Agilent 1100 MSD Trap SL - Vacuum Issue

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

9 posts Page 1 of 1
I'm trying to resurrect an old Agilent 1100 ion trap LC-MS system for my old research group. We plumbed everything in yesterday, set the gas lines to the correct pressures, etc.

It powered on as expected, but initially the roughing pump only kicked in for about 10 seconds before switching itself off. We power cycled the instrument again and this time the roughing pump stayed on continuously, but the vacuum readouts in MSD Trap Control stayed at 6.94e+00 for the foreline pressure and 4.44e+01 for the high vac pressure. These numbers varied a little over time, but didn't fall to their expected values.

I loaded up the onboard diagnostics (via the http interface) and it's reading that the turbos have reached full speed, despite the foreline vacuum being nowhere near low enough. This has got me a bit worried... I can hear them spinning up, and although I'm not familiar with the trap version of this instrument, to my ears they sound louder than they should be. No different to a normal turbo sound, just louder.

All of the vacuum system tests except for the High Vacuum Pressure and Ready Vacuum System are passed, as have all the other diagnostics except for those that can't run because the vacuum is too high.

So, any ideas why it can't pump down? I have tried switching the pump with the one from our old Waters ZMD, but no improvement. There don't appear to be any obvious points of leakage along the chamber. Next step will be to check chamber seals, etc. but this is a bit involved. I am also worried that maybe the Pirani gauge has had it and is giving faulty readbacks - maybe explaining why it's reading high but the turbos are spinning up normally.

Another bit of info - the instrument has been powered down for the past 2-5 years. I know turbos don't like being disused for a while, but I've previously had no issues spinning up turbos that have been out of action for a couple of years.

The issue of the roughing pump not staying on also recurs every second or third power-cycle, which is also odd.

Any suggestions would be most appreciated.
I have an RV5 rough pump that behaves like that on my 7000C GCMS, if I shut it down very long it is difficult to restart. If you hear a click when it turns off, then it is tripping the thermal overload at the power switch. Could be just that the bearings in the motor have gotten tight.

I would bet it is the vacuum gauge. Is that one that can be cleaned? We have had them get dirty on the ICP-MS before and had to clean them.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
I have an RV5 rough pump that behaves like that on my 7000C GCMS, if I shut it down very long it is difficult to restart. If you hear a click when it turns off, then it is tripping the thermal overload at the power switch. Could be just that the bearings in the motor have gotten tight.

I would bet it is the vacuum gauge. Is that one that can be cleaned? We have had them get dirty on the ICP-MS before and had to clean them.

I'll need to check the sounds that the pump makes at switch off - from memory, changing to a more recently used pump gave the same issue, but not certain.

I might give cleaning the vacuum gauge a go. I've seen them disassembled before, not sure if they're supposed to be though. Any tips on how to clean them?

Another thing I've considered is attaching an external vacuum gauge (just another Pirani) from a Schlenk line in the lab to see if the chamber is actually getting a decent vacuum, but I'm a bit worried about contaminating the chamber.

With the turbo pumps - if the rough vacuum is too high, will they just refuse to spin up to full speed on their own? Or are they getting their cue to spin up from the Pirani mounted on the chamber? They are a bit loud, but don't sound 'damaged' - I'm just wary as to why they might be reading full speed when the chamber pressure is so high.
I don't know the software for this instrument, but does it show the current draw on the turbo pump, usually in mAmps? If it records that it should shut down if the power to run the turbo pump is too high, to prevent damage. Otherwise it would take its cue from the vacuum gauge. Normally if the rough vacuum drops low enough the turbo will power up.

I have cleaned the Penning gauges but I don't think we ever cleaned the Pirani gauge. The one we had on the ICP-MS didn't have a way to open it up. On it the Pirani gauge measured mid level vacuum at the interface and the Penning measured the lower pressure of the analyzer area. I would think there would be either a Penning gauge or Ion gauge for the high vacuum analyzer area on the instrument. There are videos online for cleaning the Penning gauge which is fairly simple. It it is an ion gauge then usually those just have to be replaced.
The past is there to guide us into the future, not to dwell in.
I'm going in to check for leaks on the instrument tomorrow, plus maybe inspect the Pirani. If the vacuum's still bad after checking all the fittings, I'm wondering if it might be an idea to pressurise the thing with helium and go around with a leak detector... unfortunately I don't have one of these but I'm sure I can borrow one. Has anyone done this to a mass spec vacuum system?
Never tried it on a MS before. For GC/MS we spray around all the seals with Dustoff and look for the gas leaking in, but with the LC/MS I don't know if it would detect it since it normally ionizes the gas outside the instrument not inside like the EI source on the GC/MS.
The past is there to guide us into the future, not to dwell in.
really don't know what I'm talking about here, but if your high vacuum gauge is an ion-gauge, and it's been sitting at atmospheric pressure for years, it's probably not going to work. Even after a few days at atmospheric pressure they can take multiple attempts even to turn on, because they get damp, and the moment you turn the filament on, water out-gases, and destroys the vacuum badly enough that they turn themselves back off again...

I'm not convinced pressure-testing an LC-MS vacuum system will give you an accurate idea of whether it's leaking. Mostly the various panels sealed by O-rings expect to seal because of the vacuum inside; in fact I think Agilent recommend that you don't tighten the screws that hold things in place, or certainly not while it's under vacuum, because if you do, once it's relaxed back to atmospheric pressure, they may be very hard to shift. On the whole if the turbos actually turn on and go up to speed, and don't draw inordinately huge power to maintain 100%, you probably have quite a reasonable vacuum, so I'd be more worried about the vacuum detection system than the vacuum itself at that stage.
Update - the low vacuum system is actually within spec although at the high end (I found the service page on the trap's http server) and the turbos are both at full speed, pulling a nominal amount of current, so I'm considering ruling out the leak at this point. Blocking off the capillary caused the rough vac to drop, so that's a positive sign.

Trouble points to the ion gauge at this point, as lmh has suggested. I'm currently looking at sourcing a replacement, temporarily at first for testing and if it does turn out to be the problem, then a permanent replacement. The ion gauge turns on for a little bit, then shuts off and occasionally repeats until it just stays off, with the hivac readout staying static.
The agilent 1100 LCMS trap and the Bruker Esquire both monitor the MS manifold vacuum with a hivac gauge (Granville-Phillips) which is visible behind the front panel.
You may be lucky and have a system delivered with a dual filament gauge so a small switch on top of the GP gauge should allow vacuum to be monitored in the case of blown filament.
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