How to Reconstitute Peptides — Step-by-Step Research Protocol

A vial of lyophilised peptide stored at 2–8°C, a vial of bacteriostatic water (BAC water) or sterile water, an appropriately sized sterile syringe with a fine needle, alcohol swabs, and the lot-matched COA for the peptide. The COA tells you the peptide mass in the vial — you cannot calculate concentrations correctly without it.

Bacteriostatic water (0.9% benzyl alcohol) is the standard diluent for most research peptides because it allows the reconstituted material to be used over several weeks under refrigeration. Sterile water can be used for single-use applications. Acetic acid solutions are used for peptides that are poorly soluble in water (e.g. some hydrophobic sequences). The peptide COA or supplier note should specify the recommended diluent.

Decide your target concentration first, then divide vial mass by concentration to get diluent volume. Example: a 10 mg vial reconstituted to 5 mg/mL needs 2 mL of diluent. For multi-dose research vials, a 10:1 mg-to-mL ratio is common because it makes downstream volume maths simple.

Wipe both vial septa with an alcohol swab. Draw the calculated volume of diluent into the syringe. Angle the needle so the diluent runs down the inner wall of the peptide vial — do NOT inject it directly onto the lyophilised pellet. Force can damage the peptide.

Once the diluent is in, swirl the vial gently or roll it between your palms until the powder is fully dissolved. Never shake a peptide vial. Shaking introduces shear forces and foaming that can degrade the peptide. Full dissolution should take seconds to a minute for most research peptides.

Write the reconstitution date, concentration and lot number on the vial. Store reconstituted material at 2–8°C, away from light. With BAC water, most research peptides have an in-use stability window of around 2 months; sterile water shortens this significantly. Always follow the COA's stated window.

Forgetting to factor in vial overage when calculating concentration; injecting diluent directly onto the pellet; shaking instead of swirling; using room-temperature storage; leaving the reconstituted vial without a date label; reusing needles between vials. Any one of these can compromise a study.