Cavity-Enhanced Near-Infrared Laser Absorption Spectrometer for the Measurement of Acetonitrile in Breath

Elevated concentrations of acetonitrile have been found in the exhaled breath of patients with cystic fibrosis' and may indicate the severity of their condition or the presence of an accompanying bacterial infection of the airways. There is therefore interest in detecting acetonitrile in exhaled breath. For this purpose, a cavity-enhanced laser absorption spectrometer (lambda = 1.65 mu m) with a preconcentration stage was built and is described here. The spectrometer has a limit of detection of 72 ppbv and 114 ppbv of acetonitrile in nitrogen and breath, respectively, with a measurement duration of just under 5 min. The preconcentration stage, which employs a carbon molecular sieve and an adsorption/thermal desorption cycle, can increase the acetonitrile concentration by up to a factor 93, thus, lowering the overall limit of detection to approximately 1 ppbv. The suitability of the system for acetonitrile measurements in breath is demonstrated with breath samples taken from the authors, which yielded acetonitrile concentrations of 23 +/- 3 ppbv and 29 +/- 3 ppbv, respectively.