How to reconstitute a lyophilised peptide

Reconstitution is the step where a stable, lyophilised peptide becomes a solution with a much shorter life and a concentration you now have to get right. The chemistry is simple. The errors are almost always procedural: the wrong diluent, the wrong arithmetic, or the wrong handling of the vial.

This guide covers the laboratory procedure for reconstituting a lyophilised research peptide, the arithmetic for calculating concentration and withdrawal volume, and the handling details that determine whether the solution is still good a week later. A calculator is included below.

Calculator

Enter the mass on the label (or net peptide content from the certificate), the diluent volume, and the quantity you want per draw. Everything else is calculated. No account needed; nothing is stored. The procedure and the arithmetic behind it are explained below.

What you are starting with

A lyophilised (freeze-dried) peptide is a porous cake or powder at the bottom of a sealed vial, usually under an inert atmosphere or partial vacuum. In that state, with the water removed, hydrolysis and oxidation are slowed enough that the material is stable for months to years when stored cold and dark. The moment you add water you give those reactions back their medium, which is why everything that follows is about limiting damage and keeping records.

Before you open anything, check two things on the vial and the certificate of analysis: the mass stated on the label (the figure the arithmetic depends on) and the lot number, which should match the certificate you were given. How to read the certificate.

Choosing a diluent

For most research peptides the choice is between two preparations of water:

Two things that are not suitable: tap or distilled water that has not been sterilised (microbial contamination), and saline for peptides whose solubility drops in the presence of salt (several hydrophobic sequences). If the certificate of analysis lists a solubility condition, that overrides anything general.

The procedure

1. Equilibrate the vial to room temperature before opening it. Opening a cold vial draws condensation onto the cake and the stopper, which adds water you did not measure and starts degradation early. Fifteen to twenty minutes on the bench is enough.
2. Swab the stopper of both the peptide vial and the diluent vial with 70% isopropanol and let it dry.
3. Draw the diluent into a sterile syringe. Use the volume you have decided on from the arithmetic below — it determines the concentration, and you cannot change it afterwards without diluting further.
4. Add the diluent slowly down the inside wall of the vial, not directly onto the cake. A jet of liquid onto the lyophilised material causes foaming and mechanical stress; peptides in solution are sensitive to shear and to the air–liquid interface.
5. Let it dissolve. Most research peptides go into solution within a minute or two without help. If the cake persists, roll or swirl the vial gently. Do not shake. If it still will not dissolve, the peptide may need a different solvent or a brief period at 4 °C — check the certificate before adding anything else.
6. Inspect the solution. It should be clear and colourless. Cloudiness, visible particles or a colour change indicate incomplete dissolution, aggregation, or a problem with the material. Record what you see.
7. Label the vial with the date of reconstitution, the diluent and volume used, and the resulting concentration. The label is the only thing that will tell you, in three weeks, what is in the vial.
8. Store it at 2–8 °C, protected from light, immediately after use. How long it lasts, and why.

The arithmetic

Three equations, in order.

1. Concentration

C = m ÷ V. Mass of peptide divided by volume of diluent. A 10 mg vial reconstituted with 2 mL gives 5 mg/mL, which is 5,000 mcg/mL. The lyophilised cake contributes negligible volume, so the diluent volume is the working figure.

2. Withdrawal volume

V = q ÷ C. The quantity you want in a single draw divided by the concentration. For 250 mcg from a 5,000 mcg/mL solution, that is 0.05 mL.

3. Graduations

Laboratory graduated syringes marked in “units” follow the U-100 convention: 1 mL is 100 units, so 0.05 mL reads as 5 units. Smaller barrels (0.5 mL, 0.3 mL) use the same graduation size and simply stop sooner.

The mistakes that account for nearly all errors

• mg and mcg. 1 mg = 1,000 mcg. A slipped decimal is a tenfold error. Write both units on your label.
• Label mass vs. peptide mass. The mass on the label is total lyophilised solids, which include residual water and counterions. If your certificate reports net peptide content, that is the more accurate figure to use for m. Why the two numbers differ.
• Choosing V after the fact. Decide the diluent volume from the draw size you need, so the withdrawal volume lands in the readable middle of the syringe rather than at a 1–2 unit mark where reading error is proportionally large.

After reconstitution

A reconstituted peptide is a different product from the lyophilised one. The dominant degradation routes in solution are hydrolysis at susceptible bonds (Asp–Pro, Asn–Gly), deamidation of asparagine and glutamine, oxidation of methionine, cysteine and tryptophan, and aggregation — all of which run faster at room temperature and in the presence of light. Practically:

• Keep the vial at 2–8 °C between uses and minimise the time it spends on the bench.
• Avoid repeated freeze–thaw of a solution. If you need long-term storage of a reconstituted peptide, split it into single-use portions and freeze those once.
• Treat bacteriostatic-water preparations as good for roughly four weeks refrigerated, and preservative-free preparations as good for days, not weeks. These are working rules, not guarantees — the sequence matters.
• Discard on any change in clarity or colour.

Related

• Peptide storage: temperature, light, humidity and real shelf life
• How to read a peptide certificate of analysis
• Research peptide quality: how to verify what you’re buying

Looking for research material? Browse lyophilized research peptides — every lot is third-party tested and ships with a lot-matched certificate of analysis.

Quantum Peptides supplies lyophilised research peptides for in-vitro and preclinical laboratory research only. Products are not for human or veterinary use. This guide describes laboratory preparation and is not guidance on administration of any kind.