Gc Ms Voc BFB mass 50 fail too low and mass 174 to high

[Carlostek]

Hi, ive been having a problem with my gc ms with this masses around 4 days and no matter how many bfb tunes i used or how many times i use the tube wizard i cant manage to fix it, can someone help me. Thx

[Bigbear]

More information please. What system are you using? Do you tune manually or use a "canned" tune?
I think this question has been discussed many times in the past so try searches for Method 524.

[Carlostek]

Well i was using BFB tune and using tune wizard. But no matter how much i tried it always had a fail in mass 50. Whats a canned tune? Thnx in advance

[Bigbear]

Sounds like you are using one. I use Agilent BFB_Autotune which you get with their water management kit for 5973 and 75's.

I have posted the instructions of how to do this tune manually in the past.
Please spend some time searching old posts.

[James_Ball]

Definitely need to learn to manual tune the instrument if you have to pass BFB for your methods. Even the best autotune macro will sometimes not get it right.

What brand of GC/MS are you using? If we know that maybe someone will know more about how to help. But the main thing is you need to manually adjust the PFTBA masses so that you increase 50 versus 100 and reduce 131 and 219 versus 100, those are the nearest masses to the ones present in BFB.

[Bigbear]

James, did you mean m/z 69?

[Carlostek]

Well the ms is agilent, so u can do it manually? How can i do it manually? I just use autotune and BFB tune.The problem came out from nowhere. It had was functioning correctly, i had to use tune wizard and change the masses a little bit so the BFB could pass. And we had to change the source from another MS and that fixed the problem, but we still have to use tune wizard all the time.

[Bigbear]

Ok, I feel your issue may also be due to all the water transferred to the ms during desorb. Please search this forum for dealing with this.
You may need a 6mm draw out plate in your source, helps to pump out the water faster.
Here is how I do a manual tune.
Run autotune ( save) also save as another unique name.
Set ion focus to 140 ( you may need to reset the upper limit in more functions)
set masses to 69,219, and 50
Scan and adjust ion focus till mass 50 is about 0.9
Set masses to 69,219, and 502
ramp emission and then set it to the peak of the scan for 69 ( just click on the graph on the screen)
set masses to 69,131,and 219
while scanning get 219 and 131 to about 50% of 69 ( use entrance lens and entrance lens offset)
Reset masses to 69,219, and 502
Scan and adjust the em to get ~ 600000 counts for 69.
Calibrate peak widths and mass axis
Check that 69 is still ~600000 cts
save tune values

if you are still having issues wit 174/176 this is the 131/219 in the manual tune (131 affects 174 while 219 does 176)

Good luck
Bear

[James_Ball]

James, did you mean m/z 69?

Actually there is a m/z 100 in the PFTBA and when I really have trouble getting m/z 50 high enough I focus on the 50/100 ratio in manual tune. If you set them and ramp the lenses you can see if there is one that will make a large difference with a small adjustment, which will help get 50/95 to pass in the BFB. Also if you can put 100 into the masses in the dynamic entrance lens offset table you can use that to help with the ratio, if not have to use 50/131 in the offset table to reduce the 100 response(95 in BFB). If you can get PFTBA 69/100 down to about 13% and 69/50 up to about 0.9% then it will almost always pass.

[Carlostek]

Thnx a lot that was the problem. The conditions from the purge and trap were incorect. This week came a tech an fix it. Thnx a lot for all the help