You can prepare it departing from Sodium acid phosphate and Sodium diacid phosphate in the proper proportion. No K salts is needed

Hello Saba,

thank you for posting this interesting technical question. Phosphate buffer saline 0.1 M pH = 7.4 can be made completely withput potassium compounds. Please check the protocol cited below in which only sodium salt are used:

Phosphate-Buffered Saline (PBS) (0.1 M, pH 7.4)

http://cshprotocols.cshlp.org/content/2018/12/pdb.rec104604.full?rss=1

Good luck with your work!

You may want to check my post at this related query:

https://www.researchgate.net/post/How-can-I-prepare-1M-of-Potassium-phosphate-buffer-with-pH-of-68

Phosphate-buffered saline (PBS) buffer solutions are mixed Na/K monobasic and dibasic phosphate solutions with added Na/K chloride salts. The neutral salts (NaCl/KCl )do not contribute noticeably for the solution pH.

We can predict the pH of PBS buffer solutions after the following 'adapted' Henderson–Hasselbalch equation, within the effective buffer range pH = pKa2 ± 1 (6.2―8.2):

pH = pKa2 + log10{(CNa2HPO4 + CK2HPO4)/(CNaH2PO4 + CKH2PO4)}

Here C refers to nominal (formal) concentrations of the salts in the mixed solution. Ka2 is the second dissociation constant of phosphoric acid.