Solid-phase extraction employing 5-methyl-4-(2-thiazolylazo)resorcinol entrapped in sol-gel glass as a sorbent resin to remove Zinc ions

Aim: The ligand 5-methyl-4-(2-thiazolylazo)resorcinol (5-Me-TAR) was encapsulated in an optically transparent, inert and porous sol-gel glass to produce a solid resin. The synthesized composite (resin) was used as a solid phase extractant to remove (as a filter) zinc ions from water samples. Materials and Methods: A solution of the ligand in ethanol was mixed with selected alkoxysilanes in the presence of water to produce a homogeneous mixture. By hydrolysis and condensation of the alkoxysilanes, solid glass forms around the dopant. The ligand molecule is entrapped inside the glass pores, while small Zn(II) metal ions can diffuse into the pores where they are complexed by the ligand and retained inside the pores. Absorption and fluorescence spectroscopy were used to characterize 5-Me-TAR ligand and 5-Me-TAR-Zn complex both in solution and sol-gel glass. The sol-gel glass precursors were carefully selected to produce a glass composite material doped with the ligand with no leaching, especially when the glass is soaked in the solution. Results: Complexation using the batch method was employed, in which a known weight of the sorbent resin is mixed with a known concentration of Zn(II) ions. In order to attain the maximum metal ion complexation capacity; the filter was optimized to the optimum separation/pre-concentration conditions of analytes, including the effect of pH, capacity of the solid, equilibration time and coexisting ions; afterwards, the solution was filtered. The amount of zinc metal ion complexed/adsorbed was determined by the difference between the initial concentration in aqueous solution and that found in the supernatant, using flame atomic absorption. The optimum condtions (maximum uptake) was obtained at pH = 6 using 30 min shaking time, and the capacity of the solid was 0.153 mmol Zn/g. Conclusion: The ligand was successfully trapped inside the sol-gel pores, and no diffusion of the ligand was observed. Soaking of the sorbent in a solution containing Zn(II) ions results in diffusion of the zinc ions through the sorbent pores into the ligand for complexation.