Dear all,
I want to ask about a problem in our GC-MS (Agilent 7890A, 5975C inert XL EI/CI MSD/DS Turbo CI System ) The percentage of N2 is too high (20%) we checked all the sources causing an air leak (changed the bottle of Helium ,the septum and the liner) but we have always the problem.
Thank you and best regards.
Ala.
There are a few options where you may have a leak. Check that the large seals around the mass spec are clean and free of dust. You can wipe the seal i also use a small amount of MeOH if needed. It may be something as small a s a hair that is an issue.
You can also try isolating the MS from the GC and pumping down this will identify if the leak is in the MS or the GC. To do this I simply cut the column at the transfer line end and used a septa to seal the column as it enters the transfer line.
A place we found to check was the seal for the reference gas, a good way to check was to have the mass for water and N2 open and on the tune and open the valve if this is a major leak it will jump up.
Hope these may help. The best advice i can give is to take things logically step by step and you should find it.
Instead of cutting the column at the transfer line end, try removing the column from the injector and pugging the end of the column with a septum. If the nitrogen peak goes away then you only have to trouble shoot the injector. If there is still a nitrogen leak then check the mass spec side. If this an air leak, the amount of oxygen (m/z 32amu) should be about 20% of the nitrogen peak. If this is not the case check all the fittings for leaks before the purification cartridge in the Helium line to the instrument including the tank regulator.
20% of Nitrogen is too high. It seems to be a leak in MS. You should check the side plate o-ring (the large o-ring around the MS door) with a stream of CO2 or other gas or freon. You have to see m/z 44 (for CO2). The another possibility for the big leak is the cracked ferrule in transferline (the connection between GC and MS).
We had a similar problem when we moved our GC to a new lab and found that it came from the transfer line. The connecting nut loosened gradually over a few hundred injections. The problem was solved after we improved insulation around the transfer line.
If you have already checked the inlet, the most likely suspects are the transfer line and o ring around the MS door. Sometimes the transfer line nut simply needs to be tightened a bit - I find that it loosens itself up over time. You can test the o-ring seal by spraying "dust-off" (difluoroethane) around different parts of the o-ring while monitoring the mass spectrum in tune mode - you'll see m/z 51 pop up if there's a leak.
Dear all,
Thank you for the responses we found the problem it was in Column nut in the inlet part.
Thank you for all your responses it was very helpful.
Best regards.
Ala.
- Badges
- Science topic
- Similar topics
- Chemistry
- Biochemistry