Photolysis of phloxine B in water and aqueous solutions

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(1/2)) of phloxine B spiked in different water samples and 2% NaCl solution at 29 +/- 1 degreesC 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 degreesC, phloxine B photodegraded slightly faster in acidic solution than in basic solution. The photolysis t(1/2) of phloxine B at 29 +/- 1 degreesC was 25, 32, 128, and 755 min in the buffered NaF, NaCl, NaBr, and NaI solutions, respectively. The t(1/2) 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.