A: Transfer 1 Tablet to a centrifuge tube, add 1 mL of water and 4.0 mL of acetonitrile, and shake by mechanical means to disintegrate the Tablet. Sonicate for 4 minutes, and centrifuge for 4 minutes to obtain the test solution. Apply separately 5 µL each of the Standard solution and the test solution to the chromatographic plate, and proceed as directed under Thin-layer Chromatographic Identification Test 201 using 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 preparation corresponds to that of the major peak in the chromatogram of the Standard preparation as obtained in the Assay.

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

Medium: Buffer solution; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

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 C24H36O5 is dissolved in 30 minutes.

(Official January 1, 2007)

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

Dissolving solvent— Add 3.0 mL of glacial acetic acid to 900 mL of water contained in a 1 L beaker, adjust to a pH of 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-mL volumetric 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 Suitability under Chromatography 621).

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

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

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 230-nm detector and a 4.5-mm × 25-cm column that contains packing L1 and is maintained at 45. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 3000 theoretical 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 50 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C24H36O5 in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Lovastatin RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.