Competitive transport of an equimolar mixtures of Zn(II), Cd(II), and Pb(H) ions from aqueous nitrate source phase (c(Me) = 0.001 M, each) through polymer inclusion membranes (PIMs) using calix[4]crown-6 derivatives, as ion carriers, has been investigated. The influence of the group attached type to the calix[4]-crown-6 molecule on the selectivity and efficiency of Zn(II), Cd(II), and Pb(II) transport across polymer inclusion membranes containing cellulose triacetate as the support was studied. The transport selectivity orders for the PIM with 4 and 5 was: Pb(II) > Zn(II) > Cd(II), whereas for 3 was: Pb(II) > Zn(II) > Cd(II). The metal cations transport results can be explained by their tendency as the Lewis acids in chemical interaction with the bases. The selectivity coefficients of Pb(II)/Zn(II) and Pb(II)/Cd(II) decrease with the hydrochloric acid concentration increase in receiving phase. Also the influence of the plasticizers nature, i.e. o-nitrophenyl pentyl ether (o-NPPE), o-nitrophenyl octyl ether (o-NPOE), and bis(2-ethylhexyl)adipate (DOA) on the ion transport through PIMs is presented. The initial flux of metal ions insignificantly increases in the following order: DOA < o-NPOE < o-NPPE, i.e. with decrease of plasticizers viscosity. The stability of PIM with calix[4]crown-6 derivatives was confirmed in replicate experiments. (c) 2006 Elsevier B.V. All rights reserved.