GC-MS analysis
The laser captured samples (with the same size as in LCM) were extracted
with 100 μL hexane. After sonicating for 60 min,
the sample was centrifuged at 12,000 rpm,
25℃
for 10 min. 90 μL of the supernatant was transferred into a brown vial
with a glass insert and stored at 4℃ before analysis.
GC-MS analysis was performed on a Thermo-Fisher Scientific gas
chromatography (Waltham, MA, USA) combined with triple quadrupole mass
spectrometer system (TP-8030) and fitted with a DB-5MS (5% phenyl
methyl polysiloxane) capillary column (30 m × 0.25 mm, 0.25 μm) with
helium as a carrier gas at 1 mL/min. The column temperature was
programmed initially at 120 ℃, and then increased to 200 ℃ at 5 ℃/min,
and then increased to 240 ℃ at 10 ℃ / min, held for 5 min. The mass
spectrometer was operated in electron ionization (EI) mode at 70eV, with
an interface temperature of 250 ℃, an ion source temperature of 250 ℃
and a continuous scan from 50 to 550 atomic mass unit (amu). Peaks were
identified by comparison with the mass spectra data from the National
Institute of Standards and Technology (NIST) spectral library.
Standards were accurately weighted and dissolved in hexane at a
concentration of about 0.5 mg/mL. The appropriate amount of every
standard solution was diluted respectively with hexane to a series of
concentration for establishment of the calibration curves (Table S2).
The limit of detection (LOD) and limit of quantitation (LOQ) were
determined by injecting a series of diluted standard solutions until the
signal-to-noise (S/N) ratio was 3 for LOD and 10 for LOQ in all
quantitative analysis.