4.6. Gas Chromatography-Mass Spectrometry (GC-MS)

Polysaccharides extracted from F. chilensis (2 mg), and monosaccharide standards underwent the same procedure. Initially, 100 µL of the standard stock solution containing 1 mg mL⁻¹ of each monosaccharide was dried under nitrogen gas flow. The polysaccharide samples, along with a mixture containing standard monosaccharides from the I.S., were treated in a 2 mL HCl 3 M solution in MeOH at 80 °C for 24 h. The saccharides were washed using methanol and dried under a flow of nitrogen gas. Following this, the trimethylsilyl reaction was carried out using 200 µL of Tri-Sil HTP (Thermo Scientific). Each vial containing the sample was heated to 80 °C for 1 h. After the sample was derivatized, it was cooled to room temperature and dried using nitrogen. The dry residue was then extracted with 2 mL of hexane and centrifuged. Finally, the solution of silylated monosaccharides in hexane was concentrated, reconstituted (200 µL), and filtered before being transferred to a GC-MS autosampler vial. The sample was prepared and analyzed in triplicate.

GC-MS analyses were carried out using a gas chromatography Trace GC (Thermo Scientific), autosampler Tri Plus, and DSQ mass spectrometer quadrupole (Thermo Scientific). The column was ZB-5 Zebron, Phenomenex (5% Phenyl, 95% Dimethylpolysiloxane, Torrance, CA, USA), of dimensions 30 m × 0.25 mm i.d. × 0.25 µm. The column temperature was programmed from 80 °C (held 2 min) and 5 °C min-1 to a final temperature of 230 °C. The carrier gas was helium (flow 1.2 mL/min). The injection volume was 1 µL in a splitless mode at 250 °C. The source and M.S. transfer line temperature were at 230 °C. A Select Ion Monitoring Program (SIM) in electron ionization mode was set at 70 electron volts (eV) in the mass spectrometer. The TMS-derivatives were identified using characteristic retention times and a mass spectrum compared to those of authentic standards. The compounds were identified by comparing the mass spectra with those in the library of the National Institute of Standards and Technology (NIST, 2014).