A: Infrared Absorption á197Kñ.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

Chromatographic system— Proceed as directed in the Assay.

Test solution— Use the Assay preparation.

Procedure— Inject a volume (about 0.5µL)of the Test solutioninto the chromatograph,increase the column temperature by 20per minute to 140,then increase column temperature by 4per minute to 240,maintain this temperature for not less than 5minutes,record the chromatogram,and measure the peak responses.Calculate the percentage of each impurity in the portion of Triclosan taken by the formula: in which riis the peak response for each impurity;and rsis the sum of the responses of all of the peaks:not more than 0.1%of any individual impurity is found;and not more than 0.5%of total impurities is found.

Phosphate buffer— Transfer about 1.38g of anhydrous monobasic sodium phosphate and about 1.42g of dibasic sodium phosphate to a 1-liter volumetric flask,dissolve in and dilute with water to volume,and mix.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and Phosphate buffer(1:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Quantitatively dissolve accurately weighed quantities of 4-chlorophenol and 2,4-dichlorophenol in acetonitrile,dilute with an equal volume of water,and mix.Transfer a portion of this solution to a suitable container,and dilute quantitatively,and stepwise if necessary,with a mixture of acetonitrile and water (1:1)to obtain a solution having known concentrations of about 0.5µg of 4-chlorophenol and 0.1µg of 2,4-dichlorophenol per mL.

Test solution— Transfer about 250mg of Triclosan,accurately weighed,to a 25-mLlow-actinic volumetric flask,dissolve in 20mLof acetonitrile,dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a coulometric electrochemical detector with electrode 1set at 0.45Vand electrode 2set at 0.75V,both having a positive (oxidative)polarity and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 9.0%for 2,4-dichlorophenol.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.The peak responses for 4-chlorophenol and 2,4-dichlorophenol in the chromatogram of the Test solutionare not greater than the corresponding peaks in the chromatogram of the Standard solution.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile,water,and glacial acetic acid (70:30:0.1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Transfer accurately weighed quantities of 2,8-dichlorodibenzofuran,and 2,4,8-trichlorodibenzofuran to a volumetric flask,add accurately measured volumes of 1,3,7-trichlorodibenzo-p-dioxin and 2,8-dichlorodibenzo-p-dioxin,and dissolve in methanol.Dilute quantitatively,and stepwise if necessary,with methanol to obtain a solution having concentrations of about 0.5,1.0,0.5,and 1.0µg per mL,respectively.

Test solution— Transfer about 2.0g of Triclosan,accurately weighed,to a screw-capped centrifuge tube,add 5mLof 2Npotassium hydroxide,and shake for 10minutes to dissolve.Add 3mLof n-hexane,shake for 10minutes,and allow the phases to separate.Transfer the organic layer to a suitable container,add another 3mLof n-hexane to the aqueous layer,shake for 10minutes,and allow the phases to separate.Transfer the organic layer to the previous extract,discard the aqueous layer,add 3mLof 2Npotassium hydroxide to the combined organic layers,shake for 10minutes,and allow the phases to separate.Discard the aqueous layer,add another 3mLof 2Npotassium hydroxide to the combined organic layers,shake for 10minutes,and allow the phases to separate.Transfer the organic layer to a suitable container,and evaporate with the aid of a stream of nitrogen to dryness.Dissolve the residue in 1.0mLof methanol,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm ×25-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.59for 2,8-dichlorodibenzofuran,0.71for 2,8-dichlorodibenzo-p-dioxin,0.88for 2,4,8-trichlorodibenzofuran,and 1.0for 1,3,7-trichlorodibenzo-p-dioxin;and the relative standard deviation for replicate injections is not more than 15.0%,determined from the 2,8-dichlorodibenzo-p-dioxin peak.

Procedure— Inject a volume (about 20µL)of the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.The peak responses for 2,8-dichlorodibenzofuran,2,8-dichlorodibenzo-p-doxin,2,4,8-trichlorodibenzofuran,and 1,3,7-trichlorodibenzo-p-dioxin obtained from the Test solutionare not greater than the corresponding peaks obtained from the Standard solution.

Stationary phase A— Transfer about 10g of silica gel to a suitable container,add about 3mLof 1Nsodium hydroxide,and mix.

Stationary phase B— Transfer about 60g of silica gel to a suitable container,add about 74mLof concentrated sulfuric acid,and mix.

