Calculate buffer recipes with temperature-corrected pKa and ionic strength. PBS, Tris, HEPES, MOPS, and 8 more systems. Data never leaves your browser.
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Standard 1× PBS. Adjust NaCl for non-standard ionic strength.
| Reagent | Formula | MW | Mass (g) | Vol (mL) |
|---|---|---|---|---|
| Sodium dihydrogen phosphate | NaH₂PO₄ | 119.98 | 0.4642 | — |
| Disodium hydrogen phosphate | Na₂HPO₄ | 141.96 | 0.8704 | — |
| Sodium chloride | NaCl | 58.44 | 8.0063 | — |
| Potassium chloride | KCl | 74.55 | 0.2013 | — |
When to use
Do not use for
Tris loses ~0.03 pH units per °C increase (dpKa/dT = −0.028). A Tris buffer prepared at pH 7.5 at 25°C will read ~pH 8.0 at 4°C. Always adjust pH at your working temperature — not at room temperature.
Buffer ionic strength influences electrostatic interactions, protein folding, and enzyme activity. A 50 mM Tris buffer and a 50 mM PBS buffer have very different ionic strengths due to counter-ion contributions. This calculator shows ionic strength so you can match protocol requirements.
Phosphate buffers are generally stable for months at 4°C. Tris buffers can support microbial growth — add 0.02% sodium azide for long-term storage. Acetate and citrate buffers are volatile at low pH. Always check pH before use if buffer is more than a week old.
A single-point calibration can drift by ±0.2 pH units. Use two standards that bracket your target pH (e.g., pH 4.0 and 7.0 for acetate buffers, pH 7.0 and 10.0 for carbonate buffers). Calibrate at the same temperature as your buffer preparation.
Good's buffers (HEPES, MOPS, MES, PIPES) were specifically designed for biological research: minimal metal chelation, low UV absorbance, membrane impermeability, and small temperature coefficients. Prefer them over phosphate or Tris when working with cells or metal-sensitive assays.
Henderson-Hasselbalch equation with temperature-dependent pKa correction using the van 't Hoff equation. Ionic strength calculated from I = ½ Σ cᵢzᵢ². pKa values from NIST Standard Reference Database 46.
Last validated 2026-03-18. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Buffer Recipe Calculator (v1.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/buffer-calculator
Good NE, et al. Hydrogen ion buffers for biological research. Biochemistry. 1966;5(2):467-477. doi:10.1021/bi00866a011
A buffer is a solution that resists pH changes when small amounts of acid or base are added. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in equilibrium.
The Henderson-Hasselbalch equation describes this equilibrium: . At the pKa, equal concentrations of acid and base form are present, and the buffer has maximum capacity.
All buffer pKa values change with temperature, but the magnitude varies dramatically. Tris buffers are notorious — a Tris-HCl buffer prepared at pH 7.5 at room temperature (25°C) will be pH 8.0 at 4°C and pH 7.2 at 37°C.
Good's buffers (HEPES, MOPS, MES) were specifically designed for minimal temperature sensitivity. HEPES, for example, shifts only −0.014 pH units per °C — five times less than Tris.
Select a buffer whose pKa is within ±1 pH unit of your target pH. Beyond that, consider:
• Cell culture: HEPES or MOPS (low temperature sensitivity, non-toxic to cells) • Protein work: Tris (but prepare at working temperature) or phosphate (stable, but precipitates some metals) • Electrophoresis: TAE (better for cloning — DNA recovery) or TBE (sharper bands, higher resolution) • Low pH: Acetate (pH 3.7–5.6) or citrate (pH 3.0–6.2) • High pH: Carbonate-bicarbonate (pH 9.2–10.8)
