15 Inlets
Operation Manual 221
During sampling Pressure upsets caused by switching valves and trap restrictions in the
external sampling device can cause fluctuations in column flow rates. To compensate for this,
the interface is flow controlled during sampling time. The sampling flow rate is calculated from
the pressure setpoint that is active when sample introduction begins. This flow control starts
when the GC goes into the Pre Run state (when your system is automated and the Pre Run
light is on or during manual operation when you press ) and ends after the interface’s
Sampling end setpoint expires.
Sampling end is required for purge and trap or thermal desorption systems and should be set
the sampler desorb time.
During this user-specified sampling period, the solenoid valve is closed. Flow to the interface is
measured by a flow sensor and controlled by a proportional valve.
After sampling end The solenoid valve opens. The system returns to the Before Prep Run
state. Flow to the interface is again measured by a flow sensor and controlled by a
proportional valve while column flow is controlled via back-pressure regulation. The purge flow
is controlled by the user. If desired, gas saver can be turned on at the end of the run.
Valve
Frit Frit
Frit
Valve
EPC Module
Valve
Split Vent Trap
Gas Sampling Valve
Headspace
Purge and Trap
FS = Flow Sensor
PS = Pressure Sensor
Column
FS
PS
PS
Split
Carrier Supply
80 PSI
Septum Purge
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