and polymethylmethacrylate if the substrate has functional groups thereon then attachment to the linker is straightforward for instance if silica is used as a substrate then the pendant silanol groups u2014 si u2014 oh u2014 on the silica substrate are used to directly link the silanol groups of the silica substrate to a linker in a known way in another example where substrate is functionalized and therefore is provided with functional groups is where the substrate is polymethylmethacryate in this instance the hydrogen on the carboxylic group of the methylmethacrylate group is used to directly link to the linker in a known way in a situation where a substrate is devoid of a group to which a linker can be attached a linker with functional groups at two locations thereon must be used or the substrate is functionalized to provide a functional group to which a linker can be attached the linker is non polar and is characterized by a saturated hydrocarbon group that contains a minimum of 1 carbon atom and up to a large number of carbon atoms in a preferred embodiment the linker contains 1 40 carbon atoms the linker can be a straight or a branched chain hydrocarbon and the more carbon atoms in the linker the more likely that it will be a waxy solid in a preferred embodiment the linker is a straight chain hydrocarbon the longer the hydrocarbon chain on the linker the less soluble it will be in an aqueous medium and the more soluble it will be in a hydrocarbon medium for extraction of a metal ion from an aqueous medium.