Purged packed inlet troubleshooting

[chemguyb]

Hi, this is my first time posting on this forum and I am in need of assistance.

I have a GC-MC setup, with a capillary column on the front S/SL inlet and a purged packed column with a PP inlet on the back which I just inherited from someone else. The PP column leads to a TCD detector, the front column branches to an MSD and an FID. The issue concerns the back column.

There are tons of methods that the previous student used which have the back column as flow controlled at ~30mL/min which, to the best of my knowledge, have worked normally with a helium carrier pressure of 60psig on the regulator. Upon inheriting this project, I noticed that I've been getting a ton of 'back inlet flow shutdown' errors and after some troubleshooting, realized that the abovementioned methods now climb steadily up past 60psig. I've increased the supply pressure to almost 100psig and had the method finish without crashing out, but obviously there is an issue that I'd like to fix.

I spoke to Agilent, who told me that I really shouldn't be getting pressures that high normally. They claimed that since it's a PPI, there aren't very many places it can leak and it's likely an issue with the EPC instead. I doubt that a leak would manifest itself with an increased pressure demand for constant flow, but I replaced the septa on both inlets anyway to be sure, and the issue persisted.

Has anyone else had any similar issues creep up? What sorts of troubleshooting or fixes can you recommend?

Thanks!

[GasMan]

This is not an indication of a leak.

If you have a long column or are going to a high temperature you will need a much higher pressure to keep your flow at 30ml/min. Also make sure that you have the correct gas set for the packed inlet. I have seen this type of problem if you are using helium as carrier gas but you have the packed inlet set for nitrogen.

Gasman