The interactions of paracetamol, caffeine and metazachlor with humic acids studied using surface plasmon resonance...

The transport of micropollutants through soil is, inter alia, largely influenced by their interaction with humic acids (HAs). As chemically complex carbon molecules, HAs make part of natural organic matter and play a significant role in the retention of micropollutants in the environment. This study examines the interactions of pH-dependent HA fractions with metazachlor, paracetamol, and caffeine, using the surface plasmon resonance imaging (SPRi) method. Fluorescence spectroscopy and Fourier transform infrared spectroscopy were used as comparative methods in addition to the optical lab-on-a-chip sensor technique, which is certainly novel in the study of HAs. The results of the SPRi measurements demonstrate that the association (k_a) and dissociation (k_d) rate constants depend on the pH during the precipitation process. Paracetamol exhibited the highest k_a (25.3-86.8 L mol^-1 s^-1) and k_d (6.5-8.3 s^-1). The equilibrium association constant K_A was the highest (1170 L mol^-1) in paracetamol and the lowest (273 L mol^-1) in metazachlor. The study demonstrates that SPRi can be an effective tool to evaluate the potential sorption-desorption processes occurring in soils contaminated with organic micropollutants.