PerkinElmer TORION T-9, User Manual

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28 . Torion T-9 User’s Guide
This chapter provides an overview of solid phase microextraction (SPME), low thermal mass (LTM)
gas chromatography (GC) and toroidal ion trap mass spectrometry (TMS)
What is solid phase microextraction (SPME)?
Solid phase microextraction (SPME) is a sampling method for extracting target chemicals from a gas,
liquid or dissolved solid sample and concentrating them for subsequent analysis. Compared to
liquid-liquid extraction and cartridge-based solid phase extraction, SPME is faster and less prone to
user error. Following extraction, SPME allows immediate introduction of sample into the analytical
instrument.
SPME consists primarily of a fused silica or metal rod that is approximately one centimeter in length
and a tenth of a millimeter in diameter. The rod is typically coated with a polymeric material called
a sorbent. The rod and sorbent together are referred to as the SPME fiber. The chemical properties
of the sorbent determine the classes of compounds that selectively absorb or adsorb onto the fiber.
Solvents should not absorb preferentially over target chemicals, otherwise a different sorbent or
solvent may be necessary.
The SPME fiber is stored inside a protective needle called the SPME needle. The fiber is extended
out of the SPME needle during the extraction and desorption of a sample. The SPME needle is
connected to a spring loaded plunger that extends and retracts the fiber. The complete apparatus is
called the SPME syringe.
Each chemical is extracted into the SPME coating according to its equilibrium distribution between the
coating on the fiber and the liquid (or gas) phase around the fiber. This equilibrium depends on the
chemical nature of the polymeric phase, the solvent, the temperature, and the volume of both the
polymeric phase and the solvent. Extraction can take under a minute depending on sample volume
and concentration. Equilibration of the fiber with its surrounding matrix usually requires a longer
period of time (several minutes to several hours). After equilibrium has been achieved, the
concentrations of target chemicals on the fiber and in the solution remain constant. The amount of a
chemical extracted by the fiber is proportional to the concentration of the sample before and after
equilibrium.
Sensitivity to a target chemical extracted by SPME can be improved significantly in three ways:
increasing the sorbent thickness on the sampling fiber, employing a more selective sorbent, or
changing the extraction temperature. A thicker sorbent layer absorbs more target chemical, increasing
the sensitivity to all absorbed chemicals; however, thicker sorbent also increases the equilibration time
between the absorbed chemical and the chemical in solution. Rather than thicker sorbent, longer fibers
may be used to increase sensitivity; however, longer fibers may not be used on the Torion T-9 GC/MS,
the instrument is not designed to accept them and they may break inside the injection port. Sorbents
with greater selectivity to the target chemicals will improve sensitivity; however, they may also increase
the extraction of unwanted chemicals. Finally, changing the extraction temperature will affect the
sensitivity of a target chemical. The sensitivity for high mass and high boiling chemicals will generally
improve with increased temperature, particularly for headspace (gas) extractions. Increasing the
temperature will also decrease the equilibration time. High temperature extractions of volatile
chemicals in solution may decrease the sensitivity to those chemicals when sampling by immersion
because volatile chemicals are more likely to leave the solution as vapor at higher temperatures.