Smell plays a great role in our feeling of comfort and the appreciation of odour is greatly subjective. The human odour analysis is a very complex process linking the olfactive epithelium in the nasal cavity to the brain by nervous stimulation. For qualitative analysis the human nose is still the best tool and is reserved to “good noses”. For quantitative analysis where the odour intensity is measured, the dynamic dilution olfactometer is the more accurate method for now. Using a panel of persons, odour dilution is done according to a specific protocol and the responses of the panel is analyzed to evaluate the odour intensity. This method is in constant development and is considered a worldwide reference for normalization recommendations; odour units per m3 are used when odour intensity is evaluated.
In the last 10 years considerable work has been done to develop electronic noses. Many “chemical sensitive” materials with specific physical and chemical properties have been developed to react to the odour chemical components. With some materials, the reactions will produce a change in their electric resistance (MOS: Metal Oxide Sensor) or in their conductance (CP: conducting polymer) or with the QCM (Quartz Crystal Microbalance) and the SAW (Surface Acoustic Wave Sensor) a change in the oscillation frequency of the material will be measured depending of the mass of the adsorbed substance. The analysis of the signals obtained with these materials is very complex. In selecting and developing a nose it is important to consider if the results obtained are consistent over a number of samples, in time for a specific sample, and also for a sample from one machine to another(especially for comparisons between laboratories) and also to make sure that the nose is sensitive but robust and has a good lifetime. The results obtained with the nose have t be well analyzed and various methods are available.
The electronic noses are used in the food industry, the cosmetic industry and in environment to measure very specific chemicals.

This article is very interesting and gives a lot of information necessary to understand better all the processes in human smell and electronic nose. The dynamic dilution olfactometer is the method considered internationally as the electronic noses are developed for more and more applications.