Methylene Blue
C16H18ClN3S·3H2O 373.90
Phenothiazin-5-ium, 3,7-bis(dimethylamino)-, chloride, trihydrate.
C.I. Basic Blue 9 trihydrate [7220-79-3]
Anhydrous 319.86 [61-73-4]
Methylene Blue contains not less than 98.0 percent and not more than 103.0 percent of C16H18ClN3S, calculated on the dried basis.
Identification: Infrared Absorption 197K .
Loss on drying— Dry it at 75 and at a pressure not exceeding 5 mm of mercury for 4 hours: it loses
between 8.0% and 18.0% of its weight.
Residue on ignition: not more than 1.2%.
Arsenic— Prepare the Test Preparation by mixing 0.375 g with 10 mL of water in the arsine generator flask. Add 15 mL of nitric acid and 5 mL of perchloric
acid, mix, and heat cautiously to the production of strong fumes of perchloric acid. Cool, wash down the sides of the flask with water, and again heat to strong fumes.
Again cool, wash down the sides of the flask, and heat to fumes. Cool, dilute with water to 52 mL, and add 3 mL of hydrochloric acid: the resulting solution meets the
requirements of the test, the addition of 20 mL of 7 N sulfuric acid specified for Procedure being omitted. The limit is 8 ppm.
Copper or zinc— Ignite 1.0 g
in a porcelain crucible, using as low a temperature as practicable, until all of the carbon is oxidized. Cool the residue, add 15 mL of 2 N nitric acid, and boil for
5 minutes. Filter the cooled solution, and wash any residue with 10 mL of water. To the combined filtrate and washing add an excess of 6 N ammonium hydroxide, and
filter the solution into a 50 mL volumetric flask. Wash the precipitate with small portions of water, adding the washings to the filtrate, dilute the solution with
water to volume, and mix. To 25 mL of the solution add 10 mL of hydrogen sulfide TS: no turbidity is produced within 5 minutes (absence of zinc). Any dark color
produced does not exceed that of a control prepared by boiling a quantity of cupric sulfate, equivalent to 200 @g of copper, with 15 mL of 2 N nitric acid for 5 minutes
and by treating this solution as directed above, beginning with “Filter the cooled solution” (0.02% of copper).
Chromatographic purity— Quantitatively dissolve an accurately weighed quantity of Methylene Blue in methanol to obtain a Test solution containing 1.0 mg per mL
Dissolve a suitable quantity of USP Methylene Blue RS in methanol to obtain a Standard solution having a concentration of 100 @g per mL. Quantitatively dilute a portion
of this solution with methanol to obtain a Diluted standard solution having a concentration of 10 @g per mL. Apply 5 @L each of the Test solution, the Standard solution,
and the Diluted standard solution to a suitable thin-layer chromatographic plate coated with a 0.25-mm layer of octadecylsilanized chromatographic silica gel. Allow the
spots to dry, and develop the chromatogram in a chromatographic chamber with a solvent system consisting of a mixture of the upper layer separated from a well-shaken
mixture of water, n-butanol, and glacial acetic acid (100:80:20), until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from
the chamber, allow the solvent to evaporate, and visually locate the spots on the plate: the RF value of the principal spot in the chromatogram from the Test solution
corresponds to that from the Standard solution, and other spots, if present in the chromatogram from the Test solution, consist of a secondary spot that does not exceed
in size or intensity, the principal spot obtained from the Standard solution (10%), and not more than two additional spots, neither of which exceeds in size or intensity
the principal spot from the Diluted standard solution (1%)Assay— Transfer about 100 mg of Methylene Blue, accurately weighed, to a 250-mL volumetric flask, dissolve in
and dilute with diluted alcohol to volume, and mix. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, dilute with diluted alcohol to volume, and mix.
Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with diluted alcohol to volume, and mix. This solution contains about 2 @g per mL. Dissolve an
accurately weighed quantity of USP Methylene Blue RS in diluted alcohol, and dilute quantitatively and stepwise with diluted alcohol to obtain a Standard solution
having a known concentration of about 2 @g per mL. Concomitantly determine the absorbance of both solutions in 1-cm cells at the wavelength of maximum absorbance at
about 663 nm, with a suitable spectrophotometer, using diluted alcohol as the blank. Calculate the quantity, in mg, of C16H18ClN3S in the Methylene Blue taken by the
formula:
50C(AU / AS)
in which C is the concentration, in @g per mL, of anhydrous methylene blue in the Standard solution; and AU and AS are the absorbance of the solution of Methylene Blue and the Standard solution, respectively.
Methyl thioninium Chloride BP or Methyl thioninium Chloride Ph. Eur is also offered.
IUPAC name is 3,7-Bis(dimethylamino)phenothiazin-5-ylium chloride or 3,7-bis(Dimethylamino)-phenothiazin-5-ium chloride
