Reading time: ~2 min · Part of the free certification in peptide science
Reconstitution arithmetic is simple, but most errors happen in three places: mixing up units, miscalculating blends and misreading the syringe. These cases cover all three.
Case 1 — Unit conversion
A 10 mg vial reconstituted with 2 mL gives 5 mg/mL = 5,000 mcg/mL. To draw 250 mcg: 250 ÷ 5,000 = 0.05 mL = 5 units on a U-100 syringe.
Case 2 — Changing the volume to measure better
The same vial with 4 mL gives 2,500 mcg/mL. The same 250 mcg are now 0.1 mL = 10 units. The amount of peptide did not change; it just became easier to measure because the mark is further from zero.
Case 3 — Blends with a fixed ratio
A 70 mg GLOW vial (GHK-Cu 50 mg + BPC-157 10 mg + TB-500 10 mg, 5:1:1 ratio) reconstituted with 3.5 mL has 20 mg/mL of blend. Each 0.1 mL (10 units) contains 2 mg of blend, of which:
- GHK-Cu: 2 × 5/7 ≈ 1.43 mg
- BPC-157: 2 × 1/7 ≈ 0.29 mg
- TB-500: 2 × 1/7 ≈ 0.29 mg
In a blend you cannot adjust one component without moving the others: they all go up and down together.
Case 4 — Serial dilution for very small amounts
If the target amount falls below 2 units (hard to measure precisely), an intermediate dilution can be prepared: take a known volume of the stock solution and bring it to a larger volume in another sterile vial. The concentration is divided by the dilution factor. The new concentration is always labeled.
Recurring errors
| Error | Consequence | How to avoid it |
|---|---|---|
| Confusing mg with mcg | A 1,000-fold error | Always write the unit at every step |
| Confusing mL with units | A 100-fold error | Remember: 1 U-100 unit = 0.01 mL |
| Forgetting the volume of water added | Unknown concentration | Label the date and concentration when reconstituting |
| Treating a blend as a single compound | Wrong amounts per component | Calculate each component by its proportion |
Before drawing, redo the calculation backwards: units × 0.01 × concentration should return the target mass. If it does not match, there is a unit error.
Catalogue compounds mentioned in this lesson
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