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.

Mobile phase,Standard preparation,Resolution solution,and Chromatographic system— Proceed as directed in the Assay.

Test preparation— Use the Assay preparation.

Procedure— Inject a volume (about 40µL)of the Test preparationinto the chromatograph.Allow the Test preparationto elute for not less than two times the retention time of felodipine.Record the chromatograms,and measure the areas for the impurity peaks.Calculate the percentage of each impurity in the portion of Felodipine taken by the formula: in which riis the peak response for each impurity;and rsis the sum of all the responses of all the peaks:not more than 1.0%of any individual impurity is found,and the sum of all impurities is not more than 1.5%.

Mobile phase— Dissolve 6.9g of monobasic sodium phosphate in 400mLof water in a 1-liter volumetric flask.Add 8.0mLof 1Mphosphoric acid,dilute with water to volume,and mix.Prepare a filtered and degassed mixture of this solution,acetonitrile,and methanol (40:40:20).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Resolution solution— Dissolve 150mg of Felodipine in a mixture of 25mLof tertiary butyl alcohol and 25mLof 1Nperchloric acid,add 10mLof 0.1Mceric sulfate,mix,and allow to stand for 15minutes.Add 3.5mLof 10Nsodium hydroxide,and neutralize with 2Nsodium hydroxide.Shake the mixture with 25mLof methylene chloride in a separator.Draw off the lower layer,and evaporate it to dryness under a stream of nitrogen on a water bath.Dissolve 10mg of the residue (felodipine oxidation product)and 5mg of USP Felodipine RSin Mobile phase,dilute with Mobile phaseto 100mL,and mix.Transfer 1.0mLof the resulting solution to a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Felodipine RSin Mobile phase,and quantitatively dilute with Mobile phaseto obtain a solution having a known concentration of about 0.3mg per mL.[NOTE—Prepare this solution fresh prior to analysis.]

Assay preparation— Transfer an accurately weighed quantity of about 30mg of Felodipine to a 100-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.[NOTE—Prepare this solution fresh prior to analysis.]

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains 5-µm packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the capacity factor,k¢,is not less than 5.0;the column efficiency is not less than 1500theoretical plates;and the tailing factor is not greater than 1.5.Inject 20µLof the Resolution solutioninto the chromatograph,and adjust the sensitivity of the system so that the heights of the two peaks in the chromatogram are not less than 20%of recorder full scale.The resolution,R,between the first peak (felodipine oxidation product)and the second peak (felodipine)is not less than 2.5.

Procedure— Separately inject equal volumes (about 40µL)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 C18H19Cl2NO4in the portion of Felodipine taken by the formula: in which Cis the concentration,in mg per mL,of USP Felodipine RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.