Dialysis

Proteins  can  be  divided  from  little  molecules  through  dialysis  by  a  semi- permeable   membrane   like  as  cellophane or cellulose acetate.   Pores  in  the membrane   permit  molecules   up  to  approximately   10  kDa  to  pass  by, while  larger molecules  are retained  inside the dialysis  bag which is shown in figure. As most proteins have molecular masses greater than 10 kDa, this methods is not appropriate for fractionating proteins but is frequent used to remove little molecules like as ammonium sulfate and salts from a protein solution. It should be illustrious that at equilibrium the focus of small molecules inside a dialysis bag will be equivalent to that outside in another Figure, and so various changes of the surrounding solution are often needed to lower the concentration of the small molecule in the protein solution sufficiently.