A laser spectroscopic system based on a cw difference-frequency generation source with a ratiometric multipass absorption detection scheme was employed for high-resolution spectroscopic investigation of gas-phase monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA). Possible application of the system as a noninvasive human breath analyzer for renal and liver diseases is targeted. The system operates in the fundamental C-H stretch absorption region around 2740-2860 cm−1. A detection sensitivity of 2×10−6 cm−1 Hz−½ (for signal-to-noise ratio SNR=1) is achieved, corresponding to detection limits of 900 ppb (parts in 109) for MMA, 450 ppb for DMA, and 120 ppb for TMA in mixtures containing H2O and CO2 with concentrations of up to those present in human breath (2% and 5%, respectively). Future developments are discussed to further improve these detection limits that are currently still about 2 orders of magnitude higher than required for direct methylamine monitoring in human breath.
© 2008 Optical Society of America
Original Manuscript: January 15, 2008
Revised Manuscript: March 20, 2008
Manuscript Accepted: March 21, 2008
Published: April 11, 2008
Vol. 3, Iss. 5 Virtual Journal for Biomedical Optics
Dilyan Marinov, Julien Rey, and Markus W. Sigrist, "Mid-infrared spectroscopic investigation of methylamines by a continuous-wave difference-frequency-generation-based system," Appl. Opt. 47, 1956-1962 (2008)