How to Reconstitute Peptides: Lab Steps, Solvents and Water Volumes

Key facts

Let the sealed vial reach room temperature before opening: peptides are hygroscopic, and absorbed moisture lowers peptide content and stability.^[1]
Collect the powder at the bottom by briefly centrifuging or tapping the vial, then add the solvent down the inside wall rather than onto the powder, to avoid foaming.^[6]^[9]
Mix with gentle agitation, not vigorous shaking, which can cause foaming and denaturation.^[6]
Sterile water or a pH 7 buffer is the default solvent; very hydrophobic peptides may need a small amount of DMSO first.^[4]
The volume of water only sets the concentration: a 10 mg vial with 2 mL gives 5 mg/mL. Work out any vial with the peptide calculator.

How to Reconstitute Peptides

A lab reconstitutes a lyophilised peptide in six steps: bring the vial to room temperature, collect the powder at the bottom, choose a solvent, add it slowly down the vial wall, mix gently without shaking, and check the solution is clear.^[1]^[6]^[9]

1. Equilibrate the vial. Let the closed vial reach room temperature, ideally in a desiccator, before opening it. Peptides are hygroscopic, and moisture from the air lowers the peptide content and may reduce stability.^[1]^[4]
2. Collect the powder. Briefly centrifuge or tap the vial so all the lyophilised material sits at the bottom.^[6]
3. Choose the solvent. Start with sterile water or a buffer such as PBS at pH 7, and test solubility on a small amount first if the peptide is new to you.^[4]^[3]
4. Add the solvent slowly down the wall. Run the liquid down the inside wall of the vial instead of directly onto the powder, to avoid foaming.^[9]
5. Swirl or roll, don’t shake. Use gentle agitation; vigorous shaking can cause foaming and denaturation. R&D Systems allows 15 to 30 minutes at room temperature for proteins, and Bachem notes that peptides can occasionally take several hours to dissolve.^[6]^[1]
6. Check it is clear. A solution that has gelled, looks cloudy or shows particles is suspended, not dissolved. The FDA label for one lyophilised peptide, tesamorelin (Egrifta SV), says to use it only if the solution is clear, colourless and free of particles.^[3]^[9]

Wear gloves to avoid enzymatic or bacterial contamination, weigh out powder quickly and reseal the container tightly.^[4]^[1] Thermo Fisher notes that peptides should be handled only by, or under the direct supervision of, a technically qualified person.^[4]

What Is a Lyophilized Peptide?

A lyophilised peptide is one that has been freeze-dried: frozen, then placed under vacuum so the ice turns straight to vapour, in three stages of freezing, primary drying (sublimation) and secondary drying (desorption).^[10]

Products are made in lyophilised form because they are unstable in solution. The FDA lists the advantages as a more stable dry powder, water removal without excessive heating, and rapid, easy dissolution on reconstitution; the trade-off is the need for a sterile diluent.^[10] Freeze-drying is the most common way to make solid protein pharmaceuticals, though the freezing and drying steps themselves create stresses that can damage proteins.^[11]

Storage guidance for lyophilised peptide powder, as stated by each manufacturer.
Manufacturer	Lyophilised powder	Peptide in solution
Bachem	Below -15 °C in a tightly closed container; -50 °C or lower for long-term storage; 4 °C for short-term use^[1]	Not recommended for storage; aliquot and freeze below -15 °C^[1]
Thermo Fisher	-20 °C on receipt, where peptides may stay stable for several years^[4]	Use immediately; avoid repeated freezing and thawing^[4]
GenScript	-20 °C^[5]	Aliquot into tubes and store at -80 °C^[5]

Which Solvent to Use

Sterile water or a pH 7 buffer (PBS, Tris or phosphate) is the first-choice solvent for most peptides, with dilute acid for basic peptides and a small volume of DMSO for very hydrophobic ones.^[4]^[2]

Solvent choices as the manufacturer guides describe them. The right solvent depends on the peptide’s sequence.
Solvent	When the guides use it	Notes
Sterile water	First try for most peptides; GenScript says peptides under 6 amino acids usually dissolve in pure water^[5]	Contains no bacteriostat or preservative; supplied in single-dose containers only^[8]
Bacteriostatic water	Supplied in a multiple-dose container from which repeated withdrawals may be made^[7]	Water with 0.9% (9 mg/mL) benzyl alcohol as a preservative; pH 5.7 (4.5 to 7.0)^[7]
PBS, pH 7.0 to 7.4	Safest diluent for acidic or basic peptides when 1 mg/mL or less is enough^[2]	Thermo Fisher also lists Tris or phosphate buffer at pH 7^[4]
Dilute acetic acid	Basic (net positive) peptides that do not dissolve in water^[5]	GenScript uses 10% to 30% acetic acid, Sigma-Aldrich a small amount of 25% acetic acid, then dilution with water^[5]^[3]
Dilute ammonia or ammonium bicarbonate	Acidic (net negative) peptides^[2]^[3]	GenScript says not to use NH4OH if the peptide contains Cys^[5]
DMSO (or DMF, acetonitrile)	Neutral or highly hydrophobic peptides^[2]^[3]	Dissolve in the smallest volume, then add water or buffer to the target concentration^[4]

Work out the charge first. Count acidic residues (D, E, C-terminal COOH) as -1 and basic residues (K, R, N-terminal NH2) as +1; a net negative peptide is acidic, net positive is basic, zero is neutral.^[3]^[5]
Dissolve fully in the first solvent, then dilute. Add the concentrated peptide solution dropwise into the buffer with gentle, constant agitation to avoid local precipitation.^[3]
Mind the assay. High concentrations of organic solvents are incompatible with biological systems such as cells.^[2] GenScript suggests a stock of about 1 to 2 mg/mL so only small volumes go into an assay.^[5]
Protect oxidation-prone residues. Peptides with Cys, Met or Trp need oxygen-free water or buffer.^[4]^[2]

How Much Water to Add

There is no single correct volume: the water you add only sets the concentration, so 2 mL in a 10 mg vial gives 5 mg/mL and 1 mL gives 10 mg/mL.

