How to reconstitute lyophilised research peptides

Bring the vial to room temperature first

Cold glass pulls condensation out of the air. Adding diluent to a vial straight from a -20 °C freezer introduces moisture and can cause localised freezing at the powder surface.

Let the sealed vial sit at ambient temperature for 15-30 minutes before you break the seal, and keep it upright so powder stays at the base.

Choosing a diluent

• Bacteriostatic water (0.9% benzyl alcohol) — common where a solution will be stored for several weeks under refrigeration in a laboratory setting.
• Sterile water for injection — no preservative, so it suits short working sessions where the solution is consumed quickly or aliquoted and frozen.
• Dilute acetic acid — used for poorly soluble sequences that resist neutral aqueous diluent.
• Match the diluent to your assay: preservatives and pH shifts can interfere with cell-based work.

Working out the concentration

Concentration is simply peptide mass divided by diluent volume. A 5 mg vial reconstituted with 2 mL of diluent gives 2.5 mg/mL, so 0.1 mL of that solution contains 250 µg.

Choose a volume that gives you round numbers for the aliquots your protocol needs. Fewer awkward conversions means fewer pipetting mistakes later.

Technique

• Wipe both the vial stopper and the diluent stopper with an alcohol swab and let them dry.
• Draw the calculated volume and let it run slowly down the inside wall of the vial — never inject the stream directly into the powder.
• Do not shake. Swirl gently or leave the vial to stand until the solution is clear; agitation shears peptide chains and creates foam.
• Inspect against a light source. A clear, particle-free solution is expected; cloudiness or visible strands means the material has not gone into solution properly.

Storage after reconstitution

Keep reconstituted solutions at 2-8 °C, protected from light, and record the reconstitution date on the vial alongside the lot number from the certificate of analysis.

For longer projects, aliquot into single-use volumes and freeze. Repeated freeze-thaw cycles are one of the most common causes of unexplained potency loss between experiments.

Common mistakes

• Shaking the vial to speed dissolution.
• Reconstituting the entire stock when only one experiment is planned.
• Failing to log the lot number, which makes results impossible to trace back to a batch.
• Storing reconstituted solution at room temperature on the bench between sessions.