Chemistry Reference
In-Depth Information
Extraction
Trapping & clean-up
GC-analysis
W
1
W
4
10
V4
N
2
V1
2
9
3
5
P3
8
V2
W
P1
W
110°C
6
P2
70°C
V3
W
AC
7
Figure 17.7
Scheme of the DMAE-SPE-LVI-GC system: (1) microwave oven, (2) preheater, (3) extraction
vessel, (4) mixing tee, (5) thermocouple, (6) temperature regulator, (7) restrictor, (8) SPE cartridge, (9) PTV-GC-
NPD and (10) fused-silica leak.
developed their own instruments or adapted conventional ones in order to perform pressurized liquid
extraction (PLE), microwave-assisted extraction (MAE) or ultrasonic-assisted extraction of selected analytes
from solid and semisolid matrices with minimum consumption of sample, solvent and chemical reagents.
The first miniaturized PLE systems were described in the literature 10 years after the introduction of the
technique. In some of these systems, a GC oven was used to heat up the extraction cell and, when water was
used as extractant, the coil installed before the cell [66, 67]. In other cases, a dedicated instrument with a
miniaturized oven was designed [68, 69]. In one of these systems [68], a heatable 10 × 3.0 mm i.d. stainless-
steel extraction cell was used for quantitative extraction of the 16 EPA PAHs (recoveries, 90-110
%
) from
50 mg soil with only 100
l of this raw extract into a PTV system
containing an appropriated sorbent, enabled in-liner clean-up of the extracts before GC-MS analysis and
ensured LODs as low as 2-9 ng g
−1
soil for a large majority of the target compounds. Despite the very
heterogeneous samples investigated, satisfactory RSDs in the 2-15
μ
l of toluene. Direct injection of 50
μ
range were reported. Replacing the
original small size ceramic oven by a larger one resulted in an increased flexibility regarding the extraction
cell size used [69]. This contributed to wider the range of possible application studies as well as that of the
analytical strategies to be used. As an example, the system was employed for the selective pressurized
extraction of endogenous PCBs from foodstuffs of animal origin, including complex fatty matrices such as
fish, meat and eggs with satisfactory results.
The studies involving miniaturized MAE system are still extremely scarce in the literature. After the first
attempt reported by Cresswell and Haswell [70], Ericsson and Colmsjo [71] proposed inserting a preheating
column in front of the extraction cell in the microwave cavity and the back-elution of the target compounds
from the 10 ×2 mm PLRP-S SPE disposable cartridge used for on-line SPE of the extracted PAHs. The
method involved only 60 mg of sample and 400
%
l of MTDE as an eluent and demonstrated a satisfactory
performance for the determination of the target compounds in a reference sediment (recoveries 88-104
μ
%
,
RSDs 1-10
). The system was subsequently hyphenated with a GC equipped with a nitrogen-phosphor
detector (GC-NPD) for on-line analysis of organophosphate esters in air samples [72]. A schematic diagram
of the set-up used in this study is shown in Figure 17.7.
Despite its many positive features, the use of ultrasound for analytical applications is relatively recent.
Nevertheless, some applications have already demonstrated the potential of sonication for the miniaturized,
rapid, relatively inexpensive and quantitative extraction of several types of analytes, ranging from metals to
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