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J. Soc. Cosmet. Chem. 25, 535-544 (1974) ¸ 1974 Society of Cosmetic Chemists of Great Britain The thin layer chromatographic detection and determination of an imidazolidinyl urea ß preservauve antimicrobial D. S. RYDER* Synopsis--An ANTIMICROBIAL PRESERVATIVE of the IMIDAZOLIDINYL UREA type is detectable in a variety of complex cosmetic and toiletry formulations by TLC. The method is specific for the above type of preservative, even in the presence of a number of other antimicrobials. A ten-fold increase in sensitivity of the ninhydrin reacted zones is achieved when using TRANSMITTED UV LIGHT as compared to visible daylight colours. The antimicrobial is quantitatively determined in a moistu/'izing lotion with a relative standard deviation of 4-10 % using DENSITOMETRY. INTRODUCTION Cosmetics provide an ideal medium for the growth of microorgan- isms. The manufacturer must guard against the microbial contamination of his product during manufacture and storage and also against contamination by the consumer. Thus antimicrobial preservatives are added which are designed to be effective against a wide spectrum of microorganisms over a long period of time. * Analytical Services, Research Department, Ciba-Geigy (UK) Limited, Trafford Park, Man- chester. 535