Posted: Thu Dec 01, 2005 11:00 pm
In general, yes. For any equilibrium, the thermodynamics and kinetics are essentially independent of one another. That's the way catalysts work, for example.1) the rate/speed of protanation/depro has nothing to do with equilibrium(the ratio of species);
Not quite true. The equilibrium determines how much of each component is present. The rate determines whether those components will be seen as a single or a double peak.2) the rate, but not equilibrium, does determine if the peak splits;
If we are referring to simply a protonated vs unprotonate species, yes (the rate may change, but it will be so fast as to not affect the chromatography regardless). If we are referring to other pH-dependent changes (hydrolysis, for example), then changing pH can change both the rate and the equilibrium.3) more likely, changing pH shifts equilibrium, but not rate;
Again, depends on the context. If we are referring to a simple ionization (for example, a weak acid:4) conclusion is that changing pH usually does not solve spliting problem.
Further, when Roy claimed that he solved the problem by changing pH indicating his systems happened to be those rare, where the rates change significantly under different pH.
HA ↔ H+ + A-), you will never see separate peaks for the free acid (HA) and the anion (A-). You will always see a single peak corresponding to the "average" degree of ionization, as attested to by KarenJ. Peak splitting can occur for other reasons, for example:
- a mismatch in pH between the sample diluent and the mobile phase
- another pH-dependent reaction or equilibrium
in which case a change in pH can fix splitting problems.