Real-Time Measurement of CH₄ in Human Breath Using a Compact CH₄/CO₂ Sensor

The presence of an elevated amount of methane (CH₄) in exhaled breath can be used as a non-invasive tool to monitor certain health conditions. A compact, inexpensive and transportable CH₄ sensor is thus very interesting for this purpose. In addition, if the sensor is also able to simultaneously measure carbon dioxide (CO₂), one can extract the end-tidal concentration of exhaled CH₄. 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 CH₄/CO₂ values exhibit a strong interference with water vapor. Therefore, correction functions were experimentally identified and validated for both CO₂ and CH₄. A custom-built breath sampler was developed and tested with the sensor for real-time measurements of CH₄ and CO₂ in exhaled breath. As a result, the breath sensor demonstrated the capability of accurately measuring the exhaled CH₄ and CO₂ profiles in real-time. We obtained minimum detection limits of ~80 ppbv for CH₄ and ~700 ppmv for CO₂ in 1.5 s measurement time.