Hi,

When I have an option to choose Pot.Dihydrogen phosphate or Dipotassium Hydrogen phosphate to prepare a buffer (pH 6.5) with an acid or a base, which one is more preferable and why? Pl. let me know

Thanks for your time

The best method is to use both. Prepare equimolar solutions of both in the needed concentration and add the two solutions until you have the required pH. This way you donīt change the wanted conc. or ionic strength, no matter how often you need to adjust pH. If you add another base or acid to make the adjustment you will change the phosphate conc. and ionic strength, and that differently each time you do it.
See also previous discussions on buffers.