Problem with Folin Assay - (Apr/30/2011 )

I have been using the folin assay for the estimation of total proteins in a sample which has been extracted with PBS buffer containing 10mM PMSF. When this sample is concentrated with PEG and the conc. sample is subjected to the assay, after addition of the folin reagent although there is a colour development but a yellowish coloured precitpitate is being formed. Can anyone tell me why this precipitate is being formed?

Thank u!!!

how do you concentrate (precipitate with peg? dialyze against solid peg?)?

what is the buffer in the solution after concentration?

pmsf can interfere with the assay. i'm not sure if peg will.