We are using a GC with ISQ 7000 Mass Spectrometer. Today we did an air and water check and it was higher than usual, so we just tightened the ferrules. In the last two days, however, the N2 and O2 have increased and went up to 100% and 70% respectively. We checked for leaks, and there was no sign of any leakage. Any solutions?
Hi Poonam Sharma ,
It's not just about tightening the ferrules. If they are too tight and misplaced, it could also be a problem. In addition, there is also the quality of the septum.
The most probable reason is a LEAK in the system caused by irregular and/or misplaced connections
As Dr. Molteni points out there are multiple points in the GC that can leak. There is also the GC to MS interface that can leak. Your pump speed may have changed, indicating a rough pump problem which would cause what looks like a leak. Even the columns can wear and develop a small leak. A GC-MS is not a toaster. It requires real maintenance and understanding of the entire system.
First you have to detect is leak in GC or MS: change gas flow through the column, if increase flow leads to icrease N2 and O2 than leak in GC(before interface ferull), if vice versa than it is MS. Tell result, then we try next step of localization of leak.
Another reason could be a break point in the GC column. First define if the leak it is in the MS or in the GC. Disconnect the gc column from the MS interface and put a blind ferule and check the vacuum and N2. If no leaks is there, then check the column and use new ferrules in the injection port but do not connect to the interface, have a vial with acetone and put the other end of the column in the acetone and see if bubbles come out at a flow of 1ml/min. if not, the column is broken.
Yes, it could be leakage of gas. So please check it properly or else if possible replace septa & column end ferrules.
If you check for leaks by looking for positive pressure, you may be missing a leak _into_ the vacuum. Try spraying various sites in the GC and the GC-MS interface and the vacuum seal around the ion source with a volatile solvent or gas and look for the characteristic solvent peaks in the mass spectrum. Take your time because if you find a leak, it may take some time for the solvent signal to diminish. There may be more than one leak site.
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