ABSTRACT
In the early part of this century skin pH was investigated using colorimetric methods. pH indicators showed changes in different pH ranges. A large area of skin was required for the use of several indicators. A simplification of this method was the foil colorimetry in which indicator-impregnated sheets of adsorbing strips were placed on the skin with a drop of water. For buffer capacity measurements sodium hydroxide was applied directly to the skin. Then the time needed for neutralization of skin pH was measured using an indicator. For measurements of reduced or oxidized components, a redox electrode of gold or platinum is used with simultaneous adjustment of temperature and pH value. Some ion-sensitive electrodes can detect different ions such as halogens, metal ions, sodium, or potassium.
