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Odour Unit (OU) (OUE)
An odour unit is a unit of measure of odour concentration. It is defined as follows:
American and Australian Odour Unit (OU)
One odour unit is a number where a panel is presented odours in decreasing dilution (increasing concentration) until detection. This is termed the detection threshold (DT) and is 1 Odour Unit. Above all, if a sample were diluted 500 times, the odour concentration is 500 dilutions / 1 OU of the sample. This would result in 500 OU. This can be expressed as ‘dilutions to threshold’. However, the panel can only detect at 1OU (the detection threshold) and not 2OU for example.
European Calculation (OUE/m3)
One European Odor Unit, [OUE/m3], is the amount of odourant(s) evaporated into one cubic metre of neutral gas. At standard conditions, it elicits a physiological response from a panel (detection threshold). Above all, This is equivalent to that elicited by one European Reference Odor Mass (EROM), evaporated in 1 m3 of neutral gas. One EROM is equivalent to 123microg n-butanol. Subjects are standardized to n-butanol which is the reference material. When odours are detected at the threshold, it is expressed as a multiple of the reference material.
For reference, 1 EROM ≡ 123 µg of n-butanol ≡ 1 OUE for the mixture of odorants
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