Drybench Calc.
Buffer recipe with pH at your working temperature
The mass of the exact chemical form and the pH to set at the preparation temperature so the buffer reads your target where you use it.
The mass of the exact chemical form to weigh, and the pH to set on a calibrated meter at the temperature you prepare the buffer, so that it reads your target at the temperature you use it.
Worked example: Tris for a cold room
50 mM Tris base in 1 L for pH 8.0 at 4 °C, adjusted at 25 °C, computed when this page is built.
| Quantity | Value |
|---|---|
| Chemical form weighed | Tris base, C4H11NO3 |
| Formula weight (CIAAW 2021) | 121.136 g/mol |
| Mass to weigh | 6.0568 g |
| pK at the working temperature | 8.710 |
| pK at the preparation temperature | 8.072 |
| Set the meter to | pH 7.36 |
Adjust to pH 7.36 at 25 °C for about pH 8.00 at 4 °C.
Mass is for the chemical form named. Dissolve in less than the final volume, adjust to the setpoint with a calibrated pH meter at the preparation temperature, then make up to volume. The setpoint corrects the buffer's pK for temperature only (Goldberg et al. 2002, zero ionic strength). Ionic strength, other solutes and dilution after adjustment are not modelled. A meter's automatic temperature compensation corrects the electrode, not the buffer.
Open this buffer in the recipe table
Worked example
- m = C × V × M = 0.05 mol/L × 1 L × 121.136 g/mol = 6.0568 g of Tris base; weighed as Tris·HCl it is 7.8797 g, on the salt's own formula weight.
- pH to set = pH wanted + pK(preparation temperature) − pK(working temperature) = 8.0 + 8.072 − 8.710 = 7.36, from Goldberg et al. 2002, equation 12.
- Offered for the 15 buffers whose values were transcribed twice from the paper, between 274 and 350 K, within 1 pH unit of the buffer's pK at 25 °C (the Tris example is 1.2 units below the pK at 4 °C, where it buffers less well); carbonate (an open CO₂ system) and overlapping citrate steps are refused.
Method
- Buffer mass of the exact chemical form and the pH-meter setpoint at the preparation temperature. m = C × V × M (CIAAW 2021 atomic weights); pH_set(T_prep) = pH_target(T_work) + pK(T_prep) − pK(T_work) with pK(T) from Goldberg, Kishore and Lennen 2002, equation 12, zero ionic strength. Suitability is checked at the working temperature.Checked against a CIAAW 2021 sum in Python's decimal module and Goldberg's equation 12 in NumPy 2.5.3 on 18 cases, 8 of them refusals: mass to nine significant figures, setpoint within 0.01 pH (10 October 2026).
- pK at the working temperature. Goldberg RN, Kishore N, Lennen RM. Thermodynamic quantities for the ionization reactions of buffers. J Phys Chem Ref Data 2002;31:231-370 (read 6 October 2026).Checked against Goldberg's equation 12 in NumPy 2.4.6 within 0.01 on 15 buffers at 4, 25 and 37 °C (6 October 2026).
Constants
- goldberg-2002: Goldberg, Kishore and Lennen 2002, 298.15 K, zero ionic strength
Limits
- For research and education only, and not medical advice: the stock, dilution and buffer calculations here are not for dosing or clinical preparation.
- Buffer setpoints correct the pK for temperature only (Goldberg et al. 2002, zero ionic strength), for the 15 buffers transcribed twice, between 274 and 350 K; ionic strength, other solutes and titrant amounts are not modelled.