Finnigan Magnum: Major water and air leak?
Posted: Tue Sep 15, 2009 10:41 pm
I just acquired a used Finnigan Magnum ion trap MS that is giving me headaches.
The unit was in use until 2007 when it was left open to atmosphere.
The auto tune in 2007 set the multiplier voltage to 2700 V.
At that voltage I am seeing enormous peaks at masses 16-20 (one broad peak) and sharp, distinct peaks for 28 and 32 (Nitrogen and Oxygen), almost none at 40 (Argon).
I found and fixed one major air leak at the manifold flange but that didn't improve the situation.
Spraying the whole unit with argon didn't show any other leaks. The transfer line is sealed with a piece of fused silica tubing closed with a septum.
I'm currently using an RV8 forepump which gives a pressure of 5*10^-2 Pas without He being connected. The turbo pump reaches 101 percent speed after 5 min. and gets around 35°C warm after running for two hours with the manifold at 130°C.
Does the MS need Helium for a correct scan or for pumping away all the possible residue 'goo' in the trap? (The unit looked perfectly clean when changing the flange).
What pump-down times are normal for a Magnum that was left open to atmosphere for some time?
And is the multiplier voltage maybe too high?
Is it dangerous for the multipliers or the filaments to operate them with a possible leak?
Thanks in advance!
The unit was in use until 2007 when it was left open to atmosphere.
The auto tune in 2007 set the multiplier voltage to 2700 V.
At that voltage I am seeing enormous peaks at masses 16-20 (one broad peak) and sharp, distinct peaks for 28 and 32 (Nitrogen and Oxygen), almost none at 40 (Argon).
I found and fixed one major air leak at the manifold flange but that didn't improve the situation.
Spraying the whole unit with argon didn't show any other leaks. The transfer line is sealed with a piece of fused silica tubing closed with a septum.
I'm currently using an RV8 forepump which gives a pressure of 5*10^-2 Pas without He being connected. The turbo pump reaches 101 percent speed after 5 min. and gets around 35°C warm after running for two hours with the manifold at 130°C.
Does the MS need Helium for a correct scan or for pumping away all the possible residue 'goo' in the trap? (The unit looked perfectly clean when changing the flange).
What pump-down times are normal for a Magnum that was left open to atmosphere for some time?
And is the multiplier voltage maybe too high?
Is it dangerous for the multipliers or the filaments to operate them with a possible leak?
Thanks in advance!
