Novel Mass Spectrometric Instrumentation and Methods for Monitoring Headspace Volatile Organic Compounds including Breath

Volatile organic compounds (VOCs) are a group of compounds that have a high vapour pressure at room temperature. They are released or emitted from various natural and synthetic sources. Emitted VOCs can be measured to identify/detect/profile a given emitter and/or scenario.
VOC analysis in biological samples (e.g. breath, urine, sweat) is a rapidly growing research area. Breath, a massively underutilised biological sample, is abundant in information, offering immense potential in medical research. It is sampled non-invasively and is readily available in excess. The chemically rich and diverse nature of breath allows for a wide range of techniques to be used to analyse the information, but currently there is a lack of a standardised sampling or analysis method. One of the main disadvantages of VOC analysis, especially in headspace and gaseous analysis is the need for sample preparation, usually in the form of preconcentration and the lack of direct real-time measurements. Moreover, the concentration of VOCs found in biological samples can be below available detection limits. The overarching aim of this project is to develop a method that is capable of detecting VOCs direct from headspace in near teal-time. In this regard we are seeking to detect VOCs that are of importance in medical applications, with the potential to be used at point of care.
An ambient pressure photoionisation mass spectrometry (APPI-MS) method has been developed and optimised using a bespoke bias electrode setup to maximise sensitivity. A range of materials have been tested for housing the ion source and electrodes, that are amenable for direct chemical analysis. Linear calibration curves were produced for chemical standards with detection limits <10 pg and R2 > 0.99. The method was developed and optimised for on-site deployment, coupled with a portable mass spectrometer.
The developed method has been applied to a range of samples focusing on the analysis of bacteria. Samples were analysed directly using the portable method (in situ) and indirectly by capturing samples in sampling bags and returning them to the lab (ex-situ). The study could discriminate between different bacteria and correctly identify them from a blind study. A final study was performed by sampling the breaths of healthy participants. Additionally, studies have been performed to monitor VOC headspace from different sources, including coffee beans, soil, e-cigarette liquids, and aerosols.
In summary, a novel APPI-MS method has been successfully used to detect and quantify VOC standards and profile a range of samples. The method shows promising potential for clinical applications, with both direct and indirect sampling methods proving successful. The most exciting aspect is the opportunity to apply this approach to specific diseases, such as cystic fibrosis, which is the subject of ongoing research, sparking hope for improved diagnostics and treatments.