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 theresearch 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 breathresearch. To solve this problem, we previously developed an on-line breath sampling system, which can directlydeliver exhaled gases from the mouth to the proton transfer reaction mass spectrometry (PTR-MS) breathanalysis instrument. To establish a standard expiratory method for this system, four parameters that may affffectthe concentrations of exhaled volatile organic compounds (VOCs) were studied. We found inhaled gas volume,breath holding time, mouth rinsing, and ambient air all affffected the exhaled VOCs. In particular, the breathholding time and mouth rinsing signifificantly affffected the VOCs which originate from the oral cavity. Therefore,these four parameters should be taken into account in future on-line breath testing.