Inclusion Complex of o-Phthalaldehyde-Metolachlor with Cyclodextrins Using the Thermochemically-Induced Fluorescence Derivatization (TIFD) Method and Its Analytical Application in Waters

A thermochemically-induced fluorescence derivatization (TIFD) method for the determination of metolachlor (MET) based on the o-phthalaldehyde thermo product complex of MET (OPA-MET) enhanced with either hydroxypropyl-γ-CD (HP-γ-CD) or dimethyl-β-CD (DM-β-CD) was investigated. The analytical conditions of the TIFD method were the same for the complexes, except for the solvent. The fluorescence enhancement was highlighted for the OPA-MET complex in the presence of cyclodextrins (CDs). Besides the stability of the OPA-MET:CD inclusion complexes, which corroborates the reproductibility of the TIFD method, a 1:1 stoichiometric ratio between OPA-MET was obtained in both of the organized environments (CDs). The binding constants (K₁) of the inclusion complexes OPA-MET: HP-γ-CD and OPA-MET: DM-β-CD of 1:1 type are (264 ± 36) L·mol⁻¹ and (173 ± 17) L·mol⁻¹, respectively. Under the optimal conditions, the linear dynamic range of the TIFD method is 10–580 ng·mL⁻¹ and correlation coefficients obtained through calibration curves were close to unity. Limits of detection (LODs) and quantification (LOQs) are in the ranges 0.06–0.09 ng·mL⁻¹ and 0.2–0.3 ng·mL⁻¹, respectively. A solid phase extraction (SPE) procedure successfully combined with the TIFD method in the presence of cyclodextrins, for quantitative analysis of samples spiked with metolachlor, led to satisfactorly accurate values (recovery: 92.2–121% and RSD: 1.1–1.3%).