bad shape of 502 and a lot of peaks on tune 5975

[dsarf]

Hi all,

I work at a GC 7890/MSD 5975c
I have problem on the shape of 502 and the abundance when I execute autotune,
and then the amount of peaks on the tune report is unusual (more than 850 peaks).

FYI, I cleaned the ion source, and the problem still persist

What can the problem be?

[James_Ball]

Hi all,

I work at a GC 7890/MSD 5975c
I have problem on the shape of 502 and the abundance when I execute autotune,
and then the amount of peaks on the tune report is unusual (more than 850 peaks).

FYI, I cleaned the ion source, and the problem still persist

What can the problem be?

One thing to check is if you have enough PFTBA in the tune vial. If it gets low, then the instrument is pushing the sensitivity up to compensate and giving you more background peaks and the 502 shape problem is due to not enough compound being present.

Can you post a screenshot so that we may see how the peaks look?

What is your Threshold set to in tune? If it is set too low that can also give you the large number of background peaks.

What is the Autotune setting the Electron Multiplier Voltage to?

[dsarf]

Hi James,

Thank you for your explanation, I can see there is still liquid in the tune vial.
I can't post picture on this message, and here is the link for the tune picture, hope it will work

https://picasaweb.google.com/lh/photo/w ... directlink

For the threshold at autotune is 100, and have quite high EM volt 2235

[James_Ball]

Hi James,

Thank you for your explanation, I can see there is still liquid in the tune vial.
I can't post picture on this message, and here is the link for the tune picture, hope it will work

https://picasaweb.google.com/lh/photo/w ... directlink

For the threshold at autotune is 100, and have quite high EM volt 2235

I can't seem to open the image but that multiplier voltage is very high. The threshold is ok at 100, it just seems that the multiplier is getting set very high.

Are the peakwidths in the 0.50-0.65 range for 69, 219 and 502 when you use Profile scan?

What are the abundances of 69, 219 and 502 when you scan the instrument?

Normally I believe the 69 and 219 should not go above about 300,000-600,000 counts. Some applications can get by with them as low as 150,000 counts.

It could simply be that the Electron Multiplier is going bad, how old is the EM?

Also what is the High Vacuum reading when you are in tune?

[dsarf]

Hi James,

the peakwidhts on that range, and abundance for both 69 and 219 also on that range, but the problem is on 502

i try to post the pic again, to give general over view


High vacuum is ok when doing tune at 10E-6
I have used this 5975c since the end of 2008

And does any one have idea what happened with the amount of the tune peaks above (870) ?
Thanks for any help

[James_Ball]

Unless there is a specific need for 502 to be higher I really don't see any problem other than high EM voltage. I remember when if you got 502 above 3% compared to 69 you were doing well.

If you are doing work with high molecular weight analytes then I could see a need for the higher 502 response. You may improve 502 response by increasing the Repeller voltage. Ramp the repeller and see how the profiles look. Also ramp the Entrance Lens since higher voltages there can reduce the 502 sensitivity.

So repeller voltage up and Entrance Lens voltage down may improve the 502 response, but each analyzer is different so you just have to experiment to see what happens. Dropping the EM voltage a little should take care of the background noise also.

[Bigbear]

I still think it may be the source as 870 peaks indicate cleanning is needed. What method(s)) do you run on the instrument?
Have you changed the source insulators? I was told by an Agilent rep to change the lens insulators yearly for my 525 instrument and every other year for my 524.
I think you can still flamr the repeller insulators but it's still easier to just change them.

[James_Ball]

I still think it may be the source as 870 peaks indicate cleanning is needed. What method(s)) do you run on the instrument?
Have you changed the source insulators? I was told by an Agilent rep to change the lens insulators yearly for my 525 instrument and every other year for my 524.
I think you can still flamr the repeller insulators but it's still easier to just change them.

That is probably a good idea, but the insulators on my 8260 instruments are at least 4 years old and don't have any problems even with the junk I inject on that one.

After looking at that tune report again I am wondering how it is scanning with the vacuum so high? 1.00e10

If the vacuum gauge is not working, maybe contaminates have build up in there and causing the high background.

[dsarf]

Hello sorry for late response,

James,

Thanks James for the suggestion to checking the scan of repeller and entrance lens, will try to check and the EM volt too.
I noticed the high vacuum at 1E10 and i told to Agilent engineer when they replaced the rough pump, they told me if the sensor for vacuum is not work but the real vacuum condition is ok, that is why the vacuum on tune at 1E10.

Bigbear,

Thanks for other idea about insulator. But sorry Bigbear, could you please tell me which one that you mean as source insulator? is it the ceramic one (repeller place) or the insulator where the ion focus stand?. We didn't changed the insulator since this instrument exist.
I cleaned the source before this problem happened, and know I am noticed that was not really white clean ceramic on repeller when i cleaned the source.

I not work on certain method, we use this MS for research on natural flavor

FYI

We coupled this 7890A with olfactory port, does this olfactory give any effect to that huge background peak?

Thanks for all help

[mgaskins]

I have experienced this exact problem on our 7890/MSD 5795C as well. Notice that the baseline looks like a "lawn of grass" of all of the m/z across the spectrum. It is highly unlikely that a series of compounds could just appear that would contain all of these ions.

In our case, the high energy dynode (HED) was dirty. I vented the MSD, removed the HED, and wiped it clean with methanol and a lint free cloth. Chances are that a piece of lint or dust made its way into the detector and ended up on the HED when the instrument was vented and/or was being serviced.

There is a macro that can be run in the "Tune and Vacuum Control" in MSD Chemstation to verify that this is the issue before venting the spec. Type this in the white command line on the bottom of the screen:

MACRO "\MSDCHEM\diag\uphonics.mac", hit enter.

type u_phonic, hit enter.

This should generate and print a report for the instrument noise in the electronics of the instrument while the HED is being energized (0V, 1500V, and 2000V.) The noise at 0V (top graph) should look like typical instrument noise if the electronics are sound in the MSD. If the HED is dirty, you will see a number of spikes in the 2000V (bottom graph) and a high standard deviation (usually >20.) This indicates that the HED is indeed dirty.

I do have a pdf from Agilent that explains how to clean the HED if interested. Ironically, one of our 5973N mass specs had the same problem this afternoon; I also have a pdf of a normal baseline noise test as well as one with a dirty HED that I could send you as well.

I hope this helps!

[dsarf]

Hi mgaskins,

Thanks God there is some one had same problem, got some blink star, hope it will work on me.

Yes you are right I have lawn of grass and it will be very irritating to identified my peaks . Thank you for all your explanation and sharing, I will give a try to macro command and hope it will work.

I will be very thankful if I could have the copy of your HED cleaning reference and the pdf of the problem you have faced.

[mgaskins]

This problem took me awhile to troubleshoot as well. Fortunately, it is a relatively simple fix.

What is your email address?

[dsarf]

Hi mgaskins,

I tried to run macro command and that was generated report that shows me the relative standard deviation for 2000V is 5.5%. what could be possible on my HED?

I hope it will be still relatively simple to fix

Thanks for your help, my email desi.arf@gmail.com

[xutang2000]

Dsarf,

Did you clean the HED and did that fix the high noise problem? Please follow up. We really need the answer. Thanks.

[dsarf]

Hi xutang2000,

Sorry for late response, I didn't clean my HED since the instrument noise report said, there is no different noise between clean reference HED with my instrument report. And unfortunately my noise background still persist . Do you have any suggestion for this? since you seem face equal problem.

for mgaskins,

Thank you for your help to identified HED. Do you have any idea with the screen shot i shared?
About the second macro command I did

for bigbear,

The insulator suggestion, I still looking forward on that

I still struggle on this problem any advice could be very valuable for me.
Hope any other member could give other help

Thanks all