Trace dsq mass spectrometer

GC-MS analysis was carried out on a Thermo Finnigan Trace DSQ mass spectrometer coupled with a Thermo Finnigan Trace GC 2000 Ultra with a split injector (1:10). Samples were separated on an Rtx® 5ms fused-silica capillary column (15 m × 0.25 mm, df = 0.25 μm) (Restek, Bad Homburg, Germany). The column temperature was held at 90°C for 3 min, then increased to 260°C at a rate of 5°C min⁻¹, and finally maintained at 260°C for 15 min. The carrier gas was helium with 1.1 mL min⁻¹. The EI-MS ionization voltage was 70 eV (electron impact ionization). The ion source was maintained at 250°C and the interface temperature was at 280°C. GC-MS analysis of trimethylsilylated extracts from treated fruits showed compounds with major ions at m/z 239, 266, 299, and 57 that eluted at retention times of 27.5, 29, 30.4, and 23.3 min. Fragment ions and retention times correspond to H-, G-, S- monomers that were liberated by thioacidolysis and to the internal standard docosane (I.S., Fig. S1). Lignin breakdown units of each lignin sample were quantified using Xcalibur software (version 1.4). The H-, G-, and S- monomers were calculated based on the peak area of prominent ions related to that of the internal standard docosane for normalization.

GC-MS/O was performed with a Trace GC Ultra and a Trace DSQ mass spectrometer (both Thermo Fisher Scientific GmbH) using DB-FFAP and DB-5 (both 30 m × 0.32 mm, film thickness 0.25 µm; J&W Scientific) capillary columns. The aroma distillate was injected by an MPS 2 multipurpose sampler (Gerstel GmbH & Co. KG, Mülheim an der Ruhr, Germany) using the cold on-column technique (40 °C). The same temperature program as described in Section 3.6. was applied. The flow rate of the helium carrier gas was 2.3 mL/min. At the end of the capillary column, the effluent was split and led to an ODP (250 °C) and the DSQ mass spectrometer, using deactivated fused silica capillaries (0.5 m × 0.2 mm). Mass spectra were generated in electron ionization (EI) full scan mode (m/z range 35–350, 70 eV).

Alkanes were extracted in 5 ml of hexane or hexane:dichloromethane (1:1) for C₃₂. The vials were shaken vigorously. Samples were then centrifuged (4600g, 15 min). One millilitre of the upper solvent phase was taken and diluted with hexane to an appropriate concentration for GC–MS analysis. Deuterated nonadecane (C₁₉^d40) was added as an internal standard at 5 μg ml⁻¹. Alkanes were identified and quantified using a TRACE Ultra Gas Chromatograph (ThermoFisher Scientific) coupled with a TRACE DSQ Mass Spectrometer (ThermoFisher Scientific) operated at 70 eV in positive ion mode. Chromatography was performed by splitless injection with helium as the carrier gas, onto a 30 m × 0.25 mm × 0.25 mm fused silica capillary column Rtx‐5MS (Restek) (0.25 μm film thickness). The injector temperature was 300°C, and the oven program was 65°C for 2 min, increasing to 310°C at 20°C min⁻¹ then held for 18 min. External multilevel calibrations were performed using an alkane standard mix (C₈‐C₄₀) (Sigma‐Aldrich) with quantification of five levels ranging from 0.250–16 ng μl⁻¹. The mass spectrometer was operated in full scan mode (range m/z 50–650), with identification of target analytes based on retention times of the analytical standards and mass spectrum (intensity versus m/z). Quantification was performed by integrating the peak of target analytes at specific m/z ratios.