Standardization study of expiratory conditions for on-line breath testing by proton transfer reaction mass spectrometry

Breath testing is a noninvasive method with potential for diagnosing cancers and has been regarded as one of the research hotspots in metabolomics. In the conventional breath sampling process, however, degradation of exhaled metabolites and introduction of impurities from sampling bags or tubes limit the development of breath research. To solve this problem, we previously developed an on-line breath sampling system, which can directly deliver exhaled gases from the mouth to the proton transfer reaction mass spectrometry (PTR-MS) breath analysis instrument. To establish a standard expiratory method for this system, four parameters that may affect the concentrations of exhaled volatile organic compounds (VOCs) were studied. We found inhaled gas volume, breath holding time, mouth rinsing, and ambient air all affected the exhaled VOCs. In particular, the breath holding time and mouth rinsing significantly affected the VOCs which originate from the oral cavity. Therefore, these four parameters should be taken into account in future on-line breath testing.