You are probably aware of the protein concentration method by
"dialyzing" against polyethyleneglycol. My question is regarding the
MW of PEG and the pore size of the tubing: Currently, I am using
PEG20000 (avg MW 15k-20k) and a dialysis tubing with a cutoff of 14kD
for globular proteins. In my experience, this is working very well
(and cheap), esp. for large volumes.
We just got some concerns now that some of the PEG could make it
across the membrane. Is there any need to be concerned? Which would
mean to switch to PEG35k or higher and/or tubing with a lower cut/off,
both increasing the expenses. As I understand PEG, the molecules will
get quite huge due to hydratation and PEG always has some low MW size
"contaminants" i.e. molecules shorter than desired.
Anything you can suggest?