RESUMEN
We report on on-line breath gas analysis with a new type of analytical instrument, which represents the next generation of proton-transfer-reaction mass spectrometers. This time-of-flight mass spectrometer in combination with the soft proton-transfer-reaction ionization (PTR-TOF) offers numerous advantages for the sensitive detection of volatile organic compounds and overcomes several limitations. First, a time-of-flight instrument allows for a measurement of a complete mass spectrum within a fraction of a second. Second, a high mass resolving power enables the separation of isobaric molecules and the identification of their chemical composition. We present the first on-line breath measurements with a PTR-TOF and demonstrate the advantages for on-line breath analysis. In combination with buffered end-tidal (BET) sampling, we obtain a complete mass spectrum up to 320 Th within one exhalation with a signal-to-noise ratio sufficient to measure down to pptv levels. We exploit the high mass resolving power to identify the main components in the breath composition of several healthy volunteers.
RESUMEN
We present a novel method for real-time breath-gas analysis using mass-spectrometric techniques: buffered end-tidal (BET) on-line sampling. BET has several advantages over conventional direct on-line sampling where the subject inhales and exhales through a sampling tube. In our approach, a single exhalation is administered through a tailored tube in which the end-tidal fraction of the breath-gas sample is buffered. This increases sampling time by an order of magnitude to several seconds, improving signal quality and reducing the total measurement time per test subject. Furthermore, only one exhalation per minute is required for sampling and the test subject can otherwise maintain a normal breathing pattern, thereby reducing the risk of hyperventilation. To validate our new BET sampling method we conducted comparative measurements with direct on-line sampling using proton-transfer-reaction mass spectrometry. We find excellent agreement in measured acetone and acetonitrile concentrations. High variability observed in breath-by-breath isoprene concentrations is attributed to differences in exhalation depth and influences of hyperventilation on end-tidal concentrations.