Tedlar bag

We used Bruker FTIR spectrometer Vertex 70 based on thermal source, operating in the mid-infrared spectral range of our interest 500–4000 cm⁻¹ (2.5–20 µm). The spectral resolution 0.5 cm⁻¹ was kept for all the measurements. Gas samples were collected in single-use Tedlar bags (Sigma Aldrich) and measured then by using a system that significantly suppresses the amount of water vapor [30 (link)]. The minimum detectable concentration (the detection noise) reached 50 ppb (part-per-billion, Section 2 in SM). This value corresponds to 1 × 10⁻⁴ of the absorbance at 1100 cm⁻¹ in Figure 3a. The absorbance units were used throughout the text because they represent physical values measured in the experiment. Their transformation into concentrations can be done only if the corresponding spectral structure is identified as a certain VOC.

A detailed description concerning the procedures followed for participant recruitment and sampling of exhaled breath can be found in a previous publication [10 (link)]. In brief, the study population consisted of 85 patients from the General University Hospital of Larissa (Greece) who underwent bronchoscopy due to abnormal CT findings and a control group of 52 individuals of similar age were recruited from local health centers. Samples were collected from October 2018 to October 2019. After bronchoscopy, patients were categorized according to the presence of LC, according to results of the cytological/histological examination. The control group (referred to in the text as healthy controls (HC)) was selected on the basis of the absence of self-reported pulmonary diseases and cancer. The absence of these diseases was determined by self-report during the personal interviews conducted on the day of sampling.
Breath samples were collected in Tedlar^® bags (Sigma-Aldrich, St. Louis, MO, USA). Participants were asked to inhale deeply and hold their breath for 30 s, then exhale through a disposable mouthpiece into the 1 L Tedlar^® bag until filled. Two breath samples were collected with approximately two-minute intervals in between. Ambient air samples were also collected with the use of a portable Laboport^® UN 86 KTP (KNF Neuberger GmbH, Freiburg, Germany) pump.

Waste gas outflow from experimental flasks was collected for 10 min in 5 L Tedlar bags pre-rinsed with oxygen-free nitrogen (Sigma Aldrich, UK). The bag contents were pre-concentrated on a cryogenic trap at 60 mL min⁻¹. The trap was heated rapidly to inject onto the GC column and DMS quantified5 (link).

All UV-Vis spectra were taken in LC-grade methanol (⩾99.9%, VWR Chemicals BDH) using a VWR Cell Quartz 100 µl Z8.5 mm cuvette and a Beckman Coulter DU 800 spectro-photometer. IR 3-(2-benzothiazolyl)-7-(diethylamino)coumarin was purchased from Chemodex. Tedlar bags with a volume of one liter were purchased from Sigma–Aldrich. Chemical reagents were purchased from Sigma–Aldrich and used without further purification.

The University of Louisville Institutional Review Board approved the research protocol for collection of exhaled breath samples. All study subjects signed informed consent before providing breath samples. A single exhalation of 1 L of breath was collected with a Tedlar bag (Sigma-Aldrich, St Louis, MO) from each subject. Breath samples were collected from 222 subjects. Lung cancer was pathologically confirmed in 31 patients. Benign disease was confirmed pathologically in 4 patients. A breath sample after resection was collected in a similar manner. Some patients provided more than one postresection sample, but all 31 patients provided at least one sample. The time interval between collections was varied. The remaining 187 patients served as the control group that consisted of healthy patients without known lung disease, which included nonsmokers, active smokers, and former smokers.