Hi all,
I'd like to take the topic for discussion.&I believe more interaction in this
1.How a bonding chemistry alone could save the silica back bone,when dissolution at high pH,being the nature of it?
2.How is the acid hydrolysis of bonded phase prevented in few proprietry low pH columns
3.Certain coventional columns like phenomenex-Luna ODS(2) also claim to be worked at low-high pH(which is found to be true experimentally too)
4.will the Pre-Treatment done to the silica,improve the strength of it?
(Forget the polymeric back bone,and let us focus up on silca base material alone
Regards
Michael.K.Raj

1. At high pH, a dense coverage helps, but you still dissolve the silica. The only way to get to still higher pH values is to modify the matrix, as is done in XTerra packings. In this case, the matrix is an organic-inorganic hybrid with methyl groups in the matrix.
2. The acid hydrolysis can be modified by the nature of the ligand. The most important impact is to use sterically hindered ligands, as in the Zorbax line of products. While standard (monofunctional) ligands have methylgroups as the side chain, the Stablebond line has isopropyl groups, if my memory serves me correctly.
3. I believe that I covered this above. It is a question of ligand density. But this gets you only so far...
4. Why should it? Is a bumber stronger after it has rained?

Ofcourse i agree with uwe.But will the hybrid matrix alter the inorganic nature of silica?or the organic part repairs the damages caused to it?

Even in xterra, at higher pH ,inorganic buffers are not advised right?

Some buffers are more agressive than others. See the Kirkland publications! We are routinely using ammonia and ammonium bicarbonate at pH 10. These are inorganic and volatile for MS and prep use.

The hybrid matrix changes the nature of the carrier compared to silica. It is a different beast altogether. For example, the pK is much higher than the pK of silica. Therefore it is not a repair mechanism that makes the hybrid packings more stable at alkaline pH.

Now Uwe, you are perpetrating folklore. You have the "collapsed ligand" myth mostly put to rest; lets bury this one too. I have explained how Kirkland misinterpreted the data from the different buffer experiment. Buffers prepared to the same pH, where the pH is measured in the solvent actually used for the hydrolysis experiment (and not inferred by a pH measured in a substantially different solvent) will have the same hydrolysis rate. The Kirkland buffers had a greatly different hydrogen ion activity in the solvent he used for hydrolysis, and the hydrolysis difference he observed correlated perfectly with the actual pH in the solvent.

Any thing further to these?

You are right! The pK of ammonia is likely to shift to a lower pH as an organic solvent is added. I would think that Roses et al. have measured this, but I do not have a publication in front of me. The story with ammonium bicarbonate is more complex. According to the standard expectation, the pK of ammonia shifts to a lower pH and the pK of bicarbonate to a higher pH. If they shift far enough, the ammonium bicarbonate buffer ist just a solution carbondioxide and deprotonated ammonia. Don't believe that anybody has measured the pK of bicarbonate in the presence of an organic solvent.

PS: I forgot to say that we have measured the pH of an ammonium bicarbonate buffer at pH 9.8 in water. Indeed, it does barely change upon the addition of methanol and acetonitrile. It behaves as expected.