Lab Buffer Recipe Calculator (PBS, TAE, TBE, TE)

Understanding the lab buffer recipe calculator — concept and principle

This calculator scales four of the most common molecular biology buffers to any volume: 1× phosphate-buffered saline (PBS) for washing and diluting cells and proteins, 50× TAE and 10× TBE stock for agarose gel electrophoresis, and 1× TE for storing DNA. You pick the buffer and the final volume, and it lists how much of each component to weigh or pipette.

How it is calculated

Each recipe is written per 1,000 mL. The calculator multiplies every amount by the scale factor k = V ÷ 1000, where V is your volume in mL.

• 1× PBS (per L): NaCl 8 g, KCl 0.2 g, Na₂HPO₄ 1.44 g, KH₂PO₄ 0.24 g, adjust to pH 7.4.
• 50× TAE (per L): Tris base 242 g, glacial acetic acid 57.1 mL, 0.5 M EDTA (pH 8.0) 100 mL.
• 10× TBE (per L): Tris base 108 g, boric acid 55 g, 0.5 M EDTA (pH 8.0) 40 mL.
• 1× TE pH 8 (per L): 1 M Tris-HCl (pH 8.0) 10 mL, 0.5 M EDTA 2 mL.

The principle

A buffer is defined by concentrations, so the mass of each solute must grow in direct proportion to volume. In PBS, 8 g/L NaCl is about 137 mM and 0.2 g/L KCl about 2.7 mM, giving a salt level close to physiological; the phosphate pair (about 10 mM Na₂HPO₄ and 1.8 mM KH₂PO₄) holds the pH near 7.4 because phosphate has a pKa near 7.2. Diluted to 1×, TAE is 40 mM Tris, 20 mM acetate and 1 mM EDTA; 1× TBE is 89 mM Tris and 89 mM borate with 2 mM EDTA. EDTA chelates magnesium ions that nucleases need, which protects DNA.

Worked example

1. Defaults: buffer = 1× PBS, V = 1000 mL, so k = 1000 ÷ 1000 = 1.
2. NaCl 8 × 1 = 8 g; KCl 0.2 × 1 = 0.2 g; Na₂HPO₄ 1.44 × 1 = 1.44 g; KH₂PO₄ 0.24 × 1 = 0.24 g.
3. Result: NaCl 8 g · KCl 0.2 g · Na₂HPO₄ 1.44 g · KH₂PO₄ 0.24 g · pH 7.4.
4. Dissolve in about 800 mL of water, adjust pH with HCl, then bring to 1 L.

How to read the result

Masses for salts refer to the anhydrous forms. If your bottle is a hydrate (for example Na₂HPO₄·7H₂O or ·12H₂O), scale by the ratio of molar masses. TAE and TBE are stocks: dilute 50× TAE 1:50 and 10× TBE 1:10 (some labs run 0.5× TBE). TE is ready to use. Sterilise PBS by autoclaving or filtering when cells are involved.

Common mistakes

• Making up to full volume before adjusting pH, which leaves no room for acid or base.
• Using a hydrate salt with the anhydrous mass.
• Running a gel in 50× TAE or using different buffers in gel and tank.

Frequently asked questions

Why does PBS sometimes contain calcium and magnesium?

Some cell work needs them for adhesion; omit them when detaching cells or when phosphate precipitates are a concern.

TAE or TBE: which should I use?

TAE is common for routine and preparative gels and larger fragments; TBE has higher buffering capacity and gives sharper bands for small fragments in long runs.

Can I autoclave TE?

Yes, TE is commonly autoclaved; check the pH afterwards because Tris pH depends on temperature.

Sources: Cold Spring Harbor Protocols, recipes for PBS, TAE, TBE and TE · Green M.R. and Sambrook J., Molecular Cloning: A Laboratory Manual, 4th ed., Cold Spring Harbor Laboratory Press, 2012