5973 lens stack cleaning

[LALman]

I just cleaned my source and I know I assembled it correctly. Autotune is getting 69 and 219 counts that are too close in value. I have to change the ion focus to 140 to get the 219/69 ratio below 70%. Does this mean I did not get the ion focus stack clean enough? I used q-tips and alumina powder and cotton cloth with alumina-MeOH paste for polishing.

Secondly, why does PTFBA have very strong peaks that gradually decrease in strength the longer the PTFBA valve is open? If I run a tune check the first time; I might see 1-2 million counts on 69. But if I keep the valve open for 10 minutes, The counts will drop down to 400-500 thousand for peak 69. Is this normal behaviour? I still show a PTFBA vial that is half full despite using it since 2004. It is a pure compound, right?

I'm showing less than 2% nitrogen and <1 % oxygen on air and water check. So, I don't think its related to an air leak.

[cjm]

What made you decide to take the instrument down to clean it? Do you use fixed or variable entrance lens offset? After polishing with alumina, did you sonicate in water, methanol, acetone, hexane, in that order? Are you trying to pass DFTPP or BFB for EPA 8000 methods?

PFTBA ions do spike high for a few minutes on our instruments. I typically will let the instrument scan in manual tune for at least a few minutes before I evaluate 69 raw abundance. How are your peak shapes for 69, 219, 502? Is there any significant fronting on 502?

Usually if I see something this strange after reinstalling source parts, it's because I did something. You may want to take it down, re-sonicate parts, and re-install. See if there's any change.

[LALman]

I had lost a filiment and the second filiment is yttria coated and so only good for limping along.

After cleaning I sonicated each piece one at a time in 4 successive beakers, MeOH, MeOH, Acetone, Hexane. I let them air dry then assembled and put under rough pump vacuum for half an hour (about 6-13 mTorr). Then I turn on the 5973 and pump down. Its a standard turbo.

Trying to pass BFB for 8260. Its passing but barely because 174-176 is almost over the the 95 peak. Moving ion focus out to 140 just squeaks it.

I'm thinking maybe I did not get the inside of the ion focus quite shiny enough. The 502 peak looks fine on a tune report but when ramping ion focus for the 502 mass, there is a little roughness in the curve on the right side.

[cjm]

If you use variable entrance lens offset, you could fix your 174:95 ratio by turning voltage down on 131 and 69 until they drop by 5% or so. I've had good success doing like this. Another question, what temps are you running your source and quad?

[LALman]

Source 230C, Quad 150C, Inlet 200C, Aux 200C.

I think I had better re-clean the lens stack and try again. Thanks for the help y'all.

[Ian_R]

Secondly, why does PTFBA have very strong peaks that gradually decrease in strength the longer the PTFBA valve is open? If I run a tune check the first time; I might see 1-2 million counts on 69. But if I keep the valve open for 10 minutes, The counts will drop down to 400-500 thousand for peak 69. Is this normal behaviour? I still show a PTFBA vial that is half full despite using it since 2004. It is a pure compound, right?

A signal that decays away like that on any mass spec is typically caused by something being dirty/disconnected. Charges build up on the dirty/disconnected lens and these charges defocus the ion beam. As you have been working on the source that's the place to start looking. If that does not fix it, then the problem could be the quadrupole itself.
Yes, PTFBA is a single compound.

[Bigbear]

How long have you been using your source? If it's been a few years try swapping out the lens insulator.

[James_Ball]

The drop in sensitivity when first opening the calibration gas is the gas pressure coming to equilibrium and is normal. Mine have always fallen almost half if you just go into manual tune and open the valve and let it scan. If you stop and make a BFB injection then go back to manual tune and start again it will only drop about 15%, as the pressure hasn't built up again in the vial yet.

A high 219 isn't that abnormal, it can happen if a lens is in a little different position than it was before, or if the filament alignment is a little different. Every one of my instruments give a different tune ratio when they are clean relative to each other, and it is often that I get very different values after cleaning a source.

The strangest thing is when I have one instrument that passes BFB where 219 is about 30% of 69, and another will give the same BFB ratios even though 219 is about 75% of 69. The key is the 100 m/z which is present in PFTBA but is not one we normally tune on, but it is closest to the 95 required for BFB base peak.

[LALman]

The vacuum has improved and the system is tuning better since I first pumped down. This system always pumps down fast and gets operational fairly quickly but it takes at least a couple of weeks before it really gets a good vacuum. I assume this is absorbed water. I tried to mitigate by immediately closing the chamber up after removing the source and leaving it on backing pump vacuum until I was ready to reinstall the cleaned source.

I've also ordered new o-rings for the EPC interface block. Its amazingly sensitive to leaking if you poke at it while monitoring the nitrogen peak.

Question, my 8260 run is 16.6 minutes for all the compounds to elute. But I run it out to 19.5 minutes to run out late heavies like DRO and because P&T unit is so slow. I wonder if I am straining my standard turbo pump by setting a high flow for part of each run.

I desorb at 1 mL/min but at 2.00 min I ramp to 1.3 mL/min, then at 9.3 min I ramp to 1.5mL/min and finally at 19 min ramp back to 1.0 mL/min. This along with my temp program lets me almost completely separate BFB from o-xylene sufficient that I can pass BFB in my CCV standard.

[James_Ball]

The vacuum has improved and the system is tuning better since I first pumped down. This system always pumps down fast and gets operational fairly quickly but it takes at least a couple of weeks before it really gets a good vacuum. I assume this is absorbed water. I tried to mitigate by immediately closing the chamber up after removing the source and leaving it on backing pump vacuum until I was ready to reinstall the cleaned source.

I've also ordered new o-rings for the EPC interface block. Its amazingly sensitive to leaking if you poke at it while monitoring the nitrogen peak.

Question, my 8260 run is 16.6 minutes for all the compounds to elute. But I run it out to 19.5 minutes to run out late heavies like DRO and because P&T unit is so slow. I wonder if I am straining my standard turbo pump by setting a high flow for part of each run.

I desorb at 1 mL/min but at 2.00 min I ramp to 1.3 mL/min, then at 9.3 min I ramp to 1.5mL/min and finally at 19 min ramp back to 1.0 mL/min. This along with my temp program lets me almost completely separate BFB from o-xylene sufficient that I can pass BFB in my CCV standard.

I do purge and trap volatiles using a 20m 0.18ID 1um film column, either the Rxi-624SilMS or the older Rtx-502.2 columns from Restek. At 0.8 to 1.0ml/minute I can do a run out through 1,2,3-Trichlorobenzene/Naphthalene in 16-20 minutes with no problem separating BFB from other analytes.

Even 1.3ml/min though should be ok with a 5973 turbo or diffusion pump. One thing we do is use E2M2 rough pumps and I also use molecular seive traps just before the roughing pump to keep moisture out of the oil. These used to come standard on the 5971/5970s and I have just moved them across platforms as we upgraded.

[MSCHemist]

probably an insulator broke. The source heats up and expands breaking the insulators on the repeller. To avoid only tighten the nut on the repeller finger tight with your gloved finger. Don't tighten with the nut driver. Otherwise something must be assembled incorrectly, out of allignment, not plugged in well (usually that generates an error though).