Question

how would i make a lysis buffer containing 20mM NaH2PO4, 300 mM NaCl, and 30 mM imidazole with a pH of 7.5.

Please list detail steps. Thanks.

Answer 1

This is an acidic buffer solution containing weak acid and its salt with strong base imidazole.

The expression for pH of solution is

Assume that we use 1 L of 20 mM

To this we add x millimoles of imidazole. Then the pH will be 7.5

But

Hence, the volume of imidazole required is

Hence, to 1 L of 20 mM , 0.44 L of 30 mM imdazole is added.

Now the ratio of salt and acid is fixed. Hence, the pH of the solution is fixed.

To this, appropriate amount of 300 mM NaCl can be added which will not alter the pH of solution.