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These two algae metabolites have a strong muddy/musty
odour character and the human nose can detect them at
the 4 20 ng l 1 level. Some fungal metabolites (2-pentanol,
2-heptanone, etc.) are also very good indicators of water-
damaged, mould-infested building materials.205 The main
advantages of using SPME to solve these problems is that
SPME is a hand-size extraction device and it can be easily
used as a field sampler.
NEW DEVELOPMENTS
New developments in SPME sample preparation are
directed at developing smaller volumes for the extraction
fibres206 and further development of the in-tube extraction
technique.28,29 Miniaturized sample preparation methods
have been regarded as the most attractive techniques for (1) (2) (3) (4) (5)
the pretreatment of complex sample mixtures prior to the
Figure 16. Procedure of small-volume SPME extraction.
chromatographic process. The main advantages of the minia-
Reprinted from Journal of Chromatography A, 988, Zhu PL, Liu
turized systems are high-speed analysis with high efficiency,
CL, Liu MC, Solid-phase microextraction from small volumes
low cost and environmentally friendly operation due to
of sample in a glass capillary, page 27, Fig. 1, Copyright
the minimal or no solvent consumption, and highly selec-
(2003), with permission of Elsevier.
tive analysis by developing tailored systems designed for
particular applications.28 33 Extracting very small amount
A promising new application is the use of SPME extrac-
of samples (10 35 µl) is difficult but in a biological sam-
tion fibres for matrix-assisted laser desorption/ionization
ple treatment sometimes the sample amount is very limited
(MALDI)207 or direct coupling to electrospray/nanospray.208
(saliva, mouse urine, etc.) and many extractions should be
The concept of coupling SPME to MALDI is to combine
done from a small amount.206 On the other hand, the short
sample extraction with the ionization procedure on the
diffusion path (which is very important when the matrix
tip of a fused-silica optical fibre for biomolecular analy-
is highly viscous, such as plasma) favours establishment
sis. The sample end of the fibre was silanized with 3-
of equilibrium, and therefore the extraction times are much
aminopropyltriethoxysilane (APTES) for the extraction of
shorter. Next, even if the concentration of analytes is at a high
analyte. Laser energy was transferred through the other end
level, the total amount of analytes in the small volume is still
of the optical fibre to ionize and desorb the biomolecules
low and the linear range of the calibration curve obtained by
for the subsequent analysis. This SPME/MALDI fibre was
SPME will extend to higher concentrations. The technique is
combined with an ion mobility spectrometer and a tan-
less affected by experimental conditions, therefore it is more
dem quadrupole time-of-flight mass spectrometer for the
reproducible. Finally, the small-volume sample also reduces
detection of the MALDI signal. A schematic diagram of the
possible interferences from the components in the matrix.
SPME/MALDI system combined with ion mobility mass
The small-volume sampling procedure is almost the same
spectrometer can be seen in Fig. 17.207 The SPME/MALDI
as in conventional DI-SPME. A schematic of the sampling
combination possesses several attractive attributes such as
process is shown in Fig. 16.206 First take a 5 cm length of 0.65
or 1.00 mm i.d. glass capillary and suck a 0.9 1.0 cm liquid the simplicity of sample preparation, minimized sample han-
column from the sample vessel (1), then fix the capillary dling and one-step sample extraction/concentration directly
in a vial with the aid of a septum (2). Insert the needle of from the biological sample on to the sample support. Only
the SPME fibre holder into the capillary (3) and depress the the preparation of the fibres requires extra time, but the fibres
plunger to expose the fibre to the sample solution (4). Finally, can be used for about 500 extractions (or laser shots). High
retract the fibre and withdraw the needle from the vial (5) biospecificity can be expected by employing the antibody-
after equilibrium is reached. immobilized SPME technique for the extraction of comple-
A direct extraction probe has been developed by mentary antigen. The application of this technique holds
Pawliszyn s group, which is suitable for the direct extrac- promise especially in biochemical analysis, pharmaceutical
tion of metabolites from veins in in vivo pharmakokinetic research, clinical diagnostics and screening.
studies.20,21 Using a polypyrrole-coated extraction probe, Another interesting application for SPME sample prepa-
dynamic living systems can be monitored without taking ration is capillary electrophoresis (CE) or CE/MS.209 The
blood samples. This is a kind of direct immersion SPME prospects for CE in analytical applications are highly promis-
sampling, well suited for the determination of drug concen- ing because of its very high separation efficiency, short
trations and protein binding. The sensitivity of the method analysis time and low consumption of expensive and toxic
in the low µgl 1 range and shows good linearity. This also solvents. Combining the advantages of CE/MS analysis with
allows the study of drug/metabolite concentrations at mul- the simplicity of SPME extraction, off-line SPME/CE/ES-
tiple sites in one specimen, helpful for the identification of MS was developed by Rodriguez et al. for the analysis of
metabolic pathways. acidic pesticides in fruits. The CW-TPR extraction fiber was
Copyright © 2004 John Wiley & Sons, Ltd. J. Mass Spectrom. 2004; 39: 233 254
Solid-phase microextraction 251
FIMS (3 5 min extraction time) from aqueous solutions at
Vo
the low gl 1 level.
V
4
6
7
2
CONCLUSIONS
1
5
SPME is becoming widely used as an extraction and
L(td)
3
concentration step prior to MS analysis. It affords a number
Lo
of advantages in simplifying sample preparation, increasing
reliability, selectivity, sensitivity and reducing the cost and
time of analysis. The majority of early applications were
encountered in environmental applications for screening and
9 8 9
semi-quantitative purposes. Recent papers have described
the use of SPME in various fields of analytical MS, including
Figure 17. Schematic diagram of SPME/MALDI-IMS system.
quantitation. Fibre SPME for the extraction of volatile
(1) Laser source; (2) focusing lens; (3) photodiode; (4) fibre
components from HS is most widely used and novel
holder; (5) SPME/MALDI fibre; (6) IMS, (7) oscilloscope; (8)
derivatization procedures may further extend the utility of
glass tube; (9) fixing septum; V0 and V, designed and effective
this technique. The versatility of fibre SPME is enhanced by
high voltage in drift tube, respectively; L0, drift tube length; L,
the possibility of direct insertion into the sample matrix for
ion drift length; td, ion drift time. Reprinted from The Analyst,
the analysis of less volatile components. Significant benefits
127, Tong H, Sze N, Thomson B, Nacsonc S, Pawliszyn J,
may be gained this way; however, direct insertion methods
Solid phase microextraction with matrix assisted laser
often require sample agitation and require longer extraction
desorption/ionisation introduction to mass spectrometry and
times than HS methods. For the analysis of biological fluids [ Pobierz całość w formacie PDF ]