Worked example
Add 2 mL of water to a vial holding 5 mg of TB-500. The concentration is 5 ÷ 2 = 2.5 mg/mL, or 2,500 mcg in every millilitre. On a U-100 syringe, where 100 units make 1 mL, each unit holds 25 mcg and each 10 units hold 250 mcg.
Change the water and only the concentration changes. With 4 mL instead, each 10 units hold 125 mcg, half as much, and any given mass takes twice the units to measure. These numbers illustrate the arithmetic; they are not amounts to use.
Concentration table
Common TB-500 vial sizes against common water volumes. The last column is what 10 units on a U-100 syringe hold.
| Vial | Water | Concentration | 10 units (U-100) hold |
|---|---|---|---|
| 2 mg | 1 mL | 2 mg/mL | 200 mcg |
| 2 mg | 2 mL | 1 mg/mL | 100 mcg |
| 5 mg | 1 mL | 5 mg/mL | 500 mcg |
| 5 mg | 2 mL | 2.5 mg/mL | 250 mcg |
| 10 mg | 1 mL | 10 mg/mL | 1 mg |
| 10 mg | 2 mL | 5 mg/mL | 500 mcg |
Notes for TB-500 vial math
- "TB-500" is used for two different molecules. Originally it named a short synthetic fragment of thymosin beta-4 (Ac-LKKTETQ, about 889 g/mol). Many products sold today are labeled TB-500 but contain full-length thymosin beta-4 (43 amino acids, about 4,963 g/mol). The vial math is identical by mass, but 5 mg of the fragment is about 5.6 times as many molecules as 5 mg of the full protein.
- Milligram-scale amounts from a 2 mg vial quickly exceed small syringes. 1 mg from a 2 mg vial with 2 mL is 1 mL, the full capacity of a 1 mL syringe and more than three 0.3 mL syringes.
- Only a certificate of analysis with mass spectrometry tells you which molecule a vial holds. HPLC purity alone does not.
Storage and handling
- No approved label and no validated stability data exist for reconstituted TB-500 or research thymosin beta-4.
- General peptide practice: sealed vials cold and dark; once reconstituted, refrigerate (2-8 °C), avoid freezing, label with date and concentration.