Pore size of analytical column?

[dsahoo]

Dear all,
I am intersted to buy an analytical column for HPLC. The parameters like internal diameter, length, particle size, pore size and pump pressures are important for chosing a right column. I found 4.6 mm as internal diameter and particle size of 5μm is commonly used parameter for an anlytic column. I am wondering about the pore size of the column for better performance. How is the pore size of the coloumn affect the pressure/flow rate/ the performance of the colum? Which pore size is preferable for an analytical column?
Any sugggestion for considering pore size!
Thank you

[Uwe Neue]

Pore size is only determined by the type of analyte that you ae using. Use 100 A for small molecules and peptides, maybe up to a molecular weight of 1000 (at least), for larger molecules (insulin and up), Use a 300 A column.

[dsahoo]

Thank you very much for your suggestion.I hope 300A will work for my system.
With regads

[Mark Tracy]

Pore size has no direct effect on pressure or flow rate because all the bulk flow takes place in between the packed particles, transport within the particles is by diffusion. All other factors being equal, a larger pore size will have less surface area and hence lower retention. The pore volume will be somewhat larger and hence the void volume will be somewhat larger also. The larger-pore silica tends to be less physically and chemically rugged, but this is only a serious problem above 300Ã…. These comparisons get much more tricky when other factors change.

[Uwe Neue]

dsahoo: I was surprised about your answer, on the assumption that most people do small molecule separations, and not large molecule/protein separations. For small molecules, the best approach is to use a 100 A packing.
Thank you, Mark, for pointing out this possibility of a misunderstanding.

[LCGUY]

Dear dsahoo,

Mark has given a very clear explanation. Let me add a thing that pore size is not the absolute value for a column. This is a distribution curve having lesser sized pores to larger pores. The quality of the column lies in the fact that how narrow is this distribution curve so that you have most of the pores lie exactly or close to the size claimed by manufacturer.

I think most of the analytical work can be done with 100A pore sized particles unless it is proteins or peptides with larger molecular weight.