Respirometry: anhydrous drierite equilibrates with carbon dioxide and increases washout times

Respirometry is a standard technique in comparative physiology laboratories, with measurements of rates of O(2) consumption and CO(2) production available for hundreds of species. A common recommendation when carrying out respirometry is that water vapor be removed from the air stream before entering the analyzer. Often, this is accomplished with the use of chemical desiccants, such as Drierite. However, here we show that Drierite has an affinity for CO(2) when new and completely anhydrous, and therefore it has an adverse effect on the washout characteristics of this gas. Exposing the Drierite to room air reduces this CO(2) affinity, and a 2-min exposure at 20 degrees Celsius and 50% relative humidity is sufficient to reduce the 99% washout time by almost a factor of 4, at the cost of only a 5% reduction in water vapor capacity. When Drierite is exhausted and then recharged according to the manufacturer's instructions, the CO(2) affinity is further reduced, and washout times are less than 60% greater than when no desiccant is used.