Chromatography Forum

Hi,

I am working on brining an Agilent GC 6850 coupled with an FID back online. I have worked out most of the kinks, but I am stuck on maintaining front inlet pressure. I have: replaced the septum, tightened the connections, checked that there is flow through the column, and replaced all of my inlet gas tanks so I know they are full.

The column that is installed is an Agilent DB-FFAP 15mx0.10mmx0.10micro m.

I will take any and all suggestions.

Thank you ,

Catherine

Do you have the correct column dimensions entered in the GC? If this is wrong, the GC may think it can't build pressure. This needs to be correct. I have had to enter a incorrect length before to get past this problem. Yes - I know - I probably should have recalibrated the inlet pressure instead.

If this isn't the problem, then check the inlet alone to see if it will hold pressure. You can remove the column and install a no-hole furrule. If you don't have one of those, install a short length of column (or just cut the existing one off - leaving an inch or so hanging out of the inlet). Plug the end of the length of column with a septum. You may need a new gold seal at the base of the inlet. I've never needed to, but it does happen.

If the inlet holds pressure, then you have a column problem. Could be a pin-hole or small crack. It happens and you could spend hours trying to find it. Replace the column if it won't hold pressure, if you can.

I have the column programmed in so I will try the other suggestions before adjusting the computer parameters.

Thank you,

Catherine

Bad EPC?

I'd check for tightness leaks inside the column compartment, under the inlet. Like the gold seal must have a sealing washer (new is best) or use a gold seal with the vespel-type sealing ring.

Also, all the connections out through the EPC must be leak-free, as the control is actually after the injection port.

Check that the inlet is configured for the correct carrier gas type. A mis-match can cause inlet pressure and column flow issues.

Step number one needs to be to check all connections for leaks with a leak seeker.

What pressure is the inlet trying to get to ?, and what does it achieve ? Are you setting a flow or a pressure in the method, and what are the settings ?

Do you have flow out of the split outlet and septum purge, and do the volume flows match the settings ?

Peter

Hi,
...I will take any and all suggestions.

Thank you ,

Catherine

Increase split ratio in the inlet to 10:1. What happens to the pressure then ?

It sounds silly but you had to know they guy, check the bottom of your inlet where the gold seal contacts the bottom of the inlet and make sure there are no scratches or nicks in the surface. It should be slightly rounded but smooth.

I had one on an old 5995 GC/MS that would not build pressure and I noticed that when looking at the top side of the gold seal that the circular impression was not complete. I looked at the bottom of the inlet and there was a big nick in it. Seems the guy before me had an inlet liner stuck in the port and it took the bottom off and hit it with a large adjustable wrench trying to knock it loose.

What is your cylinder regulator pressure? I like mine set at 80 PSI. If that's OK, you probably have a leak or a problem with the EPC as suggested by everyone else. It could also be a bad regulator. Good luck. Please let us know what you find.

You are using a very small column on a 6850. I don't know for sure but I don't believe it is meant for 0.1 id. Can I suggest you try a 30 m X 0.25 to see if this will meet pressure?

Best regards,

AICMM