2.6.3 Gas chromatography–mass spectrometry (GC-MS)
Compounds were detected by GC-MS with Agilent 7890B/7200 (30 m × 0.25 mm ID, 0.25 μM film, J&W Scientific Inc., Folsom, CA, USA). For electron impact (EI) mass spectra, the ionization voltage was 70 eV, and the emission current was 34.6 μA (Lu et al., 2012). The temperatures of the ion source and interface were 230 °C and 280 °C, respectively (Lu et al. 2012). Ten μg of each freshly purified GmolCXE was incubated with each ester substrate (final concentration 50 μM) in 20 μL of 20 mM Tris buffer (pH = 7.4) at 28 °C for 1 h. Then the reaction was extracted with 50 μL hexane. The processed samples were measured under the same test conditions by GC-MS. The percentage of conversion was calculated by the product amount of the corresponding alcohol or ester compounds (with two independent replicates) (He et al., 2015).