j. Soc. Cosmetic Chemists 18 469-472 (1967) ¸ 1967 Society of Cosmetic Chemists of Great Britain Spectroscopic by attenuated studies of skin in situ total reflectance N. A. PUTTNAM and B. H. BAXTER* $]tnop$1$--It has been shown that it is possible by the attenuated t6tal reflectance technique to obtain ir spectra from skin in situ. The procedure involved the use of a 'V' shaped ATR crystal into which the side of the hand (the hypothenar eminence) was placed. The main features of such spectra agreed with those reported earlier from transmission studies through thin sections of various tissues, but there were relatively small differences in the ratios of the intensities of the absorptions in the wavelength range 1300-1000 cm- 1 for different indivi- duals, which were not further investigated. The application of the ATR technique was extended to show that it was possible to detect the retention by the skin of relatively major components of a hand cream applied to the skin. INTRODUCTION Several reports have been published of the application of ir spectro- scopy to study various tissues (1-3). These studies have been carried out by transmission through thin sections of the dried tissue, mounted onto silver chloride discs. Absorption studies of skin, in the wavelength range 2 to 15 microns, have however been rather limited (2, 4). The development of attenuated total reflectance (5), by which it is possible to obtain high contrast spectra from surfaces which are equivalent to those obtained by transmission through very thin films, suggested the possibility of obtaining spectroscopic information from skin in situ. Such a possibility has also been pointed out by Scheuplein (4), and more recently Hermann (6) has obtained ATR spectra from freshly removed organs, e.g. liver and kidney. The purpose of the present communication is to show that ir spectra can be obtained from skin in situ by attenuated total reflectance, and *Research and Development Dept., Colgate-Palmolive Ltd., Manchester, 5. 469

470 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS further, that by this technique it is possible to study the retention, by the skin, of components present in products applied to the skin. EXPERIMENTAL The ATR spectra were recorded on a Unicam SP 200 infrared spectro- meter with increased slit width and gain. The ATR attachment, which is shown in Fig. 1, was equipped with a 'V' shaped analysing crystal supplied by Research and Industrial Instruments Co. This shape of analysing crystal, Figure I 'V' shaped ATR unit. which was originally suggested by Harrick (7), allowed two reflections from the skin with the incident radiation striking the crystal/skin interface at angles of 45 ø . In order to record the ATR spectra, the ATR unit was placed in the sample compartment of the spectrometer and the reference beam attenu- ated to an absorbance value of approximately 0.1 at 1900 cm-l, where the sample showed no absorption, since the transmission of the ATR crystal was only about 30}/0 . The fleshy part of the right hand, the hypothenar eminence, was then placed into the 'V' of the ATR crystal using normal hand weight pressure, and the spectrum recorded over the wavelength range 650-5000 cm-1 In Fig. I is shown schematically the ATR unit, together with the position of the hand during the recording of the spectrum.