A: Place a portion of the contents of Capsules, equivalent to about 50 mg of diazoxide, in a suitable centrifuge tube, add 25 mL of 0.1 N sodium hydroxide, shake for 15 minutes, and centrifuge: the supernatant so obtained responds to the Thin-layer Chromatographic Identification Test 201, a solvent system consisting of a mixture of ethyl acetate, methanol, and ammonium hydroxide (17:4:3) being used.

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

Medium: pH 6.8 phosphate buffer (see under Buffer Solutions in the section Reagents, Indicators, and Solutions); 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C8H7ClN2O2S dissolved from UV absorbances at the wavelength of maximum absorbance at about 268 nm of filtered portions of the solution under test in comparison with a solution of USP Diazoxide RS similarly prepared.

Tolerances— Not less than 75% (Q) of the labeled amount of C8H7ClN2O2S is dissolved in 45 minutes.

Mobile phase, Internal standard solution, Standard preparation, and Chromatographic system— Prepare as directed in the Assay under Diazoxide.

Assay preparation— Remove, as completely as possible, the contents of not less than 20 Capsules, and weigh accurately. Mix the combined contents, and transfer an accurately weighed quantity of the powder, equivalent to about 100 mg of diazoxide, to a 100-mL volumetric flask, add 15 mL of water, and shake by mechanical means for 5 minutes. Add 60 mL of methanol, shake by mechanical means for 15 minutes, dilute with methanol to volume, and mix. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, add 2.0 mL of Internal standard solution, dilute with a mixture of water and methanol (4:1) to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay under Diazoxide. Calculate the quantity, in mg, of C8H7ClN2O2S in the portion of Capsules taken by the formula: in which C is the concentration, in µg per mL, of USP Diazoxide RS in the Standard preparation, and RU and RS are the peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.