Chromatography Forum

Hi.

I am trying to learn the SPME method, and then I have to change septum on my GC-MS (HP 6890 Series II gas chromatograph equipped with a HP-5 MS 5 % phenyl-methyl-siloxane capillary column (30m x 0.25m x 0,25 µm film thickness) connected to a HP 5973 Series mass selective detector). When I replaced the old septum (Agilent 5183-4757) with the new recommended Thermagreen LB-2 septum for SPME, the "front inlet pressure shutdown"-message appeared.

I tried to restart to GC-MS twice, but the same happened.

Then I replaced the old septum, restarted the GC-MS again, and everything was fine. The inlet temp was 270 as usual.

Can someone help me with this problem? How can I get my Thermogreen septa to work?

BÃ¥rd

Best guess is that the tightness of the septum nut is critical - and you are probably screwing it down too hard.

Peter

baardlassen,

I have had this problem on the 6890's and I believe Peter is right on the money. Probably too tight. With the pressure turned off (and the oven cool) pull the old septa, push the new one in and re-install the septum nut. Then turn on the pressure and start tightening the septum nut. When you see the pressure really start to jump, only 1/2 turn more. Has always worked well for me.

(and you don't have to clean pieces of smashed septum out of the inlet nut!!)

Best regards.