Sub samples of the WAFs of each oil type were
extracted in dichloromethane and stored in the dark at
20 C until analysis. A 100 ml aliquot of WAF extract
sample was added to an amber vial with a self-guiding
glass insert and teflon septum under the cap. The extract
was concentrated under a stream of high purity N2 to 90
ml and 10 ml of internal standard (C20:1 alkene) was
added. Standards of fatty acid methyl-esters (FAMES),
aromatic hydrocarbons and n-alkanes were run with
each batch of samples. Samples were analyzed on a
Hewlett Packard 6890/5973 Series GC/MS system in
pulsed split less mode with helium as a carrier gas. The
column used was a 30 m0.32 mm i.d.0.25 mm film
thickness (J&W DB-5MS, Agilent Technologies, MA,
USA). The flowrate was 1.6 ml min1 and the temperature
gradient 50–300 C at 4 C min1, held at 300 C
for 15 min. The MS scanned 50–550 AMU and was
operated at 280 C. All oil types were analyzed by GC/
MS, including the two-stroke vegetable oil additive.
Compound identification was facilitated by the
National Bureau of Standards Mass Spectroscopy
(NBSMS) library. Quantification of the aromatic components
was achieved by using response factors generated
from naphthalene and methyl-naphthalene
standards. Total hydrocarbons (THC-GC/MS) were
estimated by summing the contributions of each
component for each WAF.