TE Buffer Calculator (Tris-EDTA)
Calculate the Tris base, EDTA disodium salt and HCl for TE buffer (10 mM Tris-HCl, 1 mM EDTA, pH 8.0) as a 1×, 10× or 100× stock, with temperature-corrected Tris.
Formula
- Tris concentration
- disodium EDTA dihydrate, 372.24 g/mol
How it works
TE is the standard storage buffer for DNA: Tris holds the pH near 8 and EDTA chelates the divalent metals that nucleases need, protecting the DNA. The usual recipe is 10 mM Tris-HCl and 1 mM EDTA at pH 8.0 (pH 7 to 7.5 for RNA), often made as 10× or 100× stocks.
The Tris part is the same calculation as for a Tris buffer: the HCl is what is needed to bring Tris to pH 8.0 at the temperature given. The EDTA disodium salt dissolves only as the pH approaches 8, so it is added to the Tris and the pH adjusted before making up to volume.
Worked example
1 L of 1× TE: 10 mM Tris and 1 mM EDTA at pH 8.0, 25 °C, with 1 M HCl.
- Fraction of Tris protonated at pH 8.0 = 1 / (1 + 10^(8.0 − 8.07)) = 0.540, so 5.40 mmol of HCl.
- Tris base: 0.010 mol × 121.14 = 1.211 g. EDTA disodium dihydrate: 0.001 mol × 372.24 = 0.3722 g.
1.211 g Tris base, 0.3722 g EDTA disodium dihydrate and 5.40 mL of 1 M HCl per litre. A 100× stock is 37.22 g of EDTA per litre.
These are the values the calculator opens with, so you can check its output against this example.
Assumptions
- The pKa of Tris at the temperature you set the pH, from the linear dependence.
- EDTA is the disodium dihydrate, and its small contribution to the pH is ignored.
- An ideal solution; confirm the pH with a meter.
Common mistakes
- Forgetting to adjust the pH before adding all the EDTA, which will not dissolve at low pH.
- Carrying a large volume of TE into a PCR or enzymatic reaction, where EDTA takes up the magnesium.
- Storing RNA in TE at pH 8, when a lower pH protects it better.
Related tools
Related equipment
Service documentation, failure modes and parts for the instruments this calculation is used with.