Counterions in LC-MS

[Leda]

Hello! I'm new to the forum and have a question regarding the use of counterions in reverse phase LC-MS. Based on the literature I've read, I believe this could improve my peak shape, but I have no experience in this field. What type of counterions can I use when working with MS detector? Also, which concentrations are normally used? Any help or literature recommendations on this topic would be appreciated.

[tom jupille]

The key requirement for LC-MS is that *everything* in the mobile phase must be at least somewhat volatile. To grossly oversimplify, that means use organic rather than inorganic ions. Concentrations typically will be in the 5 - 10 mm range.

[HPLC chemist]

As Tom pointed out you are limited in the buffers you can use because of volatility. 0.1% Formic Acid is a typical acidification agent (~pH 3). You can use Ammonium Formate if the target molecule likes pH 7.

DO NOT use TEA (Polysorbate, Tween...) or other compounds that are likely to contaminate you MS source!

[BostonFSE]

most MS setups are MPA: water with 0.1% formic acid and MPB: as ACN with 0.1% formic acid. This is a good start with a C18 column