Medium: pH7.0buffer solution containing 0.5%sodium dodecyl sulfate in 0.01Msodium phosphate prepared by dissolving 30g of sodium dodecyl sulfate and 8.28g of monobasic sodium phosphate in 6000mLof water,and adjusting with 50%(w/v)sodium hydroxide solution to a pHof 7.0;900mL.

Apparatus 2: 50rpm.

Time: 30minutes.

Prewashed manganese dioxide— Transfer 10g of manganese dioxide to a suitable container,and treat as follows.Add 50mLof Dissolution Medium,and shake vigorously for 5minutes.Centrifuge,decant the supernatant layer,and discard.Repeat twice,first with Dissolution Mediumand then with water.Dry the solid at 100for 1hour before use.

Test solution— Transfer a filtered portion of the solution under test to a centrifuge tube containing about 10mg of Prewashed manganese dioxide per mLof transferred solution under test,and mix.Allow the mixture to stand for 30minutes with occasional shaking,centrifuge,and use a portion of the clear supernatant as the Test solution.

Blank— Proceed as directed for Test solution,except to use the Dissolution Medium.

Procedure— Determine the amount of C25H38O5dissolved from the difference between the UVabsorbances at the wavelengths of maximum and minimum absorbance at about 247nm and 257nm,respectively,on filtered portions of the Test solution,in comparison with a Standard solution having a known concentration of USP Simvastatin RSin the same Medium treated in the same way as the solution under test,each solution corrected for the Blank.

Tolerances— Not less than 75%(Q)of the labeled amount of C25H38O5is dissolved in 30minutes.

Diluting solution— Add 3.0mLof glacial acetic acid to 900mLof water.Adjust with 5Nsodium hydroxide to a pHof 4.0,and dilute with water to 1000mL.To 200mLof this solution,add 800mLof acetonitrile,and mix.

Buffer solution— Dissolve 3.9g of monobasic sodium phosphate in 900mLof water.Adjust,if necessary,with either 50%sodium hydroxide or 85%phosphoric acid to a pHof 4.5,dilute with water to 1000mL,and mix.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and Buffer solution(65:35).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Simvastatin RSin Diluting solution,and dilute quantitatively,and stepwise if necessary,with Diluting solutionto obtain a solution having a known concentration of about 0.1mg per mL.

Assay preparation— Transfer 10Tablets to a 250-mLvolumetric flask.Add a small volume of water (not more than 10mL),and swirl to disintegrate the Tablets.Dilute with Diluting solutionto volume,sonicate for 15minutes,and cool to room temperature.If necessary,dilute with Diluting solutionto volume.Centrifuge a portion of the mixture,and dilute a portion of the clear supernatant with Diluting solutionto obtain a solution having a concentration of about 0.1mg of simvastatin per mL.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 238-nm detector and a 4.6-mm ×25-cm column containing packing L1and maintained at a temperature of 45.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the capacity factor,k¢,is not less than 3.0;the column efficiency is not less than 4500theoretical plates;the tailing factor is not more than 2.0;and 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 areas of the major peaks.Calculate the quantity,in mg,of simvastatin (C25H38O5)in each Tablet taken by the formula: in which Lis the labeled quantity,in mg,of simvastatin in each Tablet;Dis the concentration,in mg per mL,of simvastatin in the Assay preparation;Cis the concentration,in mg per mL,of USP Simvastatin RSin the Standard preparation;and rUand rSare the peak areas of simvastatin obtained from the Assay preparationand the Standard preparation,respectively.