Measurement of odours by sensory analysis or “olfactometry”

Abstract

Olfactometry or measurement of odours by sensory analysis is used to quantify odours. The available methods are used to measure three variables: odour concentration, odour intensity and odour annoyance. The first two variables are measured by a panel of pre-selected experts and the third relies on a local population panel. Measurement of these three variables can characterise the different odour sources of a site and compare them; it can also characterise the environment of the source of odour.Article available at http://analusis.edpsciences.org or http://dx.doi.org/10. 1051/analusis:2000280188 -the first consists in correctly classifying, by order of odour intensity (see later), solutions of butan-1-ol or pyridine in water; the concentrations of these solutions are evenly distributed in a series from 1 to 1000;-the assessors are then qualified according to their individual perception threshold (see later) for five pure chemical compound (butan-1-ol, hexan-2-one, pyridine, propionic acid and tetrahydrothiophene); for each of these compounds, the individual perception threshold of the assessors should fall within a range of 0.1 to 10 times the perception threshold provided as a reference. That confirms that the aim of the selection is not to keep the most sensitive assessors. This qualification is verified on a regular basis.For the analysis of a gas sample, the operator chooses as far as possible panel members with demonstrated individual perception thresholds that are dispersed in a homogenous manner. The representativeness of the population sample formed by the panel depends directly on the number of the members: the higher is the number of panel members, the more reproducible and reliable is the measurement. Therefore, a compromise has to be reached between the cost and the validity of the results. At least 16 panel members is recommended if a good precision on the measurement result is required, 6 to 8 panel members in most cases and 4 panel members for comparative measurements. SamplingThe sampling of odorants is an important part in measuring the odour. It conditions the quality and reliability of the results of the measurement. In France, standard NF X 43-104 [3] describes different gas sampling procedures according to the type of source and analysis, as well as the conditions for the storage and the transport of the samples. The methods described in this standard include odorous atmospheres and then apply to olfactometric analysis (sensory analysis) as to physico-chemical analysis.The sources of odour can be release from stack (channelled sources), surface of a liquid, semi-liquid or solid material (diffuse sources such as lagoons, basins in sewage treatment plants, etc.) or the whole of a building with all of its openings when the release are not channelled.In the case of channelled sources or buildings with openings, the sampling probe is introduced in the gas studied that means in the release stack or directly in the ambient air of the building.In the case of diffuse sources, whether or not artific...

Chemical composition of household malodours – an overview

“…Gas chromatography–olfactometry allows independent odour assessment of each compound eluting from the chromatograph, at the exact concentration that was collected. Once a key odorant has been identified there are various techniques for assigning the level of odour contribution including combined hedonic aroma response measurement, aroma extract dilution analysis and XXXXX (Osme) . Comparison with the malodour source can assist in the determination of which detected components contribute to the odour.…”

“…Once a key odorant has been identified there are various techniques for assigning the level of odour contribution including combined hedonic aroma response measurement, aroma extract dilution analysis and XXXXX (Osme). [65][66][67][68][69][70][71][72][73][74] Comparison with the malodour source can assist in the determination of which detected components contribute to the odour. However, these approaches cannot account for syngeries that may take place upon combination of odorants.…”