Discussion Category:  GC-Tandem MS

High Nitrogen. HELP!!

Hi there

I have been having a problem with a high Nitrogen peak when doing my Air/Water checks everyday. So I went about checking all possible leaks from the gas cylinders outside, all along the pipelines by tightening the nuts and went all the way to the injector part and the column, replaced the inliet liner, septum and o-ring as well. When I ran the check again I found out that there Nitrogen was still high. One problem I had always had though was that the screws that hold the ion source housing were not tight 'cause the threads go worn out somehow, so all along the source housing was held down by vacuum. I made a pad support to push the housing down as an experiment to see if the leak would decrease and amazingly it did, to a very low number. That worked for a while and a colleague of mine came in to repair the threads so we expected the machine to maintain that Nitrogen level now that the housing was appropriately being held in place. The morning after the repairs the Nitrogen had gone up again so i left it for the weekend and hoped it would get better and when I did the report this morning I found out that it is still up.

I cannot really think of anything else to do now, I have done a bakeout.......and most things that I could. The only thing that is faulty now is the foreline pump. It leaks but not so much. Could it be the problem perhaps? Please help

Thanks in advance

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Asked by

GGugu
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avatar placemarkReply by
SiteAdmin

Hi GGugu,

Could you please specify the make and model of the equipment you are referring to?

Thanks
Danielle


info@labwrench.com

Danielle
LabWrench Site Administration
info@labwrench.com


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avatar placemarkReply by
GGugu

It is the Bruker Scion-Single Quadrupole GC-MS

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Dan Ste.MarieReply by
Dan Ste.Marie

GGugu,

I agree in that I do noyt believe it is a faulty rough pump causing your problem.  I would suggest that you try to divide and conquer this problem.  Vent the system and remove the column from the MS interface and replace the column ferrule with a blank ferrule (no hole) and then pump the system down again.  Allow it to equilibrate sufficiently to be able to remove the residual atmpspheric nitrogen, minimum of 2 hours, preferable overnight.  Check your nitrogen levels, if it is still high you have a leak in hte analyzer, if it is down, you have a leak in the carrier gas supply.

If the leak is in the analyzer, garb a can of compressed air and look up hte spectra of the propellant.  Monitor this ion and then start spraying canned air around each potential leak.  Be patient as you must allow for the canned air to reach the source and be detected before making a decision.  If you get a spike for the major ion, you found the leak and can address it.

If the leak is in hte carrier system, proceed as you would for any carrier gas leak and pressurize the system and using an electronic leak detector correct any leaks that register.

Good luck!!

 

Dan 


Dan Ste.Marie

RJ2 Instrument Services

Erie, PA

www.rj2.biz

   
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avatar placemarkReply by
GGugu

Thank you then.

Before I proceed with this though, I have just realized something though. I check the air/water every morning and the N2 is usually high (that is when the machine hasn't been running overnight) and then after each run and I've learnt that the value goes down after each run or during the run I assume. 

Does this help to tell where the leak is exactly?

 

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Dan Ste.MarieReply by
Dan Ste.Marie

GGugu

Not necessarily, but it makes me want to ask if you have a separate method for standby conditions?  If so what is different about the method?

Dan


Dan Ste.Marie

RJ2 Instrument Services

Erie, PA

www.rj2.biz

   
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avatar placemarkReply by
GGugu

Hi Dan

No I do not have a standby method. 

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avatar placemarkReply by
M.Arif

confirm with STD if you have any

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avatar placemarkReply by
GGugu

Hi Dan

Sorry for the late reply, too many vacation days in South Africa :). See funny enough after all this hustle, the Nitrogen levels have went down wonderfully and especially after replacing the Helium gas cylinder after it ran empty. I understand that sometimes gas cylinders can introduce contamination as the gas levels go lower as some may be contained at the botton of the cylinder. Is it true?

Gugu

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Dan Ste.MarieReply by
Dan Ste.Marie

Gugu,

 

Yes it is true that if you let a gas tank go completely dry you can start to see some contaminants.  It is also possible that you had a leak at the regulator on the tank causing you to see the higher nitrogen levels and when you changed the tank and replaced the regulator, you fixed the leak.

 

Dan


Dan Ste.Marie

RJ2 Instrument Services

Erie, PA

www.rj2.biz

   
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avatar placemarkReply by
GGugu

Oh okay.

Thank you so much for your help. I surely am learning a lot as a novice at this :)

Gugu

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