A: Dissolve about 0.1 g in 5 mL of sulfuric acid: an orange or brown-red color is produced.

B: The visible absorption spectrum of a portion of the Assay preparation employed for measurement of absorbance in the Assay exhibits maxima at the same wavelengths as that of a similar solution of USP Gentian Violet RS, concomitantly measured.

Standard preparation— Transfer an accurately weighed quantity of USP Gentian Violet RS, equivalent to about 13.5 mg of anhydrous gentian violet, to a 100-mL volumetric flask. Add 50 mL of hydrochloric acid, and mix until dissolved. Dilute with hydrochloric acid to volume, and mix. Pipet 5 mL of the solution into a 50-mL volumetric flask, add hydrochloric acid to volume, and mix.

Assay preparation— Transfer about 500 mg of Cream, accurately weighed, to a 100-mL volumetric flask. Add 15 mL of hydrochloric acid, warm in a water bath to disperse the cream thoroughly, cool, add hydrochloric acid to volume, and mix. Filter the mixture through a fine-porosity, sintered-glass filter. Pipet 2 mL of the solution into a 10-mL volumetric flask, add hydrochloric acid to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparation and the Assay preparation in 1-cm cells at the wavelength of maximum absorbance at about 435 nm, with a suitable spectrophotometer, using hydrochloric acid as the blank. [note—Use quartz cells having tightly fitting covers to prevent corrosion caused by the hydrochloric acid.] Calculate the quantity, in mg, of C25H30ClN3 in the portion of Cream taken by the formula: in which C is the concentration, in µg per mL, of USP Gentian Violet RS, calculated on the anhydrous basis, in the Standard preparation; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.