We have designed two odor delivery devices that use a novel approach to achieve mixing of odorant vapor in a carrier stream. The goal of both devices was to eliminate or minimize contamination between odorant channels, allow for flexible (i.e., on-the-fly) generation of odorant mixtures, and to eliminate or minimize the change in airflow to the subject when odorant is presented. Both devices achieve rapid mixing of odorant vapor with a carrier stream in a surface-free environment, which greatly minimizes any chance of cross-contamination and eliminates the need to switch airflow streams when presenting odorant, but still allows for rapid onset and offset. Here, we provide a parts list and schematics/CAD drawings for the custom parts involved.
The Odor Gun
The Odor Gun involves the ejection of odorant vapor from disposable reservoirs into a central carrier stream. It is ideal for screening many odorants in a short time without spending tons of money on a high-channel-count olfactometer or tons of time cleaning out tubing. It's total cost is about $1000, with a cost-per-odorant delivered of about 80 cents. The Odor Gun is described and characterized in detail in [Burton et al.] .
The device is designed to accommodate 8 dedicated channels arising from larger odorant reservoirs, and to achieve high dilutions of odorant. It is ideal for repeated presentations over many trials, for flexibly generating odorant mixtures among the 8 odorants, and for delivering odorant with no additional cue (e.g., valve click or airflow/pressure change) - useful for behavior. The total cost of The Turbulator is about $2300.00 (with deluxe flow control), with zero disposables cost per odorant.
We have compiled information for our odorants useful for delivering the appropriate concentration of odorant during experimentation, as well as for comparing structural and sorption properties of the odorants. The saturated headspace concentration calculations make the simplifying assumption that the odorants behave as ideal gases, though real gases exhibit different properties, such as being more compressible and occupying space. An equation of state which accounts for such differences would provide more accurate measures of these values, though reported constants for such functions are limited. Further, the mixture of the odorant and the solvent is assumed to behave as an ideal mixture; that is, the two are chemically inert, totally miscible at all proportions, and the intermolecular forces of like molecules are equal to those between dissimilar molecules. This is an assumption which is better for certain odorants and worse for others, but is necessary to apply Raoult's Law as the available miscibility/chemical potential information is limited for these systems. The presented dilution factors, owing to the assumptions made, are intended for use as approximations only.
For our lab, medium chain triglycerides oil (MCT oil), also known as caprylic/caproic acid, is used as the solvent because it is highly inert, odorless, inexpensive, and has a low viscosity. It is routinely used as a carrier oil in perfumes and other beauty products due to these properties. In addition, most odorants are readily miscible with this solvent, making it an appropriate choice when considering Raoult's Law.
Download an Excel spreadsheet of information for Wachowiak lab odorants here.