Photometric Analysis for Trichlorophenoxyacetic Acid in Water and Bottom Sediments with the Use of Extraction

Abstract

2,4,5-Trichlorophenoxyacetic acid was shown to form an ion associate (IA) with astrafloxin FF (AF), a polymethine dye. Based on mathematical modeling, the energy efficiency of the formation of an ion associate was substantiated. The molecular modeling of 2,4,5-T^– + AF⁺ systems and related calculations were carried out by the HyperChem 8.0 software for different initial mutual arrangements of counterions (“single point” procedure). The geometric optimization of ions was performed by the molecular mechanics method MM+. The formed ion associates were readily extractable by different aromatic hydrocarbons. The maximum IA extraction from the aqueous phase was attained at pH of 4.5–12.0. The effect of the dye concentration on the absorbance of the toluene extracts of 2,4,5-T^– + AF⁺ ion associates was studied. The IA extraction was maximal at a dye concentration of (1.5–3.0) × 10^–4 M. Extraction equilibrium was attained for 50–60 s. The stoichiometry of 2,4,5-T^– + AF⁺ ion associates was established by the spectrophotometric isomolar series and equilibrium shift methods; the ratio of components was 1 : 1. The scheme of the formation and extraction of ion associates was proposed. The conditional molar extinction coefficient of the ion associates was 1.2 × 10⁵. The calibration extract absorbance–2,4,5-T concentration curve was described by a linear equation А = 0.012 + 0.062c within a 2,4,5-T concentration range of 1.50–58.07 µg/cm³. The 2,4,5-T detection limit calculated from the 3s criterion (n = 5, Р = 0.95) was 0.8 µg/cm³. The intralaboratory discrepancy of the calibration curve for the determination of 2,4,5-trichlorophenoxyacetic acid was estimated by using the Cochrane test G. The calculated value of this test (n = 5, P = 0.95) was lower than the tabular value, i.e., G_calcd = 0.25 < G_tab = 0.64 to evidence variance homogeneity. A method of photometric extraction analysis for 2,4,5-trichlorophenoxyacetic acid in water and bottom sediments was developed.