Multielement characterization of metal-humic substances complexation by size exclusion chromatography, asymmetrical flow field-flow fractionation, ultrafiltration and inductively coupled - Analytical Methods & Tools for Lyophilization

Multielement characterization of metal-humic substances complexation by size exclusion chromatography, asymmetrical flow field-flow fractionation, ultrafiltration and inductively coupled
Received 21 November 2005; revised 26 June 2006; accepted 30 June 2006. Available online 21 July 2006.
E. Boleaa, , , M.P. Gorriza, M. Boubyb, F. Labordaa, J.R. Castilloa and H. Geckeisb
Journal of Chromatography A
Volume 1129, Issue 2 , 6 October 2006
ScienceDirect
Copyright ? 2006 Elsevier B.V. All rights reserved.
aAnalytical Spectroscopy and Sensors Group, Department of Analytical Chemistry, University of Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
bForschungszentrum Karlsruhe, Institut f?r Nukleare Entsorgung, P.O. Box 3640, D-76021 Karlsruhe, Germany
Abstract
The use of three different separation techniques, ultrafiltration (UF), high performance size exclusion chromatography (HPSEC) and asymmetrical flow field-flow fractionation (AsFlFFF), for the characterization of a compost leachate is described. The possible interaction of about 30 elements with different size fractions of humic substances (HS) has been investigated coupling these separation techniques with UV?vis absorption spectrophotometry and inductively coupled plasma-mass spectrometry (ICP-MS) as detection techniques. The organic matter is constituted by a polydisperse mixture of humic substances ranging from low molecular weights (around 1 kDa) to significantly larger entities. Elements can be classified into three main groups with regard to their interaction with HS. The first group is constituted by primarily the monovalent alkaline metal ions and anionic species like B, W, Mo, As existing as oxyanions all being not significantly associated to HS. The second group consists of elements that are at least partly associated to a smaller HS size fraction (such as Ni, Cu, Cr and Co). A third group of mainly tri- and tetravalent metal ions like Al, Fe, the lanthanides, Sn and Th are rather associated to larger-sized HS fractions. The three separation techniques provide a fairly consistent size classification for most of the metal ions, even though slight disagreements were observed. The number-average molecular weight (Mn), the weight-average molecular weight (Mw) and the polydispersity (?) parameters have been calculated both from AsFlFFF and HPSEC experiments and compared for HS and some metal-HS species. Differences in values can be partly explained by an overloading effect observed in the AsFlFFF experiments induced by electrostatic repulsion effects in the low ionic strength, high pH carrier solution. Size information obtained from ultrafiltration is not as resolved as for the other methods. Molecular weight cut-offs (MWCO) of the individual filter membranes refer to globular proteins and molecular weight information may therefore, deviate from that given by the other methods after calibration with polystyrene sulfonate (PSS) standards.
Keywords: Asymmetrical flow field-flow fractionation; Size exclusion chromatography; Ultrafiltration; Humic substances; ICP-MS

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