Leaky 5973

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

14 posts Page 1 of 1
Hello to all.

I am working on a 6890/5973 system. It has been giving me trouble lately. I have exhausted my admittedly minimal knowledge and am hoping I can get some assistance from the more experienced folks on this forum.

Yesterday, I ran an auto-tune because I do this daily right now due to issues with the MS popping up frequently. All looked good, water was a bit high at 10% but I did open the analyzer chamber recently to re-seat and lightly Apiezon grease the door o-ring (was leaky). Nitrogen, oxygen, and carbon dioxide were all under 3%.

This morning when I came in and ran the auto-tune again, I have terrible nitrogen, 73%. I think no problem, must need to re-tighten my transfer line and inlet connections. I do this and get about a quarter turn out of each. I then run an air-water check and it's a mess - I still have an obvious air leak.

I go into manual tune and monitor as I test with difluoroethane duster. I do not get any spikes. I cannot find this leak and I am especially confused because yesterday the machine was fine, I did not change anything, today I come in and it's leaking air. Did I over-tighten my connections this morning? Do I need to break vacuum and check my ferrules, make sure I didn't split them? I am using 60/40 vespel/graphite ferrules, standard size on the transfer line and the short ones on the inlet side. I don't have a large budget to buy anything special. Does anyone have any suggestions?

Thank you very much for your time and your help.

Erika
#1. If mine, I'd block off at the transfer line and check for water/air just in the 5973 MSD.

#2. If OK, then I'd add the column, and plug the inlet end with a septum.

#3. If OK, I'd go look at the inlet.

Or maybe I'd start at #2 because I'm impatient.
Ha ha I am nothing if not impatient as well! Thanks for the response. I will try it... I guess I am just very confused because the first thing to do is always check what's been changed, and unless we have elves I am pretty certain that nothing was changed. So much for taking off early the last day before the holiday weekend!
I have seen a leak at the PFTBA valve before -not an obvious place, but they do leak on occasion. Mine required a service call, as the part is not considered servicable by operator (that wouldn't stop me now, but it did back then :wink: :wink: )
How about a helium cylinder change ?

Do you have oxygen and moisture scrubbers on your carrier gas line ?

Peter
Peter Apps
Hello

Check your carrier gas trap. Perhaps is saturated with air.

Regards

Tomasz Kubowicz
You could also try the "dust off" where the transfer line meets the analyzer box. There is an O ring there that can fail, and if your MS has CI there is a weldment that can fail.
Is the N2 to O2 ratio 4:1? If not it's most likely not an air leak.
As for tightning the transfer line , if using graphite/vespel, should need tightening once afrer a heat cycle. Those ferules can crack a column it over tightened. Don't ask me how I know!
Hello again!! I have determined that the leak is definitely in the MS side, but I still cannot find it.

I was off for the long weekend. Thank you all so much for the responses.

My trap is brand new - just installed in February - so I don't think it is saturated yet. I use hydrogen carrier gas, UHP grade, and I have not changed the cylinder recently.

PFTBA valve - now that is one that I did not consider! Perhaps...

Transfer line - if I am spraying duster right there between the two (not inside the GC oven, but externally) I do not see any spikes. However, I have been concerned about my transfer line because it is obviously bent. Does anyone have experience with that?

I am about to break down and have a service call. Today is probably my last day of working on this as it has been an extremely long time and I am just about out of ideas. I am afraid it is going to be something really stupid, though, and I will feel like a complete fool.

I am not afraid to change just about anything on this machine, I have just about done it all because I've had to. I just jump in there, it's usually pretty self-explanatory. Additional comments welcome, please and thank you so much.
So I just checked in manual tune (because air and water check will not complete this morning), and no, my nitrogen to oxygen ratio is not 4:1. It is more like 5:4. But what would cause a large peak at m/z 28 on the autotune, and also my tunes fail (cannot achieve constant peak widths)? It was just fine, I recently changed the electron multiplier and cleaned the source, but was very careful with reassembly and have gotten a completed tune that was OK with my current setup. As I mentioned, I just came in and it was acting wonky, was perfectly fine the day before. I am at a loss. What would just spontaneously happen like that? And what can it be, if not a large air leak?
Hello

Erika.Miller wrote:
My trap is brand new - just installed in February - so I don't think it is saturated yet.


Remove trap from gas line and try to tune MSD...I know it is new and you trust it but I've seen situation when trap was responsible for problems with MS tuning.
It costs you nothing to try it... :)

Regards

Tomasz Kubowicz
kubowicz.tomasz wrote:
Hello

Erika.Miller wrote:
My trap is brand new - just installed in February - so I don't think it is saturated yet.


Remove trap from gas line and try to tune MSD...I know it is new and you trust it but I've seen situation when trap was responsible for problems with MS tuning.
It costs you nothing to try it... :)

Regards

Tomasz Kubowicz



OK, I will try it, but I am not sure how. Because the line is broken where the trap is, you know? How do I eliminate the break in the line from the trap? It is installed with 1/8" Swagelok connectors. I am sorry, this is probably a ridiculously stupid question but I just don't know how to go about it...
Oh, I think I have enough play in the line to just take the trap inlet and hook it straight into the back of the machine. That should work. I am glad I went with the 1/8" connector trap instead of the 1/4. I have to wait, though, until my run is complete. I have an FID on this machine as well that is in service and running fine, and I have a product approval sample running now that I have to wait for.
kubowicz.tomasz wrote:
Hello

Erika.Miller wrote:
My trap is brand new - just installed in February - so I don't think it is saturated yet.


Remove trap from gas line and try to tune MSD...I know it is new and you trust it but I've seen situation when trap was responsible for problems with MS tuning.
It costs you nothing to try it... :)

Regards

Tomasz Kubowicz



You are correct my friend!! I just checked and the air water check is showing vastly lower nitrogen and oxygen immediately. How on earth is my trap saturated already? I wonder if this is an issue with the gas I am using or with the trap itself? It is an Agilent trap (and it wasn't cheap) the last trap like this that I used was good for over three years. Do you think it is a faulty trap or that I have an undue amount of contaminants in my hydrogen gas?

Thank you again so much for your help. I would never have figured this out on my own!!
I thought I should update this to include final resolution so people searching in the future might be helped --

The regulator on our hydrogen tank (which is about 20 years old and was used for GC-FID work all that time) was not designed for analytical use. It has a neoprene ( :shock: ) diaphragm inside. This diaphragm has been leaching into my trap for the last few months. I need to get a new trap (with indicator, this time), as well as a new regulator. In the meantime I have taken the MS offline so that it does not get damaged by having this contaminated gas flow into it. I have the vacuum pump still running but the gas is turned off and I just put a blank nut on the transfer line. This way I can still use my GC-FID on the same machine (I only have the one machine).

So, I was paying for UHP gas, then contaminating it myself! Sounds about right.

I must say a bit THANK YOU to all the members who helped me. I would have called in a service engineer for sure had I not asked the question here. You saved me from blowing the lab budget, as well as looking rather silly. After all, I can handle that on my own. :cyclops:
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