Scientific Reference
Phosphate Buffered Saline
Evidence profile: Component evidence only — this formulation has not itself been studied
Phosphate-buffered saline (PBS) is a water-based salt solution held at near-neutral pH, usually about 7.4, by a phosphate buffer. Its main salt is sodium chloride, usually with some potassium chloride, at concentrations chosen to make the solution roughly isotonic with mammalian cells. It is one of the most common reagents in biology and biochemistry laboratories, used to rinse cells, to dilute samples and as a neutral solvent for proteins and peptides. Recipes vary, for instance in whether calcium and magnesium are included and in whether the solution is ready to use or a concentrate, so the stated composition matters. PBS has no biological activity of its own; it is a working tool rather than a subject of research.
Mechanism of Action
PBS resists changes in pH through the equilibrium between dihydrogen phosphate (H₂PO₄⁻) and hydrogen phosphate (HPO₄²⁻). The pKa of this pair is about 7.2 at 25 °C, close to physiological pH, so added acid or base shifts the pH of the solution only slightly around 7.4. The chloride salts set its osmolality near that of the cell interior, which limits water movement across cell membranes. Phosphate has known drawbacks: it precipitates with calcium and some other metal ions, it can interfere with enzymes that use or release phosphate, and sodium phosphate solutions can shift sharply in pH when frozen.
Molecular Information
- Type: Buffer solution