Measurement of trace element distributions in soils and sediments using sequential leach data and a non-specific extraction system with chemometric data processing

A chemometric mixture resolution procedure suitable for determining the number and composition of physico-chemical components in data derived from soil leachates is described. The procedure is used to determine the number of components in sequential leachate data obtained for a NIST certified soil (SRM 2710) using a widely employed leaching scheme. The resulting data show that the sequential leaching media are not specific for their designated target fractions and that erroneous identification of fractions occurs. A scoping study in which a new non-specific extraction method is tested is described. The experimental design varies the concentration of nitric acid, the reaction time and the ratio of sample to extractant. The resulting solutions were analysed by ICP-AES for major and trace metals and the data obtained from 34 experiments subjected to the chemometric resolution procedure. Four components are identified and the effects of the three variables on each component are modelled using multiple linear regression, allowing the conditions which favour dissolution of each component to be identified. Calculated element compositions of the components identified in the non-specific extraction trial are compared with those identified in the sequential extraction data. Significant correlations between the two sets of components are noted and tentative identification of the source of the components is made. In particular, there is evidence that the Tessier method extracts both Fe and Mn oxides simultaneously, whereas the non-specific method has resolved the Fe and Mn oxides as separate entities.