In order to purify a certain protein you require 01 M glycin

In order to purify a certain protein, you require 0.1 M glycine buffer at pH 9.4. Unfortunately, your stockroom has run out of glycine. However, you manage to find two 0.1 M glycine buffer solutions, one at pH 9.0 and the other at pH 10.0. What volumes of these two solutions must you mix in order to obtain 200 mL of your required buffer?

Solution

Ans:

For this problem you must calculate the concentration at all pHs.

        Therefore at pH 9.0, 10.0 and 9.4 for a 0.1 M buffer

        9.0 = 9.25 + log X/0.1-X     X = 0.36M

        10.0 = 9.25 + log X/0.1-X   X = 0.085M

        9.4 = 9.25 + log X/0.1-X     X = 0.059M

            Let a = the fraction of pH 9.0 buffer required, then

                0.036M (a) + 0.085M (1-a) = 0.059M   a = 0.53

            Thus,

                0.53 x 200ml = 106 ml of the pH 9.0 buffer + 94 ml of the pH 10 buffer gives the desired solution