Samples weighting 60 mg were extracted as previously described (Chen et al., 2017 (link)). After extraction, 1 μL prepared sample solution was injected into the Agilent 7890A-5975C gas chromatography-mass spectrometry (GC-MS) system (Agilent Corporation, United States). GC-MS analysis was carried out on a non-polar DB-5 capillary column (30 m × 250 μm I.D., J&W Scientific, Folsom, CA). High purity of helium was used as the carrier gas at a constant flow rate of 1.0 mL/min. The temperatures of injection and ion source were set to 305 and 230°C, respectively. Electron impact ionization (-70 eV) at full scan mode (m/z 30-600) was used, with an acquisition rate of 20 spectrum/second in the MS setting. QC sample was prepared by mixing aliquots of tissues samples to be a pooled sample.
Acquired data were analyzed by ChromaTOF software (v 4.34, LECO, St Joseph, MI). Internal standards and any known pseudo positive peaks were removed from the obtained data set. Data set was normalized using sum intensity of peaks in each sample. Obtained three-dimensional data sets included sample information, retention time, and peak intensities.
Acquired data were analyzed by ChromaTOF software (v 4.34, LECO, St Joseph, MI). Internal standards and any known pseudo positive peaks were removed from the obtained data set. Data set was normalized using sum intensity of peaks in each sample. Obtained three-dimensional data sets included sample information, retention time, and peak intensities.