Influence of pH and Other Modifying Factors on the Distribution Behavior of 4-Quinolones to Solid Phases and Humic Acids Studied by “Negligible-Depletion” SPME−HPLC

Flumequine, oxolinic acid, and sarafloxacin are 4-quinolone antimicrobials that are used in fish farming. The objective of this investigation was to study the influence of pH on the distribution behavior between buffer solutions and Aldrich humic acids (DOC) of these compounds. Negligible-depletion solid-phase microextraction coupled to high-performance liquid chromatography (nd-SPME−HPLC) was used to quantify the free concentration of the antimicrobials. It was shown that the distribution of the antimicrobials between buffer and the SPME fiber could be described as a function of pH and ionization constants. Distribution coefficients between buffer and DOC (D DOC) were established. It was not possible to describe this distribution using pH and ionization constants. The magnitude of the D DOC values (103.4−105.2) was found in the same range as for highly hydrophobic chemicals despite the low hydrophobicity of the 4-quinolones (K OW < 101.7).