BFB Tune issue 75/95

[srscott]

I'm having issues passing BFB tune. My 75/95 ratio is high. I'm wondering which of the dynamically ramped parameters I can adjust to get this ratio within range

[cleh]

What instrument do you have? Have you run out of or low on helium? Is it a new column? Did you have leaks at the injector or helium cylinder/regulator/lines? Has it been a while since you cleaned the source? These are the problems I've seen cause high 75/95. If your column is good and you have no leaks, clean your source and you should see an improvement. I've found if you make tune adjustments to correct the issue, it will only buy you a few runs before the problem occurs again. Good luck and please let us know what you find.

[James_Ball]

I have had problems with this on one of my Agilent 5973 systems even after cleaning the source. Some of them just have problems with 75 being too high. One thing to try if using an Agilent system is lowering the Emission Current, which will give you a slight bias to the higher weight fragments. Also when manual tuning to PFTBA look at the ratio of 69 to 100, try to keep 100 less than 15% of 69, this will help with the high 75 problem.

Entrance lens offset is usually the only one I do a dynamic ramp on, and you can disable the dynamic ramping then do a manual ramp using 69 and 131, then adjust the dynamic settings so that 69 is as max and 131 is lower than max. Keep adjusting this and 219 down (to keep your 174/176 ratio ) until you get 75 to pass.

Sometimes you just get a filament that is a little more efficient than others and you get a bias to the lower weight fragments and have to tune them down. Bringing down the Emission current a few amps while leaving the Electron volts at 70 can do this, taking it up will bias it to the lighter fragments over the heavies.