Foundations
Concentration
The single number that ties a lyophilized vial to a syringe reading, and the arithmetic that produces it.
- Last updated:
- 2026-07-22
Overview
Concentration is peptide mass divided by diluent volume. A 10 mg vial reconstituted in 2 mL of bacteriostatic water is at a concentration of 5 mg/mL. That is the only calculation on this side of the equation.
Once the concentration is known, the volume required to deliver a specific amount of peptide is that amount divided by the concentration. A 0.25 mg reported research amount at 5 mg/mL is 0.05 mL.
Why it matters
Almost every arithmetic mistake in this domain traces back to concentration. Getting concentration right first, before touching a syringe, makes every subsequent step safer.
Key concepts
Units matter
Concentration is meaningful only with its unit. "5" is not a concentration; "5 mg/mL" is. Confusing mg/mL with mcg/mL is a thousand-fold error.
The vial label is the numerator
The Preparation Calculator treats the vial mass on the label as the numerator. That number is trusted only as far as the vial itself is trusted (see "Identity testing", "Potency").
The diluent volume is the denominator
The diluent volume is what you added, not what came in a separate bacteriostatic-water vial. Use the volume you actually reconstituted with.
Common misconceptions
- Concentration is not a property of the peptide. It is a property of the vial after reconstitution. The same peptide can be at any of many different concentrations depending on how much diluent was added.
- Doubling the diluent halves the concentration. Halving it doubles the concentration.
- Concentration does not change safety by itself. Two syringes drawing the same total mass of peptide deliver the same mass regardless of concentration; concentration only changes the volume that mass occupies.
Practical interpretation
When the Preparation Calculator's example values look unfamiliar, the first thing to check is the concentration: is the vial-mass input correct, and is the diluent volume the one the source assumed?
Limitations
The arithmetic assumes the vial actually contains what the label says. Concentration arithmetic cannot detect a mislabelled or under-mass vial.