By Anonymous on Friday, March 19, 2004 - 12:29 am:
Has any one analyzed substituted nitro benzoic acids, especially fluro nitro benzoic acids by LC-MS? Would be of great help to know the ionization conditions used!
By Anonymous on Friday, March 19, 2004 - 12:31 pm:
I haven't, but try answering these questions for yourself:
1) In the easiest case, will one of the functional groups on your molecule readily gain or lose a proton in solution? (hint: yes)
2) Which functional group is it?
3) Will the functional group you answered in (2) either (a) gain or (b) lose a proton.
If you answered (a), ESI positive is probably a good bet. If you answered (b), give ESI negative a try.
4) Bonus: Electron withdrawing groups such as nitro and fluoro will stabilize (a) positive charges or (b) negative charges on adjacent groups.
If for future work you should ever answer "no" to question (1), then it might be worth trying APCI, if available.