Chromatography Forum

fbmtorres wrote:
Hello everyone,
I work with an Agilent GC 7890A coupled to a MSD 5975C. Recently the Hivac display has been showing "9.9e+9" and going blank. The micro ion gauge light is always amber or red. When we run any analyses the chromatogram shows no signal.
Can anyone shed some light on this?

Thanks in advance!

James_Ball wrote:
If the chromatogram is showing no signal then I would say you have a massive air leak in the vacuum system somewhere. Either the column is cracked, the nut on the column interface needs to be tightened more, there is a leak in the seal of the interface to the analyzer, the interface is actually leaking( I had that happen to mine once where an internal weld in the interface cracked) or the o-ring around the analyzer door is leaking.

The reading will also happen when the gauge goes bad, but you should still have a good signal if that happens so definitely look for leaks. If you go into tune and do a manual scan do you have large signal for m/z28 or maybe just a blob in that area? Or does it give no scan at all?

fbmtorres wrote:

James_Ball wrote:
If the chromatogram is showing no signal then I would say you have a massive air leak in the vacuum system somewhere. Either the column is cracked, the nut on the column interface needs to be tightened more, there is a leak in the seal of the interface to the analyzer, the interface is actually leaking( I had that happen to mine once where an internal weld in the interface cracked) or the o-ring around the analyzer door is leaking.

The reading will also happen when the gauge goes bad, but you should still have a good signal if that happens so definitely look for leaks. If you go into tune and do a manual scan do you have large signal for m/z28 or maybe just a blob in that area? Or does it give no scan at all?

Thanks for repplying!
There is a large signal for m/z 28 indeed.
Also, the micro ion gauge led goes from green (on) to red (error).

James_Ball wrote:

fbmtorres wrote:

James_Ball wrote:
If the chromatogram is showing no signal then I would say you have a massive air leak in the vacuum system somewhere. Either the column is cracked, the nut on the column interface needs to be tightened more, there is a leak in the seal of the interface to the analyzer, the interface is actually leaking( I had that happen to mine once where an internal weld in the interface cracked) or the o-ring around the analyzer door is leaking.

The reading will also happen when the gauge goes bad, but you should still have a good signal if that happens so definitely look for leaks. If you go into tune and do a manual scan do you have large signal for m/z28 or maybe just a blob in that area? Or does it give no scan at all?

Thanks for repplying!
There is a large signal for m/z 28 indeed.
Also, the micro ion gauge led goes from green (on) to red (error).

The best way to look for a leak is spraying Dustoff(computer duster spray) around the side door of the analyzer, then on the column nut at the interface and see if you have a large peak in the 50-60m/z range, if the leak is that large it will suck in the spray and you have found your leak.

If you have a no hole ferrule you can use to plug the inlet to the mass spec with that is the best way, just remove the column and place a nut with the no hole ferrule on it and seal it up there and see if the leak goes away. If it doesn't you know the leak is at the mass spec, if it goes away then the leak is in the GC.