Evaluation of a method for identification of host physico-chemical phases for trace metals and measurement of their solid-phase partitioning in soil samples by nitric acid extraction and chemometric mixture resolution

A sequential extraction methodology, designed to measure the solid phase partitioning of metals in soils and sediments, is described. The method uses centrifugation to pass increasing concentrations of HNO3 through the sample, followed by ICP-AES analysis of major and trace elements of the extracts. A data-processing algorithm is used to identify the number of physico-chemical components extracted, their composition and the proportion of each in each extract. The algorithm has been successfully tested on a synthetic data set and the combination of the extraction methodology and data-processing algorithm have been tested on a contaminated soil sample (NIST SRM 2710). The 14 extracts from each duplicate experiment were analysed for 19 elements and data analysis identified nine chemically distinct soil components: pore-water residual solutes; organic, easily exchangeable; a Cu–Zn dominated phase; a Pb-dominated phase; amorphous Fe oxide/oxyhydroxide; crystalline Fe oxide; Fe–Ti oxide; and Mn oxide.