Packaging and storage—
Preserve in well-closed containers. Store at 25
, excursions permitted between 15
and 30
.
Loss on drying 
731
—
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.
Arsenic, Method I 211—
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 µg 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 µg per mL. Quantitatively dilute a portion of this solution with methanol to obtain a
Diluted standard solution having a concentration of 10 µg per mL. Apply 5 µL each of the
Test solution, the
Standard solution, and the
Diluted standard solution to a suitable thin-layer chromatographic plate (see
Chromatography 621) 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%).
Organic volatile impurities, Method I 467:
meets the requirements.
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 µg 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 µg per mL. Concomitantly determine the absorbances 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 C
16H
18ClN
3S in the Methylene Blue taken by the formula:
50C(AU / AS),
in which
C is the concentration, in µg per mL, of anhydrous methylene blue in the Standard solution; and
AU and
AS are the absorbances of the solution of Methylene Blue and the Standard solution, respectively.
;)
