Combining centrifugal and flow field-flow fractionation with ICPAES to characterize the size and elemental composition of soil clay minerals

In this work a method was developed for determining the mass and element-based size distributions of submicron sized soil particles. The method used field-flow fractionation (FFF) to separate the particles and inline UV and inductively coupled plasma atomic emission spectrometry (ICPAES) detectors to evaluate the mass and element concentrations in the eluent respectively. The data was used to plot strategic element molar ratios versus particle diameter which greatly simplifies interpretation of the trends in terms of soil processes. The method was tested using samples collected from the A and B horizon matrix material and cutans of the Camel Hill sand near Monarto in South Australia, a soil with strongly contrasting texture. The major findings were that the size of the clay mineral components (particles <2 μm) decreased in the order A horizon>B horizon>cutans and that the mineralogy was almost identical in all soil samples. A possible implication would be that the clays in the B horizon matrix and cutans have been physically translocated from the A horizon with little chemical weathering but this does not fit the photoimages of the soil horizon. However, this study strongly indicated that the information obtained by FFF-UV-ICPAES, when combined with data derived from other analytical techniques, will be a powerful tool in understanding the mechanisms of soil formation and weathering.