Static Headspace Sampling Techniques - Agilent Technologies 7697A Advanced Operation Manual

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Introduction

Static headspace sampling techniques

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Static headspace sampling: This technique uses a closed
sample container and a sampling system. After placing the
sample matrix into the sealed sampling vial, the sample
matrix is heated for a specified time, during which the vial
can also be agitated (shaken) to help drive volatile
compounds from the matrix and into the headspace volume.
After a specified time, the vial is punctured, pressurized,
and an amount of the headspace vapors are withdrawn and
injected into the GC inlet.
Solid Phase Micro Extraction: In this technique, a probe
with an adsorbant is placed into a vial that contains the
sample matrix. The analytes of interest adsorb into the
sample probe. Use of different adsorbants provides flexibility
for analyzing different compounds of interest (while ignoring
others). After a specified time, the probe is heated to drive
off the analytes, which are swept onto the GC column.
There are two main static sampling headspace techniques,
pressure- transfer and valve and loop. (A third technique,
performing the injection manually using a gas- tight syringe,
does not provide easily reproducible results.)
Pressure transfer systems
The pressure- transfer system uses a specialized needle for
vial pressurization and sampling. The vial is heated and
agitated for the desired time. Then, the sampling needle
punctures the vial, and carrier gas pressurizes the vial. After
an equilibration time, the needle allows pressurized gas to
flow into the GC inlet for a specified duration. Typically, the
sample gas flows into the GC inlet due to the pressure
difference between the sample vial and the GC inlet. While
the results are repeatable, exact amount of sample gas is
unknown.
Advanced Operation