Abstract

Measurement of volatile organic compounds (VOCs) impacts areas as diverse as atmospheric composition and pollution studies, aroma analysis and medical diagnostics through breath analysis. Chemical Ionisation Reaction-Time of Flight-Mass Spectrometry (CIR-ToF-MS) is a novel direct mass spectrometric technique that is capable of simultaneously monitoring multiple VOC species quantitatively and in near real-time. The CIR -MS technique (a more general version of proton transfer reaction mass spectrometry (PTR-MS) but utilising alternative chemical ionisation schemes) is based upon soft ionisation by a reagent species such as H2O , NO or O2 and is capable of recording an entire mass spectrum in seconds with sensitivities in the order of 0.1 counts ppbV-1 s-1 in each unit mass channel.

This technique has been deployed by the Leicester Atmospheric Chemistry Research Group for a number of applications in the analysis of a range of trace atmospheric VOCs and oxygenated volatile organic compounds (OVOCs). For example, in several atmospheric chamber studies it has been applied in gas phase SOA forming systems to measure a variety of globally important aerosol precursors. In applications such as this, complex spectra are observed, the deconvolution of which can be used to track the formation of OVOC products following VOC photo-oxidation and has been used to provide mechanistic detail to advance and elucidate atmospheric chemistry models. In contrast, medical diagnoses and prognoses through CIR -MS measurements of breath may be possible using ‘air fingerprinting’ whereby spectra are recognised and compared with a library of breath phenotypes. These applications are discussed along with future directions in quantitative direct MS analysis.