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Culture Medium Supplement Calculator

Work out how much of each supplement (serum, penicillin-streptomycin, glutamine and others) to add to basal medium for a final volume of complete medium.

Formula

Vi=sfinal×VfinalsstockV_i = \dfrac{s_{\text{final}} \times V_{\text{final}}}{s_{\text{stock}}}
Vbasal=Vfinal−∑ViV_{\text{basal}} = V_{\text{final}} - \sum V_i
stock, final\text{stock},\ \text{final}
strength of each supplement in the stock and in the finished medium, in one unit

How it works

Complete medium is basal medium plus supplements, such as 10% fetal bovine serum, penicillin and streptomycin at 1×, and glutamine at 2 mM. Each supplement's volume is its final strength times the final volume divided by its stock strength, and the basal medium is what is left.

Serum is 100% stock diluted to a percentage; antibiotic mixes are sold at 100× and used at 1×; glutamine is often a 200 mM stock used at 2 mM. The unit only has to be the same for the stock and the final value of each supplement.

Worked example

500 mL of medium with 10% FBS, 1× penicillin-streptomycin (from 100×) and 2 mM glutamine (from 200 mM).

  1. FBS: 10 × 500 / 100 = 50 mL.
  2. Penicillin-streptomycin: 1 × 500 / 100 = 5 mL.
  3. Glutamine: 2 × 500 / 200 = 5 mL.

Use 440 mL of basal medium with the three supplements, 60 mL in all.

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

Assumptions

  • The supplements mix to the volumes stated, which holds for dilute additions.
  • The stock strengths are accurate; serum is taken as 100%.

Common mistakes

  • Adding the supplements to the full bottle of medium without removing the volume first, so the concentration is lower than intended.
  • Mixing units within a row, for example a stock in % and a final value in ×.
  • Keeping complete medium for months when glutamine degrades.

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