Can one mix PO4 salts of Na and K to make a buffer?

In a pinch I made a 20 mM pH 7.2 PO4 buffer out of 20 mM Na2HPO4 and 20 mM KH2PO4. Now I'm thinking twice about what effect using the Na salt would have on the separation. I would think minimal, and whatever effects would be more applicable to base-silanol interactions.

Russell

Before we go ahead on the discussion, is there a reason that you what to do that?

I wouldn't choose the Na salt if K was available. I am wondering what effects on the separation would occur; let's say this is a theoritical discussion.

I have not found any mention of Na vs K for separations except that K has a stronger interaction with silanols.

Regards,
Russell

there will be solubility differences, but no big effect on pH. I use them interchangably. but, as Kohthoff said, "let theory guide, experiment decide." do you see a difference on the separation?

In "CRC Handbook of HPLC for the separation of AA, Peptides, and Proteins, Vol. I, 1984", chapter "Phosphates as mobile phase modifiers", p. 155, C.A. Bishop wrote:
"different retention characteristics have also been observed when sodium, as opposed to potassium, phosphate buffers have been added to the mobile phase".
Unfortunately, there aren't references on this topic, but only on the theoretical use of phosphates in the analysis of the cited compounds.
I hope it will be of your interest.

I recomend to visit :


It's free and there is a lot of information about Buffer's and rules.


http://www.zirchrom.com

Hi Folks,
Take a look at "Tailing Factor Optimization for Sulfonates" posted on 7-25-01. I think in most cases, the cation has little effect; however, if there is a chance for some equilibrium between an organic acid or base and its salt, the inorganic portion of the salt might play an important role on peak shape or retention, as seen in the example mentioned above.
Does anyone have any thoughts on this?