Chromatography Forum

Hi

I have problems with a MSD 5973 (EI, quad, PFTBA, turbo pump). I had problems of sensivity and I cleaned the ion source.
After that, the autotune was OK. But, I performed a sample injection and sensivity had dropped again. Then, I performed a new autotune and this was very bad.

What can be the problem.

Thanks

Reload an old tune file as a starting point. Rerun autotune and watch for any odd behavior. It helps at this point if you know what normal is.
What is your max repeller voltage? Default may be 20 for atune but it can be set to 40V in the tune wizard. Voltages over 30 from a standard tune indicate either a contaminated repeller or more likely a current leak at the insulator. If you overtightened the repeller nut and cracked the insulator you could see increasing loss of sensitivity and poor autotunes.

Of course, loss of sensitivity could be from a leak that developed when you cooled the system off and vented it. Or it could be any of the usual column, inlet, injector, etc. problems.

Can you post a picture of your autotune results? It may be easier to diagnose if we see that.

Autotune OK

Autotune BAD (3 hours later)

Did you inject a sample after the second autotune and have even worse sensitivity?

If the sample response is the same even with the bad second autotune then I would say look and see if you have any PFTBA left in the vial. I have had times I thought my instrument was dead only to find I had run out of PFTBA. If that is ok, then try another multiplier if you have one. I have had the K&M multipliers go out rather quickly sometimes, but not always.

The peaks are a little wide at 219, but with such low sensitivity I don't think that is pointing to problems with the side board, or quad drivers.

First thing I would do after checking the PFTBA volume would be to switch filaments and see if that has any effect. Could be as simple as a broken or sagging filament. Sometimes a broken filament will still arc and put out enough energy to let the tune run.

After that maybe clean the HED. That is the little metal button after the quads and before the multiplier. You can remove it by removing the two screws holding it in and sliding the wire out of the connector. Clean with isopropanol and a kemwipe, especially the metal part facing the quads/multiplier.

Also, is your vacuum down to at least 5*10^-5 torr?

Those are the easy things to do, after that you have to start thinking about electronics.

Side board electronics can make it do many strange things when they go out. It houses the quad drivers/mass filter electronics and the first part of the electron multiplier signal processing. Mass filter problems usually show up as drifting peak widths over time. You tune it then the next day your peak widths are far wider than normal, you adjust again and it repeats every day.

Main board electronics usually result in a dead instrument or errors like no emission current because it won't send power to the filaments.

If I can think of any more things to try I will post again. Let us know what happens if you check those first few things I listed above.

The resolution in your first tune doesn't look that great. Agree with James. Make sure you have cal gas and tune with different filament. If it's still bad, I'd re-clean the ion source (sonicate the parts in H2O x 2 and then in MEOH after cleaning). Check the ceramics for dirt or cracks and clean or replace if necessary. Make sure your column is inserted into the transfer line properly. Doesn't look like an air leak to me. Please let us know what you find.

Thanks for your answers.

PFTBA is OK. I tried with both filaments. I cleaned HED. Vacuum is OK.

I had a very similar problem recently which I found was due to the HED supply. Basically one minute it was ok then it would drop sensitivity. Obviously you want this to be a very last resort as they are very expensive and I don't think they can be repaired.

Hi Astroguille

How old is the EM?

The EM is 10 years old, but its voltage hasn´t been increasing before problem (normally 1800 V).

ok.
A problem I have seen is the stangulation of the end of the column due to excessive force placed at nut in order to reduce air leaks.
Vent the system and bubble the end of the column in clean alcohol in order to watch the flow.
In case of low flow (a rule of thumb is that 1 mL/min produces a near continuous chain of bubbles) cut the end of the column and replace ferrule, reinstalling the column.

hi
Sorry for misleading you. I posted with reference to your original problem, lack of sensitivity.
Now you have another problem, specific of the MSD.

I would suggest to adjust RFPA values as per the manual.

I have already adjusted the RFPA, and nothing changed.

ok.
Can you isolate the MSD? Vent the system and use a blank ferrule with nut.

After pumping down, make an Air & Water check and try again an autotune.