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 %

Liquid chromatographic determination of fumonisins B1 and B2 in corn samples after reusable immunoaffinity column clean-up

The possibility of the liquid chromatographic determination of fumonisins B1 (FB1) andB2 (FB2) in corn samples with a reused immunoaffinity column (IMA) for the clean-up of the samples was investigated. After optimization of the chromatographic determination of FB1 and FB2 derivatized with o-phthaldialdehyde- 2-mercaptoethanol, the efficiency of the clean-up of spiked corn extracts with reuse of the IMA columns was studied, both with and without column regeneration. It was found that the IMAcolumn, designated for single-use only, can be used at least five times without regeneration and additional five times after regeneration. Regeneration consists of leaving the phosphate buffer saline solution on the column for one day at 4 ºC. The efficiency of the columns was tested by determining the recovery of FB1 and FB2, as well as the reproducibility of the determinations. The mean recoveries of FB1 and FB2 from corn spiked with FB1 at 1.0 mg/g and with FB2 at 0.5 mg/g (on the basis of 10 measurements) were 88.7%(RSD 10.2%) and 90.5%(RSD 6.1 %), respectively

Chemical composition of leaf extracts of Stevia rebaudiana Bertoni grown experimentally in Vojvodina

The chemical composition of leaf extracts of Stevia rebaudiana Bertoni, grown for the first time on an experimental field near Zrenjanin, was examined by GC–MS. The tested plant material was harvested in September of 2002. To analyze the chemical composition of the lipophilic components of the plant leaves, essential oils and ethyl acetate extract were isolated. Qualitative analysis of the essential oil obtained by hydrodistillation showed that among the identified 88 compounds, the majority were mono- and sesquiterpenes (50 types identified). By analysing the ethyl acetate extract, the presence of fatty acids (present as free and as esters), n-alkanes, n-alkenes, cyclic alkanes, alcohols, aldehydes, ketones, etc. was ascertained. Sesquiterpenes prevailed among the terpenes (50 types identified). Further constituents identified in ethyl acetate extract included sterols. Nerol, b-cyclocitral, safranal, aromadendrene, a-amorphene and T-muurolol were identified for the first time in this species, with match values over 90 %. Taking into consideration that these terpenes were identified for the first time in this species, it is obvious that Stevia rebaudiana grown in this area possesses certain specific characteristics that can be ascribed to cultivation on a domestic plantation

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