Intracavity CO laser photoacoustic trace gas detection: cyclic CH_4, H_2O and CO_2 emission by cockroaches and scarab beetles

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Abstract
A liquid-nitrogen-cooled CO laser and an intracavity resonant photoacoustic cell are employed to monitor trace gases. The setup was designed to monitor trace gas emissions of biological samples on line. The arrangement offers the possibility to measure gases at the 109 by volume (ppbv) level (e.g., CH4, H2O) and to detect rapid changes in trace gas emission. A detection limit of 1 ppbv for CH4 in N2 equivalent to a minimal detectable absorption of 3 × 10−9 cm−1 can be achieved. Because of the kinetic cooling effect we lowered the detection limit for CH4 in air is decreased to 10 ppbv. We used the instrument in a first application to measure the CH4 and H2O emission of individual cockroaches and scarab beetles. These emissions could be correlated with CO2 emissions that were recorded simultaneously with an infrared gas analyzer. Characteristic breathing patterns of the insects could be observed; unexpectedly methane was also found to be released.