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.

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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The applicability of differently modified glassy carbon (GC) electrodes for direct or indirect determinations of various physiologically active compounds (insecticides and pharmaceuticals) in different formulations and some real samples was investigated. Samples of selected insecticides from the group of neonicotinoids with nitroguanidine (thiamethoxam and imidacloprid), cyanoimine (acetamiprid) and nitromethilene (nitenpyram) fragments, prepared in an appropriate manner, were determined by voltammetry on bare and surface-modified GC electrodes, while in the case of pharmaceuticals such as Trodon and Akineton, the chloride anion titration was followed using bare GC and phosphorus doped (P-GC) electrodes. The P-GC was also used to monitor the chloride content in the photocatalytic degradation of the (4-chloro-2-methylphenoxy)acetic acid herbicide. It was found that apart from the nature of the electrode material, the analyte and supporting electrolyte, as well as the pretreatment of the electrode surface essentially influences the applicability of the employed sensors.