This guide explains how to reconstitute peptides — dissolving lyophilised (freeze-dried) peptide powder into a liquid so it can be measured and used in laboratory research. Good technique and the right diluent keep the peptide intact and your concentrations accurate.
What you’ll need
- Bacteriostatic water — the usual diluent for research reconstitution; the benzyl alcohol it contains inhibits microbial growth in a multi-use vial. Available in our Supplies category.
- An alcohol swab to clean the stopper.
- A syringe to add the diluent, plus a fine U-100 insulin syringe if you will measure small volumes afterward.
- Your vial of lyophilised peptide and its lot-specific Certificate of Analysis.
Choosing a diluent
- Bacteriostatic or sterile water is the usual starting point for most peptides.
- Avoid saline (sodium chloride) with acetate-salt peptides, which can form precipitates.
- Poorly soluble or hydrophobic sequences may need a small amount of a compatible co-solvent; test a small portion first.
How to reconstitute peptides — step by step
- Bring both vials to room temperature. Cold liquid dissolves powder more slowly.
- Clean the stoppers. Remove the plastic flip-cap and swab the rubber stopper of both the peptide and the water vials with alcohol; let it dry.
- Draw your measured diluent. Pull the volume of bacteriostatic water you have chosen into a syringe.
- Add it slowly down the wall. Insert the needle at an angle and let the water run down the inside of the vial wall — do not spray it directly onto the powder.
- Swirl, don’t shake. Roll or swirl the vial gently until the powder fully dissolves. Vigorous shaking foams and shears the peptide and can degrade it.
- Inspect. The solution should be clear. Discard if it is cloudy or shows visible particulate.
Working out the concentration
Concentration is simply the peptide amount divided by the water volume. A 10 mg vial in 2 mL of water gives 5 mg/mL (5,000 mcg/mL). To skip the arithmetic — and convert any target amount into U-100 insulin-syringe units — use our free peptide reconstitution calculator. As a rule, prepare stock slightly more concentrated than you need and dilute as required.
After reconstitution
Store the reconstituted solution refrigerated at 2–8 °C, protected from light, and aliquot it if you will use it repeatedly so you are not warming the whole vial each time. Reconstituted peptide has a shorter usable life than the sealed lyophilised powder — see the peptide storage guide for detail.
Common mistakes to avoid
- Spraying water directly onto the pellet instead of down the wall.
- Shaking the vial — always swirl gently.
- Using saline with acetate-salt peptides.
- Leaving the solution at room temperature or in light after reconstitution.
- Guessing the concentration instead of calculating it.
Frequently asked questions
What water is used to reconstitute peptides?
Bacteriostatic water is the most common choice for research reconstitution because the benzyl alcohol it contains inhibits microbial growth in a multi-use vial. Sterile water is an alternative for single use.
Should you shake a peptide vial to dissolve it?
No. Swirl or roll the vial gently. Shaking creates foam and shear forces that can damage the peptide; let it dissolve slowly instead.
How much bacteriostatic water should I add?
Any volume works — more water makes a more dilute, easier-to-measure solution; less makes it concentrated. Choose a volume that suits your assay and calculate the resulting concentration with the reconstitution calculator.
This guide is part of our research peptides handbook.