Potassium Phosphate Buffer
Delvac Oceandy
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
Richard P. Grant
K.D. James (mb...@s-crim1.dl.ac.uk) gibbered:
} 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.
Alternatively you can start with the two ingredients at the desired molar
concentration and use a pH meter......
Richard
Richard P. Grant University of Oxford
Nuffield Department Obstetrics and Gynaecology FFPGP
http://users.ox.ac.uk/~lady0266 http://www.molbiol.ox.ac.uk/~rgrant
---------------------# hit any user to continue #---------------------
Heinz-Juergen Schaefers
Delvac Oceandy 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 ?
Hi!
It depends on the pH you want to buffer...
Using KH2PO4 and K2HPO4 together in various ratios, you get an acidic buffer.
Using K2HPO4 and K3PO4 together in various ratios, you get a basic buffer.
the pH of the buffer depends on the ratio of the two components you use...
there must be a table somewhere in a common lab manual correlating the pH and
the ratios...
as a basic rule: if you take more of the component with more Hydrogen, you
get a buffer with lower pH (more acidic).
--
Dipl. Biol. Heinz-Juergen Schaefers
University of Erlangen, Med. IV, Nephrology Research Lab
Loschgestr. 8, D-91054 Erlangen, Germany +49 (0)9131 85-
E-mail: h-j.sc...@popHost.com -9206 (voice) -9202 (fax)
Jeff Cohlberg
Delvac Oceandy (Del...@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: cohl...@csulb.edu
John Watson
Heinz-Juergen Schaefers wrote:
> Using KH2PO4 and K2HPO4 together in various ratios, you get an acidic buffer.
> Using K2HPO4 and K3PO4 together in various ratios, you get a basic buffer.
>
> the pH of the buffer depends on the ratio of the two components you use...
> there must be a table somewhere in a common lab manual correlating the pH and
> the ratios...
> as a basic rule: if you take more of the component with more Hydrogen, you
> get a buffer with lower pH (more acidic).
What a coincidence! I was looking for this just the other day. All I had was the
formulae for various *sodium* phospahate buffers. It was getting late and I had
looked everywhere. I finally found it, in Vol. 3 of Sambrook et al. _Molecular
Cloning_.
AJW
----------------
John Watson
Bristol-Myers Squibb Co.
wats...@bms.com
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