RESUMO
The effect of adding organized supramolecular systems such as ß-cyclodextrin (ß-CD) and hydroxypropyl-ß-cyclodextrin (HP-ß-CD) on the photochemically-induced fluorescence (PIF) spectral properties of tau-fluvalinate (TFV) in aqueous solutions was examined. The influence of pH, UV irradiation time and photoproduct stability on the cyclodextrin-enhanced photochemically-induced fluorescence intensity was also investigated. The spectral changes associated with the inclusion process yielded values for the formation constants of TFV inclusion complexes between 450 and 640 M-1, which were calculated using the nonlinear iterative regression approach least squares. In addition, host-guest interaction was clearly determined by PIF enhancement and a 1 : 1 stoichiometry was found for the ß-CD and HP-ß-CD complexes formed with TFV. The negative free energy (ΔG°) value indicated that the reaction of TFV with cyclodextrins was thermodynamically favorable. Furthermore, the structures of inclusion complexes of TFV with cyclodextrins were elucidated by 3-21G ab initio calculations. The limits of detection and quantification obtained ranged between 1.3 and 4.0 ng mL-1 and from 4.4 to 13.0 ng mL-1 in ß-CD and HP-ß-CD media, respectively. The analytical application in tap and river water samples yielded satisfactory mean recoveries ranging from 98.12 to 102.97%. Due to its sensitivity and ease of use, this method can be reliably applied to routine analysis.
RESUMO
In this work, analytical study of carbofuran (CAF) and fluometuron (FLM) pesticides was carried out using direct spectrofluorimetric method in various solvents. Results showed that CAF and FLM are naturally fluorescent in all solvents under study including organic (MeOH, MeCN, DMF) and aqueous micellar one (CTAC, SDS, Brij-700). For the analysis of FLM, CTAC give the best fluorescence signal enhancement. Analytical performances, such as limit of detection (LOD) and quantification (LOQ) was evaluated after solvent optimization and were found to vary, respectively, between 0.1 and 11 ng mL- 1 and between 0.3 and 36.6 ng mL- 1. Analytical application in various environmental aqueous samples matrices (sea, tap, runoff and well waters) give satisfactory recovery rates in the limits of 73.7-113.7% for both pesticides. This method is described for its simplicity for routine analysis.
RESUMO
Improvement of the TIFD method to determine buprofezin (BUP) founded on the O-phthalaldehyde (OPA)-thermoproduct complex of buprofezin (OPA-BUP) with dimethyl-ß-cyclodextrin (DMßCD) was investigated at 25 °C. The TIFD method developed in DMßCD medium, was optimized with respect to the reaction time, DMßCD concentration and pH. Based on the inclusion reaction, the OPA-BUP: DMßCD inclusion complex was developed in two aqueous media pH 7 and pH 13. A 1:1 stoichiometric ratio of OPA-BUP: DMßCD complex was obtained. The binding constants (K) and Gibbs energy (ΔG°) values increasing and decreasing with pH, respectively, show the spontaneous and thermodynamically favorable at 25 °C of the inclusion complexes formation. Normalized TIFD spectra were measured at 425 nm for emission and at 345 nm for excitation. Limits of detection (LOD) and quantification (LOQ) obtained, according to the pH, were in the ranges 0.05-0.1 ng mL ̶ 1 and 0.2-0.4 ng mL ̶ 1, respectively. Relative standard deviation (RSD) values, less than 1.3% corroborated TIFD method repeatability in DMßCD medium. Solid phase extraction (SPE) procedure which was used for quantitative analysis of natural water samples collected from Niayes area, led to satisfactory recovery rates values 99.5-117.3%.
RESUMO
Herbicide metolachlor (MET) and insecticide buprofezin (BUP) were determined in natural waters by means of a newly-developed, simple and sensitive thermochemically-induced fluorescence derivatization (TIFD) method. The TIFD approach is based on the thermolysis transformation of naturally non-fluorescent pesticides into fluorescent complex O-phthalaldehyde-thermoproduct(s) in water at 70°C for MET and at 80°C for BUP. The TIFD method was optimized with respect to the temperature, pH, complex formation kinetic and pesticides concentrations. The limit of detection (LOD=0.8ngmL(-1) for MET and 3.0ngmL(-1) for BUP) and quantification (LOQ=2.6ngmL(-1) for MET and 9.5 ngmL(-1) for BUP) values were low, and the relative standard deviation (RSD) values were small (between 1.2% and 1.8%), which indicates a good analytical sensitivity and a great repeatability of TIFD method. Recovery studies were performed on spiked well, sea and draining waters samples collected in the Niayes area by using the solid phase extraction (SPE) procedure. Satisfactory recovery results (84-118%) were obtained for the determination of MET and BUP in these natural waters.
