I need to purify factor VIII from plasma. I used DEAE resin and dissolve cryoprecipitate in tris and sodium citrate buffer. Fibrinogen DO NOT bind to resin. I washed the column with 170 mM NaCl and Elute with 270 mM. but in my main fraction there is some impurity with very high MW, in reduce and nonreduce SDS PAGE test. Is there any advise about it, what is and how I can purify it.