Standard preparation—
Transfer about 100 mg of
USP Docusate Sodium RS, accurately weighed, to a 100-mL volumetric flask, dissolve in 2.5 mL of alcohol, dilute with water to volume, and mix. Transfer 10.0 mL of this solution to a 1000-mL volumetric flask, dilute with water to volume, and mix. The concentration of
USP Docusate Sodium RS in the
Standard preparation is about 10 µg per mL.
Procedure—
Transfer 20.0 mL each of the
Standard preparation and of the
Assay preparation to individual separators, and place 20 mL of water in a third separator to provide the blank. To each separator add 5 drops of hydrochloric acid, mix by swirling, add 1.0 mL of methylene blue solution (1 in 1000), and mix by swirling. To each separator add 20.0 mL of chloroform, and shake vigorously for 5 minutes. Wash each chloroform solution, in clean separators, with 20 mL of water, shaking vigorously for 60 seconds. Discard the washings, and filter each chloroform solution through a layer of 3 g of anhydrous granular sodium sulfate, supported on glass wool, into a 100-mL volumetric flask, washing each separator with two 10-mL portions of chloroform and filtering the washings into each flask. Dilute each flask with chloroform to volume, and mix. Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 650 nm, with a suitable spectrophotometer, using the blank to set the instrument. Calculate the quantity, in mg, of C
20H
37NaO
7S in each mL of Syrup taken by the formula:
(10C / V)(AU / AS),
in which
C is the concentration, in µg per mL, calculated on the anhydrous basis, of
USP Docusate Sodium RS in the
Standard preparation; V is the volume, in mL, of Syrup taken; and
AU and
AS are the absorbances of the solutions from the
Assay preparation and the
Standard preparation, respectively.
621
) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a two-phase solvent system consisting of ethyl acetate, water, alcohol, and ammonium hydroxide (25:20:10:1) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Expose the plate to iodine vapors in a closed chamber for about 30 minutes, and locate the spots: the test preparation produces a spot at the same RF value and of approximately the same size as that obtained from the Standard solution.