Inlet maintenance without venting?

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

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What are people's thoughts about performing inlet-end maintenance without venting an MSD? Our senior SV analyst is comfortable replacing liner, septum, and trimming the front of the column by simply cooling and depressurizing the inlet. I'm not totally convinced, so I'm hoping to get more opinions from people with GCMS experience. Thanks
Has worked for me. Typically, cool inlet, disconnect column and plug with septum. Do other inlet maintenance, then trim column, and connect to inlet.

Its also useful if you want to test the inlet for leaks by plugging the bottom. Once leak free, you can connect the column.
My experience is only with Agilent 5971, 5972, 5973, and 5975; I never vented the system just to change the liner and/or the septum.
Agreed with the other posters. If we had to vent the MS every time we performed any inlet maintenance, we'd lose way too much time!

Perhaps if you use a very short/wide column you could risk a little bit of damage to MS parts by sucking in oxygen. In that case, I would not vent the MS but cool down the source and quads to about 100°C before opening the inlet.

If you cap the column with a septum, you're building up a vacuum inside the column, so I'd rather have it continually sucking in some air.
Agreed. As long as you don't have the column open to atmosphere for more than necessary for maintenance, you should have no issues at all. Once I've completed inlet maintenance, the one thing I do is wait a couple minutes for all air to work its way through the system prior to baking.

I agree with the rest. I have to go back and forth between liquid injections and SPME sampling. I am always careful to wait an hour or so before tuning the MS to make sure that the air and water is back to normal. I haven't noticed any adverse effects.
We never vent to do inlet work. Sometimes I don't even cool the inlet, just have to be very careful not to burn my fingers :)

As long as you have 10m of 0.25ID column you should pull very little air into the MS. We use mostly 0.18ID columns and I don't even see the vacuum change while the inlet is disconnected.

I have even hot swapped an entire column in an emergency. Hitting vent to turn off the turbo pump then pulling out the column and sliding another one in with the rough pump still running, then hitting pump down all within about 1-2 minutes. Not recommended but it can be done. The MS is more resilient than most think it is.
The past is there to guide us into the future, not to dwell in.
Venting to do inlet maintenance, esp. on a typical 15-30m column, has never even crossed my mind.

Like James, I usually don't even cool inlet to change a septum and often the liner. A septum change on an HP/Agilent GC is a 2 minute job if you piddle, and I've also gotten pretty good at popping the old one out and getting the new one in place without touching the metal. For a liner change, I'll usually turn off the inlet heater but won't wait for it to cool(it can take a LONG time for an inlet at 250º to cool down to a temperature where you can touch it without burning yourself, and I often don't have that kind of time).

I typically will only cool the inlet for "bottom end" maintenance(gold seal, etc) since that involves handling a lot more parts than the top end. If I'm going to have the column off, I plug it with a septum then of course cut it before reinstalling, but that's it.

Work at the MSD end does generally call for venting, but that's about it. On 5971s where I needed to quickly swap a column or do other work, I've done something similar to James but a bit more hands on-I've unplugged the diffusion pump heater, waited 10 minutes for it to cool, and then opened the transfer line to do whatever I needed to do. Sometimes I leave the rough pump running, sometimes not. The "unplug the diffusion pump and wait 10 minutes" trick is actually the official procedure listed in the 5971 manual for shutting down/venting without a functioning data system.
Hi. To my knowledge, it is fine to do inlet maintenance e.g. change liner, change septum, change gold seal, trim column at the inlet only. As long as the column is not detached at the detector (MSD), and there is no air leak, and tuning passes, venting is unnecessary.

This is only a practice at the lab I work in.

Correct me if I am wrong.


It is fine not to vent. The flow resistance provided by the GC column will prevent too much air from being drawn into the MSD. If you have a short wide column it might be advisable to cap off the head of the column with a septa but otherwise that is overkill.
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