Qp2020 gas chromatograph mass spectrometer

The fresh leaves of each sample were hydrodistilled with a modified Clevenger-type apparatus for 2 h until the extraction was completed. The terpenoid composition analysis of each sample were performed on a SHIMADZU QP2020 gas chromatograph-mass spectrometer (SHIMADZU Corporation, Japan), fitted with a DB-5-MS silica capillary column (30 m × 0.32 mm, 0.25 μm film thickness). Helium was used as the carrier gas with a constant flowrate of 0.6 mL/min. The GC temperature program were as follows: 50 °C for 3 min, a gradient of 50–180 °C over 16.25 min followed by holding at 180 °C for 1 min, then a gradient of 180–280 °C over 10 min followed by holding at 280 °C 5 min. Alkanes were used as reference points in the calculation of relative retention indices. The GC inlet was operated at 280 °C in splitless mode with 0.6 μL injection volume. The quadrupole MS operating parameters were set as follows: electron ionization (EI) mode; EI source, 70 eV; transfer line temperature, 250 °C; ion source temperature, 200 °C; emission current, 150 μA; examination voltage, 500 V; 0.2 s for the full scan mode; scan mass range, 29–450 m/z. The peaks were identified by comparing their retention time with that of the known standards, which were determined under the same conditions. A library search was carried out using the Wiley GC-MS Library and the TBAM Library of Essential Oil Constituents.

A QP2020 gas chromatograph/mass spectrometer (Shimadzu Corp.) was used to perform the GC/MS analysis. The gas chromatograph was equipped with a split or splitless injection system and a Rxi-5 ms (30 m × 0.25 mm i.d. × 0.25 µm) capillary column, and MS was operated under ionization by electron impact at 70 eV and 200 °C. The 1-µL samples were injected in the split or splitless mode. Helium flow was maintained at 1 mL/min. The temperature of the column and duration was 40 °C for 3 min, then increased to 280 °C at 20 °C/min, and finally held for 5 min for FAMEs or 8 min for olefins. Mass spectra were recorded at m/z (mass/charge) 45–500 at a rate of 0.2/s.
The extractable olefins were quantified by directly comparing their peak areas with that of triacontane (C30 alkane, 30 carbon atoms) of known concentration, which had been added to the hexane used to extract the olefins. FAMEs were quantified by directly comparing their peak areas with that of eicosanoic acid (C20:0) of known concentration, which had been added to the sample at the beginning of the extraction procedure. For comparison of the olefin amounts produced by different Micrococcales strains, the quantitative data were normalized to a culture density of OD₆₀₀ = 1.