# The complete guide to reconstituting peptides Everything you need to know about turning lyophilised powder into a research-ready solution: the supplies, the six-step technique, storage after reconstitution, and the mistakes that ruin expensive vials. - Published: 23 February 2026 - Author: AusPep Labs - Category: Beginner guides - Reading time: 5 min - Canonical: https://www.auspeplabs.store/blog/the-complete-guide-to-reconstituting-peptides Reconstitution is the step where a lyophilised (freeze-dried) peptide becomes a solution you can actually work with. The chemistry is simple: add a measured volume of diluent and let the powder dissolve. The technique is where things go wrong. A vial that took weeks to source can be degraded in the thirty seconds it takes to reconstitute it badly, so this guide covers the whole procedure, the storage rules that follow, and the mistakes that cost researchers the most. ## What you'll need - **Your lyophilised peptide vial** — kept in the fridge, or the freezer for long-term storage, until you are ready to use it - **Bacteriostatic water** — the standard diluent for research peptides, usually supplied in 10 mL or 30 mL multi-dose vials - **Insulin syringes** — one for drawing the water, and fresh ones for every draw after that - **Alcohol swabs** — for the rubber stopper on both vials, every time a needle goes through - **A label and a marker** — for the date and the concentration you calculated Do not substitute tap water, saline or plain sterile water as your main diluent. Bacteriostatic water contains 0.9% benzyl alcohol, which stops bacteria growing in a vial that will be punctured repeatedly over several weeks. Plain sterile water has no preservative, so anything that gets into the vial on the second draw stays there. If you have to use sterile water, treat the vial as single-use. ## Step-by-step reconstitution ### Step 1 — Let the vial reach room temperature Take the peptide vial out of the fridge and leave it on the bench for 15 to 20 minutes before you open it. Warm air on a cold stopper causes condensation, and injecting cold water into a cold cake is an unnecessary thermal shock. Never warm a vial with your hands, a water bath or anything else; patience is the only tool you need here. ### Step 2 — Swab both stoppers Wipe the stopper on the peptide vial and the stopper on the bacteriostatic water vial with a fresh alcohol swab. Let them air dry for about 30 seconds. Do not blow on them and do not wipe them dry, because a wet stopper carries alcohol into the vial on the needle. ### Step 3 — Draw your bacteriostatic water Work out the volume first, using the method in our [peptide calculator guide](/blog/how-to-use-a-peptide-calculator). For a typical 5 mg to 10 mg vial, 1 to 2 mL is a sensible starting point. Draw that volume into a clean syringe from the water vial, tap out any large air bubbles, and check the reading before you go on. ### Step 4 — Run the water down the glass, slowly This is the step that matters most. **Do not squirt the water straight onto the powder.** Insert the needle so the tip rests against the inside wall of the vial, then press the plunger gently and let the water run down the glass and pool under the cake. Peptides are long, folded molecules; a hard stream of water breaks them up mechanically before they are even in solution. Keep the pressure light and steady. Delivering 1 mL should take around 15 to 30 seconds, not a single push. ### Step 5 — Swirl, never shake Once the water is in, **do not shake the vial.** Shaking creates foam and shear stress, and both damage the peptide. Instead, roll the vial slowly between your palms or swirl it gently so the water moves over the cake. Most peptides dissolve within a couple of minutes. If some powder is still visible, put the vial in the fridge for 30 minutes and let it finish dissolving on its own. ### Step 6 — Inspect the solution Hold the vial up to the light. A correctly reconstituted peptide is clear and colourless, although a few peptides carry a faint yellow tint that is normal for the compound. If the solution is cloudy, milky, or has visible particles or strands floating in it, something has gone wrong. Do not use that vial; note the batch number on the label and contact us. ## Storage after reconstitution Once the peptide is in solution, the rules change: - **Keep it at 2 to 8 °C** — in the fridge, never the freezer - **Use it within 4 to 6 weeks** — bacteriostatic water stops bacterial growth, but the peptide itself still degrades slowly in solution - **Keep it out of the light** — leave it in the original amber or clear vial inside a box, or in a dark corner of the fridge - **Never freeze it** — ice crystals and freeze-thaw cycles break peptide bonds faster than anything else on this list Unopened lyophilised vials are a different matter. Sealed and kept cold, they are stable for many months, and the freezer extends that further. Only reconstitute what you will use within the window above. ## What if the powder won't dissolve? Some sequences, particularly long or hydrophobic ones, dissolve slowly. If gentle swirling has not cleared the vial: - Put it in the fridge for 30 to 60 minutes and check again. Time does most of the work. - Add a little more bacteriostatic water, about 0.5 mL, and swirl gently. Remember to recalculate your concentration. - Check the batch documentation. A few compounds are known to need a different diluent, such as a very dilute acetic acid solution, and the certificate of analysis or product page will say so. Do not improvise with solvents. ## Common mistakes to avoid - Shaking the vial instead of swirling it - Using plain sterile water in a vial that will be drawn from more than once - Squirting the water directly onto the powder rather than down the glass - Reconstituting a vial straight from the fridge, before it has warmed up - Storing a reconstituted vial in the freezer - Using a reconstituted vial that has been left out of the fridge for more than a few hours - Reusing a needle, or skipping the swab, on a later draw Every batch we supply has been through independent HPLC purity and LC-MS identity testing before it is listed, and the batch number is on the vial. If anything about a vial looks wrong at any point in this process, that number is what we will ask for. --- For in-vitro laboratory research only. Not for human or veterinary use.