Chemistry Reference
In-Depth Information
3
4
a
3
b
3
IS
4
2
1
c
6
8
10
12 14
Time (min)
16
18
20
Figure 17.6
l
of (a) ethyl acetate from a C8-bonded silica/sample mixture, (b) ethyl acetate from a C8-bonded silica/sample
mixture and washing before extraction, and (c) n-hexane from silica/sample mixture. Peak identification:
(1) diazinon, (2) malathion, (3) permethrin, (4) cyfuthrin and (IS) parathion-methyl [59].
Comparison of GC-MS chromatograms obtained by MSPD of 40 mg Porcellio scaber with 100
m
subsequent sedimentation and homogenous packing of the slurry into a column. The two main parameters
affecting the efficiency of the extraction process are the sorbent and the eluent. Proper selection of their
nature and amount can result on specific retention of impurities on the sorbent and selective elution of the
target compounds, and so yield (virtually) ready-to-analyse extracts. When the collected extracts are not
cleaned enough (or the separation-plus-detection technique selective enough), some extra purification step(s)
should be incorporated to the sample preparation protocol. These treatments can be carried out off-line [58]
or, more interestingly, on-line or in-line with the MSPD process. Regarding the latter approach, additional
clean-up of the MSPD eluates can be accomplished by, for example, washing of the packed matrix-sorbent
mixture with a selected solvent for selective removal of interferences before analyte collection [59, 60] or by
packing of an extra sorbent layer at the bottom of the MSPD column [61, 62]. In this case, the chosen sorbent
should perform the selective retention of the interfering components washed up from the MSPD mixture with
the eluent without affecting the target analytes which should pass through this phase unaltered. Figure 17.6
shows an illustrative example of the different degree of clean-up achieved when applying some of these
different strategies to the analysis of pesticides in single insects, for example, 40 mg
Porcellio scaber
[59].
MSPD can be a particularly suitable analytical alternative when dealing with the analysis of limited-size
samples [59, 61]. Other interesting features are its simplicity, the fact it does not require any special equipment
and that it is typically completed in less than 1 h. In addition, when combined with GC-MS or LC-MS for
final determination, LODs in the low-
g g
−1
range are easily obtained even although no extra treatment of the
collected extracts was carried out [59, 63, 64]. In other words, MSPD is not only feasible for the analysis of
relatively abundant components, but also for the determination of trace analytes even if as a small amount of
sample as 25 mg were used [65].
μ
17.2.2.2
Enhanced solvent extraction techniques
The application of enhanced solvent extraction techniques to the miniaturized treatment of (semi-)solid
samples has been, up to now, rather rare in the literature. The lack of dedicated commercial instrumentation
adequate for this type of determination is probably the main reason. Nevertheless, some research groups have
