Agriculture Reference
In-Depth Information
isolation, and enrichment in one step. SPME can be connected easily to a GC and LC
system using available interfaces. Thus, SPME can reduce the time required for
sample preparation and eliminate the use of large volumes of extraction solvents.
Besides the properties of surface coating, analytes, and sample matrix, the
concentration of analytes is also an important factor for optimization with both
tube and
fiber SPME. The headspace sampling SPME is a little more complicated
because of the heterogeneous phases in sample vials at the adsorption step: one factor
is the distribution coef
liquid);
another factor is the volume ratio of the two phases. These factors are affected by
temperature, sample volume, and sample matrix. Since the introduction of SPME, it
has become a practical, low-cost alternative for sample preparation for GC
cient of the analyte in two phases (gas
-
solid or gas
-
MS. New
surface coating materials extended SPME from small molecule to large molecule
analysis, from food sample to blood or tissue samples, and from in-lab sample
preparation to on-site sample preparation. Besides the application of SPME to GC
-
-
MS, SPME has been applied to analyze mycotoxins (ochratoxins A and B) in nuts and
grain samples and insecticides in honey by LC
MS [38,39]. It is believed that SPME
will become a practical alternative for sample preparation for LC
-
-
MS in the future.
1.2.8 Microextraction by Packed Sorbent
Microextraction by packed sorbent (MEPS) is a new development in the
eld of
sample preparation and sample handling. It entails the miniaturization of conventional
SPE packed-bed devices from milliliter bed volumes to microliter volumes. MEPS
can be connected online to GC or LC without any modi
cations. In MEPS,
1mgof
∼
the solid packing material is packed inside a syringe (100
l) as a plug or between
the barrel and the needle as a cartridge. Sample preparation occurs on the packed bed.
The bed can be coated to provide selective and suitable sampling conditions. The
combination of MEPS and LC
-
250
μ
MS is a good tool for screening and determining drugs
and metabolites in blood, plasma, and urine samples [40].
MEPS has also been applied to food and beverage analysis, including the analysis
of bio
-
avonoids from red wine, diterpene glycosides from tea extract, pesticides and
PCB in fats, a
atoxin B
2
and M
2
metabolite trace analysis in milk, mycotoxin trace
analysis in cereals, fatty acid methyl esters (long chain) in fermentation medium,
omega-6 fatty acid in malt lipid, pigment anthocyanidins in wine, atrazine in cereals,
sulfonamide trace analysis in meat, penicillin in dairy products, and cork taints in
wine [41].
1.2.9 Liquid Extraction Surface Analysis
LESA was developed at Oak Ridge National Laboratory [42] to bring the bene
ts of
nano-ESI/MS to surface analysis and to automate surface sampling for faster and
more effective analyses. This approach mainly involves three steps. In step 1, a robot
aliquots a sample of extraction and sprays solvent into a pipette tip. In step 2, the
solvent in the pipette tip is dispensed/aspirated onto the sample surface (e.g., an apple
skin) to perform extraction of any chemicals on the surface of the apple. The pipette
