Scienti®c, Fulsom, CA 95630, USA) with a helium carrier
gas flow rate of 1 ml/min in constant flow mode
using electronic pressure programming. The oven temperature
programme was: 408, increased at 58/min to
2808 and held isothermally for 5 min. The quadrupole
mass spectrometer was scanned over the range 20±300
a.m.u. at 1 scan/s. The combined EI/CI source was
used in Electron Impact mode with an ionisation
energy of 70 eV and a trap current of 300 mA. Source
temperature was held at 2508. GC±MS data were processed
using the Hewlett Packard G1034 MA
Chemstation. Component identi®cation was carried
out using the Wiley 138 K mass spectral database and
from retention times and mass spectra of authentic
standards when available. For two components (E)-abergamotene
and b-sesquiphellandrene, mass spectral
identi®cation was con®rmed from analysis of essential
oil samples of bergamot (Citrus bergamia ) and ginger
(Zingiber ocinale ) respectively.