Chemical partitioning of the new National Institute of Standards and Technology Standard Reference Materials (SRM 2709-2711) by sequential extraction using inductively coupled plasma atomic emission spectrometry

Three new NIST standard reference materials (2709-2711) have been analysed by a widely-used sequential chemical extraction method to provide analyte levels that are particularly useful for the characterization of contaminated soils. Each chemical fraction is operationally defined as follows: (i) exchangeable; (ii) bound to carbonates or specifically adsorbed; (iii) bound to Fe-Mn oxides; (iv) bound to organic matter and sulfides; and (v) residual. The extraction solutions resulting from the five steps have been analysed for 15 elements (Al, Ca, Cd, Co, Cu, Fe, K, Mn, Ni, P, Pb, Sr, Ti, V, and Zn) using ICP-AES. The over-all recovery rates (the sum concentrations from the five steps/the certified total concentrations) were observed to lie between 90 and 105% for most of the elements. The precision was estimated to be approximately 5% (2s) for most extraction steps. The high concentrations and proportions of trace elements in the exchangeable fraction (step 1) in NIST 2710 suggest that this reference material can be especially appropriate for studies of mobility and bioavailability of heavy metals in contaminated soils. Using sequential extraction methods, the elemental concentrations in these reference materials determined by ICP-AES for some major elements (AI, Ca, Fe, K, Mn, P and Ti) help to indicate the mineralogical compositions actually dissolved in each step.