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.