The interactions between the water-soluble polyelectrolytes poly(acrylic acid) (PAA) and poly(vinyl sulfonic acid) (PVS), and Cu(II) and Ni(II) are studied by the liquid-phase polymer-based retention (LPR) technique. Assuming a Ni(II)-PVS interaction of electrostatic nature, the nature of the Ni(II)-PAA interaction is found to be electrostatic, while Cu(II)-PAA interactions imply the formation of coordinative bonds. The charge related formation constants for the systems Ni(II)-PAA, Ni(II)-PVS, and Cu(II)-PVS are found to be 57.57 x 10(2), 43.4 x 10(2), and 60.5 x 102 M-1, respectively in a 0.010 M NaNO3 aqueous solution at pH 5, and 1.4 x 10(2) for both systems containing Ni(II) and 1.3 x 10(2) M-1 for the system Cu(II)-PVS in a 0.10 M NaNO3 aqueous solution at pH 5. (C) 2004 Published by Elsevier Ltd.