Fluorescence characteristics of dissolved humic acids with different sources and their complexes with metal ions

This article used three-dimensional excitation-emission matrix fluorescence spectroscopy and features of fluorescence peaks to discuss fluorescence characteristics of dissolved humic acids (HA) with different sources and their complexes with different metal ions. The fluorescence peaks of dissolved product HA and dissolved natural HA had the strongest intensities at pH 10.0 and at pH 9.0 respectively. The intensities of all the fluorescence peaks gradually reduced with increasing ionic strength. The additions of Cu²⁺, Cd²⁺ and Ca²⁺ made the fluorescence peaks of two HAs quenching. The degree of fluorescence quenching was the biggest when Cu²⁺ was added at the same concentrations. With increasing total Cu²⁺ or Cd²⁺ concentrations, the peak B position of product HA got blue shift. And the emission wavelengths of peak A of product HA and peak 1 of natural HA got blue shift. The positions of all fluorescence peaks were basically unchanged with total Ca²⁺ concentrations between 1.0×10^-6 mol/L and 1.0×10^-4 mol/L.