Real-Time Measurement of CH 4 in Human Breath Using a Compact CH 4 /CO 2 Sensor.

The presence of an elevated amount of methane (CH 4 ) in exhaled breath can be used as a non-invasive tool to monitor certain health conditions. A compact, inexpensive and transportable CH 4 sensor is thus very interesting for this purpose. In addition, if the sensor is also able to simultaneously measure carbon dioxide (CO 2 ), one can extract the end-tidal concentration of exhaled CH 4 . Here, we report on such a sensor based on a commercial detection module using tunable diode laser absorption spectroscopy. It was found that the measured CH 4 /CO 2 values exhibit a strong interference with water vapor. Therefore, correction functions were experimentally identified and validated for both CO 2 and CH 4 . A custom-built breath sampler was developed and tested with the sensor for real-time measurements of CH 4 and CO 2 in exhaled breath. As a result, the breath sensor demonstrated the capability of accurately measuring the exhaled CH 4 and CO 2 profiles in real-time. We obtained minimum detection limits of ~80 ppbv for CH 4 and ~700 ppmv for CO 2 in 1.5 s measurement time.