What Is the Composition of Physiological Saline?

Physiological saline is a prepared solution composed of distilled water with 0.85 to 0.95 percent salt. The salt is generally sodium chloride; however, a phosphate buffer solution also exists. The solution is isotonic with the physiological conditions present in human blood or tissues.

Physiological saline, also simply referred to as saline, consists of 0.85 grams to 0.95 grams of sodium chloride per liter of pure, distilled water. The osmolarity of the solution is 308 milliosmoles per liter. The pH of physiological saline ranges from 4.5 to 7.0 but is most commonly 5.0. It is used medically as an isotonic volume expander and as an electrolyte replacement. It is generally administered in the case of dehydration but can also be used as a diluent or solvent for pharmaceuticals such as antibiotics.

Phosphate buffer solution is very similar to physiological saline and is also isotonic to physiological conditions. It is used more commonly in laboratory settings. The solution is made from distilled water and contains sodium chloride, sodium phosphate, potassium chloride and potassium phosphate. The pH of phosphate buffer solution matches the pH of physiological saline at 7.4. It is used to keep tissues and samples hydrated in the lab, as a diluent, and to rinse containers that hold cells or tissues.