GC-MS
300 milliliters of air sample from the canister was pulled through a cryogenic trap in the quadrupole GC-MS system (model TH-300B) and cooled to -160 °C for pre-concentration. After being trapped, the concentrated VOCs were flash desorbed by heating to 100 °C and transferred to a DB-624 column (60 m×0.25 mm×1.4 μm). CO2 and moisture are removed before injection. The initial temperature for the chromatographic column was 41 °C, maintained for 6 min, and then raised to 180 °C at a rate of 6 °C min-1. Qualitative identification of VOCs was performed using a full MS scan from 50 to 500 Th. The most probable identity of an analyte was obtained based on the first ranked matching by comparing with the reference mass spectra in the NIST library.