Introduction 1
Advanced Operation 13
Figure 2 Pressure transfer system
Valve and loop systems
The valve and loop system, as used in the 7697A, also heats
and agitates the vial for a specified time. However, the
Agilent system uses a sample loop of known size to collect
the sample. The sampling steps for the valve and loop
system are:
1 A needle probe punctures the vial.
2 The sampler pressurizes the vial with gas. See Figure 3.
3 After equilibration at pressure, the pressurized vial gases
vent through the sample loop, filling the loop with
sample. Note that the vial vents to atmospheric pressure
in this case, not to a high column head pressure. Also,
the 7697A can control the flow of gas into the sample
loop so that the sampling ends before the vial completely
depressurizes.
4 After the sample loop equilibrates, the valve switches and
the sample loop becomes part of the flow path into the
GC inlet. The carrier gas sweeps the known sample
amount into the GC inlet for analysis.
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