Mid-infrared laser spectroscopy for online analysis of exhaled CO.

Carbon monoxide (CO) detection in human breath is the focus of much research because of CO's possible use as a marker molecule for different diseases. Detecting CO in human breath remains a tough challenge because of the low concentrations of CO (ppm range) that must be detected. Another problem is that many other molecules, which can be found in human breath, can interfere in these measurements. Additionally, a time resolution of less than 1 s is needed to resolve the CO curve of an exhalation. In this study (13)CO instead of (12)CO concentration is measured. The measurements are performed with a cavity leak-out spectroscopy system. The system's properties match the above-mentioned specifications for measurements, even of the rare isotopologue with high specificity, a time resolution of less than 1 s and a detection limit of 7 ppb Hz(-1/2). Two investigations are presented here. The first is a measurement showing intraday changes between 9.5% and 23.3% of the exhaled CO level due to vigorous exercise. The second shows a long-term observation of the CO base level revealing natural variations in the recorded CO concentration. The covered time period is 25 weeks during which the differences between the minimum and maximum CO levels for each test case reached 84%.