polymer at PRLC

[jiang295]

c18 pore size is 100A, does anyone know how big polymer can go into this small pore and get interaction with stationary phase

[Uwe Neue]

Any polymer with a random coil size of 100 A will penetrate without too many difficulties... The answer depends on the polymer and its size in solution. For a polystyrene, I would think that a MW around 100 000 (or about 10 000 styrene units) will be the approximate upper limit. So it is BIG.

[jiang295]

thanks a lot.
so do you think c18 is also mixed mode of size exclusion and hydrophobic interaction.
why nobody mention there is size exclusion mode in C18.

Any polymer with a random coil size of 100 A will penetrate without too many difficulties... The answer depends on the polymer and its size in solution. For a polystyrene, I would think that a MW around 100 000 (or about 10 000 styrene units) will be the approximate upper limit. So it is BIG.

[Uwe Neue]

"why nobody mention there is size exclusion mode in C18."

A: it is obvious
B: there is plenty of literature in the polymer world that uses combinations of adsorption and size exclusion, often with some very interesting results.

[jiang295]

do you refer to LH-20?

"why nobody mention there is size exclusion mode in C18."

A: it is obvious
B: there is plenty of literature in the polymer world that uses combinations of adsorption and size exclusion, often with some very interesting results.

[jiang295]

size exclusion is important in LH-20, while it is not important in C18. is it because of contribution from entropy and enthapy term differ in their relative importance in two columns.
if so , why is that.

"why nobody mention there is size exclusion mode in C18."

A: it is obvious
B: there is plenty of literature in the polymer world that uses combinations of adsorption and size exclusion, often with some very interesting results.

[HW Mueller]

Since nobody wants to take on your question any further I would like to ask you whether you have looked at Internal surface Reversed Phase Exclusion chromatography?
Lets keep this simple: why would anybody make a column with a C-!8 surface, especially for biological macromolecules, if he wanted to have no or little contribution from adsorbance? On the other hand, if he had molecules which did not absorb on C-18, why would he not try "pure" exclusion with a C-18 surface?
Now if one were to do this the complicated way and bother about entropy and enthalpy one would have to include the analytes´ properties and then play with the free energy and distribution constants. Good Luck.
Also if you want to have a life´s project you could try to unravel a molecules shape in different solvents, thus predict if they enter a given pore size or not via a little quantum mechanics and maybe statistical thermodynamics, or you could simply picture in your mind that a molecular sphere with a diameter greater than 100 A might have trouble diffusing into a 100 A cavity, etc., etc.

[Bryan Evans]

thanks a lot.
so do you think c18 is also mixed mode of size exclusion and hydrophobic interaction.
why nobody mention there is size exclusion mode in C18.

Any polymer with a random coil size of 100 A will penetrate without too many difficulties... The answer depends on the polymer and its size in solution. For a polystyrene, I would think that a MW around 100 000 (or about 10 000 styrene units) will be the approximate upper limit. So it is BIG.

Even if the polymer is excluded from the pores, it can still interact with the surface of conventional C18.
So, to get the large polymer to be completely excluded (and favor the mobile phase), people use high
organic composition. And at high organic, some biopolymers could coagulate.

There are columns that can be used to exclude large polymers and retain small molecule.
But they aren't conventional C18 columns.

[jiang295]

if polymer get excluded from pore, then interaction should be much weaker since there is not much stationary phase on the surface.
am I right?

how high is what you mean "high content of organic solvent" like 40% percent or 90 percent?

what happen to the retention of coagulate polymer such as protein?

thanks a lot.
so do you think c18 is also mixed mode of size exclusion and hydrophobic interaction.
why nobody mention there is size exclusion mode in C18.

Any polymer with a random coil size of 100 A will penetrate without too many difficulties... The answer depends on the polymer and its size in solution. For a polystyrene, I would think that a MW around 100 000 (or about 10 000 styrene units) will be the approximate upper limit. So it is BIG.

Even if the polymer is excluded from the pores, it can still interact with the surface of conventional C18.
So, to get the large polymer to be completely excluded (and favor the mobile phase), people use high
organic composition. And at high organic, some biopolymers could coagulate.

There are columns that can be used to exclude large polymers and retain small molecule.
But they aren't conventional C18 columns.