A cathodic electrochemical application of bismuth film modified glassy carbon electrode was investigated with the objective of determining thiamethoxam insecticide. The conditions of bismuth film deposition (electrode pretreatment procedure, composition of the plating solution, plating potential and film stability) were optimized using electrochemical and microscopic techniques. It was found that the bismuth film generation on glassy carbon substrate in a plating solution of 0.02 M Bi(NO 3 ) 3 , 1 M HCl and 0.5 M KBr, at À 0.25 V (vs. Ag/AgCl/3 M KCl) for 60 s and subsequent electrochemical conditioning yielded a modified electrode suitable for analytical purposes. Thiamethoxam was determined by differential pulse voltammetry in Britton -Robinson buffer of pH 8.0 in the concentration range of 1.26 -45.0 mg/cm 3 . The reproducibility of the analytical signal was characterized by a relative standard deviation smaller than 1.5%, and the calculated values of detection and quantitation limits were 0.38 mg/cm 3 and 1.26 mg/cm 3 , respectively. The applicability of the modified electrode was tested on real, agriculturally-incurred potato and maize samples.
A simple voltammetric method using a glassy carbon working electrode was developed for the determination of two members from the neonicotinoid group of insecticides: imidacloprid and thiamethoxam. The experiments showed that the voltammetric response depends on the mode of electrode surface pretreatment and the polarization mode. The response appeared to be linear in the range from 0.028 to 0.50 mg/cm3 for both analyses. The limit of detection was 0.0077 mg/cm3 for imidacloprid and 0.0085 mg/cm3 for thiamethoxam, the limit of quantitation was 0.026 mg/cm3 and 0.028 mg/cm3, respectively. The developed method was applied for the determination of these insecticides in potato samples sprayed with Confidor 200-SL or Actara 25-WG as well as commercial formulations of imidacloprid and thiamethoxam. A recovery trial was performed to assess the accuracy of the results, the recovery values being between 95?102 % for both of neonicotinoids.
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.
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