Concentration in mg/mL is the peptide in the vial (mg) divided by the solvent added (mL). Adding more water lowers the concentration, which makes small amounts easier to measure; adding less gives a stronger stock. Labs usually pick the volume to suit the assay: GenScript suggests stocks of about 1 to 2 mg/mL, and Bachem says PBS works for many charged peptides at 1 mg/mL or less.^[5]^[2]

Concentration after reconstitution, rounded to two decimals. Vial strength is the amount of powder, not a dose.
Vial	1 mL added	2 mL added	3 mL added
5 mg	5 mg/mL	2.5 mg/mL	1.67 mg/mL
10 mg	10 mg/mL	5 mg/mL	3.33 mg/mL
20 mg	20 mg/mL	10 mg/mL	6.67 mg/mL

5 mg vial: 5 mg ÷ 2 mL = 2.5 mg/mL, so 0.1 mL of solution holds 0.25 mg.
10 mg vial: 10 mg ÷ 2 mL = 5 mg/mL, so 0.1 mL holds 0.5 mg; with 3 mL it is 3.33 mg/mL.
20 mg vial: 20 mg ÷ 2 mL = 10 mg/mL, so 0.1 mL holds 1 mg; with 3 mL it is 6.67 mg/mL.

For any other vial size or volume, and to convert mg to mL or syringe units, use the peptide reconstitution calculator.

These figures describe the concentration of a laboratory solution. They are not dosing advice, and DBR Labs products are for research use only, not for human or veterinary use.

Common Mistakes

The most common reconstitution mistake is shaking the vial: vigorous shaking can cause foaming and denaturation, so labs mix with gentle agitation instead.^[6]

Shaking or squirting onto the powder. Both cause foaming; run the solvent down the vial wall and swirl or roll gently.^[6]^[9]
Opening a cold vial. A vial opened before it reaches room temperature can pick up moisture, which lowers peptide content and may reduce stability.^[1]
Using water on a hydrophobic peptide. Peptides with mostly hydrophobic residues, or with few charged residues, need an organic solvent such as DMSO, DMF or acetonitrile first.^[3]
Putting Cys or Met peptides in DMSO. Sigma-Aldrich notes that sequences containing Cys and Met are unstable in DMSO.^[3]
Dissolving the whole vial on the first try. Test a small portion first, and prefer a solvent that can be removed by lyophilisation so the peptide can be recovered.^[3]
Overheating. Gentle warming can help, but Thermo Fisher says not to exceed 40 °C, and Bachem warns against excessive warming during sonication.^[4]^[2]
Storing the solution long term. Peptides slowly degrade in solution; aliquot, freeze and avoid repeated freeze-thaw cycles.^[1]^[4]

Eloralintide Vials

DBR Labs supplies eloralintide as a sealed lyophilised powder in 5 mg, 10 mg and 20 mg vials, for laboratory research only.

Keep sealed vials at 2 to 8 °C and away from light. Vial strength is the amount of powder in the vial, not a dose. See the vials, check concentrations with the peptide calculator, or read what eloralintide is.

This guide describes how a laboratory prepares a peptide solution. It is not dosing advice. Eloralintide is investigational and not approved for any use; DBR Labs products are for research use only and not for human or veterinary consumption.

Frequently Asked Questions

How much bacteriostatic water do I add to a 10mg peptide?

There is no single correct volume. The water only sets the concentration: 1 mL gives 10 mg/mL, 2 mL gives 5 mg/mL and 3 mL gives 3.33 mg/mL. More water means a weaker solution and larger volumes to measure. The peptide calculator works out any combination.

Should you shake a peptide vial?

No. Vigorous shaking can cause foaming and denaturation. Labs add the solvent slowly down the inside wall of the vial, then swirl or roll it gently until the powder dissolves and the solution is clear.

What is the best solvent for peptides?

There is no single best solvent; it depends on the sequence. Sterile water or a pH 7 buffer is the first try. Basic peptides may need dilute acetic acid, acidic peptides dilute ammonia, and very hydrophobic peptides a small amount of DMSO before dilution. Test a small portion first.

What does lyophilized mean?

Lyophilised means freeze-dried. The product is frozen and placed under vacuum so the ice turns straight to vapour, leaving a dry powder that is more stable than a solution and dissolves quickly when a solvent is added.

Can I use sterile water instead of bacteriostatic water?

Sterile water is a standard peptide solvent. The difference is the preservative: bacteriostatic water contains 0.9% benzyl alcohol and comes in multiple-dose vials, while sterile water has no preservative and comes in single-dose containers, with any unused portion discarded. Some compounds are incompatible with benzyl alcohol.

Why do you let a peptide vial reach room temperature before opening it?

Peptides are hygroscopic. Bachem advises letting the vial reach room temperature before opening because the powder absorbs moisture from the air, which lowers the peptide content and can reduce stability.

Sources

For research use only. Not for human or veterinary consumption. This guide summarises published research for information only. It is not medical advice and does not describe any use of products sold on this site.

How to Reconstitute Peptides: A Lab Guide to Dissolving Lyophilised Powder