Hi Parkc23--I must be honest, Jiri preceded me to this as you can see, and both of us employ similar references.
Jiri--I apologize for tailgating--I concur with everything you put down, we were both writing at about nearly the same time, and no offense is intended or meant. Being honest, Jiri's second reference is really quite good--I like it far better than the one at the bottom of my post, too!
MattM
The short answer is that you are correct in your post:
Vbed = π * r2 * L or 1/4 π * d2 * L
But I was kind of interested, so I looked a bit further (adapted/copied from Wikipedia):
"GPC separates based on the size or hydrodynamic volume (radius of gyration) of the analytes injected onto the column. The smaller-volume analytes can enter the pores of the beads packed in the column more easily and spend more time within the pores, which increases their retention time. Larger-volume analytes spend little (if any) time in the pores and are eluted quickly (Big Ones Come Out First).
If an analyte is either too large or too small it will be either not retained or completely retained respectively. Analytes that are not retained are eluted with the free volume outside of the particles (Vo), while analytes that are completely retained are eluted with volume of solvent held in the pores (Vi). The total volume can be considered by the following equation, where Vg is the volume of the polymer gel and Vt is the total volume: Vt=Vg+Vi+Vo
(Skoog, D.A. Principles of Instrumental Analysis, 6th ed.; Thompson Brooks/Cole: Belmont, CA, 2006, Chapter 28.)
As can be inferred, there is a limited range of molecular weights that can be separated by each column and therefore the size of the pores for the packing should be chosen according to the range of molecular weight of analytes to be separated. For polymer separations the pore sizes should be on the order of the polymers being analyzed. If a sample has a broad molecular weight range it may be necessary to use several GPC columns in tandem with one another to fully resolve the sample."
Bed Volume = Vt, which in turn equals the sum of the volume of the polymer gel within the column, the interstitial pore volume of the polymer gel beads and the "free" volume in between the polymer gel beads, or Vbed = π * r2 * L or 1/4 π * d2 * L
This was also an interesting file to me:
kirschner.med.harvard.edu/files/protocols/GE_gelfiltration.pdf
And this site:
http://technologyinscience.blogspot.com ... ution.html
