Scientific Reference
Phosphate Buffered Saline
Evidence profile: Component evidence only — this formulation has not itself been studied
Phosphate-buffered saline, or PBS, is a salt solution in water that a phosphate buffer holds near neutral, typically around pH 7.4. Sodium chloride supplies most of the salt, usually with some potassium chloride, at levels chosen so the solution is roughly isotonic with mammalian cells. It is among the most widely used reagents in biology and biochemistry: it rinses cells, dilutes samples, and acts as a neutral solvent for proteins and peptides. Formulations differ, for example in whether calcium and magnesium are included and whether it is ready to use or a concentrate, so the stated composition matters. PBS has no biological activity of its own and is a laboratory tool, not a research subject.
Mechanism of Action
The pH buffering comes from the equilibrium between dihydrogen phosphate (H2PO4-) and hydrogen phosphate (HPO4 2-), a pair whose pKa is about 7.2 at 25 degrees C, close to physiological pH, so added acid or base moves the pH only a little around 7.4. The chloride salts set the osmolality near that of the cell interior, which limits water flow across cell membranes. Phosphate has recognised 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 change sharply in pH on freezing.
Molecular Information
- Type: Buffer solution