PBS composition and recipe

Standard 1X PBS formula

This is the widely used 1X PBS formulation, given as one liter at pH 7.4:

If you use hydrated salts (for example Na₂HPO₄·7H₂O), adjust the mass for the extra water weight. Formulations vary a little between suppliers, so always check the label or certificate of analysis for the product you use.

How the buffer works

Phosphate buffers around its second pKa of about 7.2. The ratio of disodium phosphate (HPO₄²⁻) to monopotassium phosphate (H₂PO₄⁻) sets the pH, which is why PBS sits just above 7.2, at about 7.4. Raising the share of Na₂HPO₄ raises the pH.

1X vs 10X PBS

10X PBS is a concentrate with ten times the salt concentrations. It saves storage space and is diluted one part concentrate to nine parts water to make 1X working solution. The pH of a concentrate can shift after dilution, so check the pH of the 1X solution. Higher-concentration phosphate stocks can also form crystals when cold; warm and mix them until clear.

Making PBS vs buying sterile PBS

Making PBS takes weighing, pH adjustment, filtering or autoclaving, and quality checks. Ready-made sterile PBS skips those steps and comes with lot documentation. Our sterile 1X PBS is calcium- and magnesium-free, and the current lot measured pH 7.37 and ≤0.05 EU/mL endotoxin.

More PBS guides

• PBS vs DPBSCalcium, magnesium and when to use each
• PBS uses in the labCell culture, ELISA, Western blot
• Storage and shelf lifeKeeping PBS sterile