Does ammonium fluoride assist ionisation? (and how?)

Hi I recently read a report in which 1mM ammonium fluoride was added to the LC-MS mobile phase to increase sensitivity/ionisation. Can anyone verify this is effective for ESI positive mode analysis of drugs? Can you point me to a reference that describes how this works (if it does) 



  • You've got it, Peter. If you're only detecting M+H then ammonium fluoride wouldn't normally be used.


    You could potentially gain some benefit if you were observing a lot of sodiated species, but you may introduce the potential for competitive reaction to create the ammonium adduct of your compound. If someone was struggling with excess sodium ions I would guide them to reduce exposure to glass wherever possible (PTFE mobile phase bottles, SS inlet frits, poly propylene vials, etc.). 


    If you're looking at a broad panel of drugs and are detecting some ammonium adducts I would consider adding it to your aqueous mobile phase along with your acid as a substitute for ammonium formate. A quick experiment comparing the two would show the winner in your specific application. 

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