Exhaled breath collection and analysis
Exhaled breath was collected using an adjusted ReCIVA® breath sampler (Owlstone Medical, Cambridge, UK) combined with the CASPER® clean air supply pump (Owlstone Medical, Cambridge, UK) which provided filtered inspiratory air to minimize background contamination from ambient air. Details about the adjustments of the breath sampler can be found in supplement section 1). The influence of the adjustments to the breath sampler was assessed separately and the VOC concentrations measured were similar using both the adjusted and the original sampler (see supplement section 2). Exhaled breath samples were analysed using thermal desorption (TD) gas chromatography mass spectrometry (GC-MS) and TD selected ion flow tube mass spectrometry (SIFT-MS). Details about the GC-MS and SIFT-MS analysis of the exhaled breath samples are provide in supplement section 3.