Phosphate buffered saline

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Phosphate buffered saline (abbreviated PBS) is a buffer solution commonly used in biochemistry. It is a salty solution containing sodium chloride, sodium phosphate and potassium phosphate. The buffer helps to maintain a constant pH. The concentration usually matches the human body (isotonic).

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.

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 sorts of applications, Good's buffers are recommended. To make a 10 liter stock of 10x PBS:

1. weigh the following
   • 800 g NaCl
   • 20 g KCl
   • 144 g Na₂HPO₄
   • 24 g KH₂PO₄
2. add and dissolve in 8 L of distilled water under mixing
3. pH is ~6.8, but when you dilute the 10x PBS to 1x PBS it should change to 7.4 (try with a little sample; Phosphate buffers change their pH with the dilution)
4. fill up to 10 L with distilled water

1x PBS final concentration : 137 mM NaCl, 10 mM Phosphate, 2.7 mM KCl, pH 7.4