Stoichiometric Analysis of the Copper–Sudan II Complex via Cloud Point Extraction and the Slope Ratio Method

Copper contamination in industrial wastewater presents serious environmental concerns due to its toxicity and bioaccumulation. Conventional extraction methods often rely on hazardous organic solvents and lack specificity. This study introduces a green and selective system based on dithizone-functionalized deep eutectic solvents for copper ion extraction from aqueous media. The solvents were synthesized using L-isoleucine, aspartic acid, oleic acid, and ethyl methyl ketone, with dithizone incorporated as a metal-chelating ligand. Key operational parameters—including pH, solvent volume, Triton X-100 amount, Sudan II volume, copper concentration, temperature, and heating time—were systematically optimized. Spectrophotometric analysis at 550ௗnm was used to evaluate copper content, and both the distribution coefficient (log D) and extraction efficiency were determined. The optimized system (pH 8, 3.0ௗmL of solvent, 0.6ௗmL Triton X-100, 0.7ௗmL Sudan II, 65ௗ°C, 10 minutes heating) achieved a distribution coefficient of 1.955 and an extraction efficiency of 98.90%. Performance declined under non-optimal conditions due to reduced solubility or complexation efficiency. The method demonstrated strong selectivity and consistent performance across a wide copper concentration range. These results highlight the potential of dithizone-functionalized deep eutectic solvents as an effective, sustainable alternative for trace metal extraction in analytical and environmental applications