An electroanalytical method has been developed for the determination of two water soluble pyridine based neonicotinoid insecticides (imidacloprid and acetamiprid) by differential pulse voltammetry with a bismuth film electrode in aqueous Britton -Robinson buffer solution as supporting electrolyte. The bismuth film electrode preparation was optimized for cathodic voltammetric application. The reduction peaks of the neonicotionids appeared at potentials more negative than À 0.5 V (BiFE vs. Ag/AgCl/3.0 M KCl) and the signal characteristics depended on the pH of the supporting electrolyte. The best analysis conditions were found to be pH 8.0 for imidacloprid and pH 3.0 for acetamiprid at the following measurement parameters: pulse amplitude 50 mV, pulse width 50 ms and scan rate 25 mV. Calibration curves were linear in the concentration range of 2.43 -51.1 mg/cm 3 for imidacloprid and 2.95 -47.3 mg/cm 3 for acetamiprid, while the detection limits were 0.73 mg/cm 3 and 0.88 mg/cm 3 for imidacloprid and acetamiprid, respectively. The electroanalytical method has allowed monitoring the heterogeneous photocatalytic (O 2 /TiO 2 /UV) degradation of the two insecticides via their disappearance. The dynamics and the reaction rate determined on the basis of the electrochemical data were validated with HPLC/DAD and FTIR measurements.
Two types of bismuth modified electrodes, a bismuth-film modified glassy carbon (BiF-GCE) and a bismuth bulk modified carbon paste, were applied for the determination of selected nitroguanidine neonicotinoid insecticides. The method based on an ex situ prepared BiF-GCE operated in the differential pulse voltammetric (DPV) mode was applied to determine clothianidin in the concentration range from 2.5 to 23 μg cm−3 with a relative standard deviation (RSD) not exceeding 1.5%. The tricresyl phosphate-based carbon paste electrodes (TCP-CPEs), bulk modified with 5 and 20 w/w% of bismuth, showed a different analytical performance in the determination of imidacloprid, regarding the peak shape, potential window, and noise level. The TCP-CPE with 5% Bi was advantageous, and the developed DPV method based on it allowed the determination in the concentration range from 1.7 to 60 μg cm−3 with an RSD of 2.4%. To get a deeper insight into the morphology of the bismuth-based sensor surfaces, scanning electron microscopic measurements were performed of both the surface film and the bulk modified electrodes.
The objective of the work was to i nvestigate the possibility of using a tricresyl phosphate-based carbon paste electrode for the direct voltammetric determination of the neonicotinoid insecticide thiamethoxam. The analyte was determined by differential pul se voltammetry in Britton-Robinson buffer p H 7.0 in the concentr ation range of 3.72-41.5 µg m L -1 . The reproducibility of t he analytical signal at the 7.29 µg mL -1 level was characterized by a relative standard devi ation of 1.3 %. The applicability of the d eveloped method was ev aluated by determining thiamethoxam in a river water sa mple and a co mmercial formulation Actara 25 WG.
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