Potassium Phosphate Buffer

Jeff Cohlberg cohlberg at csulb.edu
Fri Nov 1 12:33:15 EST 1996

Delvac Oceandy (Delvac at eijkman.go.id) wrote:
: 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 ?

For buffers near neutral pH, start with a solution of KH2PO4 at the
desired molarity, then titrate to the proper pH with KOH, monitoring with
a pH meter.  You will end up with the proper mixture of H2PO4- and HPO4--.
Alternatively, if, like me, you'd rather pipet than weigh things on a
balance, start with the right molarity of H3PO4, and titrate with KOH.
You have to add an extra equivalent of KOH to neutralize all the H3PO4 to
H2PO4-, then titrate as above.  Commercial H3PO4 (85%) has a concentration
of 14.8M, so to make a 1 M solution, use 67.5 ml of conc. H3PO4 per liter
of solution.  e.g. for 0.01 M potassisum phosphate, pH 7.5, add
0.675 ml conc H3PO4 to 900 ml of
water, titrate to pH 7.5 with KOH, then adjust to 1 liter.
Jeffrey A. Cohlberg, Professor
Department of Chemistry and Biochemistry
California State University, Long Beach
1250 Bellflower Boulevard, Long Beach, CA 90840
Phone: (310) 985-4944	FAX: (310) 985-8557   E-mail: cohlberg at csulb.edu

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