Mxt 5 column

GC-MS analysis was performed on a Thermo Trace 1300 gas chromatograph, using a Thermo Scientific ISQ mass spectrometer with electron ionization source (70 eV). The system was equipped with a 30 m long Restek MXT-5 column with a diameter of 0.25 mm coated with a stationary phase, consisting of 5% diphenyl and 95% dimethylpolysiloxane and a thickness of 0.25 µm. A split injection was used with a 1/3 split ratio, an injection volume of 1 μL, an inlet temperature of 320 °C and a helium carrier gas flow of 0.9 mL/min. The column temperature was programmed as follows: 2 min at 40 °C, increase to 120 °C at 20 °C/min, increase to 200 °C at 10 °C/min, increase to 250 °C at 7 °C/min, increase to 350 °C at 5 °C/min, 4 min hold at 350 °C. The transfer line and the ion source were kept at 300 °C, the solvent delay time was set at 3 min 40 s, the examined mass range of the scans was 33–720 amu and the scan time was 0.304 s. A reference linear C₇ to C₄₀ linear alkane ladder standard (49452-U, Supelco (Bellefonte, PA, USA) at three different concentrations (0.001, 0.01 and 0.1 µg/mL) was run to determine retention times and retention indices, and for determining response factors.

Volatile compounds were determined by a FlavorSpec^®® gas chromatograph-ion mobility spectrometer (GC-IMS) (G.A.S. Instrument, Germany) equipped with an MXT-5 column (15 m × 0.53 mm × 1 μm) (Restek; Bellefonte, PA, USA). Beef samples were cooked on the pan until the core temperature reached 70 °C. The cooked samples were frozen with liquid nitrogen, and grinded. Two grams of the sample was weighed, sealed in a glass vial (20 mL), and incubated at 60 °C for 20 min. Then, 500 μL of gas was injected with a syringe at 85 °C. The column temperature was 60 °C and the IMS temperature was 45 °C. The carrier gas and drift gas were high-purity nitrogen. The flow rate of carrier gas was set as the following gradient: 0 min, 2 mL/min; 2 min, 2 mL/min; 10 min, 10 mL/min; 20 min, 100 mL/min; 30 min, 150 mL/min. The flow rate of carrier gas was 150 mL/min. Volatile compounds were identified by GC-IMS library search software.

The analysis was done on an easy-to-use FlavourSpec (G.A.S., Dortmund, Germany) HS-GCxIMS. Samples were automatically shaken for 30 min at 80 °C. 1 mL of headspace was injected into the injector at 80 °C without split flow. Substances were separated on a 15 m × 0.53 mm × 1 μm MXT-5 column (Restek, Bellefonte, PA, USA) with a nitrogen carrier gas ramp (2 mL/min for 1 min., in 14 min. up to 150 mL/min, this held for 35 min, for a total of 50 min. for the analysis). Detection was carried out with a drift tube of 15.2 mm (diameter) and 98 mm (length) ionization by ³H-source, at 45 °C, a nitrogen drift gas flow rate of 150 mL/min, and a field strength of 500 V/cm.
Reference measurements were run on a thermal-gradient HS-GC-qMS (Shimadzu, Kyoto, Japan). Using the same vials, samples were incubated for 30 min at 120 °C, afterwards injecting 2 mL of the headspace at a split of 1:10. The separation was performed on a HP-5 MS UI (Agilent, Santa Clara, CA, USA) 30 m × 0.25 mm × 0.5 μm column at a constant flow rate of 35 cm/s helium and a temperature ramp (50 °C held for 4 min, at 5 °C/min to 150 °C, at 10 °C/min to 200 °C). Analytes were ionized using electron-impact ionization at 70 eV and 200 °C with a scan range of 32–300 m/z at an event time of 300 ms.