Characterising the interactions between Cu(II) and fulvic acid subcomponents using differential fluorescence...

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Fulvic acid (FA) is a complex mixture of organic compounds found in aquatic environments.
• FA plays a crucial role in the speciation and bioavailability of metals in water.
• Understanding FA-metal interactions is vital for assessing water quality and metal transport.

Purpose of the Study:

• To investigate the interactions between different fulvic acid subcomponents and copper (II) ions.
• To identify which FA subcomponents exhibit preferential binding with Cu(II).
• To elucidate the binding mechanisms and affinities of these interactions.

Main Methods:

• Utilized fluorescence quenching titration combined with differential fluorescence spectroscopy (DFS).
• Employed parallel factor analysis (PARAFAC) to resolve complex fluorescence data into distinct components.
• Applied the modified Ryan-Weber equation to determine binding constants (log K).

Main Results:

• Fluorescence intensities of FA subcomponents decreased with increasing Cu(II) concentration, indicating binding.
• Humic-like (FA3) and protein-like (FA9) subcomponents showed preferential interaction with Cu(II) due to carboxylic groups and polarity.
• DFS successfully resolved FA into five distinct components, with a fulvic-like component showing the strongest quenching.
• Static quenching was identified as the dominant binding mechanism.
• Binding constants (log K) ranged from 4.32 to 6.14, with earlier eluted subcomponents demonstrating stronger binding affinity.

Conclusions:

• Fulvic acid subcomponents exhibit varying affinities for Cu(II) ions in aquatic systems.
• The presence of carboxylic and phenolic groups significantly influences Cu(II) binding.
• Differential fluorescence spectroscopy coupled with PARAFAC is effective for characterizing FA-metal interactions.