Chromatography Forum

Hi,
Just wondering if anyone here has seen the following type of spectrum scan from an MSD?
PFTBA off:


PFTBA on:


Note high abundance of ions and more ions PFTBA on than off.

Started an autotune but it didn't finish. Got a Stack Overflow error then the above spectra. Did the usual reboot of MSD and Chemstation but still the same.

Any ideas appreciated!

Try to attach your image again, doesn't seem to have come through.

Does it just look like grass all across the scan range?

Thanks for the reply!
Yes, Looks like grass across the mass range....

You can view the attached images by opening in a new tab.

Reposting images:

Hello

I'd check and clean dynode (2-Propanol does good job)

Regards

Tomasz Kubowicz

Hello

I'd check and clean dynode (2-Propanol does good job)

Regards

Tomasz Kubowicz

Thanks for the suggestion Tomasz. I will check it.

I have not seen any degradation in performance recently, then the multiplier is suddenly dirty? How might this have happened? No sudden venting, excessive sample amounts, nothing unusual has happened.

Regards,
Charles

Well, the Emission seems very high, I don't normally see that above 36, and 50 will probably cause you to burn through filaments more quickly.

The fact that m/z 16 is your most abundant ion with cal valve closed would point to a problem with the mass filter. You should see either m/z 18 or 28 as the most abundant for either water or nitrogen that is entering the system or in trace amounts in the carrier. Unless you are flooding the analyzer with oxygen and it is breaking it down to elemental with the high emission, but I doubt that is happening. The 5971/72 doesn't use an actual HED, but does use what they call the Xray lens in a similar fashion, if that is dirty then it won't be much of a problem, but honestly it looks more like a problem with the Top Board that controls the quads. Another thing to check if you are not afraid to disassemble the quads, is to see if the silver tape inside the quads has chips in it where the Entrance Lens sits. One engineer referred to them as "mouse bites" at the front end of the quads, and is a common failure on those models. Hope for it being something blown on the Top Board, it is probably easier to find one of those than a replacement analyzer now days.

What do you get if you do a Profile Scan? With cal valve open see what m/z 69 looks like. If it is super wide, or super narrow then start looking at the Top Board and quads.

Hi James,
Many thanks for your constructive comments. I would have to agree with you that it seems I have an electronic issue. It occurred with no warning, suddenly, with no slow change over time. I will delve deeper next week. I am looking forward to stripping it down to have a proper look at everything. System is shutdown at the moment so I can't tinker with it. I will set up another PC to run it on the bench for testing next week.

Regarding the emission current, what would you recommend as the minimal and average settings?

I need to run some urgent samples so I am bringing a 5971 (one of 2 in storage) back into service. It was odd though. I had the first one all set up with the diff pump up to temperature but the software refused to acknowledge that the bottom switch had closed (multimeter said that it had). It just sat there saying diff pump cold. Any ideas? Faulty relay on power board? Do you have a circuit diagram?

The second 5971 powered up no problems and the software was happy with the temperature switch closing. It is settling down nicely after 10 years on the shelf

By the way, do you know off-hand if the top boards from 5971/5972 are interchangeable?

Cheers, Charles

Yes, you definitely have an electronics issue, and it is the top board. On a '70 it would have been the A114 board; the good and bad of the '71 and '72 is that there is only one board. I would check to make sure that the EM didn't short to ground, but it is highly unlikely.

The '71 and '72 top boards are functionally equivalent; the cleanup was in some of the detector circuitry. You'll be able to run with a '71 board, but you'll have '71 performance.

When the one I had went out I got to looking at the top board after exchanging it and found a small resistor on the rear portion swelled out and cracked. Usually it happens without warning, which is what leaves you scratching your head trying to figure out what happened.

Normally I see emission current between about 18 and 36. One was to adjust it is to ramp the repeller and adjust the emission until you get a nice bell curve shape with the repeller maxing below the 40v max, usually in the 25-30 range. Do repeller ramps and adjust emission and watch the effect it has on where the repeller maxes out and the shape of the curve, then you get a feel for how much power the filament needs. Lower emission will give more abundance at higher masses and higher emission will give more abundance at lower masses. At 50 emission you were probably running high on mass 50 and 69 versus 219 and 502.