Thermo trace gc ultra chromatograph

We also determined the concentrations of higher alcohols and esters for each sampling time. Volatile-compound extraction and gas chromatography (GC) were performed following the protocol described in reference 71 (link). Extraction was performed using headspace solid-phase-microextraction sampling (SPME) with polydimethylsiloxane (PDMS) fibers (Supelco; Sigma-Aldrich, Barcelona, Spain). Aroma compounds were separated by GC in a Thermo TRACE GC Ultra chromatograph (Thermo Fisher Scientific, Waltham, MA) equipped with a flame ionization detector (FID), using an HP-INNOWAX 30-m by 0.25-mm capillary column coated with a 0.25-mm layer of cross-linked polyethylene glycol (Agilent Technologies, CA). Helium was the carrier gas used (flow, 1 ml min⁻¹). The oven temperature program was as follows: 5 min at 60°C, 5°C min⁻¹ to 190°C, 20°C min⁻¹ to 250°C, and 2 min at 250°C. The detector temperature was 280°C, and the injector temperature was 220°C under splitless conditions. The internal standard was 2-heptanone (0.05% [wt/vol]). Volatile compounds were identified by the retention time for reference compounds. The quantification of the volatile compounds was determined using the calibration graphs of the corresponding standard volatile compounds.