What I have: 30 mg · 2 mL · sterile water for injection.
I can do the algebra. I am not confident about the conversion factors.
If there is a standard way to lay this out, I would rather learn that than invent one.
What is the general form of this calculation?
30 ÷ 2 = 15 mg/mL. Concentration is vial content divided by diluent volume, so 30 mg of peptide in 2 mL of sterile water for injection gives 15 mg/mL. On a U-100 barrel one unit is 0.01 mL, so one unit of this solution carries 0.15 mg — 150 µg. That is the number to write on the label, because you will not reconstruct it from memory at an awkward moment.
Add the diluent down the vial wall rather than directly onto the cake. Peptides are surface-active and shear at an air–liquid interface, so a jet of water into a lyophilised puck generates foam, and foam is aggregated protein at the interface, not just air.
The order of operations matters: temperature first, then diluent measurement, then injection, then gentle dissolution, then labeling.
| Configuration | Dead volume | Loss at 5 mg/mL | Over 20 draws |
|---|---|---|---|
| Fixed-needle insulin syringe | 3–5 µL | 15–25 µg | 0.3–0.5 mg |
| Low-dead-space, detachable | <2 µL | <10 µg | <0.2 mg |
| Standard luer-lock + 30G | 35–60 µL | 175–300 µg | 3.5–6 mg |
| Luer-lock + 21G drawing needle | 70–100 µL | 350–500 µg | 7–10 mg |
On the detail: photograph the vial against a matte black card with a single point light source off to one side, not with a flash from the front.
The caveat on all of this is that it assumes the vial contains what the label says.
The practical summary: fine gauge, gentle swirl, diluent down the wall, room temperature before drawing, and check the syringe scale.
edited 7 Feb 2026 by rota_site — removed a claim I could not source
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