15. Chemically Modified Silica Gel with DETA-Silane as Complexing Bonded Sorbent for Preconcentration and Determination of Heavy Metals in Natural Water using Solid-Phase Extraction Method

Prachathipat Pongpinyo, Wirach Wongphattanagul, Sunantha Hengrasmee and Saksit Chanthai*

Department of Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand

Abstract: This study was developed as a solid-phase extraction (SPE) method using a modified chelating agent. A silica gel was chemically modified with DETA-silane, 3-[2-(2-aminoethylamino) ethylamino]propyltrimethoxysilane, at various concentrations ranging from 3% to 20 % volume by weight. Characterization of DETA-modified silica was performed by infrared and reflectance spectrophotometry. Adsorption isotherm and complexation capacity including metal extraction using cartridge method was studied. The heavy metal ions, Pb(II), Zn(II), Mn(II), Fe(III) and Cu(II) were complexed onto the immobilized silica surface through a pendant amine group. The optimum loading capacity was 25.93 mg copper per gram of the modified silica, when loaded with Cu(II) solution. The concentration factors between 20 and 40 were employed in the preconcentration of the trace metal ions. In application, 20% DETA-modified silica was used for SPE method to compare with acid digestion method for river water samples. It was found that the preconcentration/SPE method gave the metal contents in ngmL^-1 of Zn (3.61-5.39 vs 0.18-2.65), Mn (2.47-10.51 vs 0.19-0.84), Fe (23.32-29.34 vs 4.24-16.93) and Cu (not detectable-0.61 vs not detectable) higher than those of the acid digestion method. It was noted that Pb (II) was not detectable in the water samples. Since this method does not involve any toxic organic solvent, it can be a better choice of offering an eco-friendly way of extraction and preconcentration of metal ions from various samples.

Key words: modified silica, bonded stationary phase, solid-phase extraction, preconcentration, chelating agent

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