Ammonium Adduct in ESI-LC/MS without NH3 in mobile phase?

[nanzhushen]

Hello All,
Have you ever had any experience with ammonium adduct formation in ESI-LC/MS without using NH3 or NH4+ in the mobile phases?

My mobile phases are quite simple, 0.1% formic acid in water as A and 0.1% formic acid in acetonitrile as B. I did not use ammonia or ammonium formate or ammonium acetate at all but I saw [M+H+17]+, and it is much stronger than [M+H]+ peak in ion trap MS.

Thank you in advance!

[MG]

Yes, I have seen this happen for neutral compounds with *no* additives to the mobile phase and a simple water/ACN gradient.

I have two guesses as to the source of the ammonia: (1) trace contaminant in mobile phases, because it is a common additive for LC/MS; (2) a decomposition product of acetonitrile?

[nanzhushen]

Yes, I have seen this happen for neutral compounds with *no* additives to the mobile phase and a simple water/ACN gradient.

I have two guesses as to the source of the ammonia: (1) trace contaminant in mobile phases, because it is a common additive for LC/MS; (2) a decomposition product of acetonitrile?

Thank you very much for your input.
The compound I analyzed has epoxide groups.