Measuring Olfactometer Output in Odor Port

Odors are hard to measure and typical humans have little intuition for how they behave.  However, there are now ways to [relatively] easily measure the concentration of odors in clean air.  These devices are called photoionization detectors (PIDs) and they are used heavily in industry to detect specific volatiles.  Many of these devices are good at quantifying a stable odor source, but lack temporal resolution.  Some companies, however, have elected to make particularly fast PIDs.  One of these is the minPID from Aurora Scientific.  This device gives a measure of odor concentration in clean air with millisecond precision.

We use it routinely to calibrate our odor presentation and it is really the only reason we have solid idea about what odor concentration is being presented to the animal in our odor port.

Routine testing: miniPID (bottom) inserted into one of the odor ports.

The data from the PID are acquired using an A/D board while we present several concentrations of odor, in this case alpha-pinene into the port:

Calibration Output.  Left: odor kinetics measured by PID (blue trace) along with other markers; e.g. final valve opening in port 1 (green), final valve opening in port 2 (red).   X-axis units are seconds, Y-axis units are Volts.  Right: average PID reading for each step of concentration.  In this case concentrations were made by flow dilution in multiples of ~0.7. 

These calibrations are done routinely (every day or every other day) to make sure that the stimulus is controlled and repeatable across sessions.  In addition, we also test to make sure various aspects of odor presentation do not interfere with correct concentration output.  However, this is best saved for another post!