Typical vacuum 5971 with calibration valve open?

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

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I did the triode mod on my 5971. It turns out the triode tube on the 5973 works just fine in the 5971 fitting and my big old vaccuum tube was dead. So, it works great. Swapping the triode in means you have to have the 59864B controller.

Its been a few years since my 59822B controller or tube went bad and I forget what sorts of vacuum numbers I used to see on this diffusion pump system.

What sort of vacuum should I be able to get with my calibration valve open? I have been seeing apparent vacuums of 2.9E-5 Torr with the valve closed and it zooms right up to about 1.1E-4 with the valve open. My 5973 goes from 2.9E-5 to ~4E-5 Torr when I have the calibration valve open.

So, is the 5971 just that much more sloppy? Or should I suspect a leak? Guess its time to buy some canned air.
Is this with 1ml/min column flow or with the inlet capped off?

It does seem a little high, but I think mine used to run about 8^E-5torr when the cal valve was open so it isn't too far off from that one.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
Is this with 1ml/min column flow or with the inlet capped off?

It does seem a little high, but I think mine used to run about 8^E-5torr when the cal valve was open so it isn't too far off from that one.

It must have been 0.3mL/min with the chemstation software gage showing 21 Torr at the diffusion pump exit. Checking today (Triode tube): both 0.3mL/min and 0.7mL/min goes to the same 1.1E-4 with the valve open. Valve closed 0.3mL/min drops to 2.1E-5 and 0.7mL/min drops to 3.9E-5. I guess that is not that far off from what you were seeing.
If you are not seeing air and water in the tune, then you should be ok. If it is always present you could be leaking a little at the ferrule on the vial of PFTBA.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
If you are not seeing air and water in the tune, then you should be ok. If it is always present you could be leaking a little at the ferrule on the vial of PFTBA.

Air and water test at 0.3%. I tested all around the seals with canned air (difluoroethane). I got no hits on the masses. It appears that the vacuum change is solely due to the vapor pressure of the PTFBA... 5.52e-01 mmHg. Now I understand why a capillary is needed to meter it into mass spec. It now also makes sense why the valve for standard turbo is different than the one for the high capacity turbo on my 5973.

So, it would appear that the apparent pressure is mostly the PTFBA vapor from the calibration valve and to a much lesser extent, the flow from the capillary.
I replaced my filiments with the yttria coated yttrium-rhenium alloy when I repaired/replaced my diffusion pump thermal sensor, and have let it sit unused under vacuum for nearly a year. I'm getting poor tunes and ramping lenses are very ragged. I thought it might be a leak. But with leaks eliminated, I'm venting and giving the source a good cleaning and trying again. I used to clean my parts and then dry them in an oven before reassembly. But this is apparently wrong. I recently found this Agilent document: How to clean an Agilent GCMS Ion Source. The lense parts have to be assembled after three different solvent rinses and then dried by the vacuum and not heated untill under hard vacuum. It also has some very particular directions about which parts of the lenses are critical to clean and which parts must touch properly. I've been itching to try it this way and see if I get improved performance.

By the way, I took your advise about yttria coated yttrium-rhenium filaments and turned my emission current on my 5973 MS down to 19.8mA. The linearity has improved tremendously! Prior, it was saturating at about 200ppb. Now with the emission current down to 19.8, I an getting a near perfect set of concentrations from a 400 ppb 8260 standard.

With a rhenium filament, a really huge (4000 ppb) peak does not affect the next peak in the chromatogram. But, even with this 19.8mA setting, A 550 ppb 1,2,4-trimethylbenzene peak will cause the following 1-4-dichlorobenzene-d4 peak to drop by 75%. So 400 ppb OK but not 550 ppb. Perhaps I should try 15mA.

I am puzzled how I am going to coax the same fix out of this 5971 MS.
The only way to get lower emission current with the 5971 is to replace the main board with that from a 5972( or possible the top board) because the analyzer and most other parts are the same, and the 5972 was the first with the adjustable current.

When cleaning the source I always use alumina mixed in citranox as a paste and a swab to clean the repeller, source body, drawout plate, entrance lens, ion focus lens and the spacer that looks like a donut with vents in the sides. Wash with tap water (except for repeller on 5971 because that is mounted with a vespel insulator) then sonicate in water, followed by methanol, followed by DCM then pop in the GC oven at 50C until dry before reassembly. That is how the Agilent tech showed me back when I started when I was using the 5995, 5970 and 5971.

Another thing I did was get some of the sharkskin sandpaper from SIS and would work up through the grits until I had a mirror finish. A source that is polished that much seems to stay cleaner longer and cleans easier the next time. Eventually though you have to start with the green plastic sandpaper and rough it up good then re-polish. But lately I just do the above with the alumina, just have to clean a little more often.

Just remember not to use water or solvent on the vespel parts, they will take forever to dry even under vacuum.
The past is there to guide us into the future, not to dwell in.
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