Chromatographic purity—
Standard preparations—
Dissolve an accurately weighed quantity of
USP Clofazimine RS in methylene chloride, and mix to obtain
Standard preparation A having a known concentration of about 0.5 mg per mL. Dilute portions of
Standard preparation A quantitatively with methylene chloride to obtain
Standard preparations B and
C having known concentrations of 0.25 and 0.1 mg per mL, respectively.
Test preparation—
Dissolve an accurately weighed quantity of Clofazimine in methylene chloride to obtain a solution having a known concentration of about 50 mg per mL.
Ammonia solution—
Pipet 1 mL of ammonium hydroxide into a 100-mL volumetric flask, dilute with water to volume, and mix. [NOTE—Prepare this solution fresh daily.]
Chromatographic plate—
Use a thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel mixture. Immediately before use, expose the plate to ammonia vapors for 30 minutes by suspending the plate in a tank containing a shallow layer of approximately 25 mL of
Ammonia solution.
[NOTE—Prevent the plate from coming into contact with the liquid.
]
Procedure—
Separately apply 5 µL of the Test preparation and 5 µL of each Standard preparation to the Chromatographic plate. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of methylene chloride and n-propyl alcohol (10:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and air-dry. Examine the plate under short-wavelength UV light, and compare the intensities of any secondary spots observed in the chromatogram of the Test preparation with those of the principal spots in the chromatograms of the Standard preparations: no secondary spot from the chromatogram of the Test preparation is larger or more intense than the principal spot obtained from Standard preparation A (1.0%), and the sum of the intensities of the secondary spots obtained from the Test preparation corresponds to not more than 2.0%.
;)
for 3 hours: it loses not more than 0.5% of its weight.