of substances in terms of polarity can be successfully extracted by this method. The
only precondition is an insolubility of the adsorption material in both, water and
solvents. However, disadvantages are a limited potential for automatization, a
notable runtime of around 1–2 h and a more difficult and partly challenging selection
of appropriate adsorption materials.
A variation of this method is the miniaturized technique solid-phase-microextraction (SPME). It is also a liquid/solid extraction that uses a very thin polymer
fiber placed at the top of a syringe. The adsorption takes place directly in the sample
by inserting the fiber into the stirred liquid phase. After a certain time of around
20–40 min, the syringe is lifted up and protects the fiber. Thereafter, the syringe
needle including the fiber can be directly injected into a gas chromatograph (GC) and
due to the high temperature in the injector (around 250–300
C) the adsorbed
analytes can be directly vaporized and transferred to the GC column for further
analyses (see also Sect. 4.1.1 for further information about GC). According to this
procedure, the technique has been developed for volatile to semi-volatile substances
and for a direct transfer to a gas chromatograph. Therefore, polar or low-volatile
substances are excluded and more complex matrices, that need further fractionation
or cleaning steps prior to GC measurements, are not suitable for SPME. However,
the method is fast, needs no further solvents and avoids external contaminations.
Beside the direct SPME of the liquid phase, also a head space approach can be
used. Here, the vapor space above the slightly heated liquid sample is extracted by
the fiber and, consequently, only the high volatile analytes that accumulate in the
head space, are enriched on the fiber for further analyses (Fig. 3.7).
SPME (Solid Phase Micro ExtracƟon)
Piston
Injector
270 °C
Fiber holder
Direct
extracƟon
in sample
ExtracƟon
in vapor
space
Flexible
coated fiber
Fig. 3.7 Application process of SPME for liquid extraction
24
3 Sample Treatment
only precondition is an insolubility of the adsorption material in both, water and
solvents. However, disadvantages are a limited potential for automatization, a
notable runtime of around 1–2 h and a more difficult and partly challenging selection
of appropriate adsorption materials.
A variation of this method is the miniaturized technique solid-phase-microextraction (SPME). It is also a liquid/solid extraction that uses a very thin polymer
fiber placed at the top of a syringe. The adsorption takes place directly in the sample
by inserting the fiber into the stirred liquid phase. After a certain time of around
20–40 min, the syringe is lifted up and protects the fiber. Thereafter, the syringe
needle including the fiber can be directly injected into a gas chromatograph (GC) and
due to the high temperature in the injector (around 250–300
C) the adsorbed
analytes can be directly vaporized and transferred to the GC column for further
analyses (see also Sect. 4.1.1 for further information about GC). According to this
procedure, the technique has been developed for volatile to semi-volatile substances
and for a direct transfer to a gas chromatograph. Therefore, polar or low-volatile
substances are excluded and more complex matrices, that need further fractionation
or cleaning steps prior to GC measurements, are not suitable for SPME. However,
the method is fast, needs no further solvents and avoids external contaminations.
Beside the direct SPME of the liquid phase, also a head space approach can be
used. Here, the vapor space above the slightly heated liquid sample is extracted by
the fiber and, consequently, only the high volatile analytes that accumulate in the
head space, are enriched on the fiber for further analyses (Fig. 3.7).
SPME (Solid Phase Micro ExtracƟon)
Piston
Injector
270 °C
Fiber holder
Direct
extracƟon
in sample
ExtracƟon
in vapor
space
Flexible
coated fiber
Fig. 3.7 Application process of SPME for liquid extraction
24
3 Sample Treatment