Characterization of the depth distribution of Ca, Fe and Zn in skin samples, using synchrotron micro-x-ray fluorescence (SμXRF) to help quantify in-vivo measurements of elements in the skin

In vivo monitoring of trace and biometals in skin is normally quantified using phantoms that assume a constant elemental distribution within the skin. Layered calibration skin phantoms could potentially improve the reliability of in vivo calibration skin phantoms by better representing the actual in vivo distribution. This work investigates the micro-distribution of iron, calcium and zinc in prepared human skin samples taken from a number of locations on the body. Slices (orientation running from the skin surface into the dermis) were extracted from 18 formalin-fixed necropsy samples and scanned using the micro-XRF setup at the VESPERS beamline (Canadian Light Source). Elemental surface maps were produced using a 6×6 μm(2) beam in steps of 10 μm. Microscope images of histology slides were obtained for comparison. Statistically significant differences (p<0.01) were noted between the epidermal and dermal layers of skin for the elements examined (Ca, Fe and Zn), demonstrating the ability to clearly distinguish elemental content in each layer. Iron was consistently noted at the epidermal/dermal boundary. These results would indicate that when using phantoms to quantify elemental levels measured in the skin, note should be taken of the appropriate depth distribution.