Agriculture Reference
In-Depth Information
solvation power and change extraction kinetics. Raised temperature can also disrupt
the strong solute
matrix interactions. The process reduces solvent consumption and
operating time so as to increase the extraction ef
-
ciency. The automated PLE system
can automatically load up to 24 samples in one batch. The sample cell is of different
sizes, such as 1, 5, 10, 22, 34, 66, and 100ml. Azamethiphos, avermectins,
carbamates, and benzoylurea pesticides as well as chemotherapeutic agents in
seaweeds were determined using PLE and separation of analytes by LC
MS/
MS [33]. The applications of PLE in the analysis of food samples have been
comprehensively summarized by Mustafa and Turner [34].
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1.2.6 Automated 96- and 384-Well Formatted Sample Preparation as well as
Automated SPE Workstations
Although automated 96- and 384-well extractions (e.g., LLE and SPE) have been
widely used for bioanalysis [35], they have not yet been widely applied for food safety
analysis. The possible reasons are mainly attributed to the high cost of automated
extraction equipment and more varieties and relatively larger sample size of food
samples. Some new automated SPE workstations can handle a much wider range of
sample sizes (1
6ml/40ml). Therefore, they can overcome some of the limitations. For
example, an autosampler-compatible cartridge (Strata-X, 3ml/200mg, SPE cartridge)
was applied in an automated SPE workstation to detect acrylamide in brewed coffee by
LC
-
MS/MS [36]. We predict that the application of automated extraction systems will
draw more and more attention for food safety analysis in the near future.
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1.2.7 Solid-Phase Microextraction
SPME was introduced in the early 1990s as a simple and effective adsorption/
absorption (based on the solid/liquid coating) and desorption technique. Instead of
using a syringe to pick up and inject sample into a chromatography instrument, SPME
uses a piece of bonded-phase capillary tube or metal/polymer
fiber to load (adsorp-
tion) and introduce (desorption) sample into instrument. The device with a bonded-
phase capillary tube is called in-tube SPME and the device with a bonded-phase
ber
is called
ber SPME.
The capillary tube for in-tube SPME is like a short GC column. When the sample
solution goes through the tube, the bonded phase is enriched in analytes through
absorption/adsorption. After the solvent is dried by a gas
flow, the sample becomes a
film adsorbed on the surface of the tube, and is then desorbed with heat and introduced
into the instrument. The
fiber SPME uses the same steps of absorption/adsorption
-
desorption as does in-tube SPME. The difference is that the
fiber can be immersed into
a solution, which is called liquid immersion SPME, or be held above solutions or solid
particles/powders to adsorb the vapor from such samples, which is called headspace
SPME [37].
Because different surface coatings (bonded phases) have different selectivities to
different compounds, choosing an appropriate SPME
fiber or tube can differentiate
these compounds from a sample matrix. Therefore, SPME can combine sampling,
