Identification—
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 Sodium RS.
Heavy metals 
231
—
Transfer 2.0 g to a platinum crucible, and ignite until free from carbon. Cool, moisten the residue with 1 mL of hydrochloric acid, and evaporate on a steam bath to dryness. Add 2 mL of 6 N acetic acid, digest on a steam bath for 5 minutes, filter into one of a pair of matched 50-mL color-comparison tubes, and wash the residue with sufficient water to make 25 mL: the limit is 0.001%.
Limit of bis(2-ethylhexyl) maleate—
Mobile phase—
Prepare a filtered and degassed mixture of alcohol and water (78:22). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard solution—
Dissolve an accurately weighed quantity of
USP Bis(2-ethylhexyl) Maleate RS in alcohol, and dilute quantitatively, and stepwise if necessary, to obtain a solution having a known concentration of about 80 µg per mL.
Test solution—
Transfer about 1.0 g of Docusate Sodium, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with alcohol to volume, and mix. If necessary, warm the mixture using the steam bath to achieve a complete dissolution.
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm× 3-cm column that contains 3.5-µm packing L1. The column temperature is maintained at 30
. The flow rate is about 1.0 mL per minute. Chromatograph the
Standard solution, and record the peak responses as directed for
Procedure: the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 3 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure the responses for the bis(2-ethylhexyl) maleate peaks. Calculate the percentage of bis(2-ethylhexyl) maleate in the portion of Docusate Sodium taken by the formula:
5C/W(rU / rS)
in which
C is the concentration, in µg per mL, of
USP Bis(2-ethylhexyl) Maleate RS in the
Standard solution; W is the weight, in mg, of Docusate Sodium taken to prepare the
Test solution; and
rU and
rS are the peak responses of bis(2-ethylhexyl) maleate obtained from the
Test solution and the
Standard solution, respectively: not more than 0.4% is found.
Assay—
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 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 Sodium, accurately weighed, in 50 mL of chloroform in a glass-stoppered, 250-mL conical flask. Add 50 mL of
Salt solution and 0.5 mL 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 3.009 mg of C
20H
37NaO
7S.
;)