Dear scientists,

I am trying to find a way to correclty calculate the ionic strength of my phosphate buffer. I want to set it to a specific ionic strength of 0,5 (with NaCl)

Since the salts do not fully dissociate (compared to NaCl or CaCl2), I cannot use the common equation for ionic strength)

What I found so far is that I need to keep an eye on the pH dependent dissociation of my phosphate salts (H2PO4-, HPO42-, PO43-) and their respective pH.

I found this online:

http://www.iue.tuwien.ac.at/phd/windbacher/node63.html

I am stuck somewhere in the middle of my calculations because I do not know if I did this fully correct. It would be great if you could help me out! For comparison I also tried to calculate the ionic strength with the "common" equation to see about the difference (which actually is enormous)

Thanks in advance!