Hello! I know you dealt with this issue last year, but we are experiencing the same problem, but on a 7900 ICP-MS. However, we are seeing no counts of mass 140. Could you point us to the direction of the bracket plate sensor that you are referencing? I did a search on agilent's store and could not find it anywhere.
I also saw your previous posts regarding your oxide/doubly charged ratios. I'm not sure what your application is, but on our system, we have been successful in keeping ours under 1.5%. I know you posted it a while ago (so I'm assuming you figured it out already), but if not, I have some solutions that you can run through your system that might drop it lower.