Redox reactions in non-aqueous media: determination of organic isothiocyanates alone, in formulations and in important mixtures.
A simple potentiometric method for the determination of organoisothiocyanates is described. The isothiocyanate is treated in acetonitrile medium with an excess of primary amine to convert it into a substituted thiourea and the surplus amine is converted into a dithiocarbamate by addition of carbon disulphide. The solution is then titrated with a copper(II) solution in acetonitrile. The three-step titration curve enables the results to be calculated on the bash of the dithiocarbamate and/or thiourea formed. The method has been successfully applied to the analysis of a commercial insecticide formulation based on isothiocyanate and important mixtures containing isothiocyanates.
Voltammetric and electrochemical quartz crystal microbalance studies of sulforaphane and its Zn(II) complexes.
Cