Olfactometer, mixture

The Prosser olfactometer is a commercially-produced version of the portable olfactometer developed by the Warren Spring Laboratory (WSL) (2). The olfactometer (Figs. 1,2) contains two fans, which draw in ambient air through an activated carbon filter to remove extraneous odours and then mix this odour-free air with an odorous air sample before expelling the mixture through either a sample port (fan 1) or an exhaust port (fan 2) at 240 1/min. 

The olfactometer was calibrated using C02, as the odorous gas, diluted in air to 10000 ppm by volume, and contained in a 30 1 Tedlar bag (Fig. 5) (7). C02-free oxygen was used as the diluting gas. The C02 concentration was was sufficiently low to avoid significantly altering the density of the odorous air. The bag was connected by silicon rubber tubing to the rotameter inlets and the diluted gas mixture was sampled via a tube placed inside the nose-piece and analysed by an infra-red gas analyser, with an accuracy of greater than 1% (Fig. 5). 

Presentation of the odors, in unmixed and mixed form, by means of an air dilution olfactometer, which maintains constant stimulus concentration over long periods of time, independent of the stimuli being smelled or not. The Dravnieks mixture olfactometer provides this capability, and has been previously described (6). 

Apparatus. Figure 1 represents the mixture olfactometer used in the study. The apparatus consists of 16 stimuli mixing manifolds. Air at 0.5 L/min to each manifold is supplied through stainless steel capillary tubings from the air distributor manifold the 17th capillary branch serves to monitor the air supply rate. 

Three of the odorants (ammonia, hydrogen sulfide, and trl-methylamlne) were gases. Their dilutions were prepared In thick wall collapsible 18-L containers. Injecting by syringe the needed amount of the odorant gas and filling with air. The dilutions were prepared one day before their use, to allow time for a stabilization after adsorption on the walls. The diluted vapors were then supplied to the mixture olfactometer by a peristaltic pump. 

The mixture olfactometer was set In operation 1-2 hours before the panel session. Panelists circulated among the sniffing ports and characterized the odor quality of the stimuli using a 136-descriptor multidimensional scale, described elsewhere (y it is an extended Harper s scale. ( )... 

Other investigators have further explored catnip oil or the nepetalactone molecules for their repellent effects. Chauhan et al. compared the two primary isomers of nepetalactone with deet and another synthetic amide. The nepetalactone isomers and the racemic mixture of the isomers exhibited repellency that was comparable to deet in the Klun and Debboun (K D) module. However, in the testing on human subjects nepetalactones showed 85% biting deterrence, compared to 96% biting deterrence for deet. A study by Bernier et al. showed that catnip oil was a better spatial repellent than deet in a triple-cage olfactometer. However, deet was a better contact repellent against three species of mosquitoes. They also evaluated the repellency of catnip oil and deet in the presence of a human arm or several chemical attractants (lactic acid, CO2, and acetone). 

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