printing ink solvent and paraffin oil standards used for the fortification.
As is visible from the figure, the unspiked sample had no
detectable contamination (natural n-alkanes are visible in the
trace). The MOAH trace evidenced the presence of squalene as typical
for extra virgin olive oil. Average recoveries, calculated on 5
replicate analyses, ranged from 97% to 103% with RSD 6 5.
Fig. 2 shows MOSH and MOAH overlays of the LC–GC–FID traces
obtained for the plum-cake sample before and after fortification
with the printing ink solvent standard (two different fortification
levels) and for the added printing ink standard directly injected.
Since the unspiked sample was contaminated with MOSH in the
same molecular mass range of the paraffin oil, it was not fortified
with this kind of standard for the recovery test. As is visible from
the MOAH traces, the presence of olefins from palm oil interfered
slightly with MOAH detection in the fortified samples, but did
not prevent recovery calculation.
Method accuracy was also confirmed comparing the LC–GC
traces obtained for some selected samples by applying other
extraction methods, as described in Section