How to Reconstitute Peptides: Step-by-Step (with Calculator)

Lyophilized peptides arrive as a freeze-dried powder or cake and must be dissolved in a diluent before use in research. This is called reconstitution. Done carefully, it's simple. Here's the method and the math.

What you need

• The lyophilized peptide vial
• Bacteriostatic water (0.9% benzyl alcohol) for multi-session solutions, or sterile water for single use
• A sterile syringe for transferring diluent
• Alcohol wipes for the vial stoppers

Step by step

1. Decide your diluent volume

More diluent means each aliquot is a larger, more precisely pipettable volume; less means smaller aliquots. The total peptide never changes — only the concentration. A common choice is 1–2 mL of bacteriostatic water per vial.

2. Wipe both stoppers

Clean the rubber stopper on both the diluent and the peptide vial with an alcohol wipe before piercing.

3. Draw the diluent

Draw your chosen volume of bacteriostatic water into the syringe.

4. Add it slowly, down the wall

Insert the needle and let the diluent run slowly down the inside wall of the peptide vial — not directly onto the cake. This protects the peptide from shear stress.

5. Swirl, don't shake

Gently swirl the vial until the powder fully dissolves. Never shake — agitation can degrade the peptide. The solution should be clear.

The concentration math

Concentration = peptide mass ÷ diluent volume. A 5 mg vial reconstituted with 2 mL of bacteriostatic water is 2.5 mg/mL (2,500 mcg/mL). The volume containing a target analyte mass is that mass divided by the concentration: 250 mcg ÷ 2,500 mcg/mL = 0.1 mL, or 100 µL — a volume a pipette measures directly. The calculator does all of this automatically.

Storage after reconstitution

Reconstituted solutions are typically held at 2–8°C (refrigerated). Bacteriostatic water's benzyl alcohol inhibits bacterial growth, extending the usable window versus sterile water. Keep solutions out of light and minimize temperature swings.