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Ion exclusion or ligand exchange?
Posted: Mon Feb 28, 2005 5:09 pm
by Fabiano
I already heard that the separation of sugars on cation exchange columns (Ca form) is due to ligand exchange and ion exclusion, by what I know, theorically both process could hapen, am I wrong?
Posted: Tue Mar 01, 2005 12:59 pm
by tom jupille
Cation exchange resins in the H+ form are used for organic acids separations; in that situation, the dominant mechanism is "ion exclusion". There is arguably some "reversed-phase" partition chromatography going on as well.
The same resins in the Ca++, Ag++, or Pb++ form are also used for sugars; in that situation, ligand exchange certainly plays a role, because the selectivity changes with the ionic form of the resin. Retention of sugars also occurs on the H+ form resins, however. This suggests that some type of partition chromatography is also involved.
Posted: Sat Mar 05, 2005 11:21 am
by ConstantinS
Hi, Fabiano. Good to "see" you again.
Tom is right - as in Russia said - the situation is clear that the situation is unclear.
I tried to apply the principal components analysis to study this question (to study "retention mechanisms"), and even have got some interesting results, but it was for fun, and I've quickly lost interest.
All data on all - attention! commercially available phases for oligisucharide separations - is described generally only by two factors, the first about 70-80% major (exclusion) and the second is about 20% (third about 5% and so on).
So, it requires more serious approach then "for fun".