A hollow fibre flow filtration (HF-FF) was applied to perform matrix removal and analyte preconcentration before inductively coupled plasma optical emission spectrometric (ICP-OES) detection. Poly(ethylene imine), PEI, with a molecular weight of 750000 Da, was added to test solutions to form complexes with analyte elements (Ag, Cd, Co, Cu, Hg, Ni, Pb and Zn) but not the matrix elements (Ca, K, Mg and Na). Two flow streams were applied in opposing directions to introduce a large sample volume into the fibre membrane. With the use of a HF membrane made of poly(sulfone), having a pore size of 30000 Da, matrix elements were removed by filtering off through the membrane, whereas the PEI–analyte complexes remained in the channel and were subsequently eluted and detected. Various parameters were optimized to obtain a satisfactory matrix removal and preconcentration factor. These include PEI concentration, focusing time, and focusing point. With a PEI concentration of 200 mg l⁻¹, focusing time of 15 min and the focusing point nearest to the detector, matrix removal efficiency was nearly 100%.