Quick answer
Reconstituting a peptide means adding a measured volume of sterile liquid to freeze-dried powder so it dissolves into a solution of known strength. Swab both stoppers, draw your solvent with a mL-marked syringe, let it run slowly down the inside wall of the peptide vial, swirl until clear, then label and refrigerate. The volume you add only sets the concentration — divide the mg in the vial by the mL you added.
Choosing a solvent
This is the decision that matters most. If the product sheet or CoA names a solvent, use it. If not, start with water and only move down this table when a peptide truly won't dissolve.
| Solution | Preservative | Approx. pH | Best for | Once mixed (2–8 °C) |
|---|---|---|---|---|
| Bacteriostatic water | 0.9% benzyl alcohol | ~4.5–7 | Most water-soluble peptides drawn from more than once | Up to ~28 days |
| Sterile water | None | ~7 | Single-use preps; peptides that react with benzyl alcohol | 24–72 hours |
| Sterile saline (0.9% NaCl) | None (unless bacteriostatic) | ~5.5 | Peptides the supplier specifies for saline | Short, like sterile water |
| Dilute acetic acid (0.6%) | None | ~3 | Basic peptides that stay cloudy or gel in water | Per product sheet |
| DMSO | None | — | Hydrophobic peptides that resist water entirely | Freeze in aliquots |
| Dilute ammonium bicarbonate | None | ~8 | Acidic peptides that resist water and acid | Per product sheet |
When water isn't enough
A peptide's net charge decides what dissolves it. Basic (positively charged) peptides often need a mildly acidic solvent; acidic ones may need a mildly basic one; very hydrophobic ones need a small amount of organic solvent. GHK-Cu is the common example in practice — some batches stay cloudy in plain water and clear up in dilute acetic acid.
Adding more water won't fix a pH problem. For acid, base, or DMSO, dissolve the powder completely in a small volume first, then bring it up to your final volume with water or buffer.
Supplies
Use two different syringes: one to move solvent into the vial, and a finer one to measure from it afterward. Keeping them separate makes both jobs more accurate and spares the rubber stopper.
3 mL reconstitution syringes
Marked in 0.1 mL steps, so 1, 2, or 3 mL of solvent reads cleanly.
- Barrel
- 3 mL
- Gauge
- 18–23 G (blunt fill tip is easiest on stoppers)
U-100 insulin syringes
Fine unit markings for drawing precise small volumes from the finished vial.
- Barrel
- 0.3, 0.5, or 1 mL
- Gauge
- 29–31 G
- Your peptide vial, at room temperature (15–20 min out of the fridge)
- Sterile solvent, sealed and in date
- Alcohol prep pads, 70% isopropyl
- Nitrile gloves and a wiped-down surface
- Labels and a fine-tip marker
- Sharps container for every used needle
Syringes & units
Mixing syringes read in mL. Insulin syringes read in units. On a U-100 insulin syringe, 100 units = 1 mL, so each unit is 0.01 mL.
Mixing syringe
Moves solvent into the vial.
- 0.1 mL markings
- Used once per vial
Insulin, full size
For volumes over ~10 units.
- Each tick = 2 units
- Single units hard to read
Insulin, small
Most precise for small volumes.
- Each tick = 1 unit
- 0.5 mL / 50 u sits between
Step by step
Same sequence every time. Most problems come from rushing, skipping prep, or not labeling.
Do the math first
Decide your solvent volume and write down four numbers: mg in the vial, mL of solvent, resulting concentration, and the volume you'll measure out later. Check mg vs mcg now.
Set up a clean space
Wipe the surface with alcohol and let it dry. Wash hands, glove up, and lay out every supply before opening anything. Stay away from fans and vents.
Pop the caps and swab
Flip off only the plastic caps. Wipe each rubber stopper with a fresh pad and let it air-dry.Leave the metal crimp ring on — it's what holds the stopper in place.
Draw the solvent
Pull the mixing syringe back to your volume, push that air into the solvent vial, invert, and draw. Tap bubbles to the top, push them out, and check the line at eye level.
Aim for the glass
Insert the needle into the peptide vial and angle the tip toward the inside wall, not the powder.
Add it slowly
Press the plunger gently so the liquid trickles down the wall. If the vial pulls liquid in on its own, it was sealed under vacuum — that's normal.
Vent the pressure
Adding liquid can pressurize the vial and make later draws jumpy. Before withdrawing the mixing syringe, briefly insert a second sterile needle to release air, then remove it first.Optional, but it makes every later draw smoother.
Swirl, never shake
Roll the vial gently between your palms. Most peptides dissolve within a few minutes; if not, rest it in the fridge 15–30 minutes and swirl again. It should end up clear.
Label and refrigerate
Peptide, total mg, solvent, volume added, concentration, date mixed, and discard date. Store upright at 2–8 °C, away from light.
The math
Three formulas cover it. The solvent type doesn't change any of them — and if you dissolve in a little acid or DMSO before diluting, use the total final volume.
× 1,000 = mcg/mL
Example: 10 mg vial, 2 mL of solvent
- 10 ÷ 2 = 5 mg/mL (5,000 mcg/mL)
- To measure 500 mcg: 500 ÷ 5,000 = 0.1 mL
- 0.1 × 100 = 10 units
Example: 60 mg vial, 3 mL of solvent
- 60 ÷ 3 = 20 mg/mL
- To measure 2 mg: 2 ÷ 20 = 0.1 mL
- 0.1 × 100 = 10 units
Small amounts? Add more solvent, not less
It feels backwards, but a more dilute vial is easier to measure accurately. The same amount of peptide takes up more of the syringe, so a one-tick misread matters less.
