Analytical Sciences

A Reflectance Flow-through Thionine Sol-gel Sensor for the Determination of Se(IV)

Joana A. E. CARVALHIDO, Agostinho A. ALMEIDA, Alberto N. ARAÚJO, and Maria C. B. S. M. MONTENEGRO

REQUIMTE, Dep. Química-Física Fac. Farmácia U. P., R. Aníbal Cunha 164, 4099-030 Porto, Portugal

In this work, a reversible sensor to assess the total Se(IV) content in samples is described. Pre-activated glass slides were spin-coated with 100 μL of a 20-h aged sol-gel mixture of 1 mL of tetramethoxysilane, 305 μL of 50 mmol L⁻¹ HCl and 2.0 mg of thonine. The flow-cell consisted of one of those slides as a window, and was filled with beads of a polystyrene anionic exchange resin to retain Se(IV) in the form of selenite ions. A reflectance transduction scheme at a wavelength of 596 nm was adopted. The cell was coupled to a multicommutation flow system where a programmed volume of a sample solution and 373 μL of 0.4 mmol L⁻¹ iodide in a 1.6 mol L⁻¹ HCl solution were sequentially inserted into the cell. The iodine produced from the reaction of retained Se(IV) with iodide bleached the blue color of thionine. Considering a sample volume of 2.30 mL, with which the preconcentration step was minimized, a linear dynamic working range between 1.5 to 20 μg mL⁻¹ and a detection limit of 0.29 μg mL⁻¹ were obtained. The sensor enabled us to perform approximately 200 assays, and provided results similar to those of electrothermal atomic absorption spectrometry.

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