2.4. Standard addition for recovery tests
A printing ink solvent (containing 91% of MOSH and 9% of
MOAH in the n-C14–C20 range) and/or a paraffin oil (100% MOSH
in the n-C24–C40 range) were used for recovery tests. The recoveries
were calculated by comparing the chromatographic area of the
spiked sample subtracted from the area obtained for the unspiked
sample (with no detectable contamination or with low contamination
levels), with that of the same amount of standard used to spike
the sample.
The pasta samples as well as biscuits and plum-cakes were
finely ground, weighed directly into the extraction vessel (5 g),
added with mineral oil standards dissolved in 5–10 mL of pentane,
and gently stirred for 30 min to uniformly distribute the added
mineral oil (the added solvent evaporated during stirring) and
were left to age for 3 days before MAS.
The bread samples for recovery tests were prepared using a
bread machine (Severin, mod. BM 3981) to knead 400 g of flour
type ‘‘0”, 280 g of tap water, 16 g of extra virgin olive oil and 4 g
of yeast. The mineral oil standard was added to the extra virgin
olive oil used to make the bread. After kneading and leavening,
the dough was baked according to the machine program. Two
bread samples were prepared: one with the unspiked extra virgin
olive oil and the other with the same oil spiked with a known
amount of printing ink solvent and paraffin oil.