Chromatography Forum

Hi guys,

First post here.

I'm unsure how the following elution order would occur and would like some guidance.

If I have a positively charged column (anion exchanger) and I have a solution of a weak cation molecule and a strong cation molecule, which would elute first?

Would the strong cation be repelled much quicker than the weak cation or would they both elute equally.

Without changing anything, would you be able to successfuly separate these molecules?

Depends on the pH of the buffer and the pKa of the weakly basic cation. "Strong" and "weak" in this context refer to pKa values; a strong base has a high pKa while weak base has a lower pKa.

So, if your buffer pH is higher than the pKa of your weak base, the latter will be unionized and not excluded (i.e., it will elute later).

If your buffer pH is significantly lower than the pKa, then it will be ionized. The order of elution will then depend on the relative charge density of the two cations.