How to Obtain Purified Methyl Green Dye

For Methyl Green-Pyronin Staining

Some methods for methyl green-pyronin staining require purified methyl green. This dye, even in the dry state, almost always contains some crystal violet, produced by loss of one of its methyl groups. To remove this the solution of methyl green must be washed by shaking with a quantity of chloroform to extract the crystal violet until the chloroform is only very palely tinted with crystal violet. The long term stability of a cleaned solution is not universally accepted, some workers think that the cleaned solution may eventually form more crystal violet over time. It is recommended that the volume of solution cleaned be what will be used within a reasonable period of time.

Procedure to Obtain Purified Methyl Green

1. Place the aqueous methyl green solution in an Erlenmeyer flask which is about three times the volume of the solution.
2. Add an equal quantity of chloroform.
3. Shake vigorously every few minutes for half an hour or so.
4. Place into a separating funnel.
5. Allow the chloroform to separate from the solution.
6. Collect the aqueous methyl green and discard the chloroform.
7. Repeat as required.