Combination of asymmetric flow field-flow fractionation (AF4) and total-reflexion X-ray fluorescence analysis (TXRF) for determination of heavy metals associated with colloidal humic substances |
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Authors: | A Exner M Theisen U Panne R Niessner |
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Institution: | Institute for Hydrochemistry, Technical University of Munich, Marchioninistrasse 17, D-81377 Munich, Germany e-mail: reinhard.niessner@ch.tum.de, DE
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Abstract: | To assess the structural variability of colloidal humic substances and the associated heavy metals an off-line coupling of asymmetric flow field-flow fractionation (AF4) with total-reflection X-ray fluorescence analysis (TXRF) is presented. AF4 allows a rather gentle separation of colloids with a minimum of interference and artifacts as no shear forces, drying, or interactions with a stationary phase are involved. After a calibration with suitable polymer particles of known molecular weight, the molecular weight distribution of colloidal humic substances between 1 and 103 kDa can be assessed with AF4. The combination with TXRF permits a simultaneous multielement analysis after preconcentration of samples on the AF4 channel using an optimized buffer. The analysis of seepage and sewage water sample and a sewage sludge sample yielded continuous distributions of the molecular weight and the associated heavy metals. The potential of AF4-TXRF coupling for the study of metal ion exchange equilibria with colloids was demonstrated by spiking seepage water with various heavy metals and subsequent AF4-TXRF analysis of the heavy metals bound to the colloidal fraction (Cu, Cr, Zn, Ni, Co). |
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