HP 5971 EI/CI Switch?

[shelleyj]

Our MS will not autotune. It halts during the tune with an "excessive source pressure" error. We have cleaned the ion source, refilled the calibration vial (and retried several times, not overfilled either), the vacuum is good at 57 mTorr.

Inside the cover is a toggle switch that indicates CI/EI mode and also says "Excessive Source Pressure enabled (EI)/disabled (CI)". I confirmed that we do have an EI source and not a CI source.

Does anyone have experience with this type of switch and how it should be used? We did try switching to CI for the autotune, and got nice results. I'm concerned that leaving the switch in the CI position for the purposes of passing autotune might give different results than if it was in EI mode. Also, if we are overriding a source pressure error message, what the ramifications of this might be long-term. Any help would be appreciated.

[aldehyde]

I'm pretty sure a CI tune will not help you when running in EI. What is your column flow going into the MS?

[jh1]

From an Agilent document dealing with 5971 baseline issues, but it does cover some issues with source pressure.

http://www.chem.agilent.com/Library/Sup ... A20339.pdf

Excessive Source Pressure
Excessive source pressure error is frequently caused by excessive
pressure, as measured in the source. Also, foreline pressure and vacuum
manifold pressure should be checked to insure they’re within operational
parameters. However, on the 5971A, excessive source pressure can be, and more commonly is caused by a dirty source. This typically can be confirmed by executing a [STANDARD SPECTRUM] autotune. After
obtaining the Autotune print out, evaluate the tune, paying particular
attention to the ENTOFF (entrance lens offset) parameter. Under most
normal operating conditions, assuming a good clean source, good vacuum
and normal background levels, the ENTOFF parameter should be around
4.0 to 4.5. If the value is considerably higher or lower than those value's
(+/- 2 to 3 volts), there's a good possibility that cleaning the source will
correct the problem.
If there is any doubt, clean the source anyway and re-check to determine if
the problem has been corrected.

If the vacuum is holding steady I'd check your flow rate and try to determine if the source is somehow still dirty after your recent cleaning.

Anyhow CI mode on 5975 Agilent MSDs allows for a weaker vacuum and increased source pressure (I'm not sure if it directly monitors this anymore) due to the addition of a carrier gas in the source which requires a much more enclosed source body and increased vacuum pumping. If this is also true with the 5971 then switching to CI mode would loosen the specs on vacuum and source pressure so that an MSD not working within normal spec. might be allowed to tune.

[Don_Hilton]

It's been several years since I've had my hands on a '71, but I do recall this toggle switch. And I recall the toggle switch being left in the CI position. It should not make a difference in the tune in and of itself. It just keeps the instrument from damaging itself when the source is overpressure and it shoud not be.

The problem comes in that if you are really running the source over pressure, you will sputter away your filaments faster. And, if you push an instrument to the limit, it typically does not last as long.

And, if I recall correctly, there was a 0.32 mm ID column in the instrument, probably set up to give optimum linear velocity -- and too much flow for the mass spec.

So, like aldehyde, my first place to look is at column flow. And, if you are trying to run a 0.32 column, I'd look at a 0.25 ID column.

[shelleyj]

We have a .25 mm column, but have NOT checked the column flow. We will do this today.

Thanks to all who have posted so for. Keep the ideas coming!

[AICMM]

shellyj,

As long as you maintain a sufficient solvent delay so that your solvent does not cause excess source pressure with the filament on you should be fine running all the time with the CI switched on. The whole idea of that is that you don't expose the filaments to too much solvent and burn them up. I have worked with several labs that leave it on all the time.

Best regards.

[LALman]

From an Agilent document dealing with 5971 baseline issues, but it does cover some issues with source pressure.

http://www.chem.agilent.com/Library/Sup ... A20339.pdf

Excessive Source Pressure
Excessive source pressure error is frequently caused by excessive
pressure, as measured in the source. Also, foreline pressure and vacuum
manifold pressure should be checked to insure they’re within operational
parameters. However, on the 5971A, excessive source pressure can be, and more commonly is caused by a dirty source. This typically can be confirmed by executing a [STANDARD SPECTRUM] autotune. After
obtaining the Autotune print out, evaluate the tune, paying particular
attention to the ENTOFF (entrance lens offset) parameter. Under most
normal operating conditions, assuming a good clean source, good vacuum
and normal background levels, the ENTOFF parameter should be around
4.0 to 4.5. If the value is considerably higher or lower than those value's
(+/- 2 to 3 volts), there's a good possibility that cleaning the source will
correct the problem.
If there is any doubt, clean the source anyway and re-check to determine if
the problem has been corrected.

If the vacuum is holding steady I'd check your flow rate and try to determine if the source is somehow still dirty after your recent cleaning.

