Uzhorod National University

Uzhhorod, Ukraine

Uzhorod National University

Uzhhorod, Ukraine
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Vishnikin A.B.,Dnipropetrovsk National University | Vishnikin A.B.,Charles University | Svinarenko T.Ye.,Dnipropetrovsk National University | Sklenarova H.,Charles University | And 4 more authors.
Talanta | Year: 2010

The guanidinium salt of the new heteropolymolybdate 11-molybdobismuthophosphate Gua6PBiMo11O40 (11-MBP) was synthesized, characterized and used as a reagent for batch spectrophotometric (SP) and sequential injection determination of ascorbic acid (AsA). When compared to other Keggin's heteropolyanions, the reduction of 11-MBP with AsA is both fast and maximal within a pH range of 1.6-2.0. The stoichiometry of the reaction was determined using molar ratio and continuous variation methods and was shown to be 1:1. The molar absorptivity of the reduced form of 11-MBP was 6.0 × 103 L mol-1 cm-1 at 720 nm. The reaction is also specific for AsA. Only cysteine, hydroquinone and hydroxyacids were found to interfere with the reaction, while no interference was observed with the common reducing agents, including reducing sugars, catecholamines, nitrite, sulfite and iron(II) ions. Batch SP and sequential injection analysis (SIA) systems were developed for the determination of AsA, with calibration ranges of the SP methods at 2 × 10-6-8 × 10-5 M for a 10 mm cell and 5 × 10-7-3 × 10-5 M for a 50 mm cell and a limit of detection at 3 × 10-7 M. The linear range of the SIA method was 6 × 10-6-5 × 10-4 M, with a detection limit of 2 × 10-6 M and a sample throughput of 15 h-1. The proposed methods were successfully used for the determination of AsA in both pharmaceuticals and fruit juices, and the results were consistent with those provided by the 2,6-dichlorophenolindophenol method. © 2009 Elsevier B.V. All rights reserved.

Billes F.,Budapest University of Technology and Economics | Billes F.,Vienna University of Technology | Szabo A.,Budapest University of Technology and Economics | Studenyak Y.,Uzhorod National University
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2011

A new styryl dye were prepared, 2-[2-(4-dipropylamino-phenyl)-vinyl]-1,3,3- trimethyl-3H-indolium chloride (DPPTVI) chloride. Its infrared and Raman were measured. Quantum chemical calculations were computed for both the isolated and the solute cation. Optimized geometry, atomic net charges were calculated. The calculated vibrational frequencies were scaled to the experimental ones. Only 12 scale factors were used for the scaling of 174 vibrational modes. Based on these results, normal coordinate analysis were carried out for both the isolated and the solute cations. Infrared and Raman spectra were simulated. The results for the isolated and the solute cations were compared. © 2010 Elsevier B.V. All rights reserved.

Majorosova J.,Slovak Academy of Sciences | Tomasovicova N.,Slovak Academy of Sciences | Timko M.,Slovak Academy of Sciences | Koneracka M.,Slovak Academy of Sciences | And 5 more authors.
Acta Physica Polonica A | Year: 2014

Introduction of ferroelectric or magnetic nanoparticles into nematic liquid crystal is a promising method for the improvement of the electro-optic or magneto-optic properties of different nematic liquid crystals by non-chemical way. This work is devoted to the study of composite systems of liquid crystal with spherical ferroelectric or magnetic particles with the aim to study their sensitivity to electric and magnetic fields. The nematic 4-(trans-4'- n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) liquid crystal was doped with SbSI ferroelectric particles or with Fe3O4 magnetic particles. The structural transitions in ferronematic samples were indicated by capacitance measurements in a capacitor made of ITO-coated glass electrodes in combined electric and magnetic fields. The obtained results showed the increase of the shift in critical voltage with increasing magnetic field in both kinds of samples.

Lavra V.,Uzhorod National University | Bazel Y.,Uzhorod National University | Bazel Y.,University of P.J. Šafarik | Badida M.,Technical University of Košice | Andruch V.,University of P.J. Šafarik
International Journal of Environmental Analytical Chemistry | Year: 2015

A novel and simple procedure for determination of anionic surfactants has been developed. The method is based on the reaction of sodium dodecyl sulphate (SDS) with Astra Phloxine FF reagent at pH 3–8, followed by liquid–liquid microextraction of the formed ion associate into an organic phase containing a mixture of carbon tetrachloride and dichloroethane (4:1, v/v) and subsequent UV-Vis detection at 555 nm. The calibration plot was linear in the range 0.006–0.29 mg L−1 of SDS. The limit of detection (LOD), calculated based on 3s, is 0.002 mg L−1. The method was applied to the determination of anionic surfactants in real wastewater samples. © 2015 Taylor & Francis.

