A: Infrared Absorption á197Kñ.

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

C: It responds to the tests for Chloride á191ñ.

Test solution: 10mg per mL,in water.

Buffer and Mobile phase—Prepare as directed in the Assay.

Standard solution— Use the System suitability preparationprepared as directed under Assay.

Test solution— Prepare as directed for the Assay preparationin the Assay.

Chromatographic system— Prepare as directed under Assay.The relative standard deviation of the peak response for replicate injections of the Standard solutionis not more than 10.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for all of the peaks.The relative retention times are about 0.65for desacetyl diltiazem and 1.0for diltiazem.Calculate the percentage of desacetyl diltiazem hydrochloride in the specimen of Diltiazem Hydrochloride taken by the formula: in which Cis the concentration,in µg per mL,of USP Desacetyl Diltiazem Hydrochloride RSin the Standard solution,Wis the weight,in mg,of Diltiazem Hydrochloride taken,and rUand rSare the desacetyl diltiazem peak responses obtained from the Test solutionand the Standard solution,respectively:not more than 0.5%of desacetyl diltiazem hydrochloride is found.Calculate the percentage of each impurity peak,other than the main peak and the desacetyl diltiazem peak,by the formula: in which rIis the response of each impurity peak and all other quantities are as defined above:not more than 1.0%total impurities including desacetyl diltiazem hydrochloride with no individual impurity greater than 0.5%is found.

Buffer— Dissolve 1.16g of d-10-camphorsulfonic acid in 1000mLof 0.1Msodium acetate,adjust this solution by the addition of 0.1Nsodium hydroxide to a pHof 6.2,and mix.

Mobile phase— Prepare a mixture of Buffer,acetonitrile,and methanol (50:25:25),filter,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Prepare a solution in methanol having an accurately known concentration of about 1.2mg of USP Diltiazem Hydrochloride RSper mL.

Assay preparation— Transfer about 120mg of Diltiazem Hydrochloride,accurately weighed,to a 100-mLvolumetric flask,dissolve in methanol,dilute with methanol to volume,and mix.

System suitability preparation— Prepare a solution in methanol containing 0.012mg each of USP Diltiazem Hydrochloride RSand USP Desacetyl Diltiazem Hydrochloride RSper mL.

Chromatographic system— The liquid chromatograph is equipped with a 240-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 1.6mLper minute.Chromatograph the System suitability preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.65for desacetyl diltiazem and 1.0for diltiazem,the resolution,R,between desacetyl diltiazem and diltiazem is not less than 3,and the number of theoretical plates,n,for the diltiazem peak is not less than 1200.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 10µL)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 C22H26N2O4S·HCl in the Diltiazem Hydrochloride taken by the formula: in which Cis the concentration,in mg per mL,of USP Diltiazem Hydrochloride RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.