Rule of thumb: if your measurement lands under 5 units, add more solvent next time.
Vial-size reference
| Vial | Solvent | mg/mL | mcg/mL | Per 1 unit | Per 10 units (0.1 mL) |
|---|---|---|---|---|---|
| 5 mg | 1 mL | 5 | 5,000 | 50 mcg | 500 mcg |
| 5 mg | 2 mL | 2.5 | 2,500 | 25 mcg | 250 mcg |
| 5 mg | 3 mL | 1.67 | 1,667 | 16.7 mcg | 167 mcg |
| 10 mg | 2 mL | 5 | 5,000 | 50 mcg | 500 mcg |
| 10 mg | 3 mL | 3.33 | 3,333 | 33.3 mcg | 333 mcg |
| 20 mg | 2 mL | 10 | 10,000 | 100 mcg | 1,000 mcg |
| 20 mg | 3 mL | 6.67 | 6,667 | 66.7 mcg | 667 mcg |
| 30 mg | 3 mL | 10 | 10,000 | 100 mcg | 1,000 mcg |
| 60 mg | 3 mL | 20 | 20,000 | 200 mcg | 2,000 mcg |
| 100 mg | 5 mL | 20 | 20,000 | 200 mcg | 2,000 mcg |
Common mistakes
Spraying solvent onto the powder. A hard stream stresses the peptide. Run it down the glass.
Shaking. Foam and shear can break peptide chains even when the vial looks fine afterward.
Non-sterile water. Tap, bottled, and distilled water are never acceptable.
Swabbing only the first time. Every puncture is a contamination chance — swab before each one.
Reusing needles. Especially between vials, where contamination spreads fastest.
Mixing up mg, mcg, and mL. Write the unit next to every number.
Skipping the label. An unlabeled vial has an unknown concentration.
Using old bacteriostatic water. Discard an opened vial 28 days after first puncture.
Storage
Peptides are most stable dry. Only reconstitute the vial you're about to use.
| What | Where | How long |
|---|---|---|
| Lyophilized, sealed | Freezer, −20 °C | A year or more |
| Lyophilized, sealed | Fridge, 2–8 °C | Several months |
| Reconstituted in BAC water | Fridge, 2–8 °C | Up to ~28 days |
| Reconstituted in sterile water or saline | Fridge, 2–8 °C | 24–72 hours after first puncture |
| Bacteriostatic water, opened | Room temp or fridge | 28 days after first puncture |
| Bacteriostatic water, sealed | Room temp | Until printed expiry |
Keep vials upright, in the box or an opaque case, and away from light. Avoid freezing a reconstituted vial — ice crystals and freeze–thaw cycles damage peptides. If you must store long-term, split into single-use aliquots and freeze once. Don't pre-load syringes to use later; draw from the vial when you need it.
Storage cases, desiccant packs, and transport gear are in the supplies checklist.
Troubleshooting
The powder won't dissolve
Give it time: rest in the fridge 15–30 minutes and swirl again. If powder persists, the peptide likely needs a different solvent (see Choosing a solvent). Don't force it by shaking or warming.
The solution is cloudy or gel-like
Usually rough handling or the wrong solvent — sometimes a quality issue. Let it rest 30 minutes. If it's still cloudy, don't use it and contact your supplier.
There's foam on top
The solvent went in too fast or the vial was shaken. Let it settle 10–15 minutes. A few small bubbles are normal; dense, lasting foam is a warning sign.
I sprayed solvent right onto the powder
If the finished solution is clear and colorless, it may still be fine. If it turns cloudy, replace it. Angle toward the glass next time.
Drawing from the vial is difficult or jumpy
The vial is pressurized. Vent it briefly with a sterile needle, or match air in/out when you draw.
I see particles or a color change
Treat it as degraded or contaminated and discard it. The exception: a blue tint is normal for GHK-Cu, a copper complex.
FAQ
What liquid do you use to reconstitute peptides?
Bacteriostatic water for most peptides. Sterile water for single-use preps, saline when the supplier specifies it, dilute acetic acid for basic peptides that resist water, and minimal DMSO for hydrophobic ones. The product sheet always wins.
How much water do I add?
There's no single right amount — volume only sets concentration. Pick a volume (usually 1–3 mL) that makes the amounts you'll measure easy to read.
How many units are in 1 mL?
On a U-100 insulin syringe, 100. So 10 units is 0.1 mL and 1 unit is 0.01 mL.
Do I need two different syringes?
It's best practice: a 3 mL syringe to add solvent, and a fresh U-100 insulin syringe each time you measure from the vial.
Do I remove the metal cap?
No. Remove only the plastic flip-off cap. The aluminum crimp ring holds the stopper to the vial.
Can I shake the vial?
No. Swirl or roll it gently. Shaking can damage the peptide even if the solution still looks clear.
How long does a reconstituted peptide last?
Up to about 28 days refrigerated in bacteriostatic water; 24–72 hours in sterile water or saline. Discard sooner if clarity or color changes.
Is reconstitution the same as dilution?
Not quite. Reconstitution turns powder into a solution; dilution adds more solvent to a solution that already exists.