Generally, the design of stable and selective solid phase sorbents for separation and preconcentration of a target metal ion depends on different factors related to the nature
of solid support, its surface area and activity, as well as other important factors related to the organic complexing agent bound to the solid substrate. These factors include the structure of the immobilized organic compound as a whole, the nature of the incorporated donor atoms (O,N, P and S), the positioning of the functional groups along the surface of the solid support and the steric requirements of the complex formed after uptake of the desired metalion. The most successful SP-extractors for soft metal ions are those immobilized basically: sulfur and nitrogen or phosphorous containing compounds.31 Nevertheless, the inorganic sorbents have the advantages of no swelling, fast kinetics and good mechanical stability as well.