Anyhow CI mode on 5975 Agilent MSDs allows for a weaker vacuum and increased source pressure (I'm not sure if it directly monitors this anymore) due to the addition of a carrier gas in the source which requires a much more enclosed source body and increased vacuum pumping. If this is also true with the 5971 then switching to CI mode would loosen the specs on vacuum and source pressure so that an MSD not working within normal spec. might be allowed to tune.

A good link. I just cleaned my source and pumped down. I had no air leaks (did not get a hit on mass 51 when puffing difluoroethane all around the seals), but I don't seem to have good vacuum. I get 20 mTorr with 0.4mL/min but 80 mTorr with 0.8mL/min. Usually this system gets ~30 mTorr with 0.8-1.0 mL/min He flow. And I am getting Excessive source pressure errors. My ENTOFF parameter is 6.27 so dirty source may be the answer for this puzzling complaint about excessive source pressure. Possibly I should check the diffusion pump oil level also.

Oh, and I got some solvent on my repeller assembly when getting the grit off. I suppose it may be offgassing.

[James_Ball]

The 5971 used the filaments to gauge if the source was overpressure, and honestly it did't work that great which is why most people ran them with the switch in the EI mode. We had problems with one that was running volatiles using a jet separator and the ion gauge always read in the low 10e^-6torr but would trip the overpressure warning when set to EI. I am pretty sure they did away with the switch on the 5972 when it came out.

[benhutcherson]

As a daily 5971 user, I keep mine set to CI all the time even though the instrument itself isn't set up for CI.

As James indicated, the instrument is monitoring the current from the filament to repeller-it can be thought of as something of a crude, uncalibrated ion gauge.

If "excess source pressure" trips, the instrument shuts off and the entire run is trash, so it's something I want to avoid happening.

I had someone transfer a method from the neighboring 5975 not too long ago, and he was running samples that were in a mixture of about 90/10 THF:Toluene. The THF of course comes off the column in about a minute(at least the column we were using at the time) while the toluene took about 3.5 minutes. Even though the ion gauge would only measure the pressure rising to the low 10^-4 torr range when the toluene came out, it would still trip "excessive source pressure." Ultimately, the only way I could solve it was to just increase his solvent delay to 4 minutes-I'm just glad that I caught it before he wasted ~12 hours of instrument time to not get any data.

Funny enough, I never saw this error on the 5971 on which I learned, and we would often abuse it by injecting neat liquids...I never adjusted split ratios on that instrument but I'm thinking they must have been at 20:1 or better.

[LALman]

My own 5890/5971 GC/MS system has gotten much pickier since I replaced my Hot/Cold switch. I think its because the diffusion pump oil level is barely the minimum 9mm deep. I am ordering fresh oil and filling it to the 12mm level. I had no leaks but I could not reach a good enough vacuum. Figured I would also try the straight through gold interface tip.

[LALman]

The saga continues...
I had the E2M2 motor bearings replaced. Checked rotary pump and got 5.4 mTorr absolute vacuum. I replaced and/or regreased all the seals, put in a new tune vial refilled with fresh PTFBA, and replaced the diffusion pump oil with 18.5 mL of Santovac SP Ultra, and I put in the straight bore inlet line tip. I buttoned it up and pulled it down to 17 mTorr at the pump and started it up with 0.4mL/min Helium flow.

This morning I have 12.7 mTorr at the rotary pump, 28 mTorr foreline pressure, and 2.4x10E-5 Torr at the Triode tube. Its tuning up beautifully. Before I did this, I could not get below 50 mTorr foreline pressure.

But I seem to have forgotten how to specify a mass 69 abundance target? Or does the 5971 not have that? I may be spoiled by the 5973 flexibility.

[benhutcherson]

Not sure how to do it in auto tune, but from GC Top:

TuneMS->Manual Tune
From that screen, AdjParam->Edit MS Parameters

That should bring up the familiar manual tune box, and you can change the target ion from that window under "MoreParams->Acq Params..."

[James_Ball]

If you are talking about the tune parameters for autotune, there is a menu item listed as tune targets or something like that. There is also a Target Tune where you specify your own target settings. I am a little rusty on the older versions of the software to remember all the menu items, but I remember the older ones didn't have as much freedom to set limits and targets as the new versions do.

[LALman]

Yes, I can see that I can choose target masses. I was hoping to just be able to choose an abundance target for mass 69 like you can do on a 5973 rig.

[James_Ball]

Yes, I can see that I can choose target masses. I was hoping to just be able to choose an abundance target for mass 69 like you can do on a 5973 rig.

I think that ability came with the next higher version of MSDChemstation, which I also believe dropped support for the 5971 sadly.