Fig. 5. Fourier-transform infrared (FTIR) spectra for the freeze-dried humic acid (HA) and HAimazaquin (IM) complexes obtained from samples reacted at different pH values [(a) pH 5.0, (b) pH 3.0, and (c) pH 2.0] with HA = 1 g L-1 and IM = 15 mg L-1.