This work describes the interaction of alkaline, alkaline earth, transition metal, heavy metal, and lanthanide cations from nitrate solutions with synthetic polyamides. The polyamides have pendant structures acting as cation host moieties. The host subgroups are benzo-12-crown-4, benzo-15-crown-5, benzo-18-crown-6, and the three dipodal counterparts of the three benzo-crown units. This interaction has been analyzed in terms of competitive polyamide solid-phase extraction of nitrate cations from aqueous or acetronitrile solutions. The solid-phase extraction of water or acetonitrile solutions of alkaline, alkaline earth, transition metal, heavy metal, and lanthanide ions using solid-phase polyamides is performed with a degree of selectivity. Higher selectivity is observable in the extraction of Pb(II) from a set of heavy metal ions inwater and acetonitrile solutions, and the extraction of Cr(III) from a set of transition metals in acetonitrile solutions. It is a noteworthy result, which along with the reusability of the solid-phase polyamides points to potentially successful applications in the field of environmental chemistry: the decontamination and elimination of poisoning cations, the separation and modification of cation mixtures, and the development of fixed-site carrier membranes for selective transport or manufacture of cation-sensitive sensors. (c) 2007 Wiley Periodicals, Inc.