Serial Dilution for Peptide Stock Solutions: A Worked Example

Most lab protocols need a solution far weaker than the stock you start from. The tool for this is the dilution formula, C1 × V1 = C2 × V2.

The terms

• C1 = starting concentration
• V1 = volume of stock you take
• C2 = target concentration
• V2 = final volume you want

Step 1: make a stock

Dissolve 10 mg of a research peptide such as Nasal BPC-157 10mg in 2 mL of solvent. That gives 5 mg/mL.

Step 2: choose a target

Suppose a protocol calls for 0.5 mg/mL in a final volume of 1 mL.

Step 3: calculate

V1 = (C2 × V2) ÷ C1 = (0.5 × 1) ÷ 5 = 0.1 mL. Take 0.1 mL of stock and add 0.9 mL of solvent.

Serial steps

For a tenfold series, transfer 0.1 mL into 0.9 mL, mix gently, then repeat from the new tube. Each step is 10 times weaker: 5, 0.5, 0.05, 0.005 mg/mL.

Good habits

• Change the pipette tip at every step.
• Label each tube with concentration and date.
• Check units before every calculation.

This is for laboratory preparation of research solutions only. Keep reading for the molar version of this math.

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For laboratory research use only. Not for human or veterinary use, and not intended to diagnose, treat, cure or prevent any condition. This article is educational and is not medical advice.