used with ionization energy of 70 eV. Heliumwas the carrier gas, at
a flow rate of 1 ml min_1. Injector and detector (MS transfer line)
temperatures were set at 220 and 290 _C, respectively. Column
temperature was initially at 50 _C, then gradually increased to
150 _C at a 3 _C min_1 rate, hold for 10 min and finally increased to
250 _C at 10 _C min_1. Diluted samples (1/100 in acetone) of 1.0 ml
were injected manually and splitless.
Retention index (RI) of all the constituents were determined by
the Kovats method by co-injection of the samples with a solution
containing the homologous series of n-alkanes (C8eC24) (Fluka,
Buchs/sg, Switzerland) on the HP-5 MS column. Identification of
the components was made by visual interpretation, comparing
their retention indices and mass spectra with data published in the
literature (Adams, 2001) and by matching their recorded mass
spectra with reference spectra in the computer library (NIST MS
library, Version 2.0). Quantification was computed as the percentage
contribution of each compound to the total amount present.