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.
The MS/MS analysis was carried out in electron ionization
(EI) mode using the multiple reaction monitoring (MRM) mode.
The ion source was operated at 200 ◦C with electron energy of
70 eV and a filament current of 200 A. Two specific MRM transitions/compound
were chosen. The temperature ofthe interface and
source were set at 200 ◦C and 250 ◦C, respectively. Ultra pure argon
was used as collision gas and the pressure of the chamber maintained
3.5 × 10−3 mbar. The electron multiplier was set at 650V.
The collision energies of each compound were optimized and are
listed in Table 1.
2