The formula is always the same: concentration = mass ÷ volume. A 5 mg vial reconstituted with 1 mL is at 5 mg/mL; with 2 mL, at 2.5 mg/mL; with 2.5 mL, at 2 mg/mL. More solvent does not change the total amount, it only dilutes it.
To go from mg to mcg (micrograms), multiply by 1,000: 2.5 mg/mL equals 2,500 mcg/mL. From the concentration, the amount contained in any volume is obtained by multiplying: 0.1 mL of a 2.5 mg/mL solution contains 0.25 mg.
The most frequent mistakes are confusing mg with mcg (a factor of a thousand), forgetting that the volume of solvent added is not always exactly the final volume, and calculating on the vial's nominal mass without considering peptide content when precision is needed.
Choosing the reconstitution volume with the calculation in mind (a “round” concentration) reduces conversion errors, the most common source of inconsistent results in the lab.
Related terms
Learn it in depth at the Peptide University
- Practical calculation cases and common errors · Module 9
- The arithmetic of concentration · Module 9
- Pharmacokinetics: ADME and parameters · Module 2
- Pharmacodynamics: receptors and signaling · Module 2
- Reconstitution and aseptic technique · Module 9
Definition for educational and scientific purposes. It is not medical advice or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).