Distribution of pesticides in n-hexane/water and n-hexane/acetonitrile systems and estimation of possibilities of their extraction isolation and preconcentration from various matrices
RUE "Institute of Plant Protection", Minsk, Belarus. Electronic address: . Analytica chimica acta
(Impact Factor: 4.51).
04/2013; 774:33-43. DOI: 10.1016/j.aca.2013.03.003
Distribution of 150 most widely used pesticides of different chemical classes (amides, anilinopirimidines, aromatics, benzenesulfonates, carbamates, dicarboximides, organophosphorus compounds, phenyl esters, phenylureas, pyrazoles, pyrethroids, pyrimidines, strobilurins, sulfamides, triazines, triazoles, etc.) in n-hexane/water and n-hexane/acetonitrile systems was investigated at 25°C. Distribution constants of pesticides (P) have been calculated as ratio of pesticide concentration in n-hexane to its concentration in water or acetonitrile phase. HPLC and GC methods were used for pesticides determination in phases. It was found that the overwhelming majority of pesticides are hydrophobic, i.e. in n-hexane/water system LgP≫0, and the difference in LgP values can reach 9.1 units. Replacement of water for acetonitrile leads to dramatic fall of LgP values reaching 9.5 units. The majority of LgP values in this case are negative and their differences is strongly leveled in comparison with a hexane/water system. Thus, maximal difference in pesticides LgP values for n-hexane/acetonitrile system is 3.2 units. It is shown that n-hexane can be used for selective and efficient extraction and preconcentration of pesticides from water matrices. On the other hand, acetonitrile is effective for the isolation and preconcentration of pesticides from hydrocarbon and vegetable oil matrices. The distribution constants described in the paper may be effectively used for the estimation of possibilities of extraction isolation, preconcentration and separation of pesticides.
Available from: Mikhail Zayats
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ABSTRACT: The distribution of 19 azole class pesticides in hexane/aqueous–organic mixtures systems and rapeseed oil (or oil solution in hexane)/organic solvents has been studied at 20 ± 1 °C. The distribution constants (P) and coefficients (D) between hydrocarbon and polar phase are calculated. It is found that all the studied pesticides are hydrophobic, i.e., in hexane–water system log P ≫ 0. Replacement of water by organic solvents results in sharp log P falling, and their values become negative. It is revealed that solutions of strong inorganic acids in anhydrous acetonitrile extract azole class pesticides from hexane and vegetable oils most fully and selectively. In particular, the acidification of acetonitrile causes a drop of D values in 50–2000 times for the majority of the studied pesticides. This phenomenon was used for the development of the improved technique for the quantitative analysis of a widely used azole class pesticides, which can be presented at trace levels in rapeseed oil. The proposed methodology is based on dissociation extraction (DE) of azoles using perchloric acid in anhydrous acetonitrile, with following clean-up of acetonitrile extract from organic impurities by hexane and aqueous solution of dipotassium hydrogen orthophosphate, and final GC–ECD (gas chromatography with electron capture detection) determination of azole fungicides. The values of obtained recoveries were between 85% and 115% with RSD values below 10%. The obtained limits of quantitation, ranged from 3.0 to 300 μg kg−1, are below the maximum residue levels (MRLs) set by the European Union for the majority of pesticides. The developed method was successfully applied to different rapeseed oil samples.
Analytical Chemistry Research 11/2014; 3. DOI:10.1016/j.ancr.2014.11.004
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Environmental Science and Pollution Research 02/2015; 22(13). DOI:10.1007/s11356-015-4149-8 · 2.83 Impact Factor
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ABSTRACT: The graphene oxide nanocomposite (GO-Fe3O4) was synthesized by a simple and low-cost method. This nanocomposite was characterized by XRD, TEM, FT-IR, TGA, and VSM. Spherical Fe3O4 nanoparticles with an average size of 10 nm were uniformly applied to the surface of graphene oxide sheets. GO-Fe3O4 nanocomposite showed a superparamagnetic characteristic at room temperature and its saturation magnetization was 8.5 A · M2/kg. The adsorption behaviour of diquat at the surface of GO-Fe3O4 was investigated, including effects of pH, temperature, and water matrix. The adsorption kinetics, thermodynamics, and adsorption isotherm were also examined. The adsorption was strongly dependent on pH. The adsorption process obeyed the pseudo-second order kinetic model, and the rate-determining step might be chemical sorption. The Langmuir adsorption isotherm model was applicable for describing the adsorption of diquat onto GO-Fe3O4, and the adsorption capacity was 74.85 mg/g at room temperature. Thermodynamic parameters indicated that the adsorption process was spontaneous and exothermic. Most importantly, the GO-Fe3O4 could remove 96.6% of diquat from a real water sample when the concentration of diquat is 20 mg/L. This article is protected by copyright. All rights reserved
The Canadian Journal of Chemical Engineering 07/2015; 93(10). DOI:10.1002/cjce.22278 · 1.23 Impact Factor
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