Chromatography Forum

Na+ also shifts towards lower retention times on the ZIC-pHILIC when decreasing the pH we have always attributed this to the eluting power of the H3O+ and I do not see what this has to do with silanol activity.
I do not deny that it could be a small amount there but you just never see it.

What does your experiment have to do with what I have suggested? When you increase the pH toward ~6, at low ionic strength your retention time of Na+ is extremely high, it is stuck at the beginning of the column., when you inject a high acidic or high ionic strength bolus, one gets Na+ to come out with the acid, etc., near tm, the amount depends on the bolus concentration and/or volume. I did not see any significant differences between ZIC-HILIC and Atlantis.

I can for the life of me not understand how your experiments would distinguish silanol and sulfonic acid ionic interactions, but I understand you can not publish your whole paper on the chrom forum

I will read your paper with great interest when it is published, and would really apperciate a copy.

Another two ways to see what affect cation-exchange interaction on Sequant column is to run 0% organic (or very low organic) at different pH 2,3,4, 5 and 6 and look at retention of basic analytes including sodium and couple of bases. Also, making stationary phase with more ligand and less ligand will show from where cation-exchange interaction comes. If it comes from silanols, increase in loading will decrease retention of sodium. If it comes from sulfonate, then increase in ligand loading will cause increase in sodium retention. All these experiments need to be conducted at no or very low organic in order to eliminate HILIC interaction. I understand that this are scientific experiments and manufacturers might not want to make columns with more or less ligand. When we develop new stationary phase we always look at ligand loading and determine what happens.

It looks like simple experiments are disliked? I ran the 22Na+ experiment with 0.00158 M H2SO4 and 0.00001 M NaOH. No organic. The results with the ZIC-HILIC and Atlantis Silica were about the same: Absolute retention of the 22Na+ in basic mobile ph., no or low retention in acid mobile ph. I did 100reds of experiments with other ions: always very similar results including charge exclusion only with negative ions. When one considers that the ZIC has zwitter substituents and considering elution orders one must conclude that the silanols of the ZIC are responsible.
(There is one exception to the parallelism, namely, with Cl- under HILIC conditions as usually recommendet by Sequant. It has a considerable retention in ZIC, but not in the Atalntis. Due to the peculiar behavior of zwitters I conclude that one has a salting out of Cl-, not pure ion exchange.)