Seeing m/z 403 in positive mode

[Callllii]

Using a Tributylammonium Acetate mobile phase and am only seing it in the positive mode. I'm thinking it has to do with the mobile phase (as it's throughout the run), but can't figure out what it could be?

[yangz00g]

m/z 403 is not a common background ions in ESI+, TFA (triflouroacetate) will produce a 403 in ESI, it may be a possibility in your case.

[Callllii]

Okay it seems to be tributylamine oxide (2N+H) from the mobile phase. Adjusting cap exit voltage and switching to enhanced mode did the trick.