Voltammetric identification of pedogenic iron oxides in paleosol and loess

Voltammetry of immobilized microparticles was used to detect low concentrations of goethite and hematite in paleosol and loess samples. The total content of Fe oxides in the natural samples was below 2 wt% and below the detection limit of X-ray powder diffraction. Goethite was distinguished from hematite due to the different electrochemical reactivity of the product of thermal dehydroxylation of goethite (very fine crystalline hematite). The voltammetric analysis was tested using synthetic samples of ferrihydrite, goethite, hematite, magnetite, or Mg-ferrite with SiO2 and a natural sample of smectite with an admixture of goethite. The detection is most sensitive for goethite and hematite (detection limit about 0.1 wt%), and approximately an order of magnitude better than X-ray powder diffraction analysis.