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HAPSITE ER Operating Manual
The time needed by an individual compound to travel through the GC column to
the detector is referred to as retention time (RT). If the GC conditions remain
constant, the compound will elute from the column at the same retention time on
every analysis.
HAPSITE ER uses internal standards to verify the performance of the Gas
Chromatograph and Mass Spectrometer. The internal standard is composed of
two volatile organic gases which are injected into the sample inlet flow. The
internal standards’ retention times and responses are used to ensure proper
instrument performance.
A graph of eluting gases from the Gas Chromatograph is shown in Figure 2-2. This
graph is called a Total Ion Chromatogram (TIC) and is plotted as a function of time
(x-axis) verses response (y-axis).
Figure 2-2 Total Ion Chromatogram
2.4.1.1 Membrane Isolation Valve
Gas eluting from the GC column passes through the membrane isolation valve.
When the membrane isolation valve is opened, organic compounds are permitted
to enter the Mass Spectrometer.
In the Survey mode of operation, in which air samples bypass the GC directly to
the Mass Spectrometer, the sample pump draws the air sample directly across the
membrane with the isolation valve in the open position.
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