Chromatography Forum

Hi,

I have to start an GC/MS Clarus 500 which was in stand by for more 2 years.
All seems ok (He flow, Oven, Pump...) but I have a problem in the Water/Air leak leak control.

I obtain those peaks: https://www.dropbox.com/sh/a5m23b9bq64q ... rofile.bmp

The ratio of the peaks He, H2O, N2 and O2 is good so there are no leaks but what are the peaks at m/z= 14 , 16 and 17, are they contaminants ?

They shouldn't be there according to the installation manual and I should obtain that:
https://www.dropbox.com/sh/a5m23b9bq64q ... normal.bmp

Thank you for your help.

Well done for getting a 2 year system up and running.

I would give the source a clean to start. Check the higher masses perhaps with the calibration valve open to see if that matches the manual, you may some some issues with oil.

I have made the Autotune then a calibration of the system with the FC43 heptacosa and the peaks match with the manual and the peaks at 14, 16 and 17 disappeared but now I have a new problem!!!

The peaks of Helium and those of H2O are too small beside the O2 and N2 peaks:
https://www.dropbox.com/sh/a5m23b9bq64q ... le%201.bmp

The manual says that it could be due to a leak but I checked all connection (column and pump) and all seems OK!!

Do you think I can fix the problem on my own or it's better to call Perkin support ?

Anyone more experienced please correct me if i'm wrong, but isn't it very clear that there's a leak? At my previous job, i used the same instrument with N2/O2 peaks as large as that - got the job done but spectra would surely have looked better if we had fixed it. A leak doesen't have to be at the column or pump - air might also get mixed in to the carrier gas even before entering the column. Also, there are a number of places in there that could leak - all the connections between the reference gas vial and vacuum chamber, pirani & penning gauge, (plugged) CI gas port, PMT port, transfer line port and of course the source, although i guess that leaks in some of those places wouldn't cause air peaks but only a bad vacuum. Leaks at the reference gas connection will, however, give huge air peaks - been there, done that, so to say.

I would check the seal that is made between the atmosphere and the vacuum chamber. I only have experience with Agilent systems but I always put a very thin film of apiezon grease (http://www.apiezon.com/products/vacuum-greases/l-grease) on the gasket before I close it after maintenance. That might help you a little.

I have recently found some tanks of helium containing higher-than-normal concentrations of N2. Are you driving your helium through an oxygen scrubber? Make sure that the trace air is not in the carrier gas.

Thank you for your help,

I have cleaned the source and I have checked connections between cloumn and injector and column and ms and now the problem seems to be fixed, I have the normal air/water/helium response.