 Phosphate-buffered saline

Phosphate-buffered saline is an aqueous salt solution containing phosphate species that act as a buffer solution, together with salts that control its ionic strength and osmotic properties. Common formulations are designed to maintain a near-neutral pH, but their precise composition varies.

The phosphate acid-base pair consumes added acid or base, limiting small pH shifts. The salt content makes the solution useful when biological samples need a controlled ionic environment. It does not reproduce every component of a physiological fluid, and added divalent ions can interact with phosphate; the formulation must therefore be specified when comparing experiments.