A: Thin-Layer Chromatographic Identification Test 201—

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

Medium— Dissolve 1.38 g of monobasic sodium phosphate and 20 g of sodium lauryl 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; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Mobile phase— Proceed as directed in the Assay.

Standard solution— Accurately weigh approximately 44 mg of USP Lovastatin RS into a 500-mL volumetric flask, and dissolve in no more than 20 mL of methanol. Dilute with Medium to volume, and mix well. Further dilute this solution with Medium to obtain a solution containing L/900 mg per mL, with L being the Tablet label claim, in mg.

Test solution— Pass the solution under test through a suitable 0.45-µm filter.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 230-nm detector and a 4.6-mm × 5-cm column that contains 5-µm packing L1. The flow rate is about 2.0 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the capacity factor, k¢, is greater than 2.0; the tailing factor is less than 2.0; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the percentage of lovastatin dissolved by the formula: in which rU and rS are the peak responses obtained from the Test solution and the Standard solution, respectively; CS is the concentration, in mg per mL, of the Standard solution; 900 is the volume, in mL, of Medium; and L is the Tablet label claim, in mg.

Tolerances— Not less than 80% (Q) of the labeled amount of C24H36O5 is dissolved in 30 minutes.

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 fewer 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 to room temperature, and allow the solution to stand for 30 minutes. Dilute with Dissolving solvent to volume, and mix. Centrifuge a portion of this solution, transfer 5.0 mL of the clear supernatant to a 25-mL volumetric flask, dilute with Dissolving solvent to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 230-nm detector and a 4.6-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 greater than 3000 theoretical plates, the tailing factor is less 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 percentage of the labeled amount of C24H36O5 in the portion of Tablets taken by the formula: in which CS is the concentration, in µg per mL, of USP Lovastatin RS in the Standard preparation; CU is the concentration of lovastatin, in µg per mL, in the Assay preparation, based on the label claim; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.