Phosphate-buffered saline

Phosphate-buffered saline (abbreviated PBS) is a buffer solution commonly used in biological research. It is a water-based salt solution containing disodium hydrogen phosphate, sodium chloride and, in some formulations, potassium chloride and potassium dihydrogen phosphate. The buffer helps to maintain a constant pH. The osmolarity and ion concentrations of the solutions match those of the human body (isotonic).

Applications

PBS has many uses because it is isotonic and non-toxic to most cells. These uses include substance dilution and cell container rinsing. 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. PBS has been shown to be an acceptable alternative to viral transport medium regarding transport and storage of RNA viruses, such as SARS-CoV-2[1]

Preparation

There are many different ways to prepare PBS solutions (one of them is Dulbecco's phosphate-buffered saline (DPBS), which has the same composition than that of standard PBS[2]). Some formulations do not contain potassium and magnesium, while other ones contain calcium and/or magnesium (depending on whether or not the buffer is used on live or fixed tissue: the latter does not require KCl or MgCl2 ).

The most common composition of PBS (1×)
SaltConcentration (mmol/L)Concentration (g/L)
  NaCl  1378.0
  KCl  2.70.2
  Na2HPO4  101.44
  KH2PO4  1.80.24

Start with 800 mL of distilled water to dissolve all salts. Add distilled water to a total volume of 1 liter. The resultant 1× PBS will have a final concentration of 157 mM Na+, 140mM Cl−, 4.45mM K+, 10.1 mM HPO42−, 1.76 mM H2PO4− and a pH of 7.96. Add 2.84mM of HCl to shift the buffer to 7.3 mM HPO42− and 4.6 mM H2PO4− for a final pH of 7.4 and a Cl− concentration of 142 mM.

Cold Spring Harbor Protocol[3]
reagentMWmass (g) 10×[M] 10×mass (g) 5×[M] 5×mass (g) 1×[M] 1×
Na2HPO4141.9589714.19600.10007.09800.05001.419600.0100
KH2PO4136.085692.44960.01801.22480.00900.244960.0018
NaCl58.4430080.06691.370040.03350.68508.006690.1370
KCl74.551502.01290.02701.00640.01350.201290.0027
pH = 7.4

The pH of PBS is ~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.

PBS can also be prepared by using commercially made PBS buffer tablets or pouches.[4]

If used in cell culturing, the solution can be dispensed into aliquots and sterilized by autoclaving or filtration. Sterilization may not be necessary depending on its use. PBS can be stored at room temperature or in the refrigerator. However, concentrated stock solutions may precipitate when cooled and should be kept at room temperature until precipitate has completely dissolved before use.

See also

References
  1. Perchetti, G.A.; et al. (2020). "Stability of SARS-CoV-2 RNA in Phosphate-Buffered Saline". Journal of Clinical Microbiology. 58 (8): e01094-20. doi:10.1128/JCM.01094-20. PMC 7383534. PMID 32414839.
  2. Dulbecco, R.; et al. (1954). "Plaque formation and isolation of pure lines with poliomyelitis viruses". J. Exp. Med. 99 (2): 167–182. doi:10.1084/jem.99.2.167. PMC 2180341. PMID 13130792.
  3. CSH Protocol: Phosphate-buffered saline (PBS) recipe
  4. Medicago AB, (2010) Phosphate buffered saline specification sheet
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