How to reconstitute lyophilized peptides

Lyophilized peptides arrive as a dry powder or cake. Reconstituting means dissolving it in a suitable solvent so it can be measured as a solution. The right solvent and handling depend on the peptide, so start with its documentation.

Before you start: check the solvent

There is no single solvent that suits every peptide. Solubility depends on the sequence: basic peptides often dissolve best with a small amount of dilute acid before dilution, acidic ones with a small amount of dilute base, and very hydrophobic sequences may need an organic co-solvent. Manufacturers recommend checking the product's documentation or certificate of analysis for solubility first, and testing on a small portion when it's unknown [1][2].

Bacteriostatic water (sterile water with benzyl alcohol) and sterile water are common aqueous diluents. Benzyl alcohol isn't compatible with every compound, so it isn't the right choice for every peptide [3]. See bacteriostatic water vs sterile water.

Technique

1. Let the vial reach room temperature before opening. Peptides are hygroscopic; opening a cold vial lets moisture condense on the powder, which lowers the actual peptide content and can reduce stability [1][2].
2. Work clean. Swab the stoppers of the peptide and diluent vials with alcohol and let them dry. Use a sterile pipette or syringe to transfer the diluent.
3. Decide the volume first. More solvent means a lower concentration. The reconstitution calculator shows the result before you add anything.
4. Add the solvent slowly down the inside wall of the vial rather than directly onto the powder.
5. Swirl or roll gently. Avoid vigorous shaking, which can foam the solution; foaming at air–liquid interfaces can denature or aggregate some peptides.
6. Inspect the solution. It should be clear. Persistent cloudiness or particles suggest incomplete dissolution or the wrong solvent for that sequence [2].
7. Label it with the compound, lot number, concentration, solvent, date and your initials.
8. Store it correctly, or better, aliquot it. Peptides are generally less stable in solution than as powder [1][2]. See how to store peptides.

The math

Concentration = peptide mass ÷ solvent volume. A 10 mg vial with 2 mL is 5 mg/mL (5,000 mcg/mL). Volume for a given mass = mass ÷ concentration: 250 mcg ÷ 5,000 mcg/mL = 0.05 mL.

One caution: the mass on a label is the weighed powder, which includes water and counterions as well as peptide. For quantitative work, the net peptide content on a full COA gives the true peptide fraction [4]. See how to read a peptide COA.

Questions

Should you shake a peptide vial when reconstituting?

Gentle swirling or rolling is the usual technique. Vigorous shaking can foam the solution, which can damage some peptides.

What solvent do you use to reconstitute peptides?

It depends on the peptide's sequence. Aqueous diluents such as bacteriostatic or sterile water are common, but some peptides need dilute acid, dilute base or an organic co-solvent. Check the product documentation or COA for solubility first.

Why let the vial warm up before opening?

Peptides absorb moisture. Opening a cold vial lets water condense on the powder, which lowers peptide content and can reduce stability.