Help please! Column head pressure drop??

[slee]

Hi, I'm doing GC experiment with 55 m x 0.25mm ID column. I set the head pressure at 25 psi with split ratio of 100:1. During experiment, the head pressure drops from 25 psi to 5 psi, and I don't know the reason. The split flow rates also drops from 89 ml/min to 0.0 ml/min. My carrier gas is He. I checked the gas cylinder, and the pressure at the cylinder was always 60 psi.

This symptom sometimes doesn't happen.

Does anyone know a possible reason?

[Ron]

You either have a gas supply issue or a huge leak somewhere in the system. This needs to be identified and fixed immediately before the column is damaged.

The first thing I would do is verify the incoming carrier gas has the proper pressure and flow to supply the gas throughout the run. If you are on a manifold system be sure that there is not another device upstream that periodically demands high gas flow and is starving your system.

Check the method and make sure there is nothing in the method that turns down head pressure and flow during the course of the run, although this should be consistent.

Do the standard maintenance of inlet and detector, and check all consumables, no cored septum, cracked liner, bad O-ring, etc.

Reinstall the column in the injection port with a new ferrule.

These are some of the common things that cause this kind of problem.

[slee]

Hi Ron, thanks for your reply.
I've found that the problem was the septum rubber is too old and it makes Helium gas coming through the sample loading part.
Your advice helped me a lot, though.