Optimization of the determination of deoxynivalenol in corn samples by liquid chromatography and a comparison of two clean-up principles

The determination of deoxynivalenol (DON) in corn by liquid chromatography with DAD detection was optimized. The separations were achieved on a Hypersil ODS column (100 × 4.6 mm; particle size 5 mm) by isocratic elution (0.6 cm3/min), a mobile phase consisting of acetonitrile–water in the ratio of 16:84. UV Detection was performed at 220 nm. Linear calibration curves were constructed in the concentration range of 0.72 – 12.00 ng/ml (equivalent to 0.29 – 4.8 mg/g corn). The detection limit measured as the signal-to-noise ratio (3:1) was 0.16 ng/ml for DON (equivalent to 0.06 mg/g corn). The efficiencies of two clean-up principles for crude corn extract were compared: solid-phase and immunochemical extraction. The efficiency of solid-phase extraction was found to be higher, with a value of 92.7 % when MycoSep 225 columns were used, while its value was 97.6 % when self-made activated charcoal–alumina–Celite–cationic columns were used. In contrast, the efficiency of the immunochemical columns (IMA) was only 73.8%. Itwas also found that the self-made columns could be used at least three times in a row, in that way differing from the MycoSep 225 columns, which could not be reused either with or without regeneration, as well as from the IMA columns, which had a regeneration efficiency of 53.6 %

Original scientific paper Determination of various insecticides and pharmaceuticals using

Abstract: 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

Potentiometric application of boron- and phosphorus-doped glassy carbon electrodes

Acomparative study was carried out of the potentiometric application of boronand phosphorus-doped and undoped glassy carbon samples prepared at the same heat treatment temperature (HTT 1000°C). The electrochemical activities of the obtained electrode materials were investigated on the example of argentometric titrations. It was found that the electrochemical behaviour of the doped glassy carbon samples are very similar to a Sigri (undoped) glassy carbon sample (HTT 2400°C). The experiments showed that the potentiometric response depends on the polarization mode, the nature of the sample, the pretreatment of the electrode surface, and the nature of the supporting electrolyte. The amounts of iodide, bromide, and of chloridewere determined to be 1.27 mg, 0.80 mg and 0.54 mg, respectively, with a maximum relative standard deviation of less than 1.1%. The obtained results are in good agreement with the results of comparative potentiometric titrations using a silver indicator electrode. The titrationmethod was applied to the indirect determination of pyridoxine hydrochloride, i.e., vitamin B6

Photocatalytic removal of the herbicide clopyralid from water

The stability of the herbicide clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was studied under different experimental conditions of pH, illumination and initial substrate concentration. It was found that in the pH interval from 1.0 to 9.0 in the presence/absence of daylight, clopyralid solutions were stable for at least a period of two months. The kinetics of the photocatalytic degradation of clopyralid in aqueous suspensions of TiO2 (Degussa P25) under UV and visible light, as well as of direct photolysis using the same radiation sources, were also investigated. It was found that the rate of photocatalytic degradation in the presence of UV light was more than five times higher compared to direct photolysis, whereas in the presence of visible light, the corresponding rates of photocatalytic/photolytic degradation were much lower (more than 15 times). The reaction in the investigation concentration range is zero-order with respect to the degradation of the clopyralid pyridine moiety, with a reaction rate of 3.4×10−6 mol dm-3 min-1 and an adsorption coefficient of the substrate of 2.5×104 dm3 mol‑1

Voltammetric determination of imidacloprid and thiamethoxam

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 analytes. 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. Arecovery trial was performed to assess the accuracy of the results, the recovery values being between 95–102 % for both of neonicotinoids

JSCS–3677 Original scientific paper Photocatalytic removal of the herbicide clopyralid from water

Abstract: The stability of the herbicide clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was studied under different experimental conditions of pH, illumination and initial substrate concentration. It was found that in the pH interval from 1.0 to 9.0 in the presence/absence of daylight, clopyralid solutions were stable for at least a period of two months. The kinetics of the photocatalytic degradation of clopyralid in aqueous suspensions of TiO 2 (Degussa P25) under UV and visible light, as well as of direct photolysis using the same radiation sources, were also investigated. It was found that the rate of photocatalytic degradation in the presence of UV light was more than five times higher compared to direct photolysis, whereas in the presence of visible light, the corresponding rates of photocatalytic/photolytic degradation were much lower (more than 15 times). The reaction in the investigation concentration range is zero-order with respect to the degradation of the clopyralid pyridine moiety, with a reaction rate of 3.4×10-6 mol dm-3 min-1 and an adsorption coefficient of the substrate of 2.5×10 4 dm 3 mol-1