Buffer Recipe Calculator: TAE / TBE / PBS and Custom Formulas — Mass and Volume Conversions
Making one liter of 50× TAE is not a simple multiplication problem — it involves three things simultaneously: how many grams of solid to weigh out, how many milliliters of stock solution to measure, and which step, if done out of order, means the buffer simply won’t work.
How the Calculations Work
Solid mass (g) = target concentration (mol/L) × volume (L) × molecular weight (g/mol)
Stock volume (mL) = target concentration (mol/L) × volume (L) ÷ stock concentration (mol/L) × 1000
Concentration factor (×) = each component's concentration multiplied by the same factor
The last point is critical: a concentrated stock is not ‘just use less water’ — every component’s concentration is raised by the same factor. This tool writes out the full calculation for every component so you can check each one individually.
Verification
Cross-check against the standard recipe — 50× TAE, 1 liter:
Tris base 2000 mM × 1 L × 121.14 ÷ 1000 = 242 g
Glacial acetic acid 1000 mM × 1 L ÷ 17.5 mol/L × 1000 = 57.1 mL
0.5 M EDTA 50 mM × 1 L ÷ 0.5 mol/L × 1000 = 100 mL
242 g / 57.1 mL / 100 mL are exactly the three numbers in standard recipes, and they are back-calculated from the 1× working concentrations of 40 mM Tris, 20 mM acetic acid, and 1 mM EDTA. TBE and PBS check out the same way (see below).
Pitfall 1: EDTA Will Not Dissolve Without pH Adjustment
Disodium EDTA will not dissolve until the pH is raised to approximately 8.0. Many people spend an afternoon stirring their first 0.5 M EDTA stock, assuming the problem is insufficient stirring or water temperature — but the real issue is that NaOH was never added. The correct procedure is to add NaOH while stirring; the solution clears suddenly as pH approaches 8.0.
0.5 M EDTA requires 186.1 g of Na₂EDTA·2H₂O (MW 372.24) per liter. This is why TAE/TBE recipes list EDTA as ‘X mL of 0.5 M stock’ rather than ‘X grams’ — everyone prepares this stock solution first.
Pitfall 2: Tris pH Shifts with Temperature
The pKa temperature coefficient of Tris is −0.028 / °C (pKa ≈ 8.1 at 25 °C). In other words: a Tris buffer adjusted to pH 8.0 at room temperature is approximately pH 8.6 at 4 °C and approximately pH 7.7 at 37 °C.
The practical consequences are real: chromatography in a cold room and enzyme reactions at 37 °C are both running at a pH different from what you adjusted at the bench. The correct approach is to adjust pH at the temperature of use, or at minimum to record the temperature at which pH was adjusted. Phosphate (PBS) is nearly insensitive to temperature, which is one reason it is more convenient for cell culture work.
Side Note: Glacial Acetic Acid Is Measured by Volume
Glacial acetic acid is a pure liquid at approximately 17.5 mol/L, so recipes specify milliliters rather than grams. Measure it in a fume hood, and always add acid to water, not water to acid.
Related Tools
For single-component concentration/volume/mass conversions, see Molarity Calculator; to determine acid/base ratios for a target pH, see Buffer pH Calculator; to interconvert percentage concentration and molarity, see Percent Concentration Calculator.
EDTA dissolution conditions and the 0.5 M preparation procedure are from the Cold Spring Harbor Protocols EDTA recipe; the Tris pKa temperature coefficient is from buffer data published by reagent manufacturers.
FAQ
How much do I need for 50× TAE at one liter, and how do I verify the calculation?
Tris base 242 g, glacial acetic acid 57.1 mL, 0.5 M EDTA (pH 8.0) 100 mL, brought to 1 L with water. To verify, back-calculate: these three numbers come from multiplying the 1× working concentrations (40 mM Tris, 20 mM acetic acid, 1 mM EDTA) by 50, then by volume and molecular weight — 2000 mM × 1 L × 121.14 ÷ 1000 = 242 g; 1000 mM × 1 L ÷ 17.5 mol/L × 1000 = 57.1 mL; 50 mM × 1 L ÷ 0.5 = 100 mL. These match the numbers in all standard recipes, confirming the formulas are correct.
EDTA won't dissolve no matter how long I stir — what's going on?
The problem is not stirring or temperature: **disodium EDTA will not dissolve until the pH is raised to approximately 8.0**. The correct procedure is to add NaOH while stirring; the solution clears suddenly as pH approaches 8.0. A 0.5 M stock requires 186.1 g of Na₂EDTA·2H₂O per liter. This is why TAE/TBE recipes specify 'X mL of 0.5 M stock' rather than a mass — everyone prepares this stock solution first.
Why is Tris buffer pH considered unreliable?
The pKa temperature coefficient of Tris is −0.028/°C, one of the highest among common buffer systems. A solution adjusted to pH 8.0 at 25 °C is approximately pH 8.6 in a 4 °C cold room and approximately pH 7.7 in a 37 °C reaction — a span of nearly one pH unit. The correct approach is to adjust pH at the temperature of use, or at minimum record the temperature at adjustment. Phosphate is nearly insensitive to temperature, which is one reason PBS is more convenient for cell culture work.
What is the relationship between a concentrated stock and a working solution?
A concentrated stock is not 'use less water' — **every component's concentration is raised by the same factor**. A 50× stock is diluted 1 part into 49 parts water to give 1×. This tool writes out the calculation for every component so this relationship can be verified step by step, rather than simply memorizing a set of numbers.
Why is glacial acetic acid given in milliliters rather than grams?
Because it is a pure liquid at approximately 17.5 mol/L — measuring by volume is more practical than weighing. The conversion is: target concentration (mol/L) × volume (L) ÷ 17.5 × 1000 = volume in mL. Measure it in a fume hood, and always add acid to water.
Can I use this calculator for my own lab's recipe?
Yes. Select 'Custom' and enter one component per line: name, 1× target concentration in mM, and molecular weight — for example 'Sodium chloride 137 58.44'. The tool applies the same formulas and shows the calculation for each component. Note that custom mode handles solid components only; for liquid stocks, apply the volume formula above manually.
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