Borrel’s methylene blue

Recipe

MATERIALS

Methylene blue (C.I. 52015)

Silver nitrate (AgNO₃) (1% w/v)

Sodium hydroxide (NaOH) (4% aqueous)

1. Add 25 mL of 4% aqueous sodium hydroxide to 100 mL of 1% silver nitrate. Allow the precipitate of silver oxide (Ag₂O) to settle, decant off the supernatant, and wash the precipitate by shaking and decantation, with two changes of 100 mL of H₂O.
2. Dissolve 1.0 g of methylene blue in 100 mL of H₂O, boil, and add to the washed Ag₂O. Boil for 5 min, leave to cool, then filter.
3. Dilute the stock solution to five times its volume with H₂O to give the working solution.

Both the stock and the diluted solutions are stable for at least 10 yr.