The protein concentration of a bacterial supernatant is estimated at 0.75 mg/mL. You have 1.5 L of this supernatant, and you decide to concentrate the protein by using ultrafiltration (with a 10,000 Da cut-off membrane). The final volume of the supernatant retentate after ultrafiltration is 10 mL. From the change in volume of the solution, estimate the new protein concentration (and assume that no losses of protein occur in the process
Use the equation Ci x Vi = Cf x Vf where Ci is initial concentration (mg/mL) and Vi is initial volume (mL) and Cf (unknown) and Vf is final volume in mL
0.75 mg/mL x 1500 mL = Cf x 10 mL answer 112.5 mg/mL
Ci = initial concentration (mg/mL
Vi = initial volume (mL) convert L to mL (1.5 x 1000)
Cf = concentration final (mg/mL)
Vf = volume final (mL)
Peter Philbrook I appreciate your answer, that is what I taught I should do, but for some reason I was hesitant.
I would like to recommend you to measure the protein concentration of the retentate by Bradford protein assay (or other methods). If you calculate the protein concentration based on the CiVi = CfVf equation, I think that will make you overestimate the protein concentration.
PS. if you want to roughly calculate the protein concentration, I also agree with CiVi = CfVf calculation. Cheers!
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