J. Cosmet. Sci., 64, 391–400 (September/October 2013) 391 Application of Purpald® for determination of 3-cyclohexene-1-carboxaldehyde and hydroxyisohexyl 3-cyclohexene carboxaldehyde ROBERT ZAKRZEWSKI, MONIKA SKOWRON, ZANETA REMBISZ, and WITOLD CIESIELSKI, Department of Inorganic and Analytical Chemistry, University of Lódz´, 91-403 Lódz ´, Poland. Accepted for publication February 28, 2013 Synopsis A spectrophotometric method for determination of 3-cyclohexene-1-carboxaldehyde and hydroxyisohexyl 3-cyclohexene carboxaldehyde was developed. This procedure is based on the reaction of carbonyl compounds with the selective derivatization reagent Purpald® in alkaline solution. The product of reaction is a colored compound with maximum absorption at 538 nm. The linear relationship is in the range of (2.5–30) × 10−5 mol·l-1 for 3-cyclohexene-1-carboxaldehyde and (2.0–20) × 10−5 mol·l-1 for hydroxyisohexyl 3-cyclohexene carboxaldehyde. The proposed method was successfully used for determination of hydroxyisohexyl 3-cyclohexene carboxaldehyde in a cosmetic product. INTRODUCTION 3-cyclohexene-1-carboxaldehyde and hydroxyisohexyl 3-cyclohexene carboxaldehyde (Figure 1) are aldehydes with cyclohexene ring. Hydroxyisohexyl 3-cyclohexene carbox- aldehyde is used as a fragrance ingredient in cosmetic products. In the cosmetics industry, the tested compound is known as Lyral®. It may be found in decorative cosmetics, per- fumes, shampoos, toilet soaps, and other cosmetics as well as in household detergents and cleaners. The recent dermatological studies have proved that this compound is lipophilic enough to penetrate the skin (1) and it is the reason for induction and elicitation of con- tact allergy to it (2,3). Further, Scientifi c Committee on Consumer Products stated that the concentration of up to 0.02% of this fragrance compound in a cosmetic product would induce sensitization or elicit allergic contact reactions in previously sensitized consumers (4). Hydroxyisohexyl 3-cyclohexene carboxaldehyde is listed as suspected al- lergens in cosmetics by the European Union (5). According to Directive 2003/15/EC, a declaration of the listed 26 “fragrance allergens” on the label of the fi nal product when present over the concentrations 0.001% for “leave-on” and 0.01% for “rinse-off” cosmetics Address all correspondence to Robert Zakrzewski at robzak@chemia.uni.lodz.pl.

JOURNAL OF COSMETIC SCIENCE 392 is required (6). The harmfulness of fragrance ingredients in cosmetic has led to an in- creased interest in the analyses of these products. Most of the works on determination of volatile allergens used the technique of gas chromatography–mass spectrometry (GC– MS) (3,7) and high-performance liquid chromatography (HPLC) (8). 3-Cyclohexene-1-carboxaldehyde belongs to the same group of compounds as hydroxyiso- hexyl 3-cyclohexene carboxaldehyde and it is mainly used in organic chemistry (9), organic synthesis (10,11), and production of polymers (12). Moreover, it does irritate the mucous membrane of the respiratory system (13). To our knowledge, a spectrophotometric method has never been used for determination of 3-cyclohexene carboxaldehydes before. Therefore, the aim of this article was to develop a simple, accurate, and cheap method for the determination of 3-cyclohexene-1-carboxaldehydes. In our study, we used Purpald® (Figure 1) as a specific and sensitive derivatization reagent for the determination of men- tioned aldehydes. Purpald® reacts readily with aldehydes and ketones in alkaline solution at room temperature to give a colorless product, but the derivative from an aldehyde can be oxidized to give the purple tetrazine (14). The purple-colored solutions of aldehyde– Purpald® adduct absorb in the visible region at 520–555 nm (15). Several m ethods and applications have been developed for the detection and determination of aldehydes and other compounds with Purpald®. The reagent has been used in conjunction with ali- phatic aldehydes (13,14,16). Purpald® has been used for detecting the presence of alde- hydes in disinfectant (17), resin-bound aldehyde groups (18), neutral m onosaccharides (19), and lipid aldehydes (20). Several alcohol determination methods use the formation of an aldehyde by means of periodic acid, sodium periodate, or enzyme and its determina- tion using Purpald®, for example, assay of glucosamine, mannitol (21), and glyco l (22). Purpald® has also been used in thin layer chromatography as a spray reagent (19). Because of the advantages of this reagent such as selectivity, sensitivity, and ease of reaction we used Purpald® in our studies described later. EXPERIMENTAL CHEMICALS AND REAGENTS Purpald® (4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole), 3-cyclohexene-1-carboxaldehyde, hydroxyisohexyl 3-cyclohexene carboxaldehyde, sodium hydroxide, and all organic solvents (methanol, ethanol, acetonitrile, acetone, dioxane) were obtained from Sigma-Aldrich (Steinheim, Germany), POCH (Gliwice, Poland), or LABSCAN Analytical Science (Dublin, Ireland). All chemicals used were of analytical grade and water was freshly distilled. Purpald® solution was prepared as 0.1 mol·l−1 in 1.0 mol·l−1 sodium hydroxide. This solution is not stable and must be used within an hour of preparation. Stock solutions of 3-cyclohexene-1-carboxaldehyde and hydroxyisohexyl 3-cyclohexene carboxaldehyde were prepared as 0.1 mol·l−1 in acetonitrile. One milliliter of these Figure 1. The chemical structure of 3-cyclohexene-1-carboxaldehyde, hydroxyisohexyl 3-cyclohexene car- boxaldehyde, and Purpald®.