L-thyroxine stock solution (100 μM)

L-thyroxine (T4) (100 mg; Sigma T2376)

NaOH (1 M and 0.4 M)

• 1. Add 1 mL of 1 M NaOH directly to the 100 mg bottle of T4 and shake by hand to dissolve.

• 2. Bring the volume to 10 mL with 0.4 M NaOH and shake again to mix. The solution is now 12.9 mM T4.

• 3. Add 5 mL of the 12.9 mM T4 solution to a bottle containing 645 mL of H₂O. Add the remaining 5 mL of the T4 solution to a second bottle containing 645 mL of H₂O.

  The result is two containers (650 mL each) of 100 μM T4 stock solution.