Effect of Deep-Eutectic Solvents on Molecular Fluorescence Properties and Its Application on Determination of Anthracene in Soil

The fluorescence intensities of anthracene, naphthalene and 8-hydroxyquinoline in different deep-eutectic solvents (DESs) was determined by fluorescence spectrophotometer, and the effect of DESs on molecular fluorescence properties was investigated, and it was used for the quantitative analysis of anthracene in soil. It was shown that fat-soluble DESs with weak polarity, such as methyl trioctylammonium chloride-n-capric acid and methyl trioctylammonium chloride-dodecyl alcohol, could not only significantly enhance the fluorescence intensity of anthracene, but also improve its emission peak shape. The fluorescence quenching of naphthalene and 8-hydroxyquinoline occurred in DESs, resulting its emission peaks displacement. The soil sample was extracted by dichloromethane and purified by silica gel solid phase extraction column, and the residue was dissolved by 1% (volume fraction) methyl trioctylammonium chloride-n-capric acid solution. The fluorescence intensity of the testing sample solution at 362 nm was determined by fluorescence spectrophotometer with excitation wavelength of 350 nm. As shown by the results, linear relationship between the mass concentration of anthracene and the corresponding fluorescence intensity was kept in the range of 0.1-10.0 μg·L^-1, with detection limit (3s/k) of 0.3 ng·g^-1, which lower than that of dichloromethane as solvent (1.5 ng·g^-1). Test for recovery was made on the blank sample by standard addition method at 3 concentration levels, giving results in the range of 89.5%-96.5%, and RSDs (n=6) of the determined values were less 4.0%. Compared with conventional solvent dichloromethane, this method had high sensitivity and low detection limit, effectively improved emission peak shape of anthracene, and facilitated accurate quantitative analysis of anthracene in soil.