Homogeneous liquid-liquid extraction by pH dependent phase separation with a fluorocarbon ionic surfactant and its application to the preconcentration of porphyrin compounds

Aqueous perfluorooctanoate (PFOA^–) solution of water-miscible organic solvent (SOLV), such as dioxane and acetone, was separated into two immiscible phases reversibly by charge neutralization of PFOA^– ion with proton (H⁺) (pK_a value of HPFOA was 1.01, atI = 0.1, 20 °C). The transparent heavier phase, in which HPFOA was concentrated quantitatively, consisted of three components in the molar ratio of HPFOASOLVH₂O = 14.06.6 for acetone system, and 10.471.9 for dioxane system, respectively. This separation provides a new homogeneous liquid-liquid extraction method, which can be successfully applied to the ultra-high preconcentration of water-soluble porphyrin compounds: 10⁴-fold concentration was achieved within 20 min.