Reconstitution is the step where a lyophilised research peptide becomes a solution of known concentration. The chemistry is trivial; the arithmetic is where people go wrong, because three different units are in play at once – milligrams in the vial, millilitres of solvent, and the volume markings on a syringe.
This guide covers the method and the maths. Our free peptide calculator does the arithmetic for any combination if you would rather not do it by hand.
What you need
- The lyophilised vial, at room temperature. Cold glass attracts condensation.
- Bacteriostatic water – not sterile water, for reasons covered below.
- A syringe for transferring solvent, and insulin syringes for measuring afterwards.
- Alcohol prep pads for the stoppers.
The method
- Let the vial reach room temperature. Reconstituting straight from a freezer pulls moisture onto cold glass and into the powder.
- Wipe both stoppers – the peptide vial and the solvent vial – with alcohol and let them dry.
- Draw your solvent volume into the transfer syringe.
- Add it slowly, against the inside wall of the vial. Never fire the stream directly onto the powder cake. A lyophilised cake is fragile and mechanical force damages peptide structure.
- Let it sit. Most peptides dissolve on their own within a minute or two. If material remains, swirl gently or roll the vial between your palms.
- Never shake. Foaming is visible denaturation – the peptide is coming apart at the air-liquid interface.
- Refrigerate at 2–8 °C once dissolved, protected from light.
The arithmetic
Everything follows from one relationship:
Concentration (mg/ml) = peptide in the vial (mg) ÷ bacteriostatic water added (ml)
A 10 mg vial reconstituted with 2 ml gives 5 mg/ml. The same vial with 1 ml gives 10 mg/ml. Nothing about the peptide changed – only the dilution.
To find the volume for a given amount:
Volume (ml) = amount wanted (mg) ÷ concentration (mg/ml)
And to convert that to syringe units:
Units = volume (ml) × 100
Why every insulin syringe uses the same scale
This is the single most common misunderstanding. U-30, U-50 and U-100 syringes are all graduated at 100 units per millilitre. The number describes total capacity, not scale – a U-30 holds 0.3 ml, a U-50 holds 0.5 ml, a U-100 holds 1 ml.
So 20 units is 0.2 ml on any of them. What changes is whether the volume fits in a single draw.
Common vial and solvent combinations
| Vial | Water added | Concentration | 1 unit equals |
|---|---|---|---|
| 5 mg | 2 ml | 2.5 mg/ml | 25 mcg |
| 10 mg | 1 ml | 10 mg/ml | 100 mcg |
| 10 mg | 2 ml | 5 mg/ml | 50 mcg |
| 10 mg | 3 ml | 3.33 mg/ml | 33.3 mcg |
| 15 mg | 3 ml | 5 mg/ml | 50 mcg |
| 30 mg | 3 ml | 10 mg/ml | 100 mcg |
| 50 mg | 5 ml | 10 mg/ml | 100 mcg |
| 100 mg | 5 ml | 20 mg/ml | 200 mcg |
Choosing how much solvent to add
More solvent gives finer resolution on the syringe and less measurement error, at the cost of using more volume per draw. Less solvent concentrates the solution, which stores more compactly but makes small measurements imprecise.
A practical target is a dilution where a typical measurement lands between 10 and 50 units. Below about 5 units the graduations are too coarse to read accurately; above the syringe capacity you need multiple draws. The calculator flags both cases automatically.
Bacteriostatic water vs sterile water
Bacteriostatic water contains 0.9% benzyl alcohol, a preservative that suppresses bacterial growth and allows a vial to be entered repeatedly over a period of weeks.
Sterile water contains no preservative. It is intended for a single use, and once the seal is broken there is nothing inhibiting contamination.
For any vial that will be accessed more than once, bacteriostatic water is the correct solvent. This is not a matter of preference.
Storage
| Lyophilised powder, sealed | −20 °C, protected from light. Stable for the period stated on the certificate. |
|---|---|
| Reconstituted solution | 2–8 °C, protected from light. Materially shorter usable life than the dry powder. |
| In transit | Lyophilised powder is stable at ambient temperature – no cold chain required. |
Avoid repeated freeze–thaw cycles of reconstituted material. Each cycle degrades a fraction of the peptide, and the losses compound.
Things that go wrong
The powder will not dissolve
Give it time before intervening – many peptides take a minute or two. Gentle warmth from your hands helps. Persistent cloudiness after several minutes can indicate the wrong solvent, or material that has been compromised.
The solution foamed
Foaming means the peptide has been agitated at the air-liquid interface, which denatures it. It cannot be undone. Add solvent down the vial wall and swirl rather than shake.
The vial lost vacuum when I added solvent
Normal. A lyophilised vial is under partial vacuum, which is why solvent draws itself in. A vial with no vacuum at all may have lost its seal.
My measurement is under 5 units
Too small to read accurately. Reconstitute with more solvent to bring it into a readable range – the calculator shows what dilution achieves that.
For laboratory research use only. This page describes the handling and concentration arithmetic of research materials. It is not medical guidance, contains no recommendation of any quantity for use in humans or animals, and nothing sold by Cytera Peptides is approved for such use.