Hexachlorophene Liquid Soap
»Hexachlorophene Liquid Soap is a solution of Hexachlorophene in a 10.0to 13.0percent solution of a potassium soap.It contains,in each 100g,not less than 225mg and not more than 260mg of C13H6Cl6O2.It may contain suitable water hardness controls.
NOTE—The inclusion of nonionic detergents in Hexachlorophene Liquid Soap in amounts greater than 8percent 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 2g into a beaker,and add,with stirring,dilute hydrochloric acid (1in 100)until the mixture is just acid to litmus.To 10mLof the mixture,in a beaker,add 10mLof chloroform,and mix.Add 3or 4drops of ferric chloride TS,mix,and allow to stand:the chloroform layer becomes purple.
B: To 2mLof the mixture prepared in Identification test A,in a test tube,add 2mLof acetone,and mix.Add 1mLof titanium trichloride solution (1in 5),and shake vigorously:a yellow oil separates.
Microbial limits á61ñ— It meets the requirements of the tests for absence of Staphylococcus aureusand Pseudomonas aeruginosa.
Water— Place about 5g,quickly weighed to the nearest centigram,in the distilling flask of the apparatus for Water Determination—Azeotropic Method á921ñ.(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 250mLof toluene and 10g 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 5g,rapidly and accurately weighed,in 100mLof hot neutralized alcohol,collect the residue,if any,on a tared filter,thoroughly wash it with hot neutralized alcohol,and dry at 105for 1hour: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 0.5mLof phenolphthalein TS.If a pink color is produced,titrate the solution with 0.1Nsulfuric acid VSuntil the pink color is just discharged.Each mLof 0.1Nsulfuric acid is equivalent to 5.61mg of KOH.The volume of 0.1Nsulfuric acid consumed corresponds to not more than 0.05%of KOH.
Alkali carbonates— Wash the filter containing the Alcohol-insoluble substanceswith 50mLof boiling water,cool,add methyl orange TS,and titrate the filtrate with 0.1Nsulfuric acid VS.Not more than 0.5mLof 0.1Nsulfuric acid per g of Soap originally taken is required (0.35%calculated as K2CO3).
Assay for hexachlorophene—
Alkaline buffer— Dissolve 6.07g of tris(hydroxymethyl)aminomethane in 900mLof methanol.Add 25.0mLof dilute hydrochloric acid (1in 10),dilute with water to 1liter,and mix.
Standard preparation— Place about 50mg of USP Hexachlorophene RS,accurately weighed,in a 100-mLvolumetric flask,dissolve in 10mLof alcohol,and dilute with Alkaline bufferto volume.Preserve in a tight container.
Standard hexachlorophene graph— To 50-mLvolumetric flasks add,by pipet and in duplicate,2-,3-,4-,5-,6-,and 7-mLportions of the Standard preparation.To one flask of each pair of duplicates,add to volume acidified 90percent methanol containing,in each 100mL,5mLof acetic acid and 0.3mLof hydrochloric acid,and mix.To the second flask of each pair,add Alkaline bufferto 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 312nm,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 100mL,on the abscissa scale.
Procedure— Accurately weigh a portion of Soap,containing the equivalent of about 100mg of hexachlorophene,and transfer to a 100-mLvolumetric flask.Add alcohol to volume,and mix.Transfer 25.0mLof this solution to a 100-mLvolumetric flask,add 90percent methanol to volume,mix,and filter if necessary.Add 10.0mLof this solution to each of two 50-mLvolumetric flasks,and fill one flask to volume with 0.3Macetic acid in 90percent 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 312nm 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— Staff Liaison:Behnam Davani,Ph.D.,MBA,Senior Scientist
Expert Committee:(PA7)Pharmaceutical Analysis 7
USP28–NF23Page 944
Phone Number:1-301-816-8394