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j. Soc. Cosmet. Chem., 35, 157-169 (May/June 1984) Free formaldehyde in anionic shampoos MARVIN ROSEN and ANDREW G. McFARLAND, Glyco Inc., Research and Development Department, Williamsport, PA 17701, Received November 15, 1983. Presented at the Society of Cosmetic Chemists Annual Scientific Meeting, December 1, 1983. Synopsis An analytical method has been developed for determining the free formaldehyde content of anionic sham- poos preserved with formaldehyde derivatives in the absence and presence of protein. The preservatives studied were DMDM Hydantoin, Imidazolidinyl Urea, Imidazolidinyl Urea II, and Quaternium 15. The method is based upon establishing an equilibrium of formaldehyde between the sample, the vapor phase, and an aqueous trampping solution. The trapping solution is analyzed colorimetrically for free formaldehyde at 513 nanometers using phenylhydrazine hydrochloride. Studies were conducted at temperatures of 23øC and 60øC and at concentrations of 0.1-0.8% preservative. The order of formaldehyde release found was Imidazolidinyl Urea DMDM Hydantoin Imidazolidinyl Urea II Quaternium 15. The amount of free formaldehyde released was the same at 23 ø and 60øC. Protein reduced the concentration of free formaldehyde present. In the absence of protein, the ratio of free to total formaldehyde increased with decreasing preservative concentration. In a protein shampoo, this ratio was independent of preservative level. INTRODUCTION Formaldehyde-releasing preservatives are known to hydrolyze in aqueous systems. How- ever, reliable analytical techniques have not been available for quantitating this reaction in cosmetic products. Two measurements are required to understand the chemistry involved in cosmetic systems. The first is the determination of free formaldehyde where "free" is defined as (a) the formaldehyde (or methylene glycol) formed by hydrolysis of the preservative, (b) excess formaldehyde used to synthesize the preservative, (c) for- maldehyde from other formaldehyde-based raw materials used to prepare the cosmetic product, and (d) formalin used as a preservative for the raw materials themselves. The second is the determination of total formaldehyde which is the sum of free formaldehyde and formaldehyde bound to the parent preservative. Wilson, using the Hantzsch reaction, established a reliable methodology for deter- mining the total formaldehyde content of cosmetic products containing formaldehyde (1) and formaldehyde-releasing preservatives (2). Liem (3) states that differential pulse polarography can be used to determine formaldehyde in cosmetics but no data were provided for formaldehyde derived from formaldehyde-releasing preservatives. With respect to free formaldehyde, Liem recognized the lack of data on how much free formaldehyde is present in products containing donor components. Through acom- 157