Combination of asymmetric flow field-flow fractionation (AF(4)) and total-reflexion X-ray fluorescence analysis (TXRF) for determination of heavy metals associated with colloidal humic substances

To assess the structural variability of colloidal humic substances and the associated heavy metals an off-line coupling of asymmetric flow field-flow fractionation (AF(4)) with total-reflection X-ray fluorescence analysis (TX RF) is presented. AF(4) allows a rather gentle separation of colloids with a minimum of interference and artifacts as no shear forces, drying, or inte ractions with a stationary phase are involved. After a calibration with sui table polymer particles of known molecular weight, the molecular weight dis tribution of colloidal humic substances between 1 and 10(3) kDa can be asse ssed with AF(4) The combination with TXRF permits a simultaneous multieleme nt analysis after preconcentration of samples on the AF(4) channel using an optimized buffer. The analysis of seepage and sewage water sample and a se wage sludge sample yielded continuous distributions of the molecular weight and the associated heavy metals. The potential of AF(4)-TXRF coupling for the study of metal ion exchange equilibria with colloids was demonstrated b y spiking seepage water with various heavy metals and subsequent AF(4)-TXRF analysis of the heavy metals bound to the colloidal fraction (Cu, Cr, Zn, Ni, Co).