Medium: water; 500 mL.

Apparatus 2: 50 rpm, sinkers not used.

Time: 30 minutes.

Buffer solution— Dissolve about 1.534 g of monobasic ammonium phosphate in about 800 mL of water, and adjust with phosphoric acid or ammonium hydroxide to a pH of 3.5.

Mobile phase— Prepare a filtered and degassed mixture of methanol and Buffer solution (7:3).

Standard solution— [note—A volume of methanol, not exceeding 2% of the final volume of solution, may be used to aid in dissolving the USP Reference Standard.] Dissolve an accurately weighed quantity of USP Fluvastatin Sodium RS in Medium to obtain a solution having a known concentration of fluvastatin corresponding to that obtained when 1 Capsule is dissolved in 500 mL of solvent.

Test solution— Withdraw 20-mL portions of liquid under test from each vessel, and pass through a suitable filter, discarding the first 2 mL of the filtrate.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 235-nm detector, a suitable 7-µm guard column that contains packing L1, and a 4.6-mm × 10-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 relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the areas for the fluvastatin peaks. From the measured peak areas, calculate the quantity of C24H26FNO4 dissolved.

Tolerances— Not less than 80% (Q) of the labeled amount of C24H26FNO4 is dissolved in 30 minutes.

pH 7.2 Buffer, Methanol–acetonitrile mixture, Solution A, Solution B, Mobile phase, and Diluent— Proceed as directed in the Assay.

System suitability solution— Use the System suitability preparation, prepared as directed in the Assay.

Standard solution— Use the Standard preparation, prepared as directed in the Assay.

Test solution— Use the Assay preparation, prepared as directed in the Assay.

Chromatographic system— Proceed as directed in the Assay, except use the liquid chromatograph equipped with either a programmable variable wavelength detector or two separate detectors capable of monitoring at 305 nm and at 365 nm. Chromatograph the System suitability solution, and record the peak responses at 305 nm as directed for Procedure. Identify the peaks corresponding to fluvastatin and fluvastatin anti-isomer. The resolution, R, between fluvastatin anti-isomer and fluvastatin is not less than 1.4; and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 25 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms at 305 nm and 365 nm, identify the impurities listed in Table 1, and measure the peak responses. [note—3-Hydroxy-5-keto fluvastatin is monitored using a wavelength of 365 nm, and all other compounds are monitored at 305 nm.] Calculate the percentage of each impurity, except for 3-hydroxy-5-keto fluvastatin, in the portion of Capsules taken by the formula: in which F is the relative response factor as listed in Table 1 [note—Use F equal to 1.0 for unknown impurities]; 411.48 and 433.45 are the molecular weights of fluvastatin and fluvastatin sodium, respectively; CS is the concentration, in mg per mL, of USP Fluvastatin Sodium RS in the Standard solution; CT is the concentration, in mg per mL, of fluvastatin in the Test solution, based on the label claim; ri (305) is the peak response at 305 nm for each impurity obtained from the Test solution; and rS (305) is the peak response at 305 nm for the fluvastatin peak, obtained from the Standard solution.

pH 7.2 Buffer— Prepare a solution containing 40 mL of 25% aqueous tetramethylammonium hydroxide in 1 L of water, and adjust with approximately 4.5 mL of phosphoric acid to a pH of 7.2 ± 0.2.

Methanol–acetonitrile mixture— Prepare a mixture of methanol and acetonitrile (3:2).

Solution A— Prepare a filtered and degassed mixture of pH 7.2 Buffer and Methanol–acetonitrile mixture (87.5:12.5).

Solution B— Prepare a filtered and degassed mixture of Methanol–acetonitrile mixture and pH 7.2 Buffer (87.5:12.5).

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system.

Diluent— Prepare a mixture of pH 7.2 Buffer and Methanol–acetonitrile mixture (54:46).

System suitability preparation— Dissolve an accurately weighed quantity of USP Fluvastatin for System Suitability RS in Diluent to obtain a solution having a known concentration of about 0.42 mg of fluvastatin sodium per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Fluvastatin Sodium RS in Diluent to obtain a solution having a known concentration of about 0.42 mg of fluvastatin sodium per mL.

Assay stock preparation— Transfer the contents and the empty shells of 10 Capsules to a 200-mL glass-stoppered flask. Add 100.0 mL of methanol, and stir with a magnetic or mechanical stirrer for 45 minutes. Centrifuge a portion of this solution at 4000 rpm for 20 minutes.

Assay preparation— Quantitatively transfer an amount of the Assay stock preparation, containing 20.0 mg of fluvastatin based on the label claim, to a 50-mL volumetric flask, and dilute with Diluent to volume.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 305-nm detector and a 4.6-mm × 5-cm column that contains 5-µm packing Ll. The flow rate is about 2.0 mL per minute. The chromatograph is programmed as follows. [note—Adjust the start time of the gradient step and the equilibration time for each instrument.] Chromatograph the System suitability preparation, and record the peak responses as directed for Procedure: the retention time of the fluvastatin peak is about 5.4 minutes; the relative retention times are about 1.0 for fluvastatin and 1.2 for fluvastatin anti-isomer; the resolution, R, between fluvastatin anti-isomer and fluvastatin is not less than 1.4; and the relative standard deviation for replicate injections is not more than 1.5%. [note–If the retention time of the fluvastatin peak exceeds 5.7 minutes, adjust the isocratic step accordingly, so that both the fluvastatin peak and the anti-isomer peak elute within the isocratic region.]

Procedure— Separately inject equal volumes (about 25 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the fluvastatin peaks. Calculate the quantity, in mg, of fluvastatin (C24H26FNO4) in the portion of Capsules taken by the formula: in which 411.48 and 433.45 are the molecular weights of fluvastatin and fluvastatin sodium, respectively; V is the volume, in mL, of the Assay stock preparation taken to prepare the Assay preparation; C is the concentration, in mg per mL, of USP Fluvastatin Sodium RS in the Standard preparation; and rU and rS are the fluvastatin peak responses obtained from the Assay preparation and the Standard preparation, respectively.