A: Infrared Absorption á197Kñ.

B: Ultraviolet Absorption á197Uñ.

Internal standard solution— Dissolve a sufficient quantity of o-nitroaniline in a small quantity of dichloromethane,and dilute with n-hexane to obtain a solution having a concentration of about 500µg per mL.

Mobile phase— Prepare a degassed mixture of n-hexane,dichloromethane,and glacial acetic acid (82:12:6).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

System suitability preparation— Prepare a solution containing 0.1mg of USP Anthralin RSand 0.2mg of danthron per mLin dichloromethane.Transfer 5mLof this solution to a 25-mLvolumetric flask.Add 5.0mLof n-hexane,dilute with Mobile phaseto volume,and mix.

Solvent blank solution— Mix Mobile phase,n-hexane,and dichloromethane (3:1:1).

Standard preparation— Dissolve an accurately weighed quantity of USP Anthralin RSin dichloromethane to obtain a solution having a known concentration of about 250µg per mL.Pipet 5mLof this solution and 5mLof Internal standard solutioninto a 25-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Assay preparation— Weigh accurately about 250mg of Anthralin into a tared 100-mLflask,dilute with dichloromethane to volume after dissolution of the solid,and mix.Pipet 10mLof the solution into a 100-mLvolumetric flask,dilute with dichloromethane to volume,and mix.Pipet 5mLof this solution and 5mLof Internal standard solutioninto a 25-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 354-nm detector and a 4.6-mm ×25-cm column that contains packing L3.The flow rate is about 2mLper minute.Chromatograph replicate injections of the Standard preparation,and record the peak responses as directed for Procedure:relative retention times are 1.0for anthralin,about 1.2for danthron (if present),about 1.7for dianthrone (if present),and about 2.3for o-nitroaniline;and the relative standard deviation of the ratio of the peak responses is not more than 2.0%.Chromatograph the System suitability preparation:the resolution,R,is not less than 1.3;and the tailing factor,T,is not more than 1.5.Chromatograph the Solvent blank solution:no effect on the baseline is discernible at the retention time of anthralin.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in mg,of C14H10O3in the portion of Anthralin taken by the formula: in which Cis the concentration,in µg per mL,of USP Anthralin RSin the Standard preparation;and RUand RSare the response ratios of the anthralin peak to the o-nitroaniline peak obtained from the Assay preparationand the Standard preparation,respectively.