Gas-Chromatography/Mass-Spectrometry (GCMS-QP2010; Shimadzu Corporation, Japan), combined with a thermal desorption system (TD20; Shimadzu Corporation, Japan), is used for the chemical analysis of the breath samples. A Tenax® TA adsorbent tube (Sigma Aldrich Ltd.) is employed for pre-concentrating the VOCs in the breath samples. Using a custom-made pump system, the breath samples from the Mylar bags are sucked up through the TA tube at 100 ml/min flow rate, being then transferred to a thermal desorption (TD) tube (Sigma Aldrich Ltd.) before being analyzed by GC-MS. The following oven temperature profile was set: (a) 10 min at 35°C; (b) 4°C/min ramp until 150°C; (c) 10°C/min ramp until 300°C; and (d) 15 min at 300°C. An SLB-5ms capillary column (Sigma Aldrich Ltd.) with 5% phenyl methyl siloxane (30 m length, 0.25 mm internal diameter and 0.5 μm thicknesses) is employed. The splitless injection mode is used for 2 min, at 30 cm/sec constant linear speed and 0.70 ml/min column flow. The molecular structures of the VOCs are determined via the standard modular set, using 10 ppm isobutylene (Calgaz, Cambridge, Maryland, USA) as standard calibration gas during each run. GC-MS chromatogram analysis is realized using the GCMS solutions version 2.53SU1 post-run analysis program (Shimadzu Corporation), employing the National Institute of Standards and Technology (NIST) compounds library (Gaithersburg, MD 20899-1070, USA).