advantage that higher sensitivity can be reached because the sample
extract can be concentrated before injection without exceeding
the capacity of the LC column (20 mg). The higher the fat content of
the sample is, the higher the sensitivity increase reached by using
MAS prior to on-line LC–GC. Furthermore, co-extracted fat injected
into the LC column is not completely eliminated during the backflush
with dichloromethane and slowly accumulates in the column
decreasing progressively its capacity. For this reason, after a number
of fat injections, an intense wash of the LC column with isopropanol
and/or methyl tert-butyl ether is required, which can be
performed less frequently when using MAS.
Fig. 4 shows the LC–GC trace of a biscuit sample (5 g) with 25%
of fat, extracted overnight with hexane (10 mL) and directly
injected (100 lL), without previous reconcentration to not exceed
the column capacity. It also displays the trace of the same biscuit
sample processed with MAS and injected after a 5-fold reconcentration
to reach higher sensitivity (LOQ around 0.1 mg kg1).