Reconstitution calculator
Concentration from vial mass and diluent volume, the diluent volume needed to reach a target concentration, and the mass contained in a given aliquot. Everything runs in your browser; nothing is sent anywhere.
As printed on the vial label.
Bacteriostatic or sterile water.
Resulting concentration
5 mg/mL
5,000 µg/mL
Mass per aliquot volume
How much peptide is contained in a given volume drawn from the vial at the concentration above.
| Volume drawn | Peptide (mg) | Peptide (µg) |
|---|---|---|
| 0.01 mL | 0.05 | 50 |
| 0.02 mL | 0.1 | 100 |
| 0.05 mL | 0.25 | 250 |
| 0.1 mL | 0.5 | 500 |
| 0.25 mL | 1.25 | 1,250 |
| 0.5 mL | 2.5 | 2,500 |
| 1 mL | 5 | 5,000 |
Working backwards from a target
How much diluent to add to a 10 mg vial to land on a chosen concentration.
Diluent required
2 mL
Check the figure against the vial's capacity before drawing it up — a 3 mL vial will not hold 5 mL.
The arithmetic
Concentration is mass divided by volume. A 10 mg vial reconstituted with 2 mL of diluent gives 5 mg/mL, or 5,000 µg/mL. The volume of the lyophilised cake is negligible relative to the diluent and is conventionally ignored — it is well inside the error of the syringe you measured the diluent with.
Running it backwards, the diluent volume needed for a target concentration is mass divided by target. That direction is the more common one in practice, because the concentration is usually set by what the experiment needs rather than by what is convenient to add.
The error this calculator cannot correct for
Every figure above assumes the mass printed on the label is the mass of peptide. Frequently it is not. Lyophilised peptide is supplied as a salt — most often a trifluoroacetate salt left over from purification — and carries residual water on top of that. Gross weight includes both; net peptide content is the mass of peptide alone, and the gap between them can be substantial.
For most in-vitro work the difference is tolerable. Where molar accuracy matters, take net peptide content from the Certificate of Analysis and use that figure as the vial mass above. Net peptide content versus purity covers why the two numbers get confused and what each one is for.
Before you reconstitute
- Let the vial reach room temperature first. Adding diluent to cold lyophilised cake, or opening a cold vial into humid air, condenses water into material that was freeze-dried specifically to exclude it.
- Run the diluent down the inside wall of the vial rather than straight onto the cake, and swirl rather than shake. Shaking drives peptide to the air-liquid interface and aggregates it — a problem that is particularly pronounced with fatty-acid-conjugated compounds.
- Label the reconstituted vial with the concentration and the date. Once it is in solution, nothing about the vial tells you either.
Frequently asked questions
- How do I calculate the concentration of a reconstituted peptide?
- Divide the mass of peptide in the vial by the volume of diluent added. A 10 mg vial reconstituted with 2 mL of bacteriostatic water gives 10 ÷ 2 = 5 mg/mL, or 5,000 µg/mL. The volume of the lyophilised cake itself is negligible and is conventionally ignored.
- How much diluent do I add to reach a specific concentration?
- Divide the vial mass by the target concentration. A 10 mg vial at a target of 2 mg/mL needs 10 ÷ 2 = 5 mL of diluent. Check the result against the vial's capacity before drawing it up — a 3 mL vial cannot hold 5 mL.
- Does the peptide mass on the label account for salt content?
- Not necessarily, and this is the most common source of error in peptide concentration work. Labelled mass is usually gross peptide weight, which includes counter-ion salt (commonly trifluoroacetate) and residual water. Net peptide content — the actual mass of peptide — can be meaningfully lower. If your work depends on molar accuracy, use the net peptide content figure from the Certificate of Analysis rather than the label mass.
- What diluent should be used?
- Bacteriostatic water is standard for peptides intended to be stored as a solution for a period, since the benzyl alcohol in it inhibits microbial growth. Sterile water suits single-session use. Some peptides require a different solvent system to dissolve at all; the compound page and the Certificate of Analysis note where that applies.