Method for determination of xanthene dyes in guava fruits and its application in a field dissipation study

Xanthene dyes, i.e., phloxine B and uranine or phloxine B alone, are photot oxic to tephritid fruit flies infesting guava fruits. An analytical method was developed for determination of residues of these dyes used in bait solu tions for suppression of the tephritid fruit fly population in guava fruits . The procedure involved solvent extraction, anion-exchange cleanup, and de termination by liquid chromatography or capillary zone electrophoresis. The dyes were extracted from 50 g guava fruit at 45 degrees C with 400 mL meth anol-acetonitrile (1 + 1) and 5 g magnesium oxide added as an alkaline and clarifying agent, The guava extract was adjusted to pH 8.5 and subjected to an amino column cleanup. Average recoveries of xanthene dyes added to guav a purees ranged from 77 to 99% for phloxine B and from 79 to 102% for urani ne at spiking levels of 0.05-1.00 mu g/g. The method was applied to the det ermination of phloxine B residues in guava fruits collected from a dye-spra yed orchard. After phloxine B was applied at a rate of 62.5 g/ha for 14 wee kly sprayings, it was found on guava fruits at an average concentration of 111 +/- 18 ng/g 4 h after the 11th spraying. The concentration of phloxine B was 426 +/- 94 ng/g in selected fruits with high deposits of the dye 4 h after spraying, Average concentrations of phloxine B 5 days after the 7th a nd 14th sprayings were 29 +/- 7 and 19 +/- 8 ng/g, respectively.