» Simethicone is a mixture of fully methylated linear siloxane polymers containing repeating units of the formula [(CH3)2SiO]n, stabilized with trimethylsiloxy end-blocking units of the formula [(CH3)3 SiO], and silicon dioxide. It contains not less than 90.5 percent and not more than 99.0 percent of polydimethylsiloxane ([(CH3)2SiO]n), and not less than 4.0 percent and not more than 7.0 percent of silicon dioxide.
Packaging and storage Preserve in tight containers.
Identification, Infrared Absorption197F.
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. [noteWarm slightly, if necessary, to dissolve.]
Procedure [noteFor 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).
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 [(CH3)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.
Auxiliary Information Please check for your question in the FAQs before contacting USP.Chromatographic Column
USP32NF27 Page 3554Pharmacopeial Forum: Volume No. 30(4) Page 1293
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.