Reading a U-100 syringe
A U-100 insulin syringe is the standard tool for measuring small volumes. Its barrel is marked in units, not millilitres or milligrams, so the first job is knowing what a unit is, and how it relates to the mass of peptide in your solution.
Anatomy of a U-100 syringe
"U-100" means the syringe is calibrated so that 100 units = 1 mL. The graduations are a volume scale wearing a units label.
100 units = 1 mL
The full barrel of a 1 mL U-100 syringe is 100 units. So 1 unit = 0.01 mL, one hundredth of a millilitre.
10-unit blocks = 0.1 mL
The barrel is usually marked in blocks of 10 units. Each 10-unit block is 0.1 mL, a handy reference point for reading a draw.
Volume, not mass
A syringe measures volume. How much peptide mass sits in that volume depends entirely on the concentration you reconstituted to.
Converting a target mass to units
Because the syringe reads volume, you convert a target mass into units using the concentration. First find the mass held in one unit, the mcg-per-unit, then divide:
Units to draw = target mass (mcg) ÷ mcg-per-unitEach unit is 0.01 mL, so the mcg-per-unit is just the concentration expressed per 0.01 mL. Using the two reconstitutions from the concentration page:
Both examples land on 10 units for their respective target masses, a useful reminder that the same number of units holds a different mass at a different concentration.