Pressure fail on GC-17a (Shimadzu)

[jsully]

I get an error message "Leak Car1" (supposed leak with carrier gas), I first checked all the joints on the helium line, and then found end of the column bubbles when dipped in ipr-OH but inlet pressure will rarely raises to set pressure. The carrier gas is set to hold at 135kpa and 100flow, the flow stays at 100 but the stays around 6-11kPa. The wierd thing is that sometimes it will rise and stay at 135kpa and I can do several runs - everything looks great, but then I'll leave it idle for a couple hours and then the pressure goes down and won't come back up.

I'm not sure what happened when it works and pressure goes up to 135 kPa but it's difficult to do what ever I do to get it to do it. Any ideas?

[tlahren]

It sounds like a leak in the injection port. I'm not familiar with the Shimadzu instruments but you should try to open the injection port and while you're at it change the septum there. Do you have an MS detector?

[achkata]

hi
change the septum, follow the instructions in the manual. It is very easy.
Some other possible causes are noted in the manual (troubleshooting section) but probably septum change will solve the problem.

[jsully]

I'll try it thanks!

Detectors: FID & EAG

[RhysB]

I came across this problem last week. the solution was to take the septum holder off (undo the inlet and outlet links) and sonicate to clean it. The tell tale problem is small deposites of carbon on the underside of the sealing plate between the septum holder and the injector assembly, which you can't see when everything is attached. This solved my pressure problem and several others which I had been experiencing.

Cheers,
Rhys.

[R13]

"I first checked all the joints on the helium line" - do You mean on the line from the supply to GC or lines inside the instrument? In first case - it is good to check to be sure, but does not correlate directly to Your problem.

"and then found end of the column bubbles when dipped in ipr-OH" - that indicates nothing except that Your column is not broken somewhere in the middle....

"but inlet pressure will rarely raises to set pressure. The carrier gas is set to hold at 135kpa and 100flow, the flow stays at 100 but the stays around 6-11kPa. " - Did You measure this independantly or the instrument says so? Do You have column size and carrier gas type set correctly in the method?
There are two general usual main causes:
A- leak (from the most likely) - at septum, injector/column ferrule, tubings from/to injector. Keep in mind the overtightened joints can start to leak. Consult the manual for a leak test which is done with pluged injector without column.
B- not enough pressure from the supply line at the GC entrance - GC must have enough pressure "reserve" to maintain higher pressure in combination with significant flow - as in You case....

Additional GC-17A speciffic issue. This instrument automatically sets flows/pressures EXCEPT the one value - septum purge flow. You have to:
1) check (and adjust if needed using the manual valve) with the flowmeter that the flow is correct. Standard value, if I remember correctly, is 3 ml/min at 100 kPa,
2) make sure this value is set correctly in the GC configuration.

If all this fails - it is time for the service person visit. There might be something wrong with the EPC module.


Good luck,
Rolandas