Reconstituting a lyophilised vial

You need the freeze-dried peptide vial, a suitable solvent (bacteriostatic water or sterile water), a syringe and needle for transfer, and alcohol swabs for the vial stopper. Work on a clean surface. Use sterile technique throughout to keep the solution free of contamination.

Freeze-dried peptides come as a dry powder in a sealed vial. That keeps the material stable during transport and storage. Reconstitution is the laboratory step of dissolving that powder in a measured volume of solvent. The result is a solution with a known concentration, ready for use in experiments.

Getting the technique right matters. The reproducibility of an assay depends partly on the concentration of the peptide solution you use. A consistent method gives a consistent result. It also lowers the risk of damaging the material while you prepare it.

The choice of solvent is usually between bacteriostatic water and sterile water. Bacteriostatic water holds a preservative, such as benzyl alcohol. That preservative stops bacteria and other microbes growing in the solution over time. Sterile water has no preservative and is used where any extra compound could affect an assay.

For most research work where a solution will be used over several days, bacteriostatic water is the more common choice. The preservative keeps the prepared solution usable for longer. Sterile water is right when the researcher wants to avoid the preservative, but the prepared solution then has a shorter practical handling window. Nothing protects it from microbial growth.

Work in a clean, tidy laboratory area. Wear appropriate gloves and eye protection. Gather everything before you start. You need the peptide vial, the solvent, a sterile syringe, needles, alcohol swabs and labelled waste containers.

Swab the rubber stopper of the peptide vial and the neck of the solvent vial with an alcohol wipe. Let them dry before you insert any needle. This is standard sterile technique and it keeps contamination out of the vial. Use a fresh sterile needle and syringe for each vial. Never reuse a needle between different compounds or vials.

Check the batch number on the peptide vial against any accompanying documentation before you begin. That way the solution you prepare is clearly linked to the right material. This matching step is quick and stops mistakes that would be hard to undo once the vial is open.

The volume you add sets the final concentration of the solution, so choose it on purpose, not at random. A smaller volume gives a more concentrated solution. A larger volume gives a more dilute one. The right concentration depends on the assay you plan to run.

If you are unsure how the amount of peptide in the vial, the volume of solvent and the final concentration fit together, the peptide reconstitution calculator does the maths for you. That way you add the right volume first time.

Draw the chosen volume of solvent into a sterile syringe. Remove the needle, or keep it attached carefully, and slowly inject the solvent down the inside wall of the peptide vial. Aim at the glass rather than directly onto the powder. Injecting straight onto the powder can cause foaming, which is best avoided.

Peptides are sensitive to mechanical stress. Avoid vigorous shaking, which adds air bubbles and can damage the material. A gentle swirl or slow rotation lets the powder dissolve without whipping air into the solution.

Rotate the vial gently until the powder is fully dissolved. Most peptides dissolve readily with light swirling. If any material clings to the stopper, tap the vial gently or let it settle before checking again. The goal is a clear, even solution with no visible particles or froth.

If the solution does not clear even with gentle mixing, stop and check the product notes rather than shaking harder. Persistent undissolved material may point to a handling or solvent issue. That is safer to investigate than to force.

Once fully dissolved, the concentration is the mass of peptide in the vial divided by the volume of solvent added. Express it in the standard units used in peptide work, usually milligrams per millilitre or micrograms per microlitre. Record the value in your laboratory log. The calculator is a reliable way to switch between these units and to check your maths.

Double-check the conversion before you run an assay. A simple slip on the concentration can affect every result that follows. So the small effort of confirming the number with a calculator is well spent.

After reconstitution, follow the storage advice for the prepared solution. That is normally to keep it in the fridge at 2 to 8 degrees Celsius and to avoid repeated freeze-thaw cycles. Clearly label the vial with the compound, the working concentration and the date of reconstitution.

The solution is now liquid. Where bacteriostatic water is used, its preservative is what keeps the solution usable over several days. Once the practical handling window is reached, throw away any unused solution in line with institutional waste policy. Related guidance is available in the article on storing research peptides after reconstitution and the article on the difference between bacteriostatic water and sterile water.

• Peptide reconstitution on PubMed
• PubChem
• Peptide reconstitution calculator

All products referenced in this article are supplied strictly for laboratory research use only. They are not medicines, are not licensed or approved for human or veterinary consumption, and must not be administered to humans or animals. Nothing in this article is medical advice. Researchers are responsible for operating within their own institution's and jurisdiction's applicable regulations.