Chromatography Forum

Hellow ,

I have a cmpound [-NH2 is active group] and it's HCL salt. I subjected both on RP-HPLC at pH 4.5 both have same RT. Can any body tell us if we use basic pH near about 7.5 can both compound seperated or not

thanks

praveen

If that pH is at least one (preferably 1.5-2) units away from your amine's pKa, you stand a chance.

As usual, more information would be helpful.

If you are talking about separating an amine from its HCl salt (actually from ammonium in solution) the answer is NO. Any equilibria will be way to fast to "see" components via HPLC.

Sir my molecule is amine and its HCl salt . Both are present in the form of ammonium solution when we use acidic mobile phase but I want to clearification what will happened if I use basic mobile phase near about 7-8 pH .
i also want to clearification for this :

Any equilibria will be way to fast to "see" components via HPLC.


Thanks and regards

praveen

In aqueous solution, salts dissociate into their component ions. If you dissolve your salt in, for example, a potassium phosphate buffer at pH 7, your solution will contain potassium, phosphate (actually, an equilibrium mixture of hydrogen phosphate and dihydrogen phosphate), your amine (depending on the pKa, probably a mixture of the free base and the ammonium form), chloride, hydronium, and hydroxide.

All of these dissociations and equilibrations are extremely fast -- orders of magnitude faster than your chromatography -- so that there is no way to separate your amine (free base) from your amine (ammonium with chloride attached) from your amine (ammonium with hydrogen phosphate attached) from your amine (ammonium with dihydrogen phosphate attached) from your amine (ammonium with hydroxide attached). All you will see is a single peak that represents the average of all these forms.