[steve29er]

I am trying to prepare a H2PO4 solution that maintains physiological electrolyte balance and pH. Is it possible to obtain a solution with 100 mM H2PO4, 135 mM Na2+, 5 mM K+ and 109 mM Cl-?
The only solution I can currently prepare requires too much sodium or the use of too much acid and then the pH is not 7.4. Any help/advice/guidance would be greatly appreciated. I am not even sure that such a solution is possible...

[Borek]

H2PO4 or H₂PO₄^-?

Na²⁺?

[AWK]

physiological electrolyte balance and pH

What exactly does it mean for you (values of osmotic pressure and pH?)
Assuming your solution contains 100 mM of phosphates, 135 mM Na+, 5 mM K+ and 109 mM Cl- its pH can be close to 6 and ionic strength close to 0.25. Both values a rather far from physiological parameters.

[steve29er]

Yes AWK. That is the issue. The values are not close enough to physiological pH and osmotic pressure. I am not a chemistry expert (far from it actually), but I was just wondering if there was any way to create a pH balanced/physiological solution that has 100 mM of phosphate (whether you use straight H₃PO₄ or not. The concern I have is that to obtain a high phosphate solution using my current methods/solution you must add too much Na⁺ as the cation of H₂PO₄^-. The addition of Na⁺ as the cation throws off the physiological levels of Na⁺. Is there anyway around this?

[AWK]

You can prepare phosphate buffer with pH 7.4 containing chlorides and specified ratio [Na+]/[K+], but probably even 100 mM (sodium/potassium) hydrogen phosphates alone gives you to high osmotic pressure.

http://nature.berkeley.edu/soilmicro/methods/phosphate%20buffer.pdf
http://home.fuse.net/clymer/buffers/phos2.html
http://www.bioinformatics.org/JaMBW/5/4/index.html
http://www.biomol.net/en/tools/buffercalculator.htm