What does "reconstitute" mean?

It means adding a liquid (the diluent) to a freeze-dried peptide powder so it becomes a solution of known strength that can be measured in the lab.

Bacteriostatic water or sterile water?

Bacteriostatic water contains a preservative and is meant for containers that will be entered more than once. Sterile water has no preservative and is single-use. Check the supplier's sheet, because some peptides call for a different solvent.

Should I shake the vial?

No. Let the liquid run down the inside wall, then swirl gently or let it sit. Shaking can foam the solution and stress the peptide.

How do I work out the concentration?

Divide the peptide mass by the volume of diluent. A 5 mg vial plus 2 mL of diluent gives 2.5 mg/mL, which is 250 mcg in every 0.1 mL.

Is this a guide for personal use?

No. This is bench handling for research materials. Research peptides are for research use only and are not for human consumption.

Research guide

How to Reconstitute Research Peptides, Step by Step

Quick answers

What does "reconstitute" mean?: It means adding a liquid (the diluent) to a freeze-dried peptide powder so it becomes a solution of known strength that can be measured in the lab.
Bacteriostatic water or sterile water?: Bacteriostatic water contains a preservative and is meant for containers that will be entered more than once. Sterile water has no preservative and is single-use. Check the supplier's sheet, because some peptides call for a different solvent.
Should I shake the vial?: No. Let the liquid run down the inside wall, then swirl gently or let it sit. Shaking can foam the solution and stress the peptide.
How do I work out the concentration?: Divide the peptide mass by the volume of diluent. A 5 mg vial plus 2 mL of diluent gives 2.5 mg/mL, which is 250 mcg in every 0.1 mL.
Is this a guide for personal use?: No. This is bench handling for research materials. Research peptides are for research use only and are not for human consumption.

Most research peptides arrive as a dry, white "cake" or powder at the bottom of a sealed vial. That form is called lyophilized, or freeze-dried. It travels and stores better than a liquid. Before the material can be measured out for an experiment, it has to be turned back into a solution. That step is reconstitution.

Done well, reconstitution gives you a solution of known concentration and keeps the peptide intact. Done carelessly, it can introduce contamination, damage the peptide, or leave you guessing at how much material is in each measured volume. This page walks through the bench steps in order. It is written for laboratory handling only. Nothing here is guidance for human use.

Before you start

Read the supplier's documents first

Every peptide is a different sequence, and sequences behave differently in water. Some dissolve easily. Some need a small amount of a weak acid, a weak base, or an organic co-solvent first. The supplier's storage or handling sheet, and the certificate of analysis, should tell you the net peptide content, the recommended solvent, and the storage temperature. If they do not, that is worth noting about the supplier.

Pick the right diluent

Two diluents come up most often:

Bacteriostatic water. Sterile water with 0.9% benzyl alcohol added as a preservative. The preservative slows bacterial growth, which is why it is used when a container will be entered more than once. See Bacteriostatic Water: What It Is and How It's Used in the Lab.
Sterile water. Water with no preservative. Once opened, it is treated as single-use.

Neither is "better" in general. The right choice depends on the peptide, the protocol, and how many times the vial will be entered. Follow the supplier sheet and your lab's standard procedure.

Gather clean supplies

You will want the peptide vial, the diluent, sterile single-use syringes or calibrated pipettes, alcohol swabs, gloves, a clean work surface, and a label. Many labs do this step in a biosafety cabinet or laminar flow hood. At minimum, work on a surface wiped down with alcohol, away from drafts.

Step by step

Let the vial reach room temperature. If the vial was in the freezer or fridge, let it sit sealed until it warms. Opening a cold vial can pull moisture from the air onto the powder.
Check the cake. Look for an intact, dry powder. A collapsed, sticky, or discolored cake is worth recording before you go further.
Wipe the stoppers. Swab the rubber tops of both the peptide vial and the diluent vial with alcohol. Let them air-dry. Do not blow on them.
Draw the diluent. Using a fresh sterile syringe or pipette, measure the exact volume you planned. Accuracy here sets the accuracy of every later measurement.
Add it slowly, down the wall. Angle the tip so the liquid runs down the inside glass wall of the peptide vial. Do not squirt it straight onto the powder. A hard stream can foam the solution and shear the peptide.
Do not shake. Swirl gently or roll the vial between your fingers. Then let it sit. Many peptides dissolve fully within a few minutes. Some take longer.
Inspect the solution. It should be clear, with no visible particles or cloudiness unless the supplier says otherwise. If it stays cloudy, stop and check the supplier's solvent guidance rather than forcing it.
Label it immediately. Write the compound name, lot number, concentration, diluent used, date and time of reconstitution, and your initials.
Store it as directed. Most reconstituted peptides go in the fridge, protected from light. See How Long Do Reconstituted Peptides Last in the Fridge?

The concentration math, worked through

The math is simple division. Concentration equals mass divided by volume.

Example. You have a vial labeled 5 mg of peptide. You add 2.0 mL of diluent.

5 mg ÷ 2.0 mL = 2.5 mg/mL
1 mg = 1,000 mcg, so 2.5 mg/mL = 2,500 mcg/mL
0.1 mL is one-tenth of a mL, so each 0.1 mL holds 2,500 ÷ 10 = 250 mcg

Change one number and the rest follow. If you add 1.0 mL to the same 5 mg vial, you get 5 mg/mL, or 500 mcg per 0.1 mL. Adding 2.5 mL gives 2 mg/mL, or 200 mcg per 0.1 mL. More diluent means a weaker solution, and each measured volume holds less peptide.

Two cautions. First, the label mass is often the gross weight of the powder, not pure peptide. Salts and water are part of it. The COA's net peptide content tells you how much is actually the peptide. Second, a math error here carries through every later step. Write the calculation on the label or in your notebook so someone else can check it.

If you want to check your numbers, our peptide reconstitution calculator runs the same division for you.

Common mistakes

Reusing a syringe or tip. Each entry into a vial with a used tool is a contamination risk.
Forgetting the label. An unlabeled clear liquid is unusable data.
Guessing the volume. Use a calibrated tool, not a rough fill line.
Freezing and thawing over and over. If a protocol needs long storage, many labs split the solution into small single-use portions (aliquots) instead.
Ignoring a bad cake or cloudy solution. Record it and check with the supplier.

What this page does not cover

This page is about getting a research material into solution accurately, not about whether a peptide works or is safe in people. For what the "research use only" label means, read What Are Research Peptides? and What Does "Research Use Only" Actually Mean?

Sources

Manning MC, Chou DK, Murphy BM, et al. Stability of protein pharmaceuticals: an update. Pharm Res. 2010;27(4):544-75. PubMed 20143256 · DOI
Rathore N, Rajan RS. Current perspectives on stability of protein drug products during formulation, fill and finish operations. Biotechnol Prog. 2008;24(3):504-14. PubMed 18484778 · DOI

Peptide Proof reports what studies found. Research peptides are for research use only and are not for human consumption. Nothing on this page is medical advice, dosing guidance or a treatment recommendation.

Where to buy: researchers who want materials with a certificate of analysis can see our sourcing partner, Trynx Research.