Is there a specific ratio between the volume of enzyme solution in semipermeable membrane bag and the volume of the buffer outside the membrane bag? I have been looking for a specific formula or general rules to decide on the volume of the buffer outside the membrane bag but to no avail. There must be general rules to determine the volume. It can't be come up with out of thin air. What common criteria are there to determine the volume as well as the time for the dialysis?