2.4 GC–MS Analysis of geraniol and other volatiles in tea samples
Geraniol and other volatiles in samples were analyzed using solid-phase microextraction (SPME) combined with gas chromatography (Thermo Scientific TRACE 1300)/mass spectrometry (Thermo Scientific ISQ 7000 GC/MS). Briefly, the tea samples in liquid nitrogen were ground to a fine powder and transferred to a 20-mL headspace bottle. Two µl of ethyl caprate (1 ppm in methyl alcohol) was used as an internal standard. The samples were incubated at 60°C for 1 h, and the volatiles were adsorbed by SPME during the entire process. A fused-silica GC column (DB-5, 60 m × 0.25 mm, film thickness 0.25 μm, J&W Scientific, Folsom, CA, USA) was used to separate chemical compounds. Pure helium was used as the carrier gas at a flow rate of 1 mL/min. The GC injector had a split ratio of 10:1. The GC oven was maintained at 40°C for 3 min and was increased by 5°C/min to 80°C; it was then increased to 160°C at 2°C/min and then to 240°C at a rate of 10°C/min. After being held at 240°C for 5 min, the detector temperature was set to 250°C. The mass spectrometry data were acquired in full-scan mode with an m/z range of 300–600 after a solvent delay of 0 s. All compounds were identified by comparison with a mass spectrometry library (NIST) and compounds with known retention times. Geraniol, (Z)-β-ocimene, and (E)-β-ocimene were identified using standards.