When I was first getting started in the lab I made the mistake of using PVP instead of PVPP in the clean up (polyvinylpyrrolidone instead of polyvinylpolypyrrolidone). It's an easy mistake to make, but PVP is water-soluble (PVPP isn't) so it dissolves in the washing buffer.

It might seem a stupid question, but are you sure you have PVPP?

I agree with David, the PVPP should not dissolve, I had the opposite once, I tried to dissolve PVPP in a solution for enzyme extractions, and I heated and acidified put it in the ultraconic bath, nothing happend.

For your cleaning procedure, Masicadaro et al., 2008 describes a PVPP column for protein purification. Humic acids interfer with proteins and nucleic acids.

Article Comparison of extraction methods for recovery of extracellul...

Thanks for all

@ David @ Katharina

I am sure that it is PVPP. I will try with some other brand.