Enhancement of the fluorescence intensity of Se-2,3-diaminonaphthalene complex in aqueous solution by adding organic solvents

Fluorescence of the Se-2,3-diaminonaphthalene (DAN) complex has been studied in aqueous solutions with several organic solvents. With all organic solvents, the wavelength of the emission maxima in water was shifted to shorter wavelengths. However, the wavelength of the excitation maxima did not change. Fluorescence intensity (IF) of the Se-DAN complex observed with most organic media, increased with respect to the IF observed in water. However, the precision was poorer using the organic solvents than the precision found in water. Tetrahydrofuran (90%) and 1,4-dioxane (90%) exhibit the highest increases of IF. Higher enhancements of IF of the Se-DAN complex were observed when the concentration of organic solvent increased. So, the equations In IF = a + b · (% organic solvent)23 and 1/IF = a + b · (% organic solvent)12 could be established. Maximum IF of the Se-DAN complex in the studied organic media was obtained at a pH between 2.5 and 3.5. Tetrahydrofuran and acetonitrile showed the highest stability in the presence and absence of sunlight. Tetrahydrofuran (90%) and acetonitrile (60%) presented the best detection limits 1.96 and 3.00 μg Se l−1, respectively, showing a 23- and 15-fold improvement of the detection limit in aqueous medium. Acetonitrile (60%) was satisfactorily compared with hydride generation-atomic absorption spectrometry.