Chromatographic column A— Transfer 5.1g of Stationary phase A,0.5g of silica gel,6.2g of Stationary phase B,and 3.2g of sodium sulfate to a glass chromatographic column having an internal diameter of 10mm.Wash the column with 50mLof n-hexane,and discard the eluate.

Chromatographic column B— Transfer 2.5g of alumina and 2.5g of sodium sulfate to a glass chromatographic column having an internal diameter of 6mm.Wash the column with 30mLof n-hexane,and discard the eluate.

Internal standard solution— Transfer accurately measured quantities of 2,3,7,8-tetrachlorodibenzo-p-dioxin,13C-labeled,and 2,3,7,8-tetrachlorodibenzofuran,13C-labeled,in nonane,and dilute quantitatively,and stepwise if necessary,with 2,2,4-trimethylpentane to obtain a solution having known concentrations of about 1.0pg of each per µL.

Test solution— Transfer about 30g of Triclosan,accurately weighed,to a separatory funnel,add 30µLof Internal standard solution,dissolve in 200mLof 1Nsodium hydroxide,extract with four 30-mLportions of n-hexane,and combine the extracts.Wash the combined extracts with 20mLof water,extract the washing with 15mLof n-hexane,and add the extract to the other combined extracts.Add about 3g of anhydrous sodium sulfate to the combined extracts,allow to stand for 30minutes,quantitatively transfer to an appropriate round-bottom flask,and distil,using a distillation apparatus with a vigreux column,until about 1mLremains.Transfer this solution to the top of Chromatographic column A,and elute with 50mLof n-hexane.Collect the eluate on top of Chromatographic column B,and elute with 30mLof a mixture of n-hexane and methylene chloride (98:2),discarding the eluate.Elute with 40mLof a mixture of n-hexane and methylene chloride (1:1),collecting the eluates in a round-bottom flask.Distill the combined eluates,using a distillation apparatus with a vigreux column,until about 1mLremains.Further concentrate this solution with the aid of a stream of nitrogen to about 50µL,evaporate at room temperature to dryness,and dissolve in 10µLof 2,2,4-trimethylpentane.

Chromatographic system (see Chromatography á621ñand Mass Spectrometry á736ñ)— The gas chromatograph is equipped with a high-resolution mass spectrograph with an electron-impact ionization source and a 0.25-mm ×60-m capillary column coated with phase G48.The carrier gas is helium.The chromatograph is programmed as follows.Initially the temperature of the column is equilibrated at 80,then,1minute after the injection,the temperature is increased at a rate of 20per minute to 220,then increased at a rate of 2per minute to 270,and maintained at 270for not less than 20minutes.The injection port temperature is maintained at 280.Chromatograph the Internal standard solution,and record the peak responses as directed for Procedure:the signal-to-noise ratio at a mass-to-charge ratio of 321.89is not less than 50.

Procedure— Inject a volume (about 1µL)of the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses at mass-to-charge ratios of 319.90,321.89,331.88,333.93,303.90,305.90,315.94,and 317.94.The peak response for 2,3,7,8-tetrachlorodibenzo-p-dioxin at a mass-to-charge ratio of 319.90is not more than the peak response of the associated internal standard at a mass-to-charge ratio of 331.88;the peak response for 2,3,7,8-tetrachlorodibenzofuran at a mass-to-charge ratio of 303.90is not more than the peak response of the associated internal standard at a mass-to-charge ratio of 315.94.

Standard preparation— Dissolve an accurately weighed quantity of USP Triclosan RSin dichloromethane,and dilute quantitatively,and stepwise if necessary,with dichloromethane to obtain a solution having a known concentration of about 4.0mg per mL.

Assay preparation— Transfer about 40mg of Triclosan,accurately weighed,to a 10-mLvolumetric flask,dissolve in and dilute with dichloromethane to volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The gas chromatograph is equipped with a flame-ionization detector and a 0.53-mm ×15-m capillary column with G3.The carrier gas is helium maintained at about 6psi.The injector temperature is maintained at 34and is increased rapidly to 200immediately after the injection,the column temperature is maintained at 34,and the detector temperature is maintained at 260.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 0.5µL)of the Standard preparationand the Assay preparationinto the chromatograph,increase the column temperature by 20per minute to 140,then increase column temperature by 4per minute to 240,maintain this temperature for not less than 5minutes,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C12H7Cl3O2in the portion of Triclosan taken by the formula: in which Cis the concentration,in mg per mL,of USP Triclosan RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.