Imaging Mass Spectrometry of Low-molecular-weight Compounds in Skin Tissue with TOF-SIMS

Abstract

Retention of water in human skin is an important function that is performed mainly by low-molecular-weight compounds in the stratum corneum. To understand the retention mechanism, it is helpful to clarify the distribution of these compounds in the stratum corneum by methods such as imaging mass spectrometry (IMS). Especially secondary ion mass spectrometry (SIMS) has high spatial resolution. The aim of this study was to develop a high-resolution method for analyzing the distribution in the stratum corneum of low-molecular-weight compounds, such as amino acids. Skin samples were prepared by the tape stripping method and 20 successive tape-strips were collected at the same skin position. Analysis was performed using TOF.SIMS 5 instrument with Bi₃²⁺ as the primary ion, accelerated at 25 kV. There are three main findings of this study. First, in determining the relationship between molecular weight and the spatial resolution of ions detected from the skin samples, the signal counts of neighbor pixels must be accumulated to obtain a clearer image of high-molecular-weight ions. Second, the present method could reveal the distribution of Serine and Arginine in the skin samples but was unable to obtain a clear image of Lysine. Finally, the depth distribution of the exogenous components could be determined by comparing the results of the 2nd and 20th tape strips.