280 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS NIW•IJI'OI]• tl:Pl-] 1 Figure 8. Solvent-subtracted prototype finished product spectrum (moisturizer). Table II Statistical Data and Results of Four Sample Preparations of a Single Prototype Batch Sample # Sample Wt (g) Abs (a.u.) Wt % Dimethicone Found 1 1. 3637 0.1764 1.031 1 1.3637 0.1748 1.022 1 1.3637 0.1759 1.028 2 1.4422 0.1826 1.009 2 1.4422 0.1826 1.009 2 1.4422 0.1820 1.006 3 1.4107 0.1764 0.997 3 1.4107 0.1733 0.979 3 1.4107 0.1737 0.982 4 1.6236 0.2090 1.026 4 1.6236 0.2103 1. 032 4 1.6236 0.2062 1.012 Mean: 1.011% Dimethicone Standard deviation: _+ 0.018 Variance: 0. 00030 % Relative standard deviation: 1.782 In conclusion, a method for quantitating dimethicone in cream and lotion formulations via FTIR has been developed. The method shows excellent precision analyses (N = 12) of a sample containing 1% w/w dimethicone yielded a mean result of 1.011% ___ 0.018 with a relative standard deviation of 1.782%. Currently, an evaluation of the batch-to-batch variation in the formulation matrix is being made. Blank-spectral

DIMETHICONE QUANTITATION USING FTIR 281 Figure 9. Blank-subtracted dimethicone-spiked blank formulation spectrum, 1.00% w/w spiked level. storage and recall would be the most advantageous from an analysis time consideration therefore, a thorough study of the precision and accuracy of dimethicone quantitation using blank-subtraction is ongoing. REFERENCES (1) Federal Regulatory Agency, 21 CFR Part 347--Skin protectant drug products for over-the-counter human use, Federal RegistersProposed Rules, 48 (32), 6832 (1983). (2) T. Rihs, Identification and determination of dimethylpolysiloxanes in pharmaceutical preparations, Pharm. Acta Hdv., 49 (9), 550-557 (1971). (3) United States Pharmacopeial Convention, USPXX/NFXV, Twentieth Revision, (United States Phar- macopeial Convention, Inc., Rockville, MD, 1979), p 724. (4) United States Pharmacopeial Convention, USPXX/NFXV, Supplement 3, (United States Pharmacopeial Convention, Inc., Rockville, MD, 1982), p 246. (5) United States Pharmacopeial Convention, USPXX/NFXV, Addendum a to Supplement 3, (United States Pharmacopeial Convention, Inc., Rockville, MD, 1982), p 593. (6) F. Burton, Westwood Pharmaceuticals, Inc., Private communication, 1983.