Peptide Reconstitution Calculator

How reconstitution maths works

Reconstitution is a dilution problem. A vial contains a fixed mass of lyophilised (freeze-dried) peptide. Adding a known volume of bacteriostatic water produces a solution whose concentration is simply mass divided by volume:

concentration (mg/mL) = peptide mass (mg) ÷ diluent volume (mL)

A 5 mg vial reconstituted with 2 mL of bacteriostatic water gives 2.5 mg/mL, or 2,500 mcg/mL. Because a U-100 insulin syringe divides 1 mL into 100 units, each unit on that syringe holds one hundredth of the per-millilitre concentration — 25 mcg in this example.

The volume corresponding to any measured amount then follows:

volume (mL) = target amount (mcg) ÷ concentration (mcg/mL)

Why the diluent volume is a choice, not a constant

The amount of peptide in the vial is fixed; the volume of bacteriostatic water is not. Adding more diluent does not change how much peptide is present — it changes how much liquid that peptide is spread through, and therefore how many syringe units correspond to a given amount. Researchers generally choose a diluent volume that puts their target amount at a readable number of units, since drawing 2 units accurately is harder than drawing 20.

Handling notes

• Bacteriostatic water contains 0.9% benzyl alcohol as a preservative, which is what allows a reconstituted vial to be drawn from repeatedly. Sterile water has no preservative.
• Direct the diluent stream against the vial wall rather than onto the powder, and swirl rather than shake — peptides are shear-sensitive and agitation can denature them.
• Reconstituted peptides are refrigerated and light-protected; stability varies by compound. See Storage & Handling for the detail.
• Lyophilised powder is far more stable than solution, which is why vials ship dry.

Worked example

A 10 mg vial reconstituted with 3 mL of bacteriostatic water yields 3.33 mg/mL (3,333 mcg/mL). On a U-100 syringe that is 33.3 mcg per unit. A 500 mcg target amount is therefore 0.15 mL, or 15 units, and the vial yields 20 such preparations.