frustrating GC-MS leak

[LoayJabre]

Hi everyone -

I've had a leak in my TRACE1300-ISQ (GC-MS) system for the last week. At first I thought it was from the mass spec as I did some maintenance on it. However, I capped off the transfer line connection between the gc and ms with a blind (no hole) ferrule and the leak disappeared. I have reconnected the column to the transfer line a couple of times but the leak is still there. I know the obvious answer is that the leak is on the gc side but I can't seem to find where. I sprayed/used an acetone swab on every place that could leak and monitored the mass spec for any spikes in those specific ions but didn't see anything.

When I do an air and water test, I am seeing an unusual largepeak at m/z 40.

Have any of you run into this problem before or have any advice on what to do from here ?


Thanks
Loay

[Bigbear]

That large m/z 40 is Argon. That may be coming from your carrier gas.
Can you swap out the carrier gas and see if that's it?

[LoayJabre]

Thanks for your reply! I use Helium for carrier gas though .

[BMU_VMW]

Bigbear means that there might be an Argon contamination in your He supply.
Unless you have changed the He at the same time as you did maintanance, I think it would be to much of a coincidence that the argon pops up now and didn't before.

Loay: I've had a leak in my TRACE1300-ISQ (GC-MS) system for the last week

How do you notice you have a leak?
- air and water check is not ok/ not what it used to be ?
- m/z 40 is to high ?
- vacuum is not ok ?

all of the above can indicate a leak, and depending on the symptoms there is an other cause that is most likely.

I have reconnected the column to the transfer line a couple of times but the leak is still there

did you use new ferrules and nuts? if e.g. the thread of a nut is damaged it might be causing the leak.

Can you please post a screenshot of the spectrum from 10-100 m/z ?

[James_Ball]

Check to see how much pressure is left in hour Helium tank. If it is below 500psi, you will begin to see the impurities as they tend to stratify to the bottom of the helium tanks and once they are depleted you will begin to see more argon, nitrogen, carbon dioxide and such.

[LoayJabre]

I did change the Nitrogen tank at the time of maintenance (we used Nitrogen to purge our tubes during thermal desorption). so maybe that is why!

With that said:

The air and water check is not OK. I'm seeing high Water, Nitrogen and Oxygen concentrations.

I also ran a 'leak check' on the mass spec and usually it shows a leak percentage. This time is said 'Unable to compute leak check ratio' and where it tells me if it passed or failed the leak test it says "Fail. Air leak or calibration gas module is out of tolerance, calibration gas level is not greater than background."

The vacuum is showing to be good. usually the forline pressure is around 45 but now it's around 25.

I did use new ferrules and nuts as well.


Here's m/z 10-100

[img]http://s350.photobucket.com/user/Loay_Jabre/media/10-100_zps9baqhcns.png.html?filters[user]=145526605&filters[recent]=1&sort=1&o=0
[/img]

Thank you
Loay

Bigbear means that there might be an Argon contamination in your He supply.
Unless you have changed the He at the same time as you did maintanance, I think it would be to much of a coincidence that the argon pops up now and didn't before.

Loay: I've had a leak in my TRACE1300-ISQ (GC-MS) system for the last week

How do you notice you have a leak?
- air and water check is not ok/ not what it used to be ?
- m/z 40 is to high ?
- vacuum is not ok ?

all of the above can indicate a leak, and depending on the symptoms there is an other cause that is most likely.

I have reconnected the column to the transfer line a couple of times but the leak is still there

did you use new ferrules and nuts? if e.g. the thread of a nut is damaged it might be causing the leak.

Can you please post a screenshot of the spectrum from 10-100 m/z ?

[LoayJabre]

Check to see how much pressure is left in hour Helium tank. If it is below 500psi, you will begin to see the impurities as they tend to stratify to the bottom of the helium tanks and once they are depleted you will begin to see more argon, nitrogen, carbon dioxide and such.

Thanks for your reply! The pressure still above 1900 psi

[Adam Howard]

The foreline at 25 sounds like there is little to no flow going through the column. Was that reading from when you had your transfer line Capped? If 25 is the real value with the column connected, most of your column flow is going somewhere else, and not to the ms.

You should work the problem from the ms forward. You've already checked the mass spec, so try isolating the gc system by disconnecting whatever TD system you use and try with just a standard inlet with new septa, o-rings etc. If that checks good, then you know it's in the TD system or connection, and not in the gas supply, and not inside the GC. If it checks bad, and you are confident in your connections inside the gc, think about a new tank of helium.

That foreline pressure sounds way too low. I would suspect a big leak at the TD interface.

Can you lend more information on your TD system?

[LoayJabre]

The TD system is a MARKES Unity, Series 2. When the mass spec was capped, the forline pressure was around 44mTorr. At this point I really think it's the TD system, but I have no idea how to fix it haha! I'll keep toying with it until we can afford a technician to come and take a look.


Thank you very much for your help !!
Loay

[LoayJabre]

The TD system is a MARKES Unity, Series 2. When the mass spec was capped, the forline pressure was around 44mTorr. At this point I really think it's the TD system, but I have no idea how to fix it haha! I'll keep toying with it until we can afford a technician to come and take a look.


Thank you very much for your help !!
Loay