Identification—
Place a volume of Emulsion,equivalent to about 150mg of hexachlorophene,in a glass-stoppered,25-mLgraduated cylinder,dilute with a mixture of equal volumes of chloroform and methanol to volume,mix,and allow to stand for about 5minutes.Apply 10µLof this solution and 10µLof a solution of
USP Hexachlorophene RSin the same chloroform and methanol mixture containing 6mg per mLto a suitable thin-layer chromatographic plate (see
Chromatography á621ñ)coated with a 0.25-mm layer of silica gel.Develop the chromatogram in a solvent system consisting of a mixture of toluene and glacial acetic acid (9:1)until the solvent moves to about 10cm above the point of application.Remove the plate,mark the solvent front and evaporate the solvent in a current of warm air.Spray the plate with dilute nitric acid (1in 5),and warm on a hot plate until yellow spots appear:the
RFvalue of the principal spot obtained from the solution under test corresponds to that obtained from the Standard solution.
pHá791ñ—
Place 20mLof the well-shaken Emulsion and 10mLof water in a glass-stoppered,50-mLgraduated cylinder,mix,and determine the pHin a suitable pHmeter,using a glass electrode and preferably a sleeve-type calomel electrode:the pHis between 5.0and 6.0.
Assay—
Standard preparation—
Weigh accurately about 50mg of
USP Hexachlorophene RSinto a 50-mLvolumetric flask,add 10mLof methanol,shake until dissolved,add methanol to volume,and mix.Pipet 3mLof this solution into a 100-mLvolumetric flask,add 1mLof dilute hydrochloric acid (1in 10),add methanol to volume,and mix.
Assay preparation—
Transfer an accurately weighed portion of Emulsion,equivalent to about 30mg of hexachlorophene,to a 100-mLvolumetric flask,add methanol to volume,and mix.Filter the solution through paper,taking adequate precautions to prevent evaporation.Pipet a 10-mLaliquot of the filtrate into a 100-mLvolumetric flask,add 1mLof dilute hydrochloric acid (1in 10),and add methanol to volume.
Procedure—
Concomitantly determine the absorbances of the
Assay preparationand the
Standard preparationin 1-cm cells at the wavelength of maximum absorbance at about 299nm,with a suitable spectrophotometer,using a mixture of 99volumes of methanol and 1volume of hydrochloric acid as the blank.Calculate the quantity,in mg,of C
13H
6Cl
6O
2in the portion of Emulsion taken by the formula:
C(AU/AS),
in which
Cis the concentration,in µg per mL,of
USP Hexachlorophene RSin the
Standard preparation,and
AUand
ASare the absorbances of the
Assay preparationand the
Standard preparation,respectively.