Analysis was performed on a Waters Micromass Quattro micro
GC tandem mass spectrometer (Waters, USA) and an Agilent 6890
GC equipped with a 30m × 0.25 mm × 0.25 m DB-5MS capillary
column (Agilent Technologies, Foster City, CA, USA). Helium was
used as carrier at a constant flow rate of 1.0 mL/min. 1 L sample
was injected splitlessly at 280 ◦C. After a holding time of 0.5 min,
the GC oven temperature program was from 70 ◦C to 180 ◦C at a
rate of 20 ◦C/min and then increased to 220 ◦C at 2 ◦C/min followed
by 30 ◦C/min to 280 ◦C, with a final hold time of 2 min.