Phosphate buffer system

The phosphate buffer system is a principal chemical buffer system in the body, composed of sodium dihydrogen phosphate (NaH₂PO₄), which acts as a weak acid, and sodium hydrogen phosphate (Na₂HPO₄), which acts as a weak base[1][5]. It regulates pH by neutralizing added acids or bases: when a strong base is added, NaH₂PO₄ donates protons to form Na₂HPO₄ and water; when a strong acid is added, Na₂HPO₄ accepts protons to form NaH₂PO₄[1][5][9]. The system is especially important in maintaining acid-base balance inside cells and in kidney tubules, where phosphate concentrations are high and physiological conditions suit the buffer’s pK (6.8)[1][5]. In extracellular fluid, its role is limited compared to the bicarbonate buffer. Phosphate buffer systems are also widely used in laboratory and industrial settings to maintain stable pH conditions and are key components in commonly used isotonic saline solutions such as phosphate-buffered saline (PBS)[2][6][7].

Other names

Phosphate bufferPhosphate buffer solutionPhosphate buffer saline (often in practice as PBS)Phosphate-buffered saline