Packaging and storage—
Preserve in tight containers.
Defoaming activity—
Foaming solution—
Dissolve 1 g of octoxynol 9 in 100 mL of water.
Test preparation—
Transfer 200 mg of Simethicone to a 60-mL bottle, add 50 mL of tertiary butyl alcohol, cap the bottle, and shake vigorously. [NOTE—Warm slightly, if necessary, to dissolve.]
Procedure—
[NOTE—For each test, employ a clean, unused, 250-mL glass jar.] Add, dropwise, 500 µL of the Test preparation 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. Employing a radius of 13.3 ± 0.4 cm (measured from center of shaft to center of bottle), shake for 10 seconds through an arc of 10 degrees at a frequency of 300 ± 30 strokes per minute. Record the time required for the foam to collapse. The time, in seconds, 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. The defoaming activity time does not exceed 15 seconds.
Loss on heating—
Heat about 15 g, accurately weighed, in an open, tared vessel having a diameter of 5.5 ± 0.5 cm and a wall height of 2.5 ± 1.0 cm at 200
in a circulating air oven for 4 hours, and allow to come to room temperature in a desiccator before weighing: it loses not more than 18.0% of its weight.
Heavy metals—
Mix 1.0 g of Simethicone with 10 mL of chloroform, and 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. Concomitantly prepare a Standard solution as follows: 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 per 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. Immediately shake both solutions vigorously for 1 minute. Any red color in the test solution is not more intense than that in the Standard solution (5 µg per g).
Organic volatile impurities, Method IV 467:
meets the requirements.
Content of silicon dioxide—
Transfer 3.00 g of Simethicone to a screw-capped bottle, add 10.0 mL of
n-hexane, cap, and mix by shaking
(Test solution). Prepare a
Standard solution by similarly treating a 3.00-g portion of
USP Simethicone RS. Prepare a
Dimethicone preparation by similarly treating a 3.00-g portion of dimethicone having a viscosity of 500 centistokes. Using an IR spectrophotometer and 0.1-mm cells, determine the absorbance spectra of well-mixed portions of the
Test solution, the
Standard solution, and the
Dimethicone preparation between 7 and 9 µm, using
n-hexane as the blank. Determine the absorbances of the
Test solution, the
Standard solution, and the
Dimethicone preparation at the wavelength of minimum absorbance at about 8.2 µm observed in the spectrum obtained from the
Dimethicone preparation. Calculate the percentage of silicon dioxide in the Simethicone taken by the formula:
C(
AU 
AD)/(
AS AD),
in which
C is the designated percentage of silicon dioxide in
USP Simethicone RS;
AU is the absorbance of the
Test solution; AD is the absorbance of the
Dimethicone preparation; and
AS is the absorbance of the
Standard solution.
Assay—
Transfer about 50 mg of Simethicone, accurately weighed, to a round, narrow-mouth, screw-capped, 120-mL bottle, add 25.0 mL of toluene, and swirl to disperse. Add 50 mL of dilute hydrochloric acid (2 in 5), close the bottle securely with a cap having an inert liner, and shake for 5 minutes, accurately timed, on a reciprocating shaker at a suitable rate (e.g., about 200 oscillations per minute and a stroke of 38 ± 2 mm). Transfer the mixture to a 125-mL separator, and remove about 5 mL of the upper organic (toluene) layer to a 15-mL screw-capped test tube containing 0.5 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
(Assay preparation) is obtained. Prepare a
Standard preparation by similarly treating a 25.0-mL portion of a solution of
USP Polydimethylsiloxane RS in toluene having a known concentration of about 2 mg per mL. Prepare a procedural blank by similarly treating 25.0 mL of toluene. Concomitantly determine the absorbances of the solutions in 0.5-mm cells at the wavelength of maximum absorbance at about 7.9 µm, with an IR spectrophotometer, using the blank to set the instrument. Calculate the quantity, in mg, of [–(CH
3)
2SiO–]
n in the Simethicone taken by the formula:
25C(AU / AS),
in which
C is the concentration, in mg per mL, of
USP Polydimethylsiloxane RS in the
Standard preparation; and
AU and
AS are the absorbances of the
Assay preparation and the
Standard preparation, respectively.
;)
-(Trimethylsilyl)-
-methylpoly[oxy(dimethylsilylene)], mixture with silicon dioxide
