Docusate Sodium
(dok' ue sate soe' dee um).

C20H37NaO7S 444.56
Butanedioic acid, sulfo-, 1,4-bis(2-ethylhexyl) ester, sodium salt;    
Sodium 1,4-bis(2-ethylhexyl) sulfosuccinate     [577-11-7].
Docusate Sodium contains NLT 99.0% and NMT 100.5% of C20H37NaO7S, calculated on the anhydrous basis.
•  Procedure
Sample:  Place a small piece of Docusate Sodium on a salt plate, add one 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.
Acceptance criteria:  The IR absorption spectrum of the film exhibits maxima only at the same wavelengths as that of a similar preparation of USP Docusate Sodium RS.
•  Procedure
Solution A:  2.5 g/L of tetra-n-butylammonium iodide in water
Solution B:  A mixture of 100 g/L of anhydrous sodium sulfate and 10 g/L of sodium carbonate in water
Sample:  50 mg
Analysis:  Dissolve the Sample in 50 mL of chloroform in a glass-stoppered, 250-mL conical flask. Add 50 mL of Solution B and 500 µL of bromophenol blue TS. Titrate with Solution A until 1 mL from the endpoint, and shake the stoppered flask vigorously for 2 min. Continue the titration in two-drop increments, shaking vigorously for 10 s after each addition, and then allow the flask to stand 10 s. Continue the titration until the chloroform layer just assumes a blue color. Each mL of Solution A is equivalent to 3.009 mg of C20H37NaO7S.
Acceptance criteria:  99.0%–100.5% on the anhydrous basis
Inorganic Impurities 
•  Residue on Ignition 281: Between 15.5% and 16.5%, calculated on the anhydrous basis
Procedure:  Transfer about 1 g, accurately weighed, to a tared crucible, ignite until thoroughly charred, and cool. Moisten the ash with 1 mL of sulfuric acid, and complete the ignition by heating at 800 ± 25 for 15-min periods to constant weight.
•  Heavy Metals 231
Sample:  2.0 g
Analysis:  Transfer the Sample 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 min, filter into one of a pair of matched 50-mL, color-comparison tubes, and wash the residue with sufficient water to make 25 mL.
Acceptance criteria:  NMT 10 ppm
Organic Impurities 
•  Procedure: Limit of Bis(2-Ethylhexyl) Maleate
Mobile phase:  Alcohol and water (78:22), filtered and degassed
Standard solution:  80 µg/mL of USP Bis(2-ethylhexyl) Maleate RS in alcohol
Sample solution:  20 mg/mL of Docusate Sodium in alcohol. [Note—If necessary, warm the mixture using the steam bath to achieve a complete dissolution. ]
Chromatographic system  
Mode:  LC
Detector:  UV 210 nm
Column:  4.6-mm × 3-cm; 3.5-µm packing L1
Column temperature:  30
Flow rate:  1 mL/min
Injection size:  3 µL
System suitability 
Sample:  Standard solution
Suitability requirements 
Relative standard deviation:  NMT 2.0% for replicate injections
Samples:  Standard solution and Sample solution
Calculate the percentage of bis(2-ethylhexyl) maleate in the portion of Docusate Sodium taken:
Result = (rU/rS) × (CS/CU) × 100
rU== peak response of bis(2-ethylhexyl) maleate from the Sample solution
rS== peak response of bis(2-ethylhexyl) maleate from the Standard solution
CS== concentration of USP Bis(2-ethylhexyl) Maleate RS in the Standard solution (mg/mL)
CU== concentration of Docusate Sodium in the Sample solution (mg/mL)
Acceptance criteria:  NMT 0.4%
•  Clarity of Solution
Sample solution:  25 g in 100 mL of alcohol
Acceptance criteria:  The Sample solution does not develop a haze within 24 h.
•  Packaging and Storage: Preserve in well-closed containers.
•  USP Reference Standards 11
USP Bis(2-ethylhexyl) Maleate RS Click to View Structure
    C20H36O4        340.51
USP Docusate Sodium RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Elena Gonikberg, Ph.D.
Principal Scientific Liaison
(SM32010) Monographs - Small Molecules 3
Reference Standards RS Technical Services
USP35–NF30 Page 2959
Pharmacopeial Forum: Volume No. 35(5) Page 1095