During coffee roasting, numerous chemical reactions give rise to complex mixtures of volatile (VOC) and semi‐volatile (sVOC) compounds, which form the basis for distinct coffee aromas. Another complex analyte system that contains many different (s)VOCs is the “breathome”, i.e., the chemical composition of exhaled breath. It can reflect the physiological or metabolic state of an individual and indicate certain diseases. Although various mass spectrometry (MS) methods can be used to analyze these complex chemical mictures, limited ionization efficiencies and/or mass resolutions can notably reduce the available chemical information.
Klaus Dreisewerd, University of Münster, Germany, and colleagues have developed an advanced version of a direct-inlet low-pressure photoionization (LPPI) source (pictured schematically). Low‐pressure photoionization (LPPI) is a versatile tool for the mass spectrometric detection of (s)VOCs. The team then tested the device by analyzing exhaled human breath and the aroma of coffee grounds.
The researchers used custom-made electronics with three small Krypton discharge lamps for photoionization. The lamps were mounted in an ion funnel and driven with an alternating current at a standard frequency of 13.56 MHz. The design is optimized for efficient photoionization and undisturbed ion trajectories. It provides high ionization efficiencies for a range of chemical compound classes and generates primarily intact radical ions and protonated molecules. For molecular identification, a high-precision Orbitrap mass analyzer was used.
With their setup, the team was able to differentiate a few thousand substances from head-space-sampled coffee grounds and a few hundred from exhaled human breath. The method could be a useful tool for the rapid, comprehensive screening of (semi-)volatile organic compounds.
- Low‐Pressure Photoionization in a Dual‐Ion Funnel Injector Coupled to an Orbitrap Mass Spectrometer for Direct Analysis of Human Breath and Head‐Space Sampled Coffee Roasts,
Christoph Bookmeyer, Jens Soltwisch, Ulrich Röhling, Klaus Dreisewerd,