Agilent GC/MS leak & tune problem. Please help

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I recently replaced a UHP Helium cylinder and can’t seem to get rid of the leak now. I have two instruments: ancient HP 5970/GC and HP5973/GC. On both, when I do manual tune scan, He peak is only 30% of 28 amu. I spent an entire day looking for leaks and even connected the tank directly to the GC bypassing all the splitters and connectors. Still , same situation. Is it possible I got bad Helium gas tank? I don’t recall this ever happened before. Just to be clear I also tried to isolate MSD from GC and no leak whatsoever. I am now tempted to order another He tank.

On a separate note, I’m also having HP 5970 tuning issue. My tune masses (69, 219 and 502) are all off now. When scanning, 502 is more like 494. And of course it wouldn’t tune (tune error: gain at max and the high mass peak is too wide). This is when I isolated MSD from the GC so there was certainly no leak. No such tune problem with my 5973 instrument, it tunes perfectly once isolated from GC.

[dblux_]

... Is it possible I got bad Helium gas tank? I don’t recall this ever happened before. Just to be clear I also tried to isolate MSD from GC and no leak whatsoever. I am now tempted to order another He tank.
...

Yes, it is possible.

Leaks in pressurised parts of line won't allow air to enter carier gas line.

So contaminated gas in cylinder or leaks in MSD.

[adsfo]

... Is it possible I got bad Helium gas tank? I don’t recall this ever happened before. Just to be clear I also tried to isolate MSD from GC and no leak whatsoever. I am now tempted to order another He tank.
...

Yes, it is possible.

Leaks in pressurised parts of line won't allow air to enter carier gas line.

So contaminated gas in cylinder or leaks in MSD.

I will order another tank of He. Any idea what's going on with the tuning? Especially 502 ion is way off (at 494) so I'm unable to autotune at all.

[JonKlar]

Try connecting the He tank to another gcms if possible to see if you get the same result (trying a secong He tank will accomplish the same thing). If you do it's the tank, if not it may be a leak in your gc system or possibly a problem with your split flow module. I had this happen to me a month or two back and it took forever for me to diagnose.

Hope this helps,

Jon

[Peter Apps]

... Is it possible I got bad Helium gas tank? I don’t recall this ever happened before. Just to be clear I also tried to isolate MSD from GC and no leak whatsoever. I am now tempted to order another He tank.
...

Yes, it is possible.

Leaks in pressurised parts of line won't allow air to enter carier gas line.Leaks anywhere in the line, whether pressurized or not, allow air to enter by diffusion. Why, otherwise, would it be always be so difficult to get the air levels down, and why do air levels always rise the first time that a septum is punctured ? Peter

So contaminated gas in cylinder or leaks in MSD.

[adsfo]

Try connecting the He tank to another gcms if possible to see if you get the same result (trying a secong He tank will accomplish the same thing). If you do it's the tank, if not it may be a leak in your gc system or possibly a problem with your split flow module. I had this happen to me a month or two back and it took forever for me to diagnose.

Hope this helps,

Jon

Came back after the weekend and the leak has magically disappeared. However, the tune issue with HP5970 still remains. 502 peak is too wide and off by a few amu. I'm getting error: high mass peak is too wide. I will try to use a different source although this source was pretty clean...

[adsfo]

Try connecting the He tank to another gcms if possible to see if you get the same result (trying a secong He tank will accomplish the same thing). If you do it's the tank, if not it may be a leak in your gc system or possibly a problem with your split flow module. I had this happen to me a month or two back and it took forever for me to diagnose.

Hope this helps,

Jon

Came back after the weekend and the leak has magically disappeared. However, the tune issue with HP5970 still remains. 502 peak is too wide and off by a few amu. I'm getting error: high mass peak is too wide. I will try to use a different source although this source was pretty clean...

Installed a clean source, same thing. 502 peak is too wide, can't tune. I even refilled and replaced a calibraiton vial. Still same thing...

[dblux_]

Leaks anywhere in the line, whether pressurized or not, allow air to enter by diffusion. Why, otherwise, would it be always be so difficult to get the air levels down, and why do air levels always rise the first time that a septum is punctured ? Peter

Citation from initial post: "He peak is only 30% of 28 amu"

Leaving detailed % calculations aside, alleged leak in pressurised part of carrier gas line had to act as effective* ejector in this particular situation.

* - effectively replaced helium with air in carrier gas line - provioded leak in line was the culprit of dominant nitrogen percentage in mass spec chamber

[Steve Reimer]

If you still can't get the tune to work (502 too wide) reload an old tune file before you try again. Especially if you have a bad leak in the system, the tune parameters may get too far off and the algorithm won't converge. Then the system won't find a proper tune from your current starting point. The quickest fix is to load an old file and rename it to your active tune file.

[adsfo]

If you still can't get the tune to work (502 too wide) reload an old tune file before you try again. Especially if you have a bad leak in the system, the tune parameters may get too far off and the algorithm won't converge. Then the system won't find a proper tune from your current starting point. The quickest fix is to load an old file and rename it to your active tune file.

I tried to "calibrate axis" and save as new tune file. While 219 does look better now, 502 is way far off, too wide. I also tried manually adjusting tune parameters and I was still unable to make 502 to turn out... I tried a different clean source and it's the same so it's definately not the source.

[Peter Apps]

Leaks anywhere in the line, whether pressurized or not, allow air to enter by diffusion. Why, otherwise, would it be always be so difficult to get the air levels down, and why do air levels always rise the first time that a septum is punctured ? Peter

Citation from initial post: "He peak is only 30% of 28 amu"

Leaving detailed % calculations aside, alleged leak in pressurised part of carrier gas line had to act as effective* ejector in this particular situation.

* - effectively replaced helium with air in carrier gas line - provioded leak in line was the culprit of dominant nitrogen percentage in mass spec chamber

Since we are brandishing quotes at one another here is what I was responding to in your post: "Leaks in pressurised parts of line won't allow air to enter carier gas line." If you had written that a leak in a pressurized line would not allow so much air into the line that its concentration was higher than the helium, then I would be happy to a agree.

Peter

[dblux_]

...
If you had written that a leak in a pressurized line would not allow so much air into the line that its concentration was higher than the helium, then I would be happy to a agree.
...

Exactly that is what I wanted to say. I am glad to agree with you.

[Bigbear]

Stupid question, how do you know you have a leak?
When you tune do you change the inlet setting to split?
What is the 28/69 ratio?

Quick check to see if leak is inlet related, cut column flow in half. If it's the inlet your air should reduce by about half.

[mckrause]

Inability to control 502 width is either the zener diodes on the A114 board or your quad driver board. It is physical - it has nothing to do with your contaminated He tank. can you control your 219 peak width with the adjustment on the quad driver board?