[shuhuanli]

I need a 0.05M KH2PO4 (PH=3.0)Buffer Solution as part of my HPLC solvent.  Does anyone know how to make it? (KH2PO4  99.99%, H3PO4 85%)
I try to check its recipe from http://www.bi.umist.ac.uk/users/mjfrbn/buffers/makebuf.asp. However, I don't know how to set up its ionic strength.
Then, I try to check its recipe from http://www.zirchrom.com/pass.asp. However, I don't know how to set up the Desired Acid Conc.
Thanks in advance!

[Borek]

pH is described by Henderson-Hasselbalch equation - so if you know target pH first step is to calculate correct ratio of acid and conjugated base. Ionic strength of the solution is usually forced with excess neutral electrolyte - like KCl or NaCl - to calculate its concentration you have to start with ionic strength definition.