How can I prepare a PBS (Phosphate Buffer Solution)? pH=7.4
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The preparation of pH 7.4 PBS (with KCl and KH2PO4) is described on this site   here. Preparation of many other buffer systems are also described.

Here are the conditions (lifted from the linked site)

Prepare 800 mL of distilled water in a suitable container.
Add 8 g of NaCl to the solution.
Add 200 mg of KCl to the solution.
Add 1.44 g of Na2HPO4 to the solution.
Add 240 mg of KH2PO4 to the solution.
Adjust solution to desired pH (typically pH ≈ 7.4).
Add distilled water until volume is 1 L.