Photolysis of Phloxine B in Water and Aqueous Solutions

Abstract.

Phloxine B (2′,4′,5′,7′-tetrabromo-4,5,6,7-tetrachlorofluorescein disodium salt) as a potential photoactive insecticide was rapidly photodegraded in water under various light sources. Two major photolytic products characterized were 2′,4′,5′-tribromo-4,5,6,7-tetrachlorofluorescein and 4′,5′-dibromo-4,5,6,7-tetrachlorofluorescein. The photolysis rates of phloxine B were influenced by various factors including salts in medium, sample pH, and light sources. Half-lives (t_½) of phloxine B spiked in different water samples and 2% NaCl solution at 29 ± 1°C ranged from 0.70 to 1.28, 26.3 to 115, and 14.1 to 46.2 hours under 254 nm, 365 nm, and cool white fluorescent lights, respectively. Half-lives of phloxine B in tap, stream, or seawater in a beaker were from 10 to 13 min under sunlight at ambient air temperature. In a range of buffer pH 6–8 at 29 ± 1°C, phloxine B photodegraded slightly faster in acidic solution than in basic solution. The photolysis t_½ of phloxine B at 29 ± 1°C was 25, 32, 128, and 755 min in the buffered NaF, NaCl, NaBr, and NaI solutions, respectively. The t_½ of phloxine B was 31 min when phloxine B was dissolved in the sodium phosphate buffer as control. Sodium iodide and ammonium iodide photostabilized phloxine B 24 and 27 folds, respectively, when it was compared with the buffer control.