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Use of silica-based sorbents for separation and preconcentration of V (IV) and V (V)
Vanadium is one of the essential trace elements for plants and animals. While it is beneficial for normal cell growth, it becomes toxic at high concentrations. In the present study, silica-based sorbents were prepared and used for sorption/speciation of vanadium from waters prior to inductively coupled plasma mass spectrometric (ICP-MS) determination. Among the sorbents developed, 3-APTES-modified silica, has been shown to be an efficient material for the speciation of vanadium. Solution pH of 2.0 and 3.0 can be used for the respective sorption of V(V) and the total vanadium, namely, V(IV) and V(V). The concentration of V(IV) can then be calculated from the difference. Desorption from the sorbent was realized with 0.5 M thiourea prepared in 0.2 M HCl. The validity of the method was checked via spike recovery experiments with four different types of water; namely, ultra pure, bottled drinking, tap, and sea water. The method works efficiently (>85% recovery) for ultra pure, bottled drinking, and tap water; and a relatively high recovery (>70%) was obtained even for sea water which has a very heavy matrix. For trypsin-immobilized silica, the sorption percentage towards V(IV) and V(V) is almost constant (>90%) within the pH range 4.0-8.0 which demonstrates the possibility of using this sorbent for the sorption of both vanadium species. The sorption of vanadate ion was investigated both from a kinetic perspective and also in terms of Freundlich, Dubinin-Radushkevich and Langmuir isotherm models; and Langmuir model was found to describe the sorption better for both of the functionalized silicas.