Hexachlorophene Liquid Soap
» Hexachlorophene Liquid Soap is a solution of Hexachlorophene in a 10.0 to 13.0 percent solution of a potassium soap. It contains, in each 100 g, not less than 225 mg and not more than 260 mg of C13H6Cl6O2. It may contain suitable water hardness controls.
note—The inclusion of nonionic detergents in Hexachlorophene Liquid Soap in amounts greater than 8 percent on a total weight basis may decrease the bacteriostatic activity of the Soap.
Packaging and storage— Preserve in tight, light-resistant containers.
Labeling— Solutions of higher concentrations of hexachlorophene and potassium soap, in which the ratios of these components are consistent with the official limits, may be labeled “For the preparation of Hexachlorophene Liquid Soap, USP,” provided that the label indicates also that the soap is a concentrate, and provided that directions are given for dilution to the official strength.
Identification—
A: Pour about 2 g into a beaker, and add, with stirring, dilute hydrochloric acid (1 in 100) until the mixture is just acid to litmus. To 10 mL of the mixture, in a beaker, add 10 mL of chloroform, and mix. Add 3 or 4 drops of ferric chloride TS, mix, and allow to stand: the chloroform layer becomes purple.
B: To 2 mL of the mixture prepared in Identification test A, in a test tube, add 2 mL of acetone, and mix. Add 1 mL of titanium trichloride solution (1 in 5), and shake vigorously: a yellow oil separates.
Microbial enumeration tests 61 and Tests for specified microorganisms 62— It meets the requirements of the tests for absence of Staphylococcus aureus and Pseudomonas aeruginosa.
Water— Place about 5 g, quickly weighed to the nearest centigram, in the distilling flask of the apparatus for Water Determination—Azeotropic Method 921. (The Soap is most conveniently weighed in a boat of metal foil, of a size that will just pass through the neck of the flask.) Place 250 mL of toluene and 10 g of anhydrous barium chloride in the flask, connect the flask through a ground-glass joint to the distilling apparatus, fill the receiving tube with toluene, and determine the water as directed, beginning with “Heat the flask gently.” The volume of water found corresponds to between 86.5% and 90.0% by weight of the portion of Soap taken.
Alcohol-insoluble substances— Dissolve about 5 g, rapidly and accurately weighed, in 100 mL of hot neutralized alcohol, collect the residue, if any, on a tared filter, thoroughly wash it with hot neutralized alcohol, and dry at 105 for 1 hour: the weight of the residue obtained does not exceed 3.0% of the weight of Soap taken. Retain the solution and the residue.
Free alkali hydroxides— To the combined filtrate and washings obtained in the test for Alcohol-insoluble substances, add 0.5 mL of phenolphthalein TS. If a pink color is produced, titrate the solution with 0.1 N sulfuric acid VS until the pink color is just discharged. Each mL of 0.1 N sulfuric acid is equivalent to 5.61 mg of KOH. The volume of 0.1 N sulfuric acid consumed corresponds to not more than 0.05% of KOH.
Alkali carbonates— Wash the filter containing the Alcohol-insoluble substances with 50 mL of boiling water, cool, add methyl orange TS, and titrate the filtrate with 0.1 N sulfuric acid VS. Not more than 0.5 mL of 0.1 N sulfuric acid per g of Soap originally taken is required (0.35% calculated as K2CO3).
Assay for hexachlorophene—
Alkaline buffer— Dissolve 6.07 g of tris(hydroxymethyl)aminomethane in 900 mL of methanol. Add 25.0 mL of dilute hydrochloric acid (1 in 10), dilute with water to 1 liter, and mix.
Standard preparation— Place about 50 mg of USP Hexachlorophene RS, accurately weighed, in a 100-mL volumetric flask, dissolve in 10 mL of alcohol, and dilute with Alkaline buffer to volume. Preserve in a tight container.
Standard hexachlorophene graph— To 50-mL volumetric flasks add, by pipet and in duplicate, 2-, 3-, 4-, 5-, 6-, and 7-mL portions of the Standard preparation. To one flask of each pair of duplicates, add to volume acidified 90 percent methanol containing, in each 100 mL, 5 mL of acetic acid and 0.3 mL of hydrochloric acid, and mix. To the second flask of each pair, add Alkaline buffer to volume.
Arrange the two series of standard hexachlorophene solutions in pairs according to their hexachlorophene content, and determine the absorbances of the alkaline solutions at 312 nm, with a suitable spectrophotometer, using the corresponding acid solution as the blank. Plot the observed absorbance on the ordinate scale against the corresponding concentration of hexachlorophene, in mg per 100 mL, on the abscissa scale.
Procedure— Accurately weigh a portion of Soap, containing the equivalent of about 100 mg of hexachlorophene, and transfer to a 100-mL volumetric flask. Add alcohol to volume, and mix. Transfer 25.0 mL of this solution to a 100-mL volumetric flask, add 90 percent methanol to volume, mix, and filter if necessary. Add 10.0 mL of this solution to each of two 50-mL volumetric flasks, and fill one flask to volume with 0.3 M acetic acid in 90 percent methanol containing 0.1% of hydrochloric acid, and mix. Fill the other flask to volume with Alkaline buffer, and mix. Determine the absorbance of the alkaline solution at 312 nm with the same spectrophotometer used in preparing the Standard hexachlorophene graph, using the control as the blank. From the observed absorbance, calculate the weight of hexachlorophene in the Soap taken.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Behnam Davani, Ph.D., M.B.A.
Senior Scientist
1-301-816-8394		 (MDAA05) Monograph Development-Antivirals and Antimicrobials
Reference Standards Lili Wang, Technical Services Scientist
1-301-816-8129
RSTech@usp.org
61 Radhakrishna S Tirumalai, Ph.D.
Senior Scientist
1-301-816-8339		 (MSA05) Microbiology and Sterility Assurance
62 Radhakrishna S Tirumalai, Ph.D.
Senior Scientist
1-301-816-8339		 (MSA05) Microbiology and Sterility Assurance
USP32–NF27 Page 2555