Isq lt gc ms

The first leaves of 14-d-old plants and spikes from mature plants were dipped twice into 99% HPLC molecular-grade chloroform for 15 s and then 10 s, an internal standard of 0.5 μg.mL^–1 tetracosane (C₂₄n-alkane) was then added. Lemma awns were trimmed from the spikes prior to the analysis. Solvent was removed from the wax extracts under a gentle stream of N₂. Wax residues were derivatised using N,O-bis(trimethylsilyl)trifluoroacetamide + 1% trimethylcholorosilane (BSTFA + 1% TMCS; Sigma-Aldrich) and excess reagent removed again under N₂. The wax constituents were identified by their electron-impact mass spectra (70 eV, m/z 50–950) after capillary GC (Restek Rxi-1HT, 15 m × 0.32 mm, 0.1 μm [Thames Restek Ltd.]) performed on an ISQ-LT GC–MS comprising a 1300 gas chromatograph combined with a single quadrupole mass analyser (Thermo-Fisher Scientific). The samples were injected onto the analytical column at 50 °C, ramping at 0.2 °C s^–1 to a maximum of 380 °C, where it was held for 7 min. The flow rate of the He carrier gas was 5 mL min^–1. All data were acquired using the XCalibur software suite (Thermo Fisher Scientific). Leaf area and spike length were calculated using ImageJ^{87 (link)}.

Data were collected on a Thermo ISQ LT GC-MS in EI mode with an electron energy of 70 eV (Waltham, MA, USA). The column used was a Zebron ZB-5HT (30 m × 0.25 mm inside diameter, 0.25 μm film thickness, Newport Beach, CA, USA). Samples were collected in split mode with a column flow of 1 mL/min, purge flow of 10 mL/min, and a split flow of 10 mL/min. Inlet and ion source temperatures were held at 200 °C and 180 °C respectively. Samples for injection were prepared by diluting one drop of depolymerization NMR sample in 1 mL of methanol and an aliquot (1 μL) of the dilution was injected. The oven starting temperature was 70 °C held for 1 min followed by a ramp of 60 °C/min up to 300 °C which was held for 6 min. Data were collected using Chromeleon software. Mass spectra from peaks in the total ion chromatograph were compared to a NIST database using the software which listed possible matches with %probability. The results are summarized in Table 4.

The content of SCFAs in the colonic digesta was determined by using an ISQ Lt GC-MS (Thermo Fisher, USA) equipped with a flame ionization detector. A TG WAX column (30 m × 0.25 mm × 0.25 μm, Thermo Fisher) was used to separate the SCFAs. A sample injection volume of 5 μL was automatically injected into the inlet, which was kept at 240°C with a 75:1 split ratio. The carrier gas was helium at a flow rate of 1.0 mL/min. The temperatures of the flame ionization detector (FID, Thermo Fisher) and injector were 250 and 200°C, respectively.