Trouble getting agilent inlet to be leak free (mz/51)

Discussions about GC and other "gas phase" separation techniques.

4 posts Page 1 of 1
I am working with an Agilent 7890B GC system and lately I have been having some troubles with getting it be leak free. I have a Restek Rtx DHA-50 column installed. It is 0.2mmID and 0.5um df. My procedure to install the column to the inlet is to add a 0.4mm ferrule (Restek cat #20239), install the ferrule onto the column with a septa holding the column nut in place. Then I make sure to cut the column and have the 5mm of column above the ferrule before tightening the column nut onto the inlet. After finger tightening I tighten a couple turns with a wrench and then increase the inlet temp after verifying no leaks with an electronic leak detector. Then I do a leak check by scanning for mz51 and spraying duster at the inlet. I have regularly been seeing peaks for 51 when I spray the inlet. I have tried tightening the nut on a little more but it does not seem to fix the issue, and I am afraid to over tighten. I've tried installing new ferrules but each time I run into this issue.

My guess is that the way I am installing the ferrule onto the column is not ideal, and probably I could be pre-swaging it somehow and this could help to eliminate the leak. I wanted to reach out here to see if someone else ever had a similar experience and what they may have done to fix the issue. Any help is much appreciated, thanks!
Check if you don't have a leak at the other end of the column ie. transfer line ferrule/nut.
If you are using graphite ferrules then finger tight and about 1/4 turn should make it tight enough that you can pull it out and that is good. If vespel/graphite, then it may take a full turn.

Once you heat and cool the oven with a vespel/graphite ferrule, they can shrink and loosen, both at the inlet and detector end. Make sure it is tight on both ends after a few oven cycles. If you are sealed at the detector end, and still see some at the inlet end then also check that the gold seal at the bottom of the inlet is tight, you can get some leaks there also.
The past is there to guide us into the future, not to dwell in.
@dblux thanks for the suggestion. I used the air duster to confirm that it was coming from the inlet.

@james_ball thanks for these suggestions. Never knew a full turn for graphite vespel ferrules on the inlet was typical. I always thought an 8th of a turn was pushing it, so this extra tightening could very well help. That is a good point about the gold seal too, not sure about the last time I replaced this. I will check it the next maintenance. Thank you!
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