A purified protein is in a HEPES buffer at pH 7 with 400 mM NaCl.
A 1 mL sample of the protein solution is dialyzed against 1 L of the same HEPES buffer with 0 mM NaCl. Small molecules and ions (Na+, Cl−, and HEPES) can diffuse, but the protein cannot.
First Question: Once equilibrium is reached, what is the final NaCl concentration in the protein sample?
Second Question: If the original 1 mL sample is dialyzed twice, successively, against 100 mL of 0 mM NaCl HEPES buffer, what is the final NaCl concentration in the protein sample?