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?

  • $\begingroup$ You can calculate the final concentrations of solutes in your sample after dialysis, assuming complete equilibration, with C₁V₁=C₂V₂. This formula also tells you that it is more efficient to dialyze, say, twice in 500 mL instead of once in 1 L. I typically dialyze several times in 500 mL because it seems like a reasonable beaker size. $\endgroup$ – canadianer Oct 14 '15 at 2:29
  • $\begingroup$ In case I wasn't clear: you can calculate solute concentrations as mentioned above and then use this information to plan the volume(s) to use in your dialysis, depending on your specific needs. $\endgroup$ – canadianer Oct 14 '15 at 2:38
  • $\begingroup$ By "solute", do you mean the enzyme, imidazole, salt, or something else? $\endgroup$ – wswr Oct 15 '15 at 4:17
  • $\begingroup$ A solute is anything dissolved in a solvent, so all of the above and more. The point of dialysis is to remove something unwanted from your sample. You decide what concentration of that something is tolerable for your experiment and dialyze accordingly. $\endgroup$ – canadianer Oct 15 '15 at 4:22

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