By Anonymous on Monday, September 15, 2003 - 04:30 am:
I find LC packings now sell them, but there is no RP-18 for small molecules.
By Einar Pontén - SeQuant AB on Monday, September 15, 2003 - 10:16 am:
There is an inherent problem in the preparation of polymeric monoliths that makes the mass transfer properties of the column unsuitable for small molecules.
Do you have any particular molecule in mind?
By Anonymous on Tuesday, September 16, 2003 - 05:30 am:
Einar,
What is this inherent problem? I presume by polymeric monoliths that you mean organic polymer monoliths? I am not sure if silica could be described as a polymer anyway-in which case your statement does not need qualification!!!
Thanks
By Anonymous on Tuesday, September 16, 2003 - 06:15 am:
silica is a branched polymer of silic acid
By Einar Pontén - SeQuant AB on Tuesday, September 16, 2003 - 03:02 pm:
OK, I agree! That is a typical semantic issue that I would argue about.
What I meant was an organic polymer since these are the only capillary monolithic columns commercial available that I am aware of.
The problem I have in mind is the wide pore size distribution in polymeric monoliths. One may argue about the reasons for this, but a fairly good explanation is the "Tromsdorf-effect" due to free radical polymerisation. Basically the temperature and the degree of polymerisation is changing during the polymerisation of a monolith, while the molecular weight of the polymeric chains in the solvent are increasing (less diffusion capability). The temp gradient and difference in weight will give an inhomogenuos polymer. In conclusion, the pore distribution will span between suitable and unsuitable sizes and that will lead to peak spreading in the final column.
There are solutions to this problem.
By A.Mouse on Tuesday, September 16, 2003 - 05:57 pm:
Einar,
I have not yet seen a polymeric packing that matches the performance of silica.
By Anonymous on Wednesday, September 17, 2003 - 04:25 am:
Einar,
Thanks very much for your reply on the problems with organic polymer monoliths. Actually, now I think of it, it is possible that Merck are now selling capillary monoliths based on silica. The person who posed the first question might like to check this out. Merck have certainly done some research on capillary silica monoliths.