抄録
Human skin surface has been analyzed in situ after washing with fatty acid soap by attenuated total reflectance using Fourier transform infrared spectroscopy. The residue of fatty acid soap on the skin was observed when calcium ions were present in the water being used, and it was confirmed to be adsorbing onto the skin as fatty acid calcium salts. This adsorption residue was quantified using the Amide I or Amide III absorption bands of the epidermal horny proteins as an internal standard.
The behavior of adsorption residues has been examined with this method, and it was confirmed that the quantity of adsorption residue increased depending on the calcium ion concentration in the water. Furthermore, it was suggested that the adsorption residue was induced by the insoluble salt formation from fatty acid anions adsorbed onto the skin and calcium ions at the time of rinsing. Fatty acid calcium salts adsorbed onto the skin were gradually desorbed by sufficient rinsing, but the influence of calcium ions was also seen in this case. This desorption speed was slower when calcium ions were present.