Skodova I.,Slovak Academy of Sciences | Janisova M.,Slovak Academy of Sciences | Hegedusova K.,Slovak Academy of Sciences | Borsukevych L.,Botanical Garden of Ivan Franco National University | And 3 more authors.
Tuexenia | Year: 2015

We performed a survey of grassland communities in the Ukrainian Carpathians with the aim of: (1) syntaxonomically classifying the meso- and subxerophilous grassland vegetation; (2) analysing the main gradients in their species composition; (3) estimating the effect of selected environmental factors on grassland species composition; (4) assessing the species richness of vascular plants and bryophytes in relation to the measured environmental variables. We collected 46 phytosociological relevés during the growing seasons of 2010 and 2011. Species composition and species richness were studied at two spatial scales (1 m2 and 16 m2) in relation to soil parameters (soil depth, pH (KCl), content of P, K, Mg, N and C), management regime (mowing, grazing, ploughing in the past and burning), and other factors (altitude, litter cover, open soil, inclination, solar radiation and animal excrement). Seven grassland types were distinguished belonging to 3 classes and 4 alliances, namely the Nardetea strictae including the Violion caninae (mesic pastures at altitudes of 400-600 m mostly on moderate slopes) and the Nardo strictae-Agrostion tenuis (grasslands on moderate slopes at altitudes of 700-900 m usually managed by mowing and grazing the aftermath); the Molinio-Arrhenatheretea, including the Arrhenatherion elatioris (submontane grasslands originated mostly on former fields after their abandonment in the past) and the Cynosurion cristati (intensive pastures); and the Festuco-Brometea including the Cirsio-Brachypodion pinnati (abandoned grasslands dominated by Brachypodium pinnatum and Inula salicina). Detrended correspondence analysis indicated that the major compositional turnover was related to altitude and soil reaction. A canonical correspondence analysis confirmed that altitude had the strongest effect on species composition in the analysed dataset, followed by management treatments (former ploughing, grazing intensity). For vascular plant species richness, regression tree analysis identified grazing intensity as the most important predictor at the 1 m2 scale. At the 16 m2 scale, soil humus content was evaluated as the most important predictor of vascular plant species richness, followed by litter cover and grazing intensity. The number of bryophytes was not determined by the studied environmental factors at either of the two spatial scales. Although the number of analysed relevés in this study was limited, our results significantly contribute to the understanding of submontane grass-lands in the Ukrainian Carpathians.

Tomasovicova N.,Slovak Academy of Sciences | Haysak I.,Uzhorod National University | Kovac J.,Slovak Academy of Sciences | Kubovcikova M.,Slovak Academy of Sciences | And 5 more authors.
Acta Physica Polonica A | Year: 2014

The aim of the presented work was to investigate the stability of biocompatible magnetic fluid, i.e. water-based magnetic fluid containing magnetite nanoparticles stabilized by surfactant sodium oleate and modified by bovine serum albumin (BSA) after electron irradiation. Samples with the same concentration of Fe3O4 but different mass ratio BSA/Fe3O4 (w/w= 0:25, 1.0 and 2.5) were studied. The electron irradiation caused about 10% reduction of the saturation magnetization in the samples with w/w BSA/Fe3O4 ratio of 0.25 and less than 5% in the samples with w/w BSA/Fe3O4 ratio of 1 and 2.5.

Leskova M.,University of P.J. Šafarik | Bazel Y.R.,University of P.J. Šafarik | Bazel Y.R.,Uzhorod National University | Torok M.,University of P.J. Šafarik | Studenyak Y.,Uzhorod National University
Chemical Papers | Year: 2013

The structure of styryl dye, 2-[(E)-2-(4-dipropylaminophenyl)-1-ethenyl]-1, 3,3-trimethyl-3H-indolium chloride (I), was investigated using methods such as UV-VIS, fluorescence spectroscopy, and NMR (1H, 13C, APT, HMQC, COSY) and also by examining its electrochemical properties. A study of the acid-base properties revealed the existence of three different forms of the dye. The mechanisms of protolysis and hydrolysis are discussed. The reagent exists in a reactive single-charged form I + over a wide range of acidity (pH 4-11). The optimum analytical wavelength of the singlecharged form is 550 nm, where the molar absorptivity is 5.51 × 104 L mol-1 cm-1. The values of the optimum analytical wavelength and molar absorptivity of the protolysed and hydrolysed forms are: λ max(I-H2+) = 380 nm, Eε(I-H2+) = 2.01 × 104 L mol-1 cm-1; λ max(I-OH) = 320 nm, Eε(I-OH) = 1.12 × 104 L mol-1 cm-1. A theoretical study of the spectral and chemical properties of I was carried out by performing quantum chemical calculations. © 2012 Institute of Chemistry, Slovak Academy of Sciences.

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