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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