pore size and exclusion and exclusion limit

[jiang295]

Hi it there any equation to describe this relationship?
i read it somewhere that 50A will equal to 5000Da exclusion limit.
so how about 100A pore size.
why this info cannot always get from manufacturer?

[Uwe Neue]

You can get calibration curves with molecular weight standards from manufacturers' catalogues. For people doing SEC, this is more meaningful than a pore size. The MW scale of one polymer can easily be translated into that for another one with the known Mark-Houwink constants for the polymers.

For getting to the size of a polymer that is just excluded from the pores, you can use the Flory-Fox equation in conjunction with the Mark-Houwink equation.

The other thing is, what do you know about a packing with "100 A pores"? Is this the upper limit, equivalent to the exclusion limit? Is this the average pore size? Any idea? And to what polymer does the exclusion limit refer to? This makes of course a difference, since a polyethylene has a much lower molecular weight per unit chain length than a polystyrene or an oligosaccharide.

[jiang295]

sure, I think I need to learn more about SEC.

You can get calibration curves with molecular weight standards from manufacturers' catalogues. For people doing SEC, this is more meaningful than a pore size. The MW scale of one polymer can easily be translated into that for another one with the known Mark-Houwink constants for the polymers.

For getting to the size of a polymer that is just excluded from the pores, you can use the Flory-Fox equation in conjunction with the Mark-Houwink equation.

The other thing is, what do you know about a packing with "100 A pores"? Is this the upper limit, equivalent to the exclusion limit? Is this the average pore size? Any idea? And to what polymer does the exclusion limit refer to? This makes of course a difference, since a polyethylene has a much lower molecular weight per unit chain length than a polystyrene or an oligosaccharide.