Clarus 600 gc ms system

BVOC sampling procedure and quantitative method were as described in Chen et al. (2019) [21 (link)]. The healthy leaves were carefully enclosed in a glass sampling chamber (Figure 2). The BVOCs emitted from leaves to the chamber were collected with sampling tubes (200 mg Tenax TA, mesh 60/80, Supelco, Bellofonte, PA, USA), installed in a modified autosampler (STS-25^®; PerkinElmer, Waltham, MA, USA) with 150 mL min⁻¹ flow rate for BVOCs to flow into the absorbent. Each sampling tube collected BVOCs emitted for a period of 60 min, every h during daytime (04:00–16:00) and every 2 h during nighttime (18:00–04:00), with 8.25 L BVOCs collected per sample tube. BVOC sampling tubes were brought back to laboratory every day for analysis on contents and concentrations of BVOCs. The sample tube was analyzed using gas chromatography mass spectrometer (GC-MS) (Clarus 600 GC-MS system, PerkinElmer Instruments, USA) equipped with a thermal desorption system (Turbo Matrix ATD, PerkinElmer Instruments, USA). The data of 17 sampling tubes in one day were combined to represent the BVOCs emitted by the sapling. After sampling, shoots in the sampling chamber were cut, then placed in 100 °C for 48 h, and finally weighed to obtain the absolute dry biomass.

P. minus essential oil compounds were identified using GC-MS analysis (Ahmad et al., 2014[2 ]) using the Clarus 600 GC-MS system (PerkinElmer, USA). Volatile compounds were separated using a 30 m x 0.25 mm x 0.25 µm Elite-5MS column. The injector port was heated to 250 °C with helium as carrier gas at a constant flow of 1 mL·min^-1. All mass spectra were acquired in the electron impact mode (EI). The MS parameters were as follows: EI mode, an ionization voltage of 70 eV, an ion source temperature of 200 °C and a scan range of 40 - 600 Da. The peaks were tentatively identified based on a library search using NIST and Wiley Registry 8 Edition (Ahmad et al., 2014[2 ]).