Turbomatrix 300 td

Captured VOCs were released by a thermal desorption instrument (TurboMatrix 300 TD, PerkinElmer, USA) and analyzed by a Profile-3 SIFT-MS instrument (Instrument Science, Crewe, UK)^{17 (link),18 (link)}. Primary desorption was performed by pre-purging the TD tube for 1 min with helium at 50 ml min⁻¹ and heated to 280 °C for 10 min to desorb the VOCs onto a cold trap containing Tenax GR backed by Carbopack B. During secondary desorption stage, the cold trap was initially cooled to 10 °C and heated to 290 °C at 5 °C sec⁻¹ and hold for 4 min. The instrument had a head pressure of helium set to 8.5 psi which resulted in a flowrate of 100 mL/min within the transfer line between the TD device and the SIFT-MS at splitless mode. Ionisation was carried out using either H₃O⁺ (m/z 19, 37, 55 and 73) or NO⁺ (m/z 30, 48 and 66) as precursors with a total count rate of approximately 8 × 10⁵ or 4 × 10⁵ counts s⁻¹, respectively. Multi-ion monitoring mode (MIM) was mainly employed for this study. Desorbed VOCs were analysed for a total of 60 s, and the measured concentrations were averaged over the analysis time for each VOC.

The composition analysis procedure was completed via a thermal desorption (TD) instrument (TurboMatrix 300 TD, PerkinElmer, Waltham, MA, USA) and gas chromatography-mass spectrometry (GC-MS) (QP2010 Plus, Shimadzu, Tokyo, Japan). TD was used to desorb the VOCs adsorbed in the Tenax TA stainless steel tube. GS-MS analyses were performed following the desorption procedure. The VOCs, then, were sent into an Rtx-5 column (30.0 m Length × 0.25 mm ID × 0.25 μm Thickness, Restek) to be separated. The carrier gas was helium. The column temperature program was 40 °C initially, held for 1 min, and increased to 250 °C at 5°/min, and held for 1 min at 250 °C. The MS was in scan mode in the 45–500 mass to charge (m/z) range. The scan time was 2.5–38 min. The temperatures of the electron impact ion source and interface were set at 200 °C and 250 °C, respectively.

Data were obtained from a previous case–control study where 236 subjects were asked to participate [15 (link)]. All cases were confirmed with an incident of lung cancer histologically or pathologically, while controls were confirmed with a negative result of LDCT scan. The detailed inclusion criteria and exclusion criteria of subjects were listed in Supplementary materials (S1).
Sample collection and analysis were performed as previously published [15 (link)]. Briefly, to collect breath samples, subjects were asked to breathe tidally into a self-developed collection device with which VOCs in 1000 mL exhaled breath were captured and concentrated into a Tenax TA stainless steel tube (PerkinElmer, Waltham, MA). Then, each sampling tube was shipped to laboratory for chemical analysis which was performed on GC-MS (QP2010 Plus, Shimadzu, Tokyo, Japan) coupled with a thermal desorption (TD) instrument (TurboMatrix 300 TD, PerkinElmer, Waltham, MA). Subsequently, spectrum analysis including peak identification and background removal was done. Details of collection, detection and data pre-treatment are illustrated in Supplementary materials (S2). Metabolites which can be annotated to HMDB were then used for following analysis.