Electronic nose odors

These results demonstrate the ability of the electronic nose to remember the odor of different analytes and to recognize them over extended periods of time. Therefore, we are able to create an odor memory library that can be maintained from one array to another over time10. 

A sensor array named the electronic nose is a rapid and relatively simple technique that can be used for monitoring wastewater odors (Stuetz et al., 2000). The electronic nose uses sensors of varying affinities to characterize an odor without reference to its chemical composition. 

In the last decade much effort has been oriented to the fabrication of artificial olfaction machines able to determine chemical images (also odor images) of complex volatile compounds. Today many different electronic noses and tongues are available for odor detection and classification and for the creation of chemical images of liquids. 

Common electronic noses are so called as they are often aimed at detection of odorous compounds it is generally not clear that discriminations are based on odorous rather than non-odorous, and possibly incidental, components of the headspace. In the headspace of a food sample, odorants contributing to the flavour may be present in low concentrations, whereas non-odorous molecules can be present in much larger numbers and higher concentration. In such cases. 

Borjesson, T., Eklov, T., Jonsson, A., Sundgren, H., Schnurer, J. (1996) Electronic nose for odor classification of grains. Cereal Chem. 73 457-461. 

In the old days. chemists prided themselves on their ability to identify compounds by odor. Smelling unknown chemicals is a bad idea because some vapors are toxic. Chemists are developing electronic noses to recognize odors to assess the freshness of meat, to find out if fruit is internally bruised, and to detect adulteration of food products.13... 

Interdigitated electrodes coated with conductive polymer to create an electronic nose. The conductivity of the polymer changes when it absorbs odor molecules. The spacing between fingers is 0.25 mm. 

Electronic nose technology relies on the use of solid-state sensors, which can either be chemoresistors, chemodiodes, or electrodes. Primary odors are... 

This technology allows the analyzers to be small, credit card-size devices. A sensor can be designed to be as specific or as broad in application as desired. There are many possible applications in industrial operation and safety. Wherever an odor can be used to detect the presence or even absence of a substance, these electronic noses can be used. From a water pollution perspective, the analyzer that detects the odor of hydrocarbons in water is valuable. 

It is tempting to speculate if metabolic shifts and shifts in the physiological state of the culture can be more precisely monitored with the electronic nose. Physiologically important odorant metabolites in antibiotic strains such as geosmin and oxolone have been analyzed with conventional methods in the fermentation off-gas [38]. Recently, responses from electronic noses have been possible to relate to plasmid copy number [39]. Other types of intracellular shifts, such as viral infection, inclusion body formation or increase in mRNA level, could challenge the capacity of electronic noses. 

Special problems are related to odor measurement, its quantification and to odor policy (Frechen, 2000). Odors usually consist of many different compounds of very low concentrations that may exert synergistic or antagonistic effects. Four generally accepted dimensions of odor exist which include the concentration of odorants, the intensity of odor, its character, and its hedonic tone (i. e. its pleasantness or unpleasantness). It is extremely difficult to relate conventional analytical measurements (e. g. gas chromatographic determinations or sensor array measurements with an electronic nose ) to the intensity, character, and hedonic tone of an odor perceived by the human nose. 

It is obvious that this method of odor measurement is a very time-consuming and expensive method. However, Stuetz et al. (2000) were able to correlate the global parameters BOD, COD and TOC of sewage samples by headspace measurements of odor using a commercial sensor array system. Thus, the electronic nose seems to have several interesting applications in wastewater treatment technologies. 

VAN DEVENTER D and MALLiKARJUNAN P (2002), Comparative performance analysis of three electronic nose systems using different sensor technologies in odor analysis of retained solvents on printed packaging , J Food Sci, 67(8), 3170-3183. 

The human nose and tongue are excellent quality-control sensors. For example, we can tell whether food is spoiled by its disagreeable odor and taste. Because it s impractical to use humans as sensors in industrial settings, several companies are now developing electronic noses. 

Another type of electronic nose was developed at Lund University in Sweden specifically to detect the odors associated with spoiled fish. In this case the sensor uses two enzymes linked to a polymer to detect the presence of amines such as histamine, putrescine, and cadaverine. Such amines are produced by microbes as fish spoil. 

Recent advances in the technology of multisensor arrays and neural computing have made the development of the electronic nose of great interest to the food industry for discrimination between odors (26). Provided the instrument has been calibrated properly, the technique is rapid, nondestructive, and objective. Shen et al. (27) found the electronic nose was capable of measuring changes in volatile compounds associated with lipid oxidation in canola, com, and soybean oils stored under accelerated conditions and Aparicio et al. (28) found the electronic nose could be calibrated to detect rancidity levels in good quahty ohve oil spiked with rancid olive oil. 

J.L. Solis, L.B. Kish, R. Vajtai, C.G. Granqvist, J. Olsson, J. Schnurer, V. Lantto, "Identifying natural and artificial odors through noise analysis with a sampling-and-hold electronic nose". Sensors and Actuators B 77 (2001) 312. 

Several instruments have emerged in the marketplace and have been popularly described as electronic noses . In reality, these are volatile chemical sensor arrays. To give them more likeness to the human nose (or, more accurately, olfactory system), they are coupled to artificial intelligence systems that require development. The instruments currently available detect most vapours, odorous and non-odorous, including water vapour (to which they are all highly sensitive). Sensitivity to other volatiles, however, is highly variable, dependent... 

One of the main advantages of the electronic nose for malodour measurement is the possibility to use it as a field continuous monitor of odorous emissions (Nicolas and Romain 2000). This technique has probably the best potentialities to answer to the expectations of the various actors of the environmental problems in relation with the odour annoyance. 

Aromas and odors are mixture of different classes of chemical species often found in foods, beverages, and medicines. It is difficult to use a single chemosensor to discriminate these analytes. Sensor arrays, in which different sensor elements are used with data analysis, and subsequent pattern recognition will make it possible to characterize gas mixtnres quantitatively or odors qualitatively. Sensors that incorporate pattern recognition software are usually referred to as electronic noses [74]. Recently, there has been much interest in the composition of the suites of organic vapors emitted by food products. 

British and Italian researchers have reported on the use of an electronic nose for the detection of moulds in libraries and archives [38], The aim was to ascertain whether the device could be suitable for detecting mould activity on paper. It was fonnd that it was possible to discriminate in vitro between affected and unaffected (by mould) paper samples at both 100% and 75% relative humidity by measuring the odor hngerprint. Three different species of actively growing fungi were detected and cluster analysis allowed differentiation between specific species. However, PCA indicated that only samples analyzed at 100% RH could be separated, suggesting that further research is required before electronic nose technology could be applied. 

Portable electronic noses were used for outdoor air monitoring of sewage odors. One conducting polymer system and one MOS nose were used to compare results... 

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