pH dependence of binding benzohquinoline and humic acid and effects on fluorescence quenching

The binding constant (KDOC) between humic acid and the nitrogen-containing polycyclic aromatic compound (N-PAC), benzo[h]quinoline, was measured at varying pH levels using fluorescence quenching (FQ). Because fluorescence characteristics of benzo[h]quinoline change with pH, determination required two optimum sets of excitation and emission wavelength pairs. A simple mixing model was used to eliminate the inherent fluorescence interference between benzo[h]quinoline and its protonated form, benzo[h]quinolinium, when estimating binding constants. Hydrophobic interaction is likely to control the binding between humic acid and benzo[h]quinoline and benzo[h]quinolinium, in lower and higher pH ranges (pH