The question we receive most often is not about the compound but about the solvent: how many millilitres of bacteriostatic water go into the vial? There is no single right answer. The volume sets the concentration, and the concentration decides whether the volume you later draw per sample is comfortable to measure on a syringe. This guide shows how to choose it.
The arithmetic
Three numbers are involved: the peptide amount in the vial (mg), the solvent volume (mL) and the amount you want per sample (µg). Divide the first by the second and you have the concentration in mg/mL. Divide the amount per sample by the concentration and you have the volume per sample. On a U-100 insulin syringe one unit is 0.01 mL, so multiply the volume in mL by 100 to get units.
Example: 10 mg in 2 mL gives 5 mg/mL. A 250 µg sample is 0.25 mg, which at 5 mg/mL is 0.05 mL, or 5 units. Our peptide calculator does this for any combination.
What makes a volume comfortable
Very small volumes are hard to measure. Below 2 units the error of a syringe becomes a large fraction of the sample. Very large volumes have the opposite problem: a 3 mL vial does not take 5 mL of solvent, and large draws are slow. A practical range is 5 to 50 units per sample. If your result falls outside it, change the solvent volume, not the sample.
Typical volumes by vial size
| Vial | Solvent | Concentration | 250 µg sample |
|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 5 units |
| 10 mg | 2 mL | 5 mg/mL | 5 units |
| 10 mg | 1 mL | 10 mg/mL | 2.5 units |
| 50 mg | 2 mL | 25 mg/mL | 1 unit (too small, use larger samples or more solvent) |
High-amount vials such as 50 mg GHK-Cu or 100 mg Epitalon are usually reconstituted at higher concentration and drawn in larger samples, or partly reconstituted in a second vial. Both options are legitimate as long as the record states what was done.
Vial capacity
Most 2 mL and 3 mL glass vials in the research market hold the labelled volume plus a small headspace. Adding more than about 3 mL to a small vial can exceed the volume. If you need a lower concentration, dilute a measured portion in a second sterile vial rather than overfilling the first.
Technique
Add the solvent slowly along the inside wall so that it runs down onto the powder, then let the vial stand. Lyophilised peptides dissolve on their own within a minute or two; swirling is fine, shaking is not. Air bubbles and foam indicate mechanical stress that can affect the peptide. Keep the reconstituted vial refrigerated at 2 to 8 °C and note the date on the label.
For laboratory research use only. This guide describes unit conversion and handling for laboratory work. It is not dosing or medical advice.