Chromatography Forum

Hi all,

I encounter bfb evaluation fail for voc method. Ion 75 fail (can not fall in the range). The reason may be due to ion source is dirty. However the source is just clean by engineer. May i know anyone also encounter this problem?

Thanks
Seet

What GC/MS are you using?

It can be a problem even with a clean source. The autotune macro is normally based on PFTBA instead of BFB directly in the MS so it can only approximate what the actual BFB ion ratios will be. Often you have to manually adjust the lenses to get a perfect tune result.

Hi James,

I am using GCMS 5975C. I am using BFB target tune due to requirement of method 8260 (voc method).

Thanks
Seet

Is it too high or too low?
What are the values for your ion focus and repeller voltage?

As James said, a manual tune should work best. I never liked the BFB target tune. I now use the BFB_Autotune which comes with the water management kit from Agilent.
Search this forum as I have posted instructions for a manual tune to pass BFB.

As above, target tune will get you close, then you usually have to tweak it in to get it passing on a consistent basis. Also once you get it to pass, don't run another autotune until it begins to fail, you will just be making headaches for yourself.

Usually if it is using the Variable setting on the Entrance Lens Offset, you can move those numbers up or down one unit at a time to adjust if you are only failing by a tiny margin. If m/z75 is high, you will need to bring m/z131 up versus m/z69, if it is failing low you need to do the opposite.

If not using variable entrance lens offset, you will need to move the Ion Focus and Repeller to do the same adjustment.