using PEG to concentrate proteins

[robert b burrows]

I have been using PEG (Aquacide III, Calbiochem) to concentrate protein 
solutions. I have placed the solution in a dialysis bag and buried it in 
solid Aquacide. Now I hear that there may be impurities in the Aquacide 
that can diffuse into the protein solution. Does anyone know what these 
these impurities are, and if they can be removed by gel filtration?

Thanks,

-- 
Robert Burrows
rbb at world.std.com