Medium: 0.2 M pH 7.5 phosphate buffer prepared by dissolving 545 g of monobasic potassium phosphate in 5 L of water, adding 131 g of sodium hydroxide, diluting with water to about 19.5 L, and mixing well. Adjust with either 1 N phosphoric acid or 1 N sodium hydroxide to a pH of 7.5, and dilute with water to 20 L; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C15H22O3 dissolved from UV absorbances at the wavelength of maximum absorbance at about 276 nm on filtered portions of the solution under test, suitably diluted with 1 N sodium hydroxide, in comparison with a Standard solution obtained as follows. Prepare a Standard stock solution of USP Gemfibrozil RS having a known concentration of about 0.33 mg per mL in Medium. [note—Initially dissolve the USP Reference Standard in an amount of methanol not to exceed 1% of the volume of the Standard stock solution.] Quantitatively dilute the Standard stock solution with 1 N sodium hydroxide to obtain a Standard solution having a concentration estimated to correspond to that of the filtered and diluted solution under test.

Tolerances— Not less than 80% (Q) of the labeled amount of C15H22O3 is dissolved in 30 minutes.

Mobile phase, Standard preparation, System suitability preparation, and Chromatographic system— Proceed as directed in the Assay under Gemfibrozil.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of gemfibrozil, to a 100-mL volumetric flask, add about 80 mL of methanol, and shake to dissolve. Dilute with methanol to volume, mix, and filter. Transfer 5.0 mL of this clear solution to a 25-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay under Gemfibrozil. Calculate the quantity, in mg, of gemfibrozil (C15H22O3) in the portion of Tablets taken by the formula: in which the terms are as defined therein.