inlet pressure

Discussions about GC and other "gas phase" separation techniques.

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The front inlet is able to hold the pressure when GC is idle. However, once a sample is injected and analysis begins, the front inlet pressure and column flow rate immediately decrease. How can I fix this?

Many thanks.
Replace the septum.
Peter Apps
Peter Apps wrote:
Replace the septum.


And check the syringe needle for burrs. Wouldn't hurt to check tightness of septum nut AFTER the inlet had warmed it up some.

Decades ago, we had consistent leaking septa issue, would not re-seal after the first injection. These were from the same vendor, same part number as we had used in the past. We tried several, then contacted the supplier; later heard that a bad batch of resin/polymer was the cause.
Thanks for your replies. I will implement your suggestions and see what happens.

Here’s another observation I have - even when I do blank runs (no sample is inserted, initial oven temp is 70 degrees Celsius), the pressure drops immediately. However, when I ramp the oven temperature to 230 degrees Celsius, the GC is able to hold pressure and flow rate.
The septum/loose septum nut was the problem. Thanks again
Good to hear, but be aware an over tightened septa can cause it's own problems. If this is an Agilent S/S injector all you need do is tighten the nut just until the c clamp on top stops turning with the nut.
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