By Jon on Tuesday, January 21, 2003 - 05:35 pm:
Hello,
We've been having an ongoing debate in my lab. Some of us are doing ion exchange using a resin (Dionex), its not a silica base. We can preconcentrate the analyte using a weak salt m.p., then elute off with the salt gradient. The question is "Is this partitioning into the s.p. or is it adsorbing."
Thanks
Jon
By Chris Pohl on Tuesday, January 21, 2003 - 06:16 pm:
I guess if you want to be really generous about your interpretation of the terms you could say that both are correct but, strictly speaking neither term is correctly applied to this case. Generally, the term partitioning is only applied to partitioning between two liquid phases one of which is the mobile phase and one of which adheres to the support particles. Adsorption is generally only applied to the case where the mode of retention is hydrogen bonding or other weak forces (e.g. van der Waals forces). The correct term would be ion exchange unless the analytes are nonionic. In the case of nonionic components interacting with an ion exchange resin, its open to debate which of the terms is more appropriate. In this latter case, more detailed information might help sort it out.
By Jon on Wednesday, January 22, 2003 - 07:51 am:
Chris Thanks for the clarification.
I take it then that the functionalized s.p. isn't really considered a "liquid"
Would that be correct in saying?
Jon
By Chris Pohl on Wednesday, January 22, 2003 - 11:04 am:
Jon,
Strictly speaking, the bonded phase can't really be considered a liquid (it's generally a polymeric gel in the case of polymeric materials) but it's also true that the aqueous phase within the stationary phase is quite different in structure to that of bulk water in the mobile phase. If the analyte is actually partitioning into the water within the stationary phase it could probably be considered a partition process but if it is associating with the fixed ion exchange site, I think it would be more appropriate to refer to it as ion exchange.