328 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS acid. The carboxyl group of lactic acid ethoxylates almost exclusively when it is ethox- ylated with one mole of ethylene oxide without a catalyst. 3. Despite the fact that the carboxyl group of 12-hydroxystearic acid ethoxylates almost exclusively under base catalyst, and predominately with no catalyst, the reaction rate does not show an induction period, which would be expected for carboxyl group ethox- ylation. This difference in kinetics would suggest another mechanism for the reaction under both conditions. Ethoxylation of lactic acid likewise shows no induction period. 4. The ethoxylation of both 12-hydroxystearic acid and lactic acid, which predomi- nately occurs on the carboxyl group, follows reaction rates approximating that of pri- mary alcohols under base catalyst, despite the fact that the hydroxyl groups in both acids are secondary hydroxyl groups. 5. The following is the relative order of reaction of various hydrophobes with one mole of ethylene oxide arranged from the fastest to the slowest: Fastest ethoxylation nonyl phenol lactic acid stearyl alcohol = castor oil = 12-hydroxystearic acid stearic acid Slowest Ethoxylation ACKNOWLEDGMENT The authors gratefully acknowledge the assistance of Ethox Chemical in Greenville, S.C., for preparation of many of the ethoxylates studied. REFERENCES (1) A. J. O'Lenick and R. McCutchen, An overview of alkoxylated alcohols, Soap Cosmet. Chem. Spec., 64(1) (1988). (2) C. F. Stevens, Nonionic surfactants, JAOCS, 34 (1957). (3) U.S. Patent 4,360,698, issued Dec 1981. (4) U.S. Patent 4,456,697, issued June 1984. (5) U.S. Patent 4,568,774, issued February 1986. (6) U.S. Patent 4,593,142, issued June 1986. (7) A. N. Wrigley, F. D. Smith, and A. J. Stirton, Comparative detergents from animal fats, JAOCS, 34 (1957). (8) K. Nagse and K. Sakaguchi, Kogyo Kagaku Zassi, 64, 1035 (1961). (9) H. F. Drew and J. R. Schaffer, Ind. Eng. Chem. 50, 1253 (1958). (10) G. Tishbirek, Proceedings of the Third International Congress on Surface Activity, Cologne, 1, 126 (1960). (11) J. D. Malkemus andJ. D. Swan, J. Am. Oil Chem. Soc., 31, 71 (1954). (12) A. T. Bullen, J. N. Schumaker, G. E. Kapella, and J. V. Karabinos, Comparative detergency of several built polyethenoxy alkanoates, JAOCS, 31 (1954).

j. Soc. Cosmet. Chem., 44, 329-336 (November/December) Preservative efficacy testing by a rapid screening method for estimation of D-values D. S. ORTH and D. C. ENIGL, Neutrogena Corporation, Los Angeles, CA 90045 (D.S.O.) and Watson Pharmaceuticals, Inc., Corona, CA. 91720 (D.C.E.)o Received July 20, 1993. Synopsis This report describes a rapid screening method for estimating D-values to determine whether products are adequately preserved. Estimated D-values (ED-values) are determined using aerobic plate counts of test organisms immediately after inoculation into test samples and at 24 hr for pathogenic microorganisms or at 7 days for non-pathogenic bacteria, yeasts, or molds. Products are judged to be adequately preserved if they meet the acceptance criteria of the linear regression method. There was excellent agreement between D-values and ED-values for 60 sets of data (correlation coefficient -- 0.98). The mean D-values and ED-values for the 60 samples differed by 0.5 hr (6.6%) even though the D-values ranged from 0.1 hr to 39 hr. Where differences were observed, the ED-values generally were larger (i. e., more conservative) than D-values for the same samples. The rapid screening method offers about 50% savings in the labor and materials required for preservative efficacy testing by the original linear regression method. INTRODUCTION Preservative efficacy testing is used to determine whether experimental formulas, sta- bility test samples, and finished products are adequately preserved. The goal of preser- vative efficacy testing is to determine the type and minimum effective concentration of preservatives required fbr adequate preservation of the formula during manufacturing, distribution, and use by consumers. The methods of preservative efficacy testing currently in use include official methods such as the United States Pharmacopeia (USP) method (1) and the British Pharmacopeia (BP) method (2) trade association methods such as the Cosmetic, Toiletry & Fragrance Association (CTFA) method (3) and rapid methods such as the linear regression method (4). The procedures used in these methods are similar however, the times at which samples are taken for analysis and the interpretation of test results--the acceptance criteria by which products are judged to be effectively preserved-- are different (5). The acceptance criteria of the USP, BP, and CTFA methods were converted to decimal reduction times (D-values) by Orth (5,6). Use of D-values enables a laboratory to determine the effect of the product preservative system on rates of death of test organ- isms, to compare rates of death in different products tested in different labs, to use 329