Chromatography Forum

Concerning reversed-phase chromatography, at pH-values of 5 and above your acid should be protonated

I think you may have gotten turned around there. An acid will be neutral *below* its pKa. A base will be neutral above its pKa

Damn! Of course, you're right. *Embarassed*

vkbojja, concerning pHs of mobile phases, just do the opposite of what I originally suggested

Analyte PKa is 3. I am playing with my mobile phases arround that only.

Typically, you would want to stay away from the pKa by at least one unit. So for reversed phase, you'd want to work around pH 2 (0.i% H3PO4 would do nicely enough), for normal phase perhaps consider pH 4 or above.

*Embarassed*

Cheer up, it happens to us *all* now and then!

Mixed-mode is always a good option, but I am getting tired enforcing this approach

If you can send me info on compound I will advice you what to do. Alternatively we can develop a method for your free of charge.

Hi,
I am trying to develop a method for highly polar compound. Mol. Wt. 940.

I am expecting suggestions over this forum.
Regars,
vkbojja :

Without divulging too much, it would help tremendously if you could tell us a little more about the chemical nature of this solute.

Soluble only in water and partially soluble in Methanol

Hi VKbojja-
How many ionizable groups does your compound have?
Above pH 3, is it positively or negatively charged?