A: Place a small piece of it on a salt plate, add 1 drop of acetone, and promptly cover with another salt plate. Rub the plates together to dissolve the specimen, slide the plates apart, and allow the acetone to evaporate: the IR absorption spectrum of the film so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Docusate Calcium RS.

B: Dissolve 25 mg in 2 mL of acetone. Add 2 mL of water, mix, and add 2 drops of sulfuric acid: a white precipitate is formed.

C: Prepare a solution of it in isopropyl alcohol containing 10 mg per mL, and mix. Apply, with the aid of a stream of nitrogen, 10 µL of this solution and 10 µL of an isopropyl alcohol solution of USP Docusate Calcium RS containing 10 mg per mL to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of ethyl acetate, ammonium hydroxide, and alcohol (5:2:2) until the solvent front has moved 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 RF value of the spot obtained from the test solution corresponds to that obtained from the Standard solution.

Electrolyte solution— In a 250-mL borosilicate glass beaker dissolve 21.2 g of lithium perchlorate in 175 mL of water, and adjust by the dropwise addition of glacial acetic acid to a pH of 3.0. Transfer to a 200-mL volumetric flask, dilute with water to volume, and mix.

Sample stock solution— Transfer the equivalent of 12.5 g of anhydrous Docusate Calcium, accurately weighed, to a 150-mL beaker, add about 85 mL of isopropyl alcohol, stir to dissolve, and transfer to a 250-mL volumetric flask. Rinse the beaker with another 85-mL portion of isopropyl alcohol, stirring, if necessary, to dissolve any residual Docusate Calcium, combine the rinsing with the solution in the volumetric flask, dilute with isopropyl alcohol to volume, and mix.

Standard solution— Transfer 25 mg of USP Bis(2-ethylhexyl) maleate RS, accurately weighed, to a 25-mL volumetric flask, dissolve in isopropyl alcohol, dilute with isopropyl alcohol to volume, and mix. In a second 100-mL volumetric flask combine 10.0 mL of this solution, 50.0 mL of Sample stock solution, and 20.0 mL of Electrolyte solution, mix, and allow to stand for 2 minutes. Dilute with isopropyl alcohol to volume, and mix.

Test solution— In a 100-mL volumetric flask combine 50.0 mL of Sample stock solution with 20.0 mL of Electrolyte solution, mix, and allow to stand for 2 minutes. Dilute with isopropyl alcohol to volume, and mix.

Procedure— Transfer a portion of the Test solution to a polarographic cell, and deaerate by bubbling through the solution, for 15 minutes, nitrogen that has previously been passed through isopropyl alcohol. Continue to flush the surface of the solution with the nitrogen, insert the dropping mercury electrode of a suitable polarograph (see Polarography 801), and record the polarogram from 0.9 to 1.5 volts, using a saturated calomel electrode as the reference electrode. Determine the height of the polarogram at the half-wave potential, at about 1.2 volts, measuring from the baseline. From this height subtract the height, at the same potential, of the polarogram obtained from a blank solution prepared by diluting 20.0 mL of Electrolyte solution with isopropyl alcohol to 100 mL in a volumetric flask and mixing. Designate this corrected height as HT. Concomitantly and similarly determine the height of the polarogram of the Standard solution, and subtract the blank value from it. Designate the result as HS. The value, HT, is not greater than one-half HS, corresponding to not more than 0.4% of bis(2-ethylhexyl) maleate.

(Official January 1, 2007)

Tetra-n-butylammonium iodide solution— Transfer 1.250 g of tetra-n-butylammonium iodide to a 500-mL volumetric flask, dilute with water to volume, and mix.

Salt solution— Transfer 100 g of anhydrous sodium sulfate and 10 g of sodium carbonate to a 400-mL beaker, and add sufficient water to dissolve the two salts. Transfer the solution to a 1000-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Dissolve about 50 mg of Docusate Calcium, accurately weighed, in 50 mL of chloroform in a glass-stoppered, 250-mL conical flask. Add 50 mL of Salt solution and 500 µL of bromophenol blue TS, and mix. Titrate with Tetra-n-butylammonium iodide solution until about 1 mL from the endpoint, and shake the stoppered flask vigorously for about 2 minutes. Continue the titration in 2-drop increments, shaking vigorously for about 10 seconds after each addition, and then allow the flask to stand about 10 seconds. Continue the titration until the chloroform layer just assumes a blue color. Each mL of Tetra-n-butylammonium iodide solution is equivalent to 2.989 mg of C40H74CaO14S2.