Preconcentration and decomposition of perfluorinated carboxylic acids on an activated charcoal cartridge with sodium biphenyl reagent and its determination at μg L−1 level on the basis of flow injection-fluorimetric detection of fluoride ion

Perfluorinated surfactants of heptafluorobutylate and pentadecafluorooctanoate ions were adsorbed on an activated charcoal cartridge and decomposed with sodium biphenyl (SBP) reagent to form inorganic fluoride ion. The fluoride ion thus formed was determined by flow injection analysis (FIA) using quercetin-Zr complex as a fluorimetric reagent, where λex and λem were 422 and 491 nm, respectively. The limit of detection for fluoride ion by the FIA system was developed to 1.1 × 10−6 M (signal to noise ratio of three), when 50% (v/v) tetrahydrofuran (THF) was used as a dissolving solvent for quercetin. The perfluorinated surfactants in the sample solution were quantitatively adsorbed on the cartridge containing 100 mg of activated charcoal and were decomposed with 0.5 mL of sodium biphenyl reagent after drying thoroughly by flowing through dry nitrogen gas. The fluoride ion formed was recovered with 3 mL of purified water as an eluent, and it was determined by the fluorimetric flow injection system. The blank fluorescence signal accompanied during the adsorption/decomposition on the cartridge was reduced by washing the activated charcoal with acetone. The blank signal was also observed from dimethoxyethane, which was used in sodium biphenyl reagent. When 600 mL sample solution was used and 200 times enrichment was applied, the heptafluorobutylate and pentadecafluorooctanoate ions at the concentrations of 2.1 μg L−1 were quantitatively recovered as fluoride ion, and the limit of detections for the perfluorinated surfactants were 0.3 and 0.3 μg L−1 for the two perfluorinated surfactants, respectively (3 sigma of the blank signal).