How to Reconstitute Lyophilised Peptides: A Step-by-Step Laboratory Gu

Lyophilisation preserves peptides for storage and transport by removing water under vacuum. Before research use, the lyophilised peptide must be reconstituted — dissolved in an appropriate solvent to produce a solution of known concentration. The reconstitution process is straightforward but technique matters: errors at this stage can compromise the entire downstream research application.

Why bacteriostatic water, and what alternatives exist

Bacteriostatic water (BAC water) is sterile water containing 0.9% benzyl alcohol (w/v) as a preservative. Benzyl alcohol is a broad-spectrum antimicrobial agent that inhibits the growth of bacteria in aqueous solution. This matters because once reconstituted, a peptide solution can support microbial growth if the reconstitution solvent does not contain a preservative. Bacterial contamination would degrade the peptide and render the solution unsuitable for research use.

The 0.9% benzyl alcohol concentration in standard BAC water is effective without being harmful to the peptide at research-relevant concentrations. For most lyophilised peptides, BAC water is the correct reconstitution solvent.

Alternatives include: sterile water for injection (SWFI, no preservative — suitable only for single-use reconstitution, not storage); 0.9% sodium chloride (saline — sometimes preferred for peptides that interact with benzyl alcohol); and acetic acid at 0.1-1% (used for certain peptides that are poorly soluble in aqueous solution at physiological pH, such as some GLP-1 analogues). Unless you have a specific reason to use an alternative, BAC water is appropriate for the peptides in the Nexapep catalogue.

Equipment required

Lyophilised peptide vial; bacteriostatic water vial; appropriately sized syringes (29-gauge insulin syringes are standard for research peptide reconstitution; 1ml or 0.5ml for small draw volumes); alcohol swabs (isopropanol or ethanol, 70%); a clean, flat work surface; gloves. Do not use cotton swabs — fibres can contaminate the solution.

Reconstitution protocol — step by step

Allow to reach room temperature

Remove the peptide vial from cold storage and allow it to reach room temperature before opening. This prevents condensation forming on and inside the cold vial when it contacts warm air. Condensation introduces water into the headspace and can begin hydrolysis before reconstitution is complete.

Swab and dry both stoppers

Using an alcohol swab, clean the rubber stopper of both the peptide vial and the BAC water vial. Allow to air dry for at least 30 seconds. The alcohol must evaporate completely before needle insertion; residual alcohol can contaminate the solution.

Calculate and draw the BAC water volume

Determine the volume of BAC water to add based on your target concentration. Use the Nexapep reconstitution calculator for precise values. Draw this volume into the syringe from the BAC water vial.

Inject down the glass wall — not onto the cake

Insert the needle into the peptide vial at an angle, directing the tip toward the inside glass wall. Inject the BAC water slowly, allowing it to run down the glass and accumulate at the bottom of the vial. Injecting directly onto the lyophilised cake forces liquid into the matrix under pressure, which can cause local heating and peptide degradation. If you feel resistance from the vacuum in the vial, pause and allow the liquid to be drawn in naturally before continuing.

Swirl gently — never shake

After adding the BAC water, gently swirl the vial in a circular motion. The lyophilised cake should dissolve within 30-60 seconds for most peptides. Do not shake. Shaking introduces air into the solution, creates foam, and can cause peptide aggregation through hydrophobic interactions at the air-water interface.

Inspect and label

The reconstituted solution should be clear and colourless. Any cloudiness, colour, or particulate matter is abnormal and should be investigated before use. Label the vial with the reconstitution date, concentration, and your name or identifier for research records.

Concentration calculations

The calculation is: concentration (mg/ml) = vial amount (mg) ÷ BAC water volume added (ml). For a 5mg vial with 2ml of BAC water: concentration = 5 ÷ 2 = 2.5 mg/ml. To calculate the draw volume for a given dose: draw volume (ml) = dose (mg) ÷ concentration (mg/ml). For a 250mcg (0.25mg) dose at 2.5mg/ml: draw volume = 0.25 ÷ 2.5 = 0.1ml.

Common concentrations reference

1ml

water → 5mg/ml

2ml

water → 2.5mg/ml

5ml

water → 1mg/ml

10ml

water → 0.5mg/ml

Based on a 5mg vial. Use the Nexapep calculator for other vial sizes and precise draw volumes.

Insulin syringe units conversion

U100 insulin syringes are graduated in "units" where 1 unit = 0.01ml. Therefore 10 units = 0.1ml, 50 units = 0.5ml, and 100 units = 1ml. When calculating draw volumes in ml, multiply by 100 to get the equivalent reading on a U100 insulin syringe. For a draw of 0.1ml: 0.1 × 100 = 10 units on the syringe scale.

Post-reconstitution storage

Refrigerate at 2-8°C immediately after reconstitution. Do not return to the freezer. Discard any reconstituted solution that has been stored for more than 6 weeks, or sooner if you observe any change in appearance. Use the Nexapep reconstitution calculator, which includes a dose reference table, to manage your research protocol efficiently.

Quick reference

Mini Reconstitution Calculator

For a full version with dose tables and syringe references, use the full calculator.

Vial (mg)

BAC water (ml)

Dose (mcg)

Concentration — mg/ml

Draw volume — ml

U100 insulin units — units

Open full calculator →