Potassium Phosphate Buffer

K.D. James mbkdj at s-crim1.dl.ac.uk
Thu Oct 31 06:12:20 EST 1996

Delvac Oceandy (Delvac at eijkman.go.id) wrote:
: Dear everyone,

: Does somebody know the right content of Potassium Phosphate Buffer ?
: Is it a solution of Dipotassium hidrogen phosphate (K2HPO4), Potassium
: dihidrogen phosphate (KH2PO4), or Potassium phosphate tribasic (K3PO4) ?
: Or a mixture of those component ?

: Thank you,

: Delvac Oceandy
: Eijkman Institute
: Jakarta Indonesia

For potassium phosphate buffer as I know it, you need a mixture of
K2HPO4 and KH2PO4 in a ratio that determines the final pH of the
solution. You can work out the ratio for the pH you need from the
Henderson Hasselbalch equation:

pH = pK' + log( (proton acceptor)/proton donor )

pK' here is 6.68 at 25C (if I remember correctly- best to check
this value!).

Alternatively, you can find a ready-made table of quantities in most
lab manuals.

Keith James- k.james at bangor.ac.uk
Biodegradation Group, University of Wales, Bangor, UK.

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