How to Reconstitute Peptides
Most research peptides ship as a freeze-dried (lyophilized) powder. Before they can be measured or administered, they need to be dissolved into a sterile liquid — a process called reconstitution. This guide walks through the math, the materials, and the technique step by step.
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What you'll need
- Lyophilized peptide vial
- Bacteriostatic water (0.9% benzyl alcohol)
- Insulin syringe, U-100 (1 mL)
- Alcohol prep pads
Step 1 — Do the dosing math
The math is simple: the volume of bacteriostatic water you add determines how many units on an insulin syringe equal one dose. A U-100 syringe has 100 units per 1 mL.
Reconstitution Calculator
Enter your vial size, the bacteriostatic water you'll add, and the dose you want — get the exact units on a U-100 insulin syringe.
Educational tool only. Values assume a standard U-100 insulin syringe (100 units = 1 mL). Always verify dosing with a qualified clinician.
Dilution quick-reference
Units shown are marks on a U-100 insulin syringe (100 units = 1 mL).
| Vial size | Water added | Dose | Units on syringe |
|---|---|---|---|
| 5 mg | 2 mL | 250 mcg | 10 units |
| 5 mg | 2 mL | 500 mcg | 20 units |
| 5 mg | 1 mL | 250 mcg | 5 units |
| 10 mg | 2 mL | 500 mcg | 10 units |
| 10 mg | 3 mL | 500 mcg | 15 units |
| 2 mg | 1 mL | 200 mcg | 10 units |
Step-by-step procedure, illustrated
Sanitize the vials
Wipe the rubber stoppers of both the peptide vial and the bacteriostatic water vial with an alcohol prep pad. Let them air-dry for a few seconds.
Draw the bacteriostatic water
Pull the calculated volume of bacteriostatic water into the insulin syringe. Tap out any large air bubbles.
Add water to the peptide — slowly
Insert the needle into the peptide vial and angle the tip so the water runs down the inside wall of the glass. Never inject water directly onto the powder — the force can denature the peptide.
Swirl, do not shake
Gently roll the vial between your palms until the powder fully dissolves into a clear solution. Shaking introduces foam and can damage the molecule.
Inspect
The reconstituted solution should be clear. Cloudiness, particles, or discoloration mean the vial should not be used.
Refrigerate
Store the reconstituted vial at 2–8°C (standard fridge). Most reconstituted peptides are stable for 2–4 weeks; check the specific peptide's stability data.
Storage at a glance
Common mistakes to avoid
- • Using sterile water or saline instead of bacteriostatic water for multi-use vials.
- • Shaking the vial — this can fragment the peptide.
- • Injecting the diluent directly onto the powder pellet.
- • Storing reconstituted peptides at room temperature.
- • Skipping the dosing math and guessing volumes on the syringe.
Frequently asked questions
How much bacteriostatic water should I add to a vial?
There is no single correct volume — the amount of water only changes the concentration, not the total peptide. Researchers commonly choose 1–3 mL so that a typical dose lands on an easy-to-read mark (5–20 units) on a U-100 insulin syringe.
Can I use sterile water instead of bacteriostatic water?
Sterile water contains no preservative, so a vial reconstituted with it is generally treated as single-use. Bacteriostatic water contains 0.9% benzyl alcohol, which is why multi-dose vials in the research literature typically use it.
Why can't the vial be shaken?
Shaking creates shear forces and foam at the air-liquid interface, which can unfold or aggregate the peptide chain. Slow rolling or swirling dissolves the powder without that stress.
How long does a reconstituted peptide last?
Most reconstituted research peptides are reported as stable for roughly 2–4 weeks refrigerated at 2–8°C, though stability is peptide-specific. Unmixed lyophilized powder stored at -20°C keeps far longer.
What does cloudy solution mean?
Cloudiness, visible particles, or color change suggest aggregation or contamination. A vial in that state is not used for research purposes.
How do I convert a dose in mcg to syringe units?
Units per dose = (dose in mcg ÷ total mcg in the vial) × (mL of water added × 100). A 5 mg vial with 2 mL of water gives 10 units for a 250 mcg dose.
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