How to Reconstitute Peptides: A Laboratory Guide
How lyophilized research peptides are reconstituted in the lab: choosing a solvent, careful dissolving technique, concentration math in mg/mL and µL, and storage.
For laboratory and analytical research only. Not for human or veterinary use. This is general educational information, not medical advice.
Most research peptides are supplied as a lyophilized (freeze-dried) powder. Before a peptide can be measured out for an experiment, it is reconstituted: dissolved in a suitable solvent to a known concentration. This guide covers choosing a solvent, a careful dissolving technique, the concentration math, and storage.
Choosing a solvent
Check the product's documentation first. Many peptides dissolve in sterile water. Bacteriostatic water (sterile water with 0.9% benzyl alcohol) is used when a stock solution will be sampled repeatedly over several days. Some hydrophobic or basic peptides need a dilute acid, such as 0.1% acetic acid, or a small amount of an organic co-solvent. Use the solvent your protocol and the peptide's documentation call for.
Dissolving technique
- Let the vial reach room temperature before opening, so condensation doesn't form on the powder.
- Add the measured volume of solvent with a calibrated pipette, running it down the inside wall of the vial rather than straight onto the powder. That reduces foaming and denaturation.
- Let the powder dissolve on its own, swirling gently if needed. Don't shake or vortex hard.
- A properly dissolved solution is clear. Persistent cloudiness or particles can point to the wrong solvent, too little volume, or a degraded product.
The concentration math
Concentration = mass of peptide ÷ volume of solvent.
- Example: 5 mg dissolved in 2.0 mL gives 2.5 mg/mL, which is 2.5 µg per µL.
- To take a set amount for an assay, divide the amount you need by the concentration. For 0.5 mg at 2.5 mg/mL, pipette 200 µL.
- Choose the volume to suit the concentrations your experiment needs. Many labs make a concentrated stock, then dilute it for each experiment.
Storage after reconstitution
Reconstituted peptides are usually kept refrigerated (2–8 °C) and protected from light, for a limited period that depends on the peptide and the solvent. For longer storage, many labs split the stock into single-use portions and freeze them, so the solution isn't thawed and refrozen repeatedly. Always confirm the stability data for the specific peptide.
Check the product first
Before working with any peptide, confirm the vial against its Certificate of Analysis: the identity, purity and measured content for that lot. Our guide to verifying a COA yourself shows how to check a certificate against the laboratory's own record.
Frequently Asked Questions
What solvent is used to reconstitute peptides?
Usually sterile water. Bacteriostatic water (sterile water with 0.9% benzyl alcohol) is used when a stock solution will be sampled over several days, and a dilute acid such as 0.1% acetic acid for peptides that do not dissolve in water. Follow the product's documentation.
Why should you not shake a peptide solution?
Vigorous shaking foams and can denature the peptide. Add the solvent slowly down the inside wall of the vial and swirl gently if needed.
How do I calculate peptide concentration?
Divide the peptide mass by the solvent volume. 5 mg dissolved in 2.0 mL gives 2.5 mg/mL, which is 2.5 µg per µL.