Simethicone Emulsion
DEFINITION
Simethicone Emulsion is a water-dispersible form of Simethicone composed of Simethicone, suitable emulsifiers, preservatives, and water. It may contain suitable viscosity-increasing agents. It contains an amount of polydimethylsiloxane ([–(CH3)2SiO–]n) that is NLT 85.0% and NMT 110.0% of the labeled amount of simethicone.
IDENTIFICATION
•  Infrared Absorption 197A
[Note—Use the Blank to set the instrument. ]
Blank, Standard solution, and Sample solution: Prepare as directed in the Assay.
Analysis: Place a suitable amount of the Sample solution (typically 5–25 drops) in the sample trough, and dry it with a stream of nitrogen or other appropriate means to evaporate the solvent. Examine the spectrum in the range between 1400 cm1 and 700 cm1.
Acceptance criteria: It exhibits maxima only at the same wavelengths as a similarly obtained spectrum of the Standard solution.
ASSAY
•  Procedure
[Note—Use glass apparatus only; avoid use of plasticware. Proper mixing of the Emulsion before sampling and testing is crucial. ]
Standard solution: 2 mg/mL of USP Polydimethylsiloxane RS in toluene. [Note—Treat a 25.0-mL aliquot in the same manner as the Blank, beginning with “add 50 mL of dilute hydrochloric acid (2 in 5)…”. ]
Sample: Equivalent to 50 mg of simethicone from Emulsion
Sample solution: To the Sample add 25.0 mL of toluene, and treat in the same manner as the Blank, beginning with “add 50 mL of dilute hydrochloric acid (2 in 5)…”.
Spectrometric conditions 
Mode: IR spectrophotometry
Cell: 0.5 mm
Analytical wavelength: Maximum absorbance at about 7.9 µm (1259 cm1)
Blank: To 25.0 mL of toluene add 50 mL of dilute hydrochloric acid (2 in 5), close the bottle securely with a cap having an inert liner, vigorously shake by hand for 5 s, and then shake for 5–20 min on a suitable shaker. [Note—The following shakers were found suitable: (1) a reciprocating shaker at a rate about 200 oscillations/min and a stroke of 38 ± 2 mm or (2) a wrist-action shaker with a radius of 13.3 ± 0.4 cm (measured from center of shaft to center of bottle) using an arc of 10 at a frequency of 300 ± 30 strokes/min. The recommended shaking time is about 20 min, which can be adjusted as needed. ] Centrifuge the mixture. [Note—The following centrifuging conditions were found suitable: at 1500 × g for 30–40 min. ] Remove from the centrifuge, and immediately transfer about 5 mL of the upper organic (toluene) layer to a 15-mL screw-capped test tube, containing about 1 g of anhydrous sodium sulfate. Close the tube with a screw-cap having an inert liner, agitate vigorously, and centrifuge the mixture until a clear supernatant is obtained. [Note—The following centrifuging conditions were found suitable: at 1500 × g for about 10 min. ]
Analysis 
[Note—Wash the cell with copious amounts of toluene, to ensure that there is no carryover or residue. ]
Samples: Standard solution, Sample solution, and Blank
Calculate the percentage of [–(CH3)2SiO–]n in the Emulsion:
Result = (AU/AS) × (CS/CU) × 100
AU== absorbance of the Sample solution
AS== absorbance of the Standard solution
CS== concentration of USP Polydimethylsiloxane RS in the Standard solution (mg/mL)
CU== nominal concentration of simethicone in the Sample solution (mg/mL)
Acceptance criteria: 85.0%–110.0%
IMPURITIES
Inorganic Impurities 
•  Heavy Metals
Standard solution: To 20 mL of chloroform add 1.0 mL of a freshly prepared 0.002% solution of dithizone in chloroform, 0.5 mL of Standard Lead Solution (see Heavy Metals 231) (containing 10 µg of lead/mL), and 0.5 mL of a mixture of 1 volume of ammonia TS and 9 volumes of a 0.2% solution of hydroxylamine hydrochloride.
Sample solution: 1.0 g of simethicone from Emulsion in 10 mL of chloroform. Dilute with the same solvent to 20 mL. Add 1.0 mL of a freshly prepared 0.002% solution of dithizone in chloroform, 0.5 mL of water, and 0.5 mL of a mixture of 1 volume of ammonia TS and 9 volumes of a 0.2% solution of hydroxylamine hydrochloride.
Analysis: Immediately shake both solutions vigorously for 1 min.
Acceptance criteria: NMT 5 ppm. Any red color in the Sample solution is not more intense than that in the Standard solution.
SPECIFIC TESTS
•  Microbial Enumeration Tests 61: The total aerobic microbial count does not exceed 100 cfu/g.
•  Defoaming Activity
Foaming solution: 10 mg/mL of octoxynol 9 in water
Sample solution: Transfer a quantity of Emulsion, equivalent to 300 mg of simethicone, to a 60-mL bottle. Dilute with water to 30 g, cap the bottle, and shake vigorously.
Analysis 
[Note—For each test, use a clean, unused, 250-mL glass jar. ]
Add, dropwise, 500 µL of the Sample solution to a clean, unused, cylindrical 250-mL glass jar, fitted with a 50-mm cap, containing 100 mL of the Foaming solution. Cap the jar, and clamp it in an upright position on a wrist-action shaker. Using a radius of 13.3 ± 0.4 cm (measured from the center of the shaft to the center of the bottle), shake for 10 s through an arc of 10 degrees at a frequency of 300 ± 30 strokes/min. Record the time required for the foam to collapse. The time, in s, for foam collapse is determined at the instant the first portion of foam-free liquid surface appears, measured from the end of the shaking period.
Acceptance criteria: The defoaming activity time does not exceed 15 s.
ADDITIONAL REQUIREMENTS
•  Packaging and Storage: Preserve in tight containers.
•  USP Reference Standards 11
USP Polydimethylsiloxane RS Click to View Structure
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/QuestionContactExpert Committee
MonographElena Gonikberg, Ph.D.
Principal Scientific Liaison
1-301-816-8251
(SM32010) Monographs - Small Molecules 3
61Radhakrishna S Tirumalai, Ph.D.
Principal Scientific Liaison
1-301-816-8339
(GCM2010) General Chapters - Microbiology
Reference StandardsRS Technical Services
1-301-816-8129
rstech@usp.org
USP35–NF30 Page 4638
Pharmacopeial Forum: Volume No. 35(6) Page 1477