New tool for epidermal and cosmetic formulation studies by attenuated total-reflection spectroscopy using a flexible mid-infrared fiber probe

The potential of mid-infrared attenuated total-reflection spectroscopy for dermatology studies has been increased by the development of a flexible fib er-optic probe from silver halide material. Such a tool significantly eases epidermal surface characterization. Spectra of human forearm skin and of b ovine udder skin (BUS-model), which is used as a substitute for in-vivo tes ts on man, were compared, and as an example low concentrations of vitamin E acetate (alpha -tocopherol acetate) in the stratum corneum were measured a fter topical skin application. Depth profiling was enabled by repeated step s of tape stripping and subsequent skin measurement. The infrared methodolo gy is rapid and can be applied to small areas of skin. It is also sufficien tly sensitive for analysis of a large variety of cosmetic formulations and dermatopharmaca. Discrimination of vehicle formulations is possible because of the large information content of mid-infrared spectra.