A: Infrared Absorption 197S—

Standard solution— Prepare a solution of USP Cilostazol RS in chloroform having a known concentration of 100 mg per mL.

Test solution— Accurately transfer a quantity of finely powdered Tablets, equivalent to about 100 mg of cilostazol, into a glass container. Add 1 mL of chloroform, shake for 1 minute, and filter through a 0.5-µm or finer filter.

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

Mobile phase— Prepare a filtered and degassed mixture of water, acetonitrile, and methanol (10:7:3). Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Prepare a solution of benzophenone in methanol having a known concentration of 4 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Cilostazol RS and an appropriate amount of Internal standard solution and dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 0.1 mg of USP Cilostazol RS and 0.04 mg of the internal standard per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 50 mg of cilostazol, to a suitable volumetric flask and add an appropriate quantity of Internal standard solution. Dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 0.1 mg of USP Cilostazol RS and 0.04 mg of the internal standard per mL. Pass a portion of this solution through a membrane filter having a 0.5-µm or finer porosity, and use the filtrate.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 150-cm column that contains packing L1. The flow rate is about 1 mL per minute. The column temperature is maintained at ambient temperature. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the cilostazol and benzophenone peaks eluted in this order is not less than 9.0; and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the percentage of the labeled amount of C20H27N5O2 in the portion of Tablets taken by the formula: in which CS is the concentration, in mg per mL, of USP Cilostazol RS in the Standard preparation; CU is the concentration of cilostazol in the Assay preparation, based on the labeled quantity per Tablet and the extent of dilution; and rU and rS are the peak responses of cilostazol obtained from the Assay preparation and the Standard preparation, respectively.