BioDeviceHub

Reagent and Buffer Recipe Calculator

Turn a recipe into a bench sheet: the mass of each solid to weigh and the volume of each stock solution to pipette for the final volume you choose.

Formula

solid:m=C×V×MW\text{solid:}\quad m = C \times V \times \mathrm{MW}
stock:Vstock=Cfinal×VCstock\text{stock:}\quad V_{\text{stock}} = \dfrac{C_{\text{final}} \times V}{C_{\text{stock}}}
mm
mass of a solid component, in grams
CC
final concentration of that component
VV
final volume of the finished reagent
MW\mathrm{MW}
molecular weight of the solid, in g/mol

How it works

Most working reagents combine a few solids that are weighed with a few concentrated stocks that are pipetted. Each line of a recipe is either a molarity calculation (mass from concentration, volume and molecular weight) or a dilution (stock volume from C₁V₁ = C₂V₂).

The calculator runs every line against the same final volume and lists the result as a bench sheet. The solvent is not given as a volume to add, because dissolved solids change the volume: dissolve and combine everything in less than the final volume, then make up to the mark.

Worked example

500 mL of 50 mM Tris, 150 mM NaCl, 1 mM EDTA, 1% Triton X-100, from Tris base (121.14 g/mol), NaCl (58.44 g/mol), 0.5 M EDTA and 10% Triton X-100.

  1. Tris base: 0.05 mol/L × 0.5 L × 121.14 g/mol = 3.029 g.
  2. NaCl: 0.15 mol/L × 0.5 L × 58.44 g/mol = 4.383 g.
  3. EDTA: 1 mM × 500 mL / 500 mM = 1 mL of stock.
  4. Triton X-100: 1% × 500 mL / 10% = 50 mL of stock.

Dissolve the solids in about 400 mL of water, add the two stocks, adjust the pH, then make the volume up to 500 mL.

These are the values the calculator opens with, so you can check its output against this example.

Assumptions

  • Each stock and its final concentration are entered in the same unit.
  • Solids are 100% pure and their molecular weights match the form in the bottle.
  • pH adjustment is not calculated. The acid or base used for it is part of the final volume.

Common mistakes

  • Adding the full final volume of water first, leaving no room for the solids and stocks.
  • Adjusting the pH after making up to volume, which changes the volume again.
  • Entering a stock in M and its final concentration in mM. Both must use one unit.

Related tools

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