Gas chromatography-mass spectrometry
GC-MS analyses was performed on a Fisons Instrument GC 8000
equipped with an electron impact quadrupole, MD 800 mass spectrometer
detector. The electron ionisation energy was 70 eV, ion-source temperature
200°C and the interface temperature 280°C.
A fused silica capillary column 5% phenyl-poly-dimethyl-siloxane
(DB-5MS 30 m x 0.32 mm i.d. and 0.25 μm film thickness, J&W Scientific)
was used. The column temperature was programmed as follows: from 40°C
(3 min hold) raised at 4°C/min to 250 °C and finally held at 250 °C for 10
min. A split-splitless injection (split ratio 1:30) at 280 °C was employed.
The carrier gas (helium) flow rate was 2 mL/min. Two μL of sample were
injected. Data acquisition was performed with MassLab software for the
mass range 30 - 600 u with a scan speed of 1 scan/s. The identification of
compounds was performed by comparing their mass spectra with data from
Adams [19], US National Institute of Standards and Technology (NIST,
USA), WILEY 1996 Ed. mass spectra library and a personal library of 600
spectra. The identification of compounds was also based on the Kovats
retention indices.
The Kovats retention indices were calculated using n-alkanes C8-C20
and C21-C40 and the experimental values were compared with those reported
in literature [20, 21].