Packaging and storage— Preserve in tight containers.

USP Reference standards 11—
USP Polydimethylsiloxane RS.

Identification— The IR absorption spectrum, determined in a 0.5-mm cell, of the solution of Emulsion prepared as directed in the Assay, exhibits maxima only at the same wavelengths as that of a similar preparation of USP Polydimethylsiloxane RS. If necessary, the dilute hydrochloric acid may be omitted to improve separation. [note—Prepare a procedural blank by similarly treating 25.0 mL of toluene, and use this blank to set the instrument.]

Microbial enumeration tests 61 and Tests for specified microorganisms 62— Its total aerobic microbial count does not exceed 100 cfu per g.

Heavy metals— Using Simethicone Emulsion instead of Simethicone, proceed as directed for Heavy metals under Simethicone. The limit is 5 µg per g.

Defoaming activity—

Assay— Transfer an accurately weighed quantity of Emulsion, equivalent to about 50 mg of simethicone, to a round, narrow-mouth, screw-capped, 120-mL bottle, add 25.0 mL of toluene, and swirl to disperse. Proceed as directed in the Assay under Simethicone, beginning with “Add 50 mL of dilute hydrochloric acid.” Calculate the quantity, in mg, of [–(CH3)2SiO–]n in each g of the Emulsion taken by the formula: in which C is the concentration, in mg per mL, of USP Polydimethylsiloxane RS in the Standard preparation; S is the weight, in g, of Emulsion taken; and AU and AS are the absorbances of the Assay preparation and the Standard preparation, respectively.

Topic/Question	Contact	Expert Committee
Monograph	Elena Gonikberg, Ph.D. Senior Scientist 1-301-816-8251	(MDGRE05) Monograph Development-Gastrointestinal Renal and Endocrine
Reference Standards	Lili Wang, Technical Services Scientist 1-301-816-8129 RSTech@usp.org
61	Radhakrishna S Tirumalai, Ph.D. Senior Scientist 1-301-816-8339	(MSA05) Microbiology and Sterility Assurance
62	Radhakrishna S Tirumalai, Ph.D. Senior Scientist 1-301-816-8339	(MSA05) Microbiology and Sterility Assurance

USP32–NF27 Page 3555