States
Chemical and Biological Point Sensors for Homeland Defense II
26 October 2004 | Philadelphia, Pennsylvania, United States
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