Electronic nose

An electronic nose is a device intended to detect odors or flavors.

Over the last decade, “electronic sensing” or “e-sensing” technologies have undergone important developments from a technical and commercial point of view. The expression “electronic sensing” refers to the capability of reproducing human senses using sensor arrays and pattern recognition systems. For the last 15 years as of 2007, research has been conducted to develop technologies, commonly referred to as electronic noses, that could detect and recognize odors and flavors. The stages of the recognition process are similar to human olfaction and are performant for identification, comparison, quantification and other applications. However, hedonic evaluation is a specificity of the human nose given that it is related to subjective opinions. These devices have undergone much development and are now used to fulfill industrial needs.

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Other techniques to analyze odors and flavors

In industry, aroma assessment is usually performed by human sensory analysis, Chemosensors or by gas chromatography (GC, GC/MS). The latter technique gives information about volatile organic compounds but the correlation between analytical results and actual odor perception is not direct due to potential interactions between several odorous components.

Electronic Nose working principle

The electronic nose was developed in order to mimic human olfaction that functions as a non-separative mechanism: i.e. an odor / flavor is perceived as a global fingerprint.

Electronic Noses include three major parts: a sample delivery system, a detection system, a computing system.

The sample delivery system enables the generation of the headspace (volatile compounds) of a sample, which is the fraction analyzed. The system then injects this headspace into the detection system of the electronic nose. The sample delivery system is essential to guarantee constant operating conditions.
The detection system, which consists of a sensor set, is the “reactive” part of the instrument. When in contact with volatile compounds, the sensors react, which means they experience a change of electrical properties. Each sensor is sensititive to all volatile molecules but each in their specific way. Most electronic noses use sensor-arrays that react to volatile compounds on contact: the adsorption of volatile compounds on the sensor surface causes a physical change of the sensor. A specific response is recorded by the electronic interface transforming the signal into a digital value. Recorded data are then computed based on statistical models.^[1]
The more commonly used sensors include metal oxide semiconductors (MOS), conducting polymers (CP), quartz crystal microbalance, surface acoustic wave (SAW), and field effect transistors (MOSFET).
In recent years, other types of electronic noses have been developed that utilize mass spectrometry ^[2] or ultra fast gas chromatography ^[3] as a detection system.
The computing system works to combine the responses of all of the sensors, which represents the input for the data treatment. This part of the instrument performs global fingerprint analysis and provides results and representations that can be easily interpreted. Moreover, the electronic nose results can be correlated to those obtained from other techniques (sensory panel, GC, GC/MS).

How to perform an analysis

As a first step, an electronic nose need to be trained with qualified samples so as to build a database of reference. Then the instrument can recognize new samples by comparing volatile compounds fingerprint to those contained in its database. Thus they can perform qualitative or quantitative analysis.

Range of applications

Electronic nose instruments are used by Research & Development laboratories, Quality Control laboratories and process & production departments for various purposes:
in R&D laboratories for:

• Formulation or reformulation of products
• Benchmarking with competitive products
• Shelf life and stability studies
• Selection of raw materials
• Packaging interaction effects
• Simplification of consumer preference test

in Quality Control laboratories for at line quality control such as:

• Conformity of raw materials, intermediate and final products
• Batch to batch consistency
• Detection of contamination, spoilage, adulteration
• Origin or vendor selection
• Monitoring of storage conditions.

In process and production departments for:

• Managing raw material variability
• Comparison with a reference product
• Measurement and comparison of the effects of manufacturing process on products
• Following-up cleaning in place process efficiency
• Scale-up monitoring
• Cleaning in place monitoring.

Various application notes describe analysis in areas such as Flavor & Fragrance, Food & Beverage, Packaging, Pharmaceutical, Cosmetic & Perfumes, Chemical companies. More recently they can also address public concerns in terms of olfactive nuisance monitoring with networks of on-field devices. ^[4]

References

1. ^ [1]
2. ^ [2]
3. ^ [3]
4. ^ [4]