Formation, Extraction and Analytical Application of Ionic Associates of Dicamba with 5-thiocyanato-diindocarbocyanine

The formation and extraction of an ionic associate (IA) between dicamba (Dik) and the polymethine dye 5-thiocyanato- diindocarbocyanine (TIC) were investigated. Quantum chemical calculations confirmed the energetic feasibility of IA formation. The resulting IA demonstrated efficient extraction with various aromatic hydrocarbons, with maximum extraction observed in the pH range of 4.0–11.0. The effect of dye concentration on the optical density of toluene extracts of the Dik-TIC IA was studied, revealing optimal extraction at a dye concentration of (1.5–3.0) × 10-⁴ M. The extraction equilibrium was established within 50–60 seconds. Spectrophotometric methods, including isomolar series and equilibrium shift, determined the stoichiometric ratio of Dik to TIC in the IA as 1:1. A mechanism for IA formation and extraction was proposed, and the conditional molar absorption coefficient was found to be 8.2 × 10⁴. A calibration curve was constructed for the dependence of the optical density of extracts on the concentration of Dik in the range of 0.67–8.21 μg/mL. Based on these findings, an extraction-photometric method for the determination of Dik in commercial formulations was developed.