Chromatography Forum

Hi,

Im very new in GCMS and currently facing some issues with front inlet pressure and total flow. Actual pressure of the front inlet pressure is about 1.1psi where it should have been 1.7psi. This makes the septum purge flow lower than the required with an actual flowrate of 0.3ml/min where it should have been 3. Even with changing the old septum, I see the same pressure and flowrate. I hope some of the experts in the group would take time to answer my beginner question.

Thank you very much.

Jerwin

A little background on your instrument would be helpful. What is the brand of instrument? What type of inlet system (split/splitless, PTV, etc.)? What analytical column are you trying to use.

Usually, when you ask for help here, you'll get better answers if you can more fully describe your situation.

What detector do you have ?, an MS ?

Peter

A little background on your instrument would be helpful. What is the brand of instrument? What type of inlet system (split/splitless, PTV, etc.)? What analytical column are you trying to use.

I am using an Agilent 7890A GC with MS (5975C). My inlet system is a split-splitless type, and a DB-1 Column.

Usually, when you ask for help here, you'll get better answers if you can more fully describe your situation.

I really appreciate your reply. Well its a new equipment for us( not more than a year, not used much), and we bought it for simple gas analysis. It was off for a month bec I need to replace He cylinder. After installing the tank, turning on everything, you can not change GC parameters and its flashing pressure at inlet. Noticed it is below the required, so even by loading a previous method, the GC does not accept the command.

I tried replacing the septum, but it didnt work. Both pressure and septum purge flow is below requirement. Am not really sure with my problem, is it a leak in the system? Tank regulated output pressure is 75 psi.

What is the split ratio, what is the flow out of the split vent (measure it with a flow meter do not trust the GC readout) ?. What column do you have ? Do you have a shut off valve downstream of the cylinder regulator ?, is it open ?. Have you checked for leaks with a leak seeker ?

Peter

A little background on your instrument would be helpful. What is the brand of instrument? What type of inlet system (split/splitless, PTV, etc.)? What analytical column are you trying to use.

I am using an Agilent 7890A GC with MS (5975C). My inlet system is a split-splitless type, and a DB-1 Column.

Usually, when you ask for help here, you'll get better answers if you can more fully describe your situation.

I really appreciate your reply. Well its a new equipment for us( not more than a year, not used much), and we bought it for simple gas analysis. It was off for a month bec I need to replace He cylinder. After installing the tank, turning on everything, you can not change GC parameters and its flashing pressure at inlet. Noticed it is below the required, so even by loading a previous method, the GC does not accept the command.

I tried replacing the septum, but it didnt work. Both pressure and septum purge flow is below requirement. Am not really sure with my problem, is it a leak in the system? Tank regulated output pressure is 75 psi.

Check to make sure the column is not broken just downstream from the inlet, if it is it will not be able to build enough pressure in the inlet on the 7890. If it is broken you will also have a high air/water test if you run the air/water check on the 7975.

Did someone remove the inlet liner while the instrument was sitting idle? Also make sure the bottom of the inlet has not become loose since the injector was cooled off for a long time while there was no column flow.
The gold seal at the bottom could have a leak there if the bottom fitting comes loose from the expansion/contraction cycle of being shut down.

Hi

As Peter says, what are your column dimensions? 1.7psi sounds a bit low to be running a GCMSD. Increase the inlet pressure to 10 or higher and see what happens. Also check the method conditions are all correct.