]. Cosmet. Sci., 58, 443-450 (July/August 2007) Determination of the substantivity of emollients to human hair HANS-MAR TIN HAAKE, HELENE LAG RENE, ANGELA BRANDS, WOLF EISFELD, and DAVID MELCHIOR, Cognis Deutsch/and GmbH & Co. KG, Henkelstr. 67, 40 5 51 Diisseldorf, Germany. Synopsis The determination of silicones and hydrogenated didecenes deposited on human hair from shampoo appli- cations is described. For silicones, induced coupled plasma optical emission spectroscopy (ICP-OES) of extracts and X-ray fluorescence analysis (XRF) of hair strands without any further sample preparation have been applied. Three shampoos from the European and Asian markets have been investigated at repeated shampoo applications followed by the determination of the removability with sodium laureth sulfate. Hydrogenated didecenes have been quantified by GC-MS of extracts. A transparent shampoo containing 1.8% of hydrogenated didecenes delivered via a nanoemulsion was examined in the same way as the commercial shampoos. Finally, the substantivity data were compared with performance data from combabil- ity determination and hair volume measurements. Good correlations of analytical data and performance profiles have been obtained. INTRODUCTION In addition to basic ingredients like surfactants, preservatives and fragrances, modern shampoos contain several "care" products such as polymers, emollients and waxes to improve sensorial and conditioning properties and the appearance of both the shampoo and the treated hair. These ingredients must be carefully selected and formulated to ensure that sufficient quantities of the substances adsorb to the hair to provide the desired effect, yet avoiding overloads or build-up effects. Therefore, the determination of the adsorbed amounts of each "care" ingredient can help select the type and concentra- tion of a specific ingredient used and all other ingredients of a formulation. This can be achieved either directly-if an appropriate analytical method for the detection at surfaces is available-or by extraction and analytical determination of the specific substance, whereby both steps must be specifically adapted to the specific ingredient. In this paper, we describe our approaches for the determination of silicones and hydrocarbons applied as conditioning agents via shampoos. For silicones detection methods specifically determining Si can be applied. In the Address all correspondence to Hans-Martin Haake. 443

444 JOURNAL OF COSMETIC SCIENCE literature, several methods for the direct detection of silicones on human hair have been described including atomic absorption spectroscopy (AAS 1), electron spectroscopy for chemical analysis (ESCA 2), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS 3), and X-ray fluorescence spectroscopy (XRF 4). We have selected X-ray fluorescence due to the ease of use without sample preparation. Organic extracts of human hair can be evaluated by a wide range of analytical methods, for silicones we have applied induced coupled plasma optical emission spectroscopy (ICP-OES 5) due to a very low limit of detection. Hydrogenated didecene was selected as example for the use of hydrocarbons in hair rinse products. Since there is no specific method available for hydrocarbons, a GC-MS method was developed to quantify the amount of hydrogenated didecene in extracts of hair. The results of build-up effects and removability of substances by pure surfactant solutions are presented. In addition, two examples of how these analytical data can be linked to consumer relevant performance properties, like conditioning and hair volume effects, are presented. EXPERIMENT AL Strands of human hair were purchased from International Hair Importers (New York). Shampoos containing dimethicone and dimethiconol were taken from the current mar- kets in Germany and Thailand. The shampoos from the German market were tested with dark brown Caucasian hair and the shampoo purchased in Thailand was tested with Japanese hair. The shampoo with hydrogenated didecene was formulated according to Table I. Tests with this shampoo were performed using the dark brown Caucasian hair. Hair strands were washed with the shampoos at 1 g shampoo/1 g hair, incubated for 5 min and rinsed off using a special device to ensure reproducibility for all experiments. With this device each hair strand is rinsed with water at 38 ° C, 1 1/min and combed during rinsing. After rinsing the hair strands were dried for 60 min with warm air (65°C). The removability of the emollients from the hair was tested by repeating the procedure described above 5 or 9 (for the hydrogenated didecene) times followed by 1, 2 and 3 times shampooing with a solution of 12% Sodium laureth sulfate (SLES) (pH 6.5) respectively. All strands were treated together and samples were taken out of the process after 1, 3, 5 (7 and 9 for the shampoo with hydrogenated didecene) and also after 1, 2 and 3 times treatment with SLES. Hair strands which were just cleansed by SLES were extracted to determine Table I Test Shampoo with Hydrogenated Didecene Ingredient (INCI) Sodium laurethsulfate Cocoamidopropylbetain Polyguaternium 10 Methyldibromo glutaronitrile and phenoxyethanol PEG-150 distearate Hydrogenated didecene (via a nanoemulsion) Water Concentration [%} 9 3 0.2 0.1 1.25 1.8 ad 100