Concentration = mass ÷ volume. The volume of the powder itself is negligible at these masses, so the diluent volume is the solution volume. Figures assume the label mass is the peptide mass; see the note on net peptide content below.
The formula
Concentration (mg/mL) = peptide mass (mg) ÷ diluent volume (mL). Multiply by 1,000 for µg/mL. To find the mass in any smaller volume, multiply the concentration by that volume: at 5 mg/mL, 0.1 mL contains 0.5 mg, which is 500 µg.
Worked examples with our vial sizes
| Vial | Diluent | Concentration | Per 0.1 mL | Per 0.01 mL |
|---|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 500 µg | 50 µg |
| 5 mg | 2 mL | 2.5 mg/mL | 250 µg | 25 µg |
| 10 mg | 1 mL | 10 mg/mL | 1,000 µg | 100 µg |
| 10 mg | 2 mL | 5 mg/mL | 500 µg | 50 µg |
| 20 mg | 2 mL | 10 mg/mL | 1,000 µg | 100 µg |
| 50 mg | 5 mL | 10 mg/mL | 1,000 µg | 100 µg |
| 100 mg | 5 mL | 20 mg/mL | 2,000 µg | 200 µg |
A 1 mL syringe graduated in hundredths reads 0.01 mL per mark, so the last column is the mass per single graduation on that syringe. Larger diluent volumes give lower concentrations and therefore larger, easier-to-measure volumes for the same mass.
Net peptide content
The label mass is the gross mass of lyophilised powder in the vial. That powder is the peptide plus bound water and the counter-ion left from purification, typically trifluoroacetate or acetate. If the certificate of analysis states a net peptide content, multiply the label mass by it before using the calculator: a 10 mg vial at 85% net content holds 8.5 mg of peptide. Most research certificates do not report this figure, in which case the label mass is the only number available and the result is an upper bound. See how to read a certificate of analysis.
Handling notes
- Let the vial reach room temperature before opening, so no condensation forms on cold powder.
- Run the diluent slowly down the inside wall of the vial rather than onto the powder, then swirl. Do not shake; agitation can denature or foam a peptide solution.
- Most lyophilised peptides dissolve in water within a minute or two. A solution that stays cloudy usually means a hydrophobic sequence or a concentration above its solubility, not a bad batch; more diluent is the first thing to try.
- Bacteriostatic water contains 0.9% benzyl alcohol as a preservative. Sterile water contains none; a vial reconstituted with it should be used promptly.
- Label the vial with the date and the concentration at the moment it is made. Concentration is the number every later calculation depends on.
- Store reconstituted solutions at 2–8°C protected from light. Storage guidance by form is in the storage and stability guide.
Diluent we stock
Bacteriostatic water, 0.9% benzyl alcohol in water for laboratory solution preparation, stocked alongside the catalog.