]. Cosmet. Sci., 55, 265-279 (May/June 2004) Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of the application of a cationic conditioner to "clean" hair A. HAR VEY and C. M. CARR, Department of Textiles, UMIST, PO Box 88, Manchester, UK, and A. PEREIRA, Croda Inc., North America Technical Center, 180 Northfield Avenue, Edison, NJ 08837-3873. Accepted for publication March 17, 2004. Synopsis In this study the applicability of the surface-sensitive ToF-SIMS technique to hair analysis and associated aqueous processing is evaluated. ToF-SIMS analysis of "as received" human hair indicates the presence of silicones, anionic surfactants, and cationic conditioners, from previous treatments, on the fiber surface. Cleaning of the hair with SLS or SLES results in adsorption of the surfactants onto the fiber surface. In particular, the more non-polar surfactant components have greater substantivity for the fiber surface, as indicated by the relative increase in their ToF-SIMS intensity. Application of the Incroquat Behenyl 18-MEA conditioner to both "virgin" and bleached hair results in the adsorption of the cationic C 18 , C20, C22 , and C21 surfactant components onto the hair surface. The ToF-SIMS data indicate higher levels of conditioner on the bleached hair relative to the undamaged hair. INTRODUCTION The keratin fiber consists of an inner cortex and an outer cuticle, and is composed primarily of both a-helical and amorphous proteinaceous material, the latter rich in the amino acid cystine (1,2). The cuticle itself is composed of an inner endocuticle, a "hard" highly crosslinked exocuticle, and an outer hydrophobic epicuticle membrane. The epicuticle has been regarded as a resistant protein/lipid membrane, 3-5 nm in thickness, although this model has been challenged by Phan and co-workers, who propose that the lipids are directly bonded to the exocuticle and that no distinct epicuticle exists (3). The major lipid component at the fiber surface is 18-methyleicosanoic acid (18-MEA), which is primarily covalently bound to the protein via a thioester linkage (4-7): CH 3 -CH 2 -CH-(CH2) i 6 CO-S-wool I CH3 Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an excellent system for characterizing surface chemistry and fiber surface adsorbates in particular (8). The sur- 265

266 JOURNAL OF COSMETIC SCIENCE face-sensitive technique, with its sampling depth of 1-2 nm, provides both elemental and molecular mass spectral data by bombarding the sample surface with a primary ion beam and by analyzing the masses of the sputtered secondary ions emitted from the surface. The spectral assignments are commonly based on the analysis of "pure" stan­ dards, "model" systems, or the utilization of the ToF-SIMS Spectral Library (9). In this study we examine the applicability of the ToF-SIMS technique in investigating the nature of the surface of "as received" European brown hair, the effect of cleaning in aqueous sodium dodecyl sulphate (SDS) and sodium laureth sulphate (SLES) solutions, and the subsequent adsorption of surfactant components from the surfactant formula­ tions. In addition, as the surface of hair can influence the combing, handling and appearance of the fiber, the nature and surface adsorption of a novel conditioner, In­ croquat Behenyl 18-MEA, onto hair was investigated using ToF-SIMS. This conditioner formulation has been enriched with an 18-MEA derivative in order to mimic the performance properties of virgin hair where the 18-MEA lipid-rich epicuticle is still intact. EXPERIMENTAL MATERIALS Untreated European dark hair was supplied by De Meo Brothers, New York, and is designated "as received." Merino wool top (carded and combed wool fibers) was supplied by Chargeur Wool, Bradford, UK, and had been commercially scoured. The sample fibers were further extracted by acetone and distilled water prior to further use. The sodium dodecyl sulphate (SDS) was 99% pure (BDH Ltd.), and the sodium laureth (EO2) sulphate (SLES) was kindly donated by Albright and Wilson Ltd as the com­ mercial product Empicol ESP 70. The acetone and petroleum ether (30°-60°C) were Analar grade and obtained from Fisher Scientific. The ammonium persulphate and hydrogen peroxide (30%) were obtained from Aldrich Chemical Ltd. The Incroquat Behenyl 18-MEA and alkylamidopropyl ethyl dimonium ethosulfate derived from 18- MEA were supplied by Croda. CLEANING The hair was either solvent extracted or aqueous cleaned using surfactant solutions. The solvent extraction involved repeatedly extracting the hair in excess petroleum ether, then acetone, followed by rinsing in excess water and finally air drying. The hair was also cleaned in a 1 % solution of either SDS or SLES, at 35 ° C for 15 minutes, with gentle agitation, and with a hair:liquor ratio of 1: 100. The hair was then rinsed in excess water and air dried. BLEACHING The hair was bleached in a 6% v/v hydrogen peroxide solution containing 5 % wt/wt ammonium persulphate, adjusted to pH 9.5 using sodium hydroxide solution, over 60