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Phosphate buffered saline (abbreviated PBS) is a buffer solution commonly used in biological research. 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 osmolarity and ion concentrations of the solution usually match those of 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 to rinse containers containing cells. PBS can be used as a diluent in methods to dry biomolecules, as water molecules within it will be structured around the substance (protein, for example) to be 'dried' and immobilized to a solid surface^{citation needed}. The thin film of water that binds to the substance prevents denaturation or other conformational changes. Carbonate buffers may be used for the same purpose but with less effectiveness^{citation needed}. PBS can be used to take a reference spectrum when measuring the protein adsorption in ellipsometry^{citation needed}.

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 result in precipitation. For these types of applications, Good's buffers are recommended.

Preparation

There are many different ways to prepare PBS. Some formulations do not contain potassium, while others contain calcium or magnesium^[1]. One of the most common preparations is described below.

A 10 liter stock of 10x PBS can be prepared by dissolving 800 g NaCl, 20 g KCl, 144 g Na₂HPO₄ · 2H₂O and 24 g KH₂PO₄ in 8 L of distilled water, and topping up to 10 L. The pH is ~6.8, but when diluted to 1x PBS it should change to 7.4. When making buffer solutions, it is good practice to always measure the pH directly using a pH meter. If necessary, 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.

Another preparation is described in Molecular Cloning by Sambrook, Fritsch and Maniatis, Apendix B.12^[2] as follows:

For 1 litre of Phosphate-buffered saline (PBS buffer) use:

- Dissolve in 800 ml of distilled H2O:
- 8 g of NaCl
- 0.2 g of KCl
- 1.44 g of Na2HPO4 and
- 0.24 g of KH2PO4.
- Adjust the pH to 7.4 with HCl.
- Add H2O to 1 liter.

Dispense the solution into aliquots and sterilize them by autoclaving (20 min, 121°C, liquid cycle). Store at room temperature.

References

1. ^ Dulbecco, R. et al. (1954): Plaque formation and isolation of pure lines with poliomyelitis viruses. In: J. Exp. Med. vol. 99 (2), pp. 167-182. PMID 13130792
2. ^ Sambrook, Fritsch, and Maniatis (1989) Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, volume 3, apendix B.12

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