Hi Guillermo,

The pH you observed is exactly what you can expect upon a weak acid like KH2PO4 in water. The pKs of this compound is 7.0, but this only means that at pH 7.0 there are equal amounts of (H2PO4)- anions and its conjugated base (HPO4)2- present in solution. This does not mean that dissolving the acidic salt will yield a pH of 7.0, you have to adjust it by using base, as you did. We usually use aqueous solutions of KOH for this purpose with different molarities (10 M, 5 M, 1 M...), making it easier to dropwise add small amounts of base at a time. When using solid KOH pellets, insoluble K3PO4 precipitates can form due to high local concentrations of KOH. 10 mM is not much of a buffer substance, and adding pure KOH seems a bit over the top here. Maybe you overtitrated your buffer? Did you check pH after autoclaving, too?

Best, Joscha

sir according to me....

you used 1 m MgSO4*7H2O and KOH pellets also you are adding in the reaction mixture and pH was high than 7 this will Leeds to MgO nano crystals are formation by precipitation reaction at the bottom after autoclave.

maybe I should adjust the pH with NaOH instead of KOH? I used KOH to not add sodium to the buffer...

So maybe I should not sterilize this buffer. I mean, if it's the heating in the autoclave what is accelerating or making possible the reaction that forms the salt precipitate.

This is only for the dilution/resuspension of a phage lysate.

The important thing in my buffer, I think, is the ionic strength and the pH to preserve viral capsids.

any thoughts?

Hi there Guillermo, what kind of buffer is this? How do you buffer it? If I were you I would raise the pH with K2HPO4 or add the salts prefiltered in sterile water! and then I would check my personal messages my good old Malagueño friend!

Guillermo Domínguez Huerta always filter sterilize MgSO4 and add after autoclaving to avoid precipitation. MgSO4 addition would not affect pH changes!