Rxi 5sil

Samples of the SFE-CO₂ extracts were diluted in n-hexane (Suprasolv, Merck, Germany) (1 mg/mL), transferred to GC-vials, and analyzed using a GC–MS system (GCMS-QP2010 Ultra; Shimadzu Corporation, Kyoto, Japan) equipped with an MS column (Rxi-5Sil; 30 m × 0.25 mm i.d.; film thickness, 0.25 μm; Restek Corporation, Bellefonte, PA, USA). The samples were injected (1 μL) using an autosampler at a 1:100 split ratio. The GC conditions were: injector temperature, 250 °C; helium (99.99%) as the carrier gas; and flow rate, 1 mL/min. The initial temperature was 50 °C, which was raised to 250 °C over 5 min, with a total analysis time of 91.67 min. MS conditions were: electrospray ionization mode; ionization voltage, 70 eV; ion source temperature, 200 °C; m/z range, 40.0–400.0; and scanning frequency, 5 Hz.
The identification of the compounds was based on a comparison of their mass spectra and retention indices with those of the synthetic compounds spectral library of the National Institute of Standards and Technology (NIST11) [50 ], and the Flavors and Fragrances of Natural and Synthetic Compounds spectral library (FFNSC2) [51 ].

The main volatile substances related to the fermentation bouquet or secondary wine aroma compounds (esters, higher alcohols, fatty acids, etc.) were analyzed using headspace solid phase microextraction (HS-SPME), together with gas chromatography and mass spectrometry (GC-MS; (7890A and MS 5977B, Agilent)) using the multipurpose sampler MPS2 (Gerstel GmbH & Co. KG) for HS-SPME injection [23 (link)]. The determination followed the analytical method [28 (link)] according to the reported approach [26 (link),29 ], which was correspondingly adjusted and adapted [30 ]. A model wine (10% (v/v) solution of ethanol in water, 3 g/L of tartaric acid, adjusted to pH 3) was used for the calibration. SPME extraction was performed with a 65 µm polydimethylsiloxane and divinylbenzene fiber (Supelco). The gas chromatography column of 60 m × 0.25 mm × 1 µm (Rxi-5Sil, Restek, Bellefonte, PA, USA), together with particular GC-MS software and technical settings, was utilized for the aroma compound separation. The Agilent MassHunter workstation software provided by the GC-MS instrumentation was used for the instrumental control, acquisition of data and analysis of qualitative and quantitative data.

The volatile analysis was carried out on an Agilent 7890B GC combined with time-of-flight mass spectrometer (TOFMS) detection (LECO Pegasus 4D, Leco Corporation, St. Joseph, MI, USA). Rxi-5Sil (30 m × 250 µm × 0.25 µm; Restek, Bellefonte, PA, USA) and RXi-17Sil MS (1.9 m × 100 µm × 0.10 µm; Restek, Bellefonte, PA, USA) were employed for the first-dimensional and second-dimensional separation, respectively. High purity helium (99.999%) was used as carrier gas with a constant flow of 1.0 mL/min. The temperature of the transfer line was set at 250 °C in splitless mode, and the modulation period was 5.00 s. The initial temperature of the 1st D column was 50 °C for 2 min, and then it was ramped to 265 °C at 8 °C/min holding for 5 min. The temperature of the 2nd D column was initially set at 55 °C for 2 min, and increased to 270 °C at 8 °C/min, and held for 5 min. The mass spectrometer operated at an ion source temperature of 220 °C with a scan mass range of 33–500 m/z, and the electronic energy was −70 eV. The interface temperature was 270 °C.