Mobile phase and System suitability solution— Proceed as directed in the Assay.

Standard solution— Dissolve accurately weighed quantities of USP Carbamazepine RS,10,11-dihydrocarbamazepine,and iminostilbene in methanol,and dilute quantitatively,and stepwise if necessary,with methanol to obtain a solution having known concentrations of about 0.02mg per mLof each component.Transfer 5.0mLof this solution to a 100-mLvolumetric flask,dilute with a mixture of methanol and water (50:50)to volume,and mix.

Test solution— Transfer about 100mg of Carbamazepine,accurately weighed,to a 50-mLvolumetric flask,and dissolve in and dilute with methanol to volume.Transfer 25.0mLof this solution to a 50-mLvolumetric flask,add about 20mLof water,and shake.Allow the mixture to cool to room temperature,and dilute with water to volume.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 230-nm detector and a 4.6-mm ×25-cm column that contains packing L10.The flow rate is about 1.5mLper minute.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the resolution,R,between the 10,11-dihydrocarbamazepine and carbamazepine is not less than 1.70;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the quantities,in mg,of 10,11-dihydrocarbamazepine and iminostilbene in the portion of Carbamazepine taken by the formula: in which Cis the concentration,in mg per mL,of 10,11-dihydrocarbamazepine or iminostilbene in the Standard solution;andri and rSiare the peak responses obtained for either 10,11-dihydrocarbamazepine or iminostilbene from the Test solutionand the corresponding peak obtained from the Standard solution,respectively.Calculate the quantities,in mg,of all other impurities found in the portion of Carbamazepine taken by the formula: in which riis the peak response for any other impurity;and rSis the peak response for carbamazepine obtained from the Standard solution:not more than 0.2%of any individual impurity is found;and the total of all impurities (including 10,11-dihydrocarbamazepine and iminostilbene)is not more than 0.5%.

Solvent— Use dimethyl sulfoxide.

Mobile phase— Prepare a 1000-mLmixture of water,methanol,and tetrahydrofuran (85:12:3),add 0.22mLof formic acid,mix,then add 0.5mLof triethylamine,and mix.Filter and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

System suitability solution— Dissolve accurately weighed quantities of USP Carbamazepine RSand 10,11-dihydrocarbamazepine in methanol,and dilute quantitatively,and stepwise if necessary,with methanol to obtain a solution having known concentrations of about 0.1and 0.5mg per mL,respectively.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,and dilute with a mixture of methanol and water (1:1)to volume.

Standard preparation— Dissolve an accurately weighed quantity of USP Carbamazepine RSin methanol,and dilute quantitatively with methanol to obtain a solution having a known concentration of about 2mg per mL.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,and dilute with a mixture of methanol and water (1:1)to volume.

Assay preparation— Transfer about 100mg of Carbamazepine,accurately weighed,to a 50-mLvolumetric flask,and dissolve in and dilute with methanol to volume.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,and dissolve in and dilute with a mixture of methanol and water (1:1)to volume.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 230-nm detector and a 4.6-mm ×25-cm column that contains packing L10.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparationand the System suitability solution,and record the peak responses as directed for Procedure:the resolution,R,between 10,11-dihydrocarbamazepine and carbamazepine in the System suitability solutionis not less than 1.70;and the relative standard deviation for replicate injections of the Standard preparationis not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C15H12N2Oin the portion of Carbamazepine taken by the formula: in which Cis the concentration,in mg per mL,of USP Carbamazepine RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.