Diafiltration is carried out to exchange the buffers used to suspend a globular
ID: 517211 • Letter: D
Question
Diafiltration is carried out to exchange the buffers used to suspend a globular protein. Initially, the protein is contained in 3000 liters of solution containing 45 g/L salt. The aim is to remove 99.9% of the salt and suspend the protein in new, salt-depleted buffer. As indicated in the figure below, a microporous ultrafiltration membrane is applied to separate the salt from the protein. The membrane retains the protein but allows passage of all smaller molecules such as salt and water into the permeate stream. The permeate flow rate is 750 L/h. The total volume of protein solution is kept constant by addition of new buffer. Assume that the solution is well mixed and the salt concentration in the permeate is the same as that in the solution. (a) Estimate the time required to complete this process. (b) What mass of salt is present in the new solution?Explanation / Answer
a) Volume of protein solution = 3000 L; the permeate flow rate is 750 L/h.
Therefore time required to remove the salt from the protein solution = (volume of protein solution)/(permeate flow rate) = (3000 L)/(750 L/h) = 4 h (ans).
b) The salt concentration in the protein solution is 45 g/L; we have 3000 L of the protein solution.
Therefore, mass of salt in the protein solution = (3000 L)*(45 g/L) = 135000 g.
The aim of the diafiltration process is to remove 99.9% of the salt from the protein solution; therefore, the new salt-depleted buffer must contain (100 – 99.9)% = 0.1% salt.
Therefore, mass of salt present in the new solution = 0.1%*(135000 g) = (0.1/100)*(135000 g) = 135 g (ans).