Rotating coiled columns in the speciation analysis of natural samples: Dynamic fractionation of element forms in soils, sludges, and bottom sediments

The potentials of dynamic extraction in rotating coiled columns (RCCs) for the speciation analysis of soils, sludges, and bottom sediments is discussed on an example of the fractionation of element forms. A comparative study of the results of the fractionation of the forms of heavy metals differing in physicochemical mobility and bioavailability (Zn, Cd, Pb, Cu, Ni, Cr), obtained using a number of procedures of sequential extraction, is performed. Particular attention is paid to mercury, which is quite different from other metals in biogeochemical properties. Conditions are described for the dynamic fractionation of arsenic species occurring in natural samples in anionic forms. It is revealed that, in contrast to batch extraction, the continuous renewal of the eluent in a rotating column eliminates the problem of readsorption and overlapping of isolated fractions and enables the correct assessment of the concentration of the most mobile and bioavailable forms of toxic elements. A hyphenated method for the fractionation and determination of certain forms of elements (based on the ICP-AES detection of elements in the column eluate in the on-line mode) is described, ensuring the processing and a real-time control of the dynamic extraction of the forms of elements. The kinetic aspects of selective leaching are considered. It is shown that a comparison of the elution curves of micro- and macrocomponents makes possible a judgment about the selectivity of the leaching reagent, optimization of the conditions for the isolation of each fraction, and the investigation of the features of the binding of heavy metals and matrix elements in soils and bottom sediments. Some recommendations are given for the dynamic fractionation of the forms of elements in soils, sludges, and bottom sediments in RCCs.