Phosphate buffered saline
Phosphate buffered saline (abbreviated PBS) is a buffer solution commonly used in biochemistry. It is a salty solution containing sodium chloride, sodium phosphate, and (in some formulations) potassium chloride and potassium phosphate. The buffer helps to maintain a constant pH. The concentration usually matches the human body (isotonic).
Applications
PBS has many uses because it is isotonic and non-toxic to cells. It can be used to dilute substances. It is used as a cellular cleaning solution. To ensure the prolonged dry-storage of immobilized-biomolecules like proteins, enzymatic proteins etc., PBS is used as biomolecule diluent since it can structure water around biomolecules immobilized to the solid surface. Such thin film of water prevents denaturing of biomolecules or conformational changes to them. Carbonate buffers may be used for the same purpose but with less effectiveness. PBS can be used as a reference spectra when measuring the protein adsorption in ellipsometry.
Additives can be used to add function. For example, PBS with EDTA is also used to disengage attached and clumped cells. Divalent metals such as zinc, however, cannot be added as this will cause precipitation. For these types of applications, Good's buffers are recommended.
Preparation
Many variant formulations of PBS exist in the literature. One of the more commonly used versions is described below. Some formulations don't contain potassium, while others additionally contain calcium or magnesium.
A 10 liter stock of 10x PBS can be prepared by dissolving 800 g NaCl, 20 g KCl, 144 g Na2HPO4 and 24 g KH2PO4 in 8 L of distilled water, and topping up to 10 L. When making buffer solutions, it is good practise to always measure the pH directly using a pH meter. For PBS, the pH can be adjusted using hydrochloric acid or sodium hydroxide.
On dilution, the resultant 1x PBS should have a final concentration of 137 mM NaCl, 10 mM Phosphate, 2.7 mM KCl, and a pH of 7.4.