Fluorescence Enhancement of Ethanolic Solution of Nitroarenes and Its Analytical Application

When ethanolic solutions of 1-nitropyrene (1-NP) and 3-nitrobenzanthorone (3-NBA) were irradiated with intense light, which they absorb, for several minutes, the fluorescence characteristics of the solutions were significantly changed. After such preliminary irradiation, the fluorescence intensity of 1-NP increased immediately by a factor of 104 with a blue shift of 100 nm and that of 3-NBA 700 with a red shift of 10 nm. The findings were applied to high performance liquid chromatography with a fluorescence detector so that the two nitroarenes could be quantitatively analyzed by preliminary irradiation of their solutions before measurements. The calibration curves were linearly drawn over the concentration range from 1.0 × 10−9 to 1.0 × 10−7 M for 1-NP and 1.0 × 10−8 to 1.0 × 10−6 M for 3-NBA and the limits of detection were 2.3 pg for 1-NP and 28 pg for 3-NBA. From the results, fluorescence enhancement was found to be very effective for determining nitroarenes, being practically non-fluorescent and very important in environmental health-risk assessment, easily and sensitively. The mechanism of the fluorescence enhancement of 1-NP and 3-NBA was also discussed.