Electrochemical investigation of copper(II)–imazaquin complex formation: stoichiometry, stability, and behavior in acidified natural waters

Abstract Imazaquin (IMZ), an imidazolinone herbicide widely used in agriculture, exhibits high environmental mobility due to its predominantly anionic form in soils, which promotes interactions with naturally occurring metal ions. Such interactions may alter the herbicide's speciation, mobility, and environmental fate. In this study, the interaction between Cu(II) and IMZ was investigated by cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) using a pencil graphite electrode. To ensure optimal voltammetric signal definition and stability, measurements were conducted under controlled acidic conditions (pH 2.0). Cyclic voltammetry revealed shifts in the redox potentials of both Cu(II) and IMZ, indicating the formation of a stable Cu–IMZ complex in solution. Scan rate studies demonstrated a diffusion electron-transfer mechanism. The complex stoichiometry was investigated by DPASV titration experiments, which indicated the formation of a Cu(II) complex with a 1:2 stoichiometric ratio. The formation constant of the complex was determined to be Log K = 6.2. Furthermore, experiments performed with natural water samples collected from the Billings Dam produced voltammetric responses similar to those obtained in the supporting electrolyte, demonstrating that complex formation is preserved even in the presence of naturally occurring interferents. The formation constant was also determined in this matrix, with a value of Log K = 5.3. These findings demonstrate that voltammetric techniques provide a simple, sensitive, and effective approach for investigating metal–pesticide interactions and contribute to a better understanding of the environmental behavior of imazaquin in the presence of copper ions.