Abstract
The weak absorption spectra of isoprene and acetone have been measured in the wavelength range of 261–275 nm using cavity ringdown spectroscopy. The measured absorption cross-sections of isoprene in the wavelength region of 261–266 nm range from 3.65 × 10−21 cm2·molecule−1 at 261 nm to 1.42 × 10−21 cm2·molecule−1 at 266 nm; these numbers are in good agreement with the values reported in the literature. In the longer wavelength range of 270–275 nm, however, where attractive applications using a single wavelength compact diode laser operating at 274 nm is located, isoprene has been reported in the literature to have no absorption (too weak to be detected). Small absorption cross-sections of isoprene in this longer wavelength region are measured using cavity ringdown spectroscopy for the first time in this work, i.e., 6.20 × 10−23 cm2·molecule−1 at 275 nm. With the same experimental system, wavelength-dependent absorption cross-sections of acetone have also been measured. Theoretical detection limits of isoprene and comparisons of absorbance of isoprene, acetone, and healthy breath gas in this wavelength region are also discussed.
Highlights
Noninvasive breath gas analysis for the detection of established biomarkers is rapidly gaining much attention in a variety of scientific and medical communities [1,2,3]
We have studied breath acetone using a portable cavity ringdown spectroscopy (CRDS) device operating with a single wavelength, palm-size 266 nm laser [27,28]
In the lower concentration region, i.e. at 3 ppm and 5 ppm, which were close to the detection limit of 4 ppm for isoprene at 266 nm with the present CRDS system, the ringdown signals were noisy
Summary
Noninvasive breath gas analysis for the detection of established biomarkers is rapidly gaining much attention in a variety of scientific and medical communities [1,2,3]. Techniques, such as the proton transfer reaction-mass spectrometry (PTR-MS) and laser spectroscopy, have demonstrated ultra trace detection capability and real-time monitoring of volatile organic compounds (VOCs). PTR-MS based instrument can be designed in a compact configuration and employed for the detection of environmentally important trace gases as well exhaled breath VOCs [7,8]. Laser-based analysis has made significant strides in the detection and measuring of trace species in a host of environments, and considerable attention has been given to technological advances in the manufacture of lasers for numerous applications over a broad wavelength range [2]. The NIR telecommunications’ diode lasers will be significantly hindered in their detection selectivity because the majority of the volatile breath gas constituents have weak absorption at those wavelengths, which typically consists of an asymmetric
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