Chromatography Forum

Hello,

I am getting very low sensitivity in negative mode with an LCQ advantage max using Meoh/water ammonium. Positive mode is getting fine.

Thermo told me to clean the APCI stack. But, nothing really improved. Any suggestions?

On these instruments, negative mode just does give much lower signals than positive. If that is what you are seeing, then you are seeing normal operation, not a fault. Remember that signal:noise is more important than gross signal strength, and that all chemicals differe in their relative signal strength in negative and positive mode anyway, so unless you are comparing to how an Advantage worked for someone else, it's hard to be sure anything has actually gone wrong.