This work demonstrates the potential of the simultaneous on-line hyphenation of asymmetric flow field flow fractionation (AF4) to inductively coupled plasma-mass spectrometry (ICP-MS) and ultra violet-visible/multi angle light scattering (UV-vis/MALS) detection as a promising and simple tool to obtain information on the multi-element speciation and absolute molecular mass of human plasma proteins such as albumin and transferrin: the two main proteins that have been proposed to bind and transport metal ions in this biological fluid.