further questions on buffer and modifiers

[firework1]

Sometimes people buffer pH with buffers, sometimes people simply add acid or base in mobile phase, based on what should I choose?

[Mark Tracy]

You need at least 1 millimolar capacity in order to have a stable pH, reasonable equilibration times, reproducible preparation, and resistance to sample effects.

Therefore, if you need a pH between 3 and 11, use a real buffer. For pH <2 a dilute acid is OK; for pH > 12 dilute base is OK. For pH 2-3 or 11-12 you can do it either way.

[firework1]

thanks