Sub-parts-per-billion level detection of dimethyl methyl phosphonate (DMMP) by quantum cascade laser photoacoustic spectroscopy

The need for the detection of chemical warfare agents (CWAs) is no longer confined to battlefield environments because of at least one confirmed terrorist attack, the Tokyo Subway [Emerg. Infect. Dis. 5, 513 (1999)] in 1995, and a suspected, i.e., a false-alarm of a CWA in the Russell Senate Office Building [Washington Post, 9 February 2006, p. B01]. Therefore, detection of CWAs with high sensitivity and low false-alarm rates is considered an important priority for ensuring public safety. We report a minimum detection level for a CWA simulant, dimethyl methyl phosphonate (DMMP), of <0.5 ppb (parts in 10 ⁹) by use of a widely tunable external grating cavity quantum cascade laser and photoacoustic spectroscopy. With interferents present in Santa Monica, California street air, we demonstrate a false-alarm rate of 1 : 10 ⁶ at a detection threshold of 1.6 ppb.