Olfactometers

The most noteworthy attempts to remedy this defect are those of. Zwaardemaker, C. van Dam, and Foumie, but for details of the olfactometers devised by them the original papers should be consulted. These instruments are of distinct value for the matching of perfumes but they all suffer from a fundamental defect inasmuch as they make no allowance for the relative vapour pressures of the substances under examination. 

In Alloxysta victrix, 6-methylhept-5-en-2-one 16, which is produced by both males and females, was identified as potentially attractive to the males and slightly repellent to the females in Y-tube olfactometer assays [60]. In this study, the activity was also dependent on prior exposure of the insects to the compound. Naive insects responded more strongly than previously exposed ones. This underscores a second difficulty in the bioassay-guided identification of parasitoid hymenopteran pheromones the responses are very dependent on the context and on prior exposure. Learning has been demonstrated in several species of parasitic hymenoptera [61-65]. 

The existence of volatile spacing cues has been demonstrated in a number of species. Recently, 6-methylhept-5-en-2-one 16 was shown to be slightly repellent in Y-tube olfactometer assays to Alloxysta victrix (see above). The same compound appears to be involved in defense (see below). 

A laboratory where the measurement takes place must be free from odor and is typically air-conditioned with air filtration. The odor sample is placed in an olfactometer that basically is a device for dilution of the sample. Typically, the meter has two outlet ports diluted odorous air flows from one, and clean odor-free air flows from the other. In dynamic olfactometry, panel members assess the two ports of the olfactometer. The assessors indicate from which of the ports the diluted sample is flowing. The measurement starts with a dilution that is large enough to make the odor concentration beyond the panelists threshold. This concentration is normally increased by a factor of two in each successive presentation. Only when the correct port is chosen and the assessor is certain that the choice is correct and not just a guess, is the response considered a true value. 

Latest state of the Olfactometer and guidelines for its use Odour control of pig housing and land spreading Odour control problems in the UK, some case histories Dust filters to reduce odour from broiler houses Legislation in France, some case histories... 

The use of the dynamic or static sampling procedure depends not only on the type of the olfactometer used (mobile or stationary) but also on the field of application, and on the expenses (11). In industry dynamic sampling and mobile olfactometers are preferred (10). However, practical limitations often mean that the analysis will be conducted in a laboratory which implies static sampling (12). In agriculture mobile sniff-cars and large panels are usually too expensive. Therefore simple measuring devices like the Mannebeck-Olfactometer TO 4 were introduced (13). 

Both dynamic and static sampling procedures are suitable for taking samples for olfactometric measurements (15), (16). If the olfactometer and the panel are available close to the source dynamic sampling may be preferred. The equipment for preventing condensation in the sampling pipe and contamination of the sampling pipe and the olfactometer by dust should be provided. 

Four different standards or guidelines for olfactometric measurement are compared and an inventory is made of the diffences between the olfactometers. 

This review concentrates on the olfactometer The sampling procedures are reviewed by J.Hartung and the selection of panelist by M.Hangartner. 

The olfactometer is a device which dilutes odourous air with odour free air. This dilutions are offered to a panel in order to determine the odour threshold. There can be distinguished between static and dynamic dilution... 

Static olfactometers dilute by mixing known volume of two gases in the same vessel. In France they are considered as abandoned since —the consumption of considerable quantities of gas —the time needed for changes in concentrations... 

Dynamic olfactometers dilute the gas by mixing known flow rates of two gases at the same outlet. The dilution factor is calculated from the flow rates. 

In France the olfactometer must be adjust from a dilution factor of 10 up to 10.000 in at least two stages without a factor of more than 100 between one stage and the next. 

As it should be taken for sure that the olfactometer gives the dilution which it is supposed to realize, it is surprising that so little is said about calibration (method and frequency). 

Olfactometry—Odour Threshold Determination—Olfactometers Types 1158 and TO-4... 

The following summery can be given. Odour measurements with olfactometers is only a small part of the whole field of odour determination in ambient air and the measurement of odour nuisance must be approached in the near future with appropriate urgency. 

For some purposes an olfactometer can be installed permanently in a laboratory and used to assess samples generated on the same site or nearby. However, if the samples have to be taken at factories or farms nationwide, then obviously it is impractical to transport the samples long distances and the olfactometer and associated equipment must be sufficiently transportable to set up at different locations. Originally the WSL... 

It must be made clear that WSL has only used olfactometers constructed on its own premises and calibrated by WSL staff one such instrument is the WSL Transportable model. (It is emphasised that this olfactometer is not the same as the commercially-available Portable model.) The WSL Transportable olfactometer and its operation have been described in detail previously (1) and only its main features need be reviewed here. From time to time, certain applications have required a special re-design of the olfactometer, e.g. to measure very weak odours, but the basic principles and the mode of operation have remained unchanged for some years. The main features of the standard WSL Transportable olfactometer are as follows ... 

Table I indicates the 95% confidence limits determined with a WSL high-flow rate olfactometer (1) and suggests various options (underlined) with respect to panel screening, panel size, number of replicate samples and dilution steps ...

The intention here is to list and comment very briefly on the range of tasks to which the WSL Transportable olfactometer has been applied, as background to the views expressed in section 6 on possible standardisation. 

It is known that odour detection thresholds measured by different types of olfactometer can vary substantially. Not unreasonably, there are well-intentioned calls for standardisation of odour measurements , possibly as the basis for odour emission regulations, and so it might be useful to express some cautionary views. 

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