Gentian Violet
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C25H30ClN3 407.98

Methanaminium, N-[4-[bis[4-(dimethylamino)phenyl]methylene]-2,5-cyclohexadien-1-ylidene]-N-methyl-, chloride.
C. I. Basic violet 3.
[4-[Bis[p-(dimethylamino)phenyl]methylene]-2,5-cyclohexadien-1-ylidene]dimethylammonium chloride [548-62-9].
» Gentian Violet contains not less than 96.0 percent and not more than 100.5 percent of gentian violet (C25H30ClN3), calculated on the anhydrous basis.
Packaging and storage— Preserve in well-closed containers.
A: Sprinkle about 1 mg on 1 mL of sulfuric acid: it dissolves in the acid with an orange or brown-red color. When this solution is diluted cautiously with water, the color changes to brown, then to green, and finally to blue.
B: Dissolve about 20 mg in 10 mL of water, and add 5 drops of hydrochloric acid. To 5 mL of this solution add tannic acid TS dropwise: a deep blue precipitate is formed.
C: To the remainder of the solution prepared for Identification test B add about 500 mg of zinc dust, and warm the mixture: rapid decolorization occurs. Place a drop of the decolorized solution adjacent to a drop of 6 N ammonium hydroxide on a filter paper: a blue color is produced at the zone of contact.
Water, Method I 921: not more than 7.5%.
Residue on ignition 281: not more than 1.5%.
Alcohol-insoluble substances— Boil 1.0 g, accurately weighed, with 50 mL of alcohol under a reflux condenser for 15 minutes, filter through a tared filtering crucible, wash the residue on the filter with hot alcohol until the last washing is not colored violet, and dry the crucible at 105 for 1 hour: not more than 1.0% of insoluble residue remains.
Arsenic, Method I 211 Mix 300 mg with about 2.5 g each of powdered potassium nitrate and anhydrous sodium carbonate, and heat the mixture in a crucible until the organic matter is completely oxidized. Dissolve the cooled residue in 15 mL of 2 N sulfuric acid, and evaporate the solution by heating until copious white fumes begin to evolve. Dissolve the residue in 35 mL of water. The limit is 0.001%.
Lead— Place 1.0 g in a small Kjeldahl flask, add 5 mL of sulfuric acid, and insert a small funnel into the flask. Gently rotate the flask until the sulfuric acid has completely wetted the Gentian Violet, then heat gently until complete carbonization has taken place. Allow to cool, and add, in small quantities, 5 mL of nitric acid. Again heat gently until copious white fumes are evolved. Allow to cool, add another 5 mL of nitric acid, and again heat until white fumes are evolved. Allow to cool, cautiously add about 25 mL of water, and boil for a few minutes. After cooling, neutralize to litmus paper with ammonium hydroxide, and add 5 mL of nitric acid. Transfer the solution to a 100-mL volumetric flask, dilute with water to volume, and mix. Use 20 mL of this solution for the limit test for Lead 251. Perform a blank determination, and make any necessary correction. The limit is 0.003%.
Zinc standard stock solution— Transfer about 1 g of zinc, accurately weighed, to a 1000-mL volumetric flask, add 50 mL of nitric acid, and mix to dissolve. Dilute with water to volume, and mix.
Standard preparation— Dilute the Zinc standard stock solution with water to obtain a Standard preparation containing 0.50 µg of zinc per mL.
Test preparation— Weigh accurately 0.50 g of Gentian Violet in a suitable tared crucible. Place in a low-temperature plasma ashing apparatus, and ash until a constant weight is attained. Pipet 10 mL of 6 N nitric acid into the crucible, and heat to dissolve the ash. Transfer the solution to a 500-mL volumetric flask, dilute with water to volume, and mix. Prepare a reagent blank.
Procedure— Concomitantly determine the absorbances of the Standard preparation, the Test preparation, and the reagent blank at the zinc emission line at 213.9 nm, with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a zinc lamp and an air–acetylene flame, using water as the blank. The absorbance of the Test preparation, corrected for that of the reagent blank, is not greater than the absorbance of the Standard preparation, similarly corrected (0.05%).
Chromatographic purity— Dissolve 10 mg in 10 mL of methanol to obtain the Test solution. Transfer 1.0 mL of Test solution to a 100-mL volumetric flask, dilute with methanol to volume, and mix (Diluted test solution). Apply 5 µL each of the Test solution and the Diluted test 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 suitable chromatographic chamber with a solvent system consisting of the upper layer separated from a well-shaken mixture of water, butyl alcohol, 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 Test solution exhibits a principal spot and not more than one secondary spot which, if present in the chromatogram from the Test solution, is not more intense than the principal spot obtained from the Diluted test solution (1.0%).
Assay— Transfer about 400 mg of Gentian Violet, accurately weighed, to a 300-mL conical flask, add 25 mL of water and 10 mL of hydrochloric acid, displace the air in the flask with carbon dioxide, and pass a stream of carbon dioxide through the flask during the assay. Add 50.0 mL of 0.1 N titanium trichloride VS, heat to boiling, and boil gently for 10 minutes, swirling the liquid occasionally. Cool the solution, add 5 mL of ammonium thiocyanate solution (1 in 10), and titrate with 0.1 N ferric ammonium sulfate VS until a faint red color is produced. Perform a blank determination (see Residual Titrations 541). Each mL of 0.1 N titanium trichloride is equivalent to 20.40 mg of C25H30ClN3.
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Monograph Behnam Davani, Ph.D., M.B.A.
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