How about basic buffers in positive mode?

[Anna01]

How about adjusting the pH to below 8-9, and operate the MS in positive mode? Possible or just poor ionization effiency? I am working with neutral compounds with low ionization effiency, but want to get rid of interfering substances.

Or could I adjust pH of the mobile phase during a run? Which is best?

[ym3142]

if I understand correctly, you have to be pH 8-9 to get the separation adn wsnt M+.

I guess you may be still able to get Na adduct.

If not, do postcolumn addition

[Uwe Neue]

You loose some ionization efficiency, but it still works well. We went to pH 10 for analytes like amitriptyline and were surprised that we still got a good signal. The signal was around 2 to 3 times less than at pH 3, but this is not a big deal if you can get around other problems, such as ion suppression from interferences.