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

[James_Ball]

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

Try reducing the EM volts to 2200 and see if you still get enough sensitivity for your work and also lose the high background noise.

It could be that your EM is starting to go bad slowly. Also if you are not getting enough vacuum, it could be the tune is compensating and raising the EM too high giving you the high background. A Electron Multiplier that is in good shape should give you those abundances you see there at below 1400 volts if all else is working well.

[Fernando_Vilela]

Hi Guys, we have the same problem describe above. The baseline of the nosso 5975C is high and we can see a lot of peaks on the tune report. We already cleaned the EI, the interface GC/MS e the problem still persist.

Can someone give me some advices?

Thank you

[cangulersonmez]

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!

Dear Mgaskins,

I recently experienced the same problem with the HED of my GC-5975C MSD. Unfortunately, I found only one video how to clean it in Agilent website. And I couldn't find any info in the manuals or troubleshooting.

Would it be possible for you to send that pdf that you have?

Thanks in advance! Really good tip for this problem.

[espx_2]

How did you solved the problem? We also got a lot of peaks (835 Peaks) when we ran an autotune.

[runpao]

Dear All,

we had the same problem, high number of peaks (970 peaks!) in a 5975 MSD tune (stune).
We solved it by nitrogen blowing both the EM and the detector body.
Indeed a very small lint of paper was accidentally inside the EM horn.

Hope this could help you.
Ciao

[kartoffel]

Talking of MS settings, can somebody tell me in which area the repeller voltage should be? And what could it mean when the repeller value increases about 30% from one atune to another. In my last tune, i had a value of 19.9, in the next tune it was 27.9.

Thanks

[James_Ball]

Talking of MS settings, can somebody tell me in which area the repeller voltage should be? And what could it mean when the repeller value increases about 30% from one atune to another. In my last tune, i had a value of 19.9, in the next tune it was 27.9.

Thanks

A dirty repeller, dirty source or less vacuum can all cause this problem.

If you manually ramp the repeller it should give you a somewhat gaussian curve shape, you may have to change the setting to allow it to go to full voltage of 40V to see the shape though.

The peak of the gaussian curve is where you really want the repeller voltage. If you change the Emission Current it will change where the repeller voltage peaks. You can use this to adjust the peak down to about 19-22 volts if need be.

[mckrause]

I'm surprised that the repeller voltage is that low. It really affects the high mass. I'd personally run it higher.

I have older Agilent systems that wish they could achieve your idea of a "bad" 502 peak shape and response!

Whenever you see grass like this it normally indicates either an electronic issue or charging somewhere in your system. Clean your system well including the detector components and check your connections.

[blackmetalchem]

I am replying to this because I had this problem last year after doing a PM and went round and round for a week before giving in and calling a tech. I felt so dumb when we found the issue.

Check that the column going into the MSD is only 1-2mm. I, for some reason, had it 4mm or so and it was long enough that it was sticking into the source body. I had all kinds of trouble! Bad 502 peak shape, lawn of grass, and it would not tune and error with inconsistent peak shape. The 502 sensitivity was garbage. The tech found it within 5 min of venting the system.

Noticed this is one of the first results when you do a google and thought I would throw this in for future goofs like me

[Rick_Reiley]

I had this problem and tried everything suggested on this thread. After spending a bit of time with my agilent engineer, it turns out to be a bad hed power supply. To check this out, use a high voltage probe and multimeter on the hed wire (looks like a spark plug) with the ms off and ground it on the chassis. Turn it back on in manual tune (scan in manual and make sure Hed is enabled) and measure voltage- if it reads less than 3000v (4-10kv is typical), then your ps is dead. We swapped it out and it works perfectly (new ps is £2000 from Agilent). Prior, the 502 peak looked like a bush... we had to load the default tune files (updated the instrument, then restarted masshunter). It’s an easy fix if you know what you’re looking for and you can get a ps.

Good luck

[aldehyde]

Yeah if the HED power supply itself isn't bad you can get a problem where you see ~800 peaks in the tune spectrum if a piece of dust or ceramic fragment falls onto the HED surface or into the electron multiplier. I would blow off the detector with air duster as a first attempt to get rid of the problem. Cleaning the detector may be necessary but that is best left to an agilent tech. If you call them for help ask if you can watch, as long as you carefully follow the steps it isn't too difficult once you've seen it done.

The HED power feedthrough has an o-ring and so the feed through you connect the orange HED power cable CAN develop a leak that could also be responsible for seeing all those peaks. I would only check this if air-dusting / cleaning the detector didn't solve it. Reseating the feed through and o-ring usually solves a leak here. If the o-ring is really old it could require replacement.

If none of that gets it, then I'd suspect the HED power supply and at least try a replacement.

The HED itself holds 10,000 volts during operation, so when you vent and open the analyzer if there is some residual charge here it can suck dust onto the surface. The dust acts as an electron emitter and because it is after the quadrupole any signal created by amplifying these electrons is mass-independent and will appear to create "a peak at every mass."

The reason you can see signal caused by a leak at the high voltage feed through is because the high voltage will ionize oxygen in the air leak, and the closest ground is the signal-out. Again, it appears as mass-independent noise.