Medium: water; 500 mL.

Apparatus 2: 50 rpm.

Time: 15 minutes.

Procedure— Place 1 Capsule in each vessel, and allow the Capsule to sink to the bottom of the vessel before starting rotation of the blade. Observe the Capsules, and record the time taken for each capsule shell to rupture.

Tolerances— The requirements are met if all of the Capsules tested rupture in not more than 15 minutes. If 1 or 2 of the Capsules rupture in more than 15 but not more than 30 minutes, repeat the test on 12 additional Capsules. Not more than 2 of the total of 18 Capsules tested rupture in more than 15 but not more than 30 minutes.

solid-filled capsules: meet the requirements for Content Uniformity.

solution-filled capsules: meet the requirements for Weight Variation.

Methanol–water solution— Transfer 180 mL of water to a 1000-mL volumetric flask, dilute with methanol to volume, and mix.

Tetrabutylammonium hydroxide–methanol solution— Prepare a solution of tetrabutylammonium hydroxide in methanol containing 25 g per 100 mL.

Mobile phase— Mix 180 mL of water, 6.0 mL of glacial acetic acid, and 8.0 mL of Tetrabutylammonium hydroxide–methanol solution in a 1000-mL volumetric flask, dilute with methanol to volume, and mix. The water concentration may be varied to meet system suitability requirements and to provide a suitable elution time (about 5 minutes) for docusate potassium.

Standard preparation— Dissolve in Methanol–water solution a suitable quantity, accurately weighed, of USP Docusate Sodium RS, and dilute quantitatively with the same solvent to obtain a solution having a known concentration of about 4 mg per mL, calculated on the anhydrous basis.

Assay preparation for solid-filled capsules— Open and empty into a suitable container the contents of a counted number of Capsules, equivalent to about 1000 mg of docusate potassium. Place the capsule shells in the container, and add 250.0 mL of Methanol-water solution. Shake by mechanical means for 20 minutes, and clarify a portion of the mixture by centrifuging. Pass a portion of the clear supernatant through a membrane filter having a 0.5-µm or finer porosity.

Assay preparation for solution-filled capsules— Cut open a counted number of Capsules, equivalent to about 2.5 g of docusate potassium, and place the shells and contents in a suitable container. Add about 25 mL of methanol, agitate for not less than 2 minutes, and decant the liquid into a 200-mL volumetric flask. Repeat the addition of methanol, agitation, and decanting not less than four times. Dilute with methanol to volume, and mix. Pipet 8 mL of this solution into a 25-mL volumetric flask, add 4.5 mL of water, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)—The chromatograph is equipped with a refractive index detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1.8 mL per minute. Chromatograph five replicate injections of the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation is not more than 3.0%.

Procedure— Separately inject equal volumes (about 100 µL) of the Standard preparation and the appropriate Assay preparation into the chromatograph by means of a suitable microsyringe or sampling valve, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of docusate potassium (C20H37KO7S) in each solid-filled Capsule taken by the formula: and calculate the quantity, in mg, of docusate potassium (C20H37KO7S) in each solution-filled Capsule taken by the formula: in which 460.67 and 444.56 are the molecular weights of docusate potassium and docusate sodium, respectively; C is the concentration, in mg per mL, of anhydrous USP Docusate Sodium RS in the Standard preparation; N is the number of Capsules taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.