PBSs

PBSs refer to phosphate-buffered saline solutions, a class of isotonic buffers widely used in biology and medicine. These solutions combine a phosphate buffer with sodium chloride and trace amounts of potassium chloride to maintain a near-physiological pH and osmolarity. The most common formulation, PBS, typically contains about 137 mM NaCl, 2.7 mM KCl, and 10 mM phosphate, yielding a pH around 7.4 and an osmolality in the range of 275–295 mOsm/kg. Variants exist that either include or exclude divalent cations such as calcium and magnesium, depending on the needs of a protocol.

Composition and variants: PBS without calcium and magnesium is widely used for routine washing and rinsing of cells, tissues, and reagents, as the absence of divalent cations reduces cell adhesion and enzymatic activity that might confound results. PBS with calcium and magnesium is used for procedures where maintenance of cell–substrate or cell–cell interactions is desired, or where certain enzymes require these cations. Some protocols also call for additional buffering components or preservatives, but these are not part of the standard PBS formulation.

Preparation and handling: PBS is prepared by dissolving the appropriate amounts of sodium chloride, potassium chloride, and a phosphate buffer in water, then adjusting the pH and filtering or autoclaving for sterility. For long-term use, aliquots are stored refrigerated or at room temperature, with sterile handling to prevent contamination. When working with live cells, the choice of calcium/magnesium content and temperature can influence viability and reaction outcomes.

Uses: PBSs are used to rinse, dilute, or suspend cells and tissues, to wash reagents in immunoassays and Western blot protocols, for antigen or antibody incubation steps, and as a general, non-toxic zero-buffer environment during procedures that require stable osmolarity.

Note: PBS also stands for Public Broadcasting Service in the United States. This article concerns phosphate-buffered saline solutions.