A: Transfer 1Tablet to a centrifuge tube,add 1mLof water and 4.0mLof acetonitrile,and shake by mechanical means to disintegrate the Tablet.Sonicate for 4minutes,and centrifuge for 4minutes to obtain the test solution.Apply separately 5µLeach of the Standard solution and the test solution to the chromatographic plate,and proceed as directed under Thin-layer Chromatographic Identification Test á201ñusing a prepared mixture of cyclohexane,chloroform,and isopropyl alcohol (5:2:1)as the developing solvent.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that of the major peak in the chromatogram of the Standard preparationas obtained in the Assay.

Buffer solution— Dissolve 1.38g of monobasic sodium phosphate and 20g of sodium dodecyl sulfate in 900mLof water.Adjust with 1Nsodium hydroxide to a pHof 7.0,dilute with water to 1000mL,and mix.

Medium: Buffer solution;900mL.

Apparatus 2: 50rpm.

Time: 30minutes.

Procedure— Determine the amount of Lovastatin dissolved using the method given under Assay,making any necessary volumetric adjustments.

Tolerances— Not less than 80%(Q)of the labeled amount of C24H36O5is dissolved in 30minutes.

Buffer solution— Dissolve 3.45g of monobasic sodium phosphate in 900mLof water,adjust with phosphoric acid to a pHof 4.0,dilute with water to 1000mL,and mix.

Dissolving solvent— Add 3.0mLof glacial acetic acid to 900mLof water contained in a 1liter beaker,adjust to a pHof 4.0,determined electrometrically,by the addition of a solution of sodium hydroxide (20%),and mix.Transfer the contents of the beaker to a 1000-mLvolumetric flask,dilute with water to volume,and mix.Prepare a mixture of acetonitrile and the resultant solution (80:20).

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile,Buffer solution,and methanol (5:3:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Lovastatin RSin Dissolving solventto obtain a solution having a known concentration of about 40µg per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 40mg of lovastatin,to a 200-mLvolumetric flask.Add about 150mLof Dissolving solvent,and sonicate for 20minutes.Cool,dilute with Dissolving solventto volume,and mix.Transfer 20.0mLto a 100-mLvolumetric flask,dilute with Dissolving solventto volume,and mix.Centrifuge a portion of this solution.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 230-nm detector and a 4.5-mm ×25-cm column that contains packing L1and is maintained at 45.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency is not less than 3000theoretical plates,the capacity factor,k¢,is not less than 3.5,the tailing factor is not greater than 2.0,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50µL)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 C24H36O5in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Lovastatin RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.