TL;DR: To make 1 L of 1 M Tris-HCl, dissolve 121.14 g Tris base in about 800 mL water, adjust to the required pH with HCl at the intended working temperature, then bring to 1 L. Tris pH falls as temperature rises, so temperature control matters.
Tris-HCl is one of the most common biological buffers and is a building block for TBS, RIPA, TE, SDS-PAGE buffers and many enzyme-assay solutions. The key practical issue is that Tris has a relatively large temperature coefficient, so a solution adjusted to pH 8.0 cold will not remain pH 8.0 when warmed.
1 M Tris-HCl recipe
| Final volume | Tris base | Water before pH adjustment |
|---|---|---|
| 100 mL | 12.11 g | ~80 mL |
| 500 mL | 60.57 g | ~400 mL |
| 1 L | 121.14 g | ~800 mL |
Preparation
- Dissolve the required Tris base in approximately 80% of the final volume of purified water.
- Allow the solution to equilibrate near the temperature at which you will set the pH.
- With continuous stirring, add HCl gradually until the target pH is reached.
- Do not make the final volume until after pH adjustment.
- Bring to the final volume with purified water and mix again.
Which pH should I choose?
- pH 7.4: common for physiologically oriented buffers and selected protein workflows.
- pH 7.6: common in TBS and immunoblotting systems.
- pH 8.0: common for nucleic-acid and protein purification workflows.
Why Tris pH changes with temperature
Tris has a substantial negative temperature coefficient. Reference measurements around the physiological range report roughly a 0.026–0.03 pH-unit decrease for each 1°C rise in temperature. That means a buffer adjusted at 4°C can be several tenths of a pH unit lower at room temperature or 37°C.
For reproducible work, record the pH-adjustment temperature in the lab SOP. This matters especially for enzyme kinetics, protein purification and assays performed away from room temperature.
Do I need to calculate the exact volume of HCl?
No. Published recipes give approximate concentrated-HCl volumes, but the exact requirement depends on reagent purity, HCl concentration, temperature and target pH. A pH meter and gradual titration are more reliable than blindly adding a fixed acid volume.
Tris-HCl vs Tris base
“Tris-HCl buffer” describes a mixture of protonated Tris and unprotonated Tris. Many labs prepare it by dissolving Tris base and titrating with HCl. Commercial Tris-HCl salt can also be used, but the base/acid ratio still determines final pH.
Safety note
Concentrated hydrochloric acid is corrosive and releases fumes. Use appropriate PPE and a fume hood, and add acid slowly to the aqueous Tris solution rather than adding water to concentrated acid.
Troubleshooting
| Problem | Cause | Fix |
|---|---|---|
| pH drifts after preparation | Temperature changed | Measure and adjust at the intended working temperature. |
| Final concentration is wrong | Volume was made up before HCl addition | Adjust pH first, then bring to final volume. |
| Buffer turns yellow/cloudy | Contamination or poor-quality reagent | Discard and remake with clean reagent and water. |
Frequently asked questions
What is the pKa of Tris?
Approximately 8.1 at 25°C, making it useful around neutral to mildly alkaline pH.
Can Tris be used at 37°C?
Yes, but its pH should be considered at that temperature rather than assuming the room-temperature value is unchanged.