Buffer Calculator for Phosphate, Tris, Citrate, Acetate, PBS and TBS

Calculate buffer recipes from pH, pKa, concentration, and final volume, or scale common PBS, TBS, TE, and TAE recipes directly.

Buffer calculator

Buffer system

Target pH

Total buffer concentration

Final volume

Recipe result

Acid form

2.354e+3 mg NaH2PO4 anhydrous

Base form

4.313e+3 mg Na2HPO4 anhydrous

Base / acid ratio

1.549

Useful range

pH 6.2-8.2

Worked example: sodium phosphate buffer

For 500 mL of 100 mM sodium phosphate buffer at pH 7.40, pKa = 7.21, so base/acid = 10^(7.40 - 7.21) = 1.55.

ratio=10^(pH - pKa)=1.55

Total buffer = 0.05 mol. Acid form = 0.0196 mol NaH2PO4; base form = 0.0304 mol Na2HPO4. That is about 2.35 g acid salt and 4.31 g base salt before pH verification.

Why different buffer options use slightly different logic

Phosphate, acetate, citrate, carbonate, MES, HEPES, and MOPS are best treated as acid/base pairs with Henderson-Hasselbalch math.

Tris-HCl is often prepared by mixing Tris base and Tris-HCl, or by dissolving Tris base and titrating with HCl; temperature matters because Tris pKa shifts with temperature.

PBS, TBS, TE, and TAE are practical recipes. They are usually scaled from a known formulation, then pH-adjusted and brought to final volume.

Practical checks before using the recipe

Check hydrate form and molecular weight on the bottle. A dihydrate and anhydrous salt are not interchangeable gram-for-gram.

Prepare with about 80-90% final water, adjust pH at the intended temperature when needed, then bring to final volume.

For high ionic strength or temperature-sensitive work, treat this as a first-pass recipe and verify with a calibrated pH meter.

Design note

The workflow follows competitor patterns without copying them: Sigma-style raw material selection, Liverpool-style pH and temperature awareness, and Boston BioProducts-style mass-by-concentration and Henderson-Hasselbalch explanation.

Buffer Calculator for Phosphate, Tris, Citrate, Acetate, PBS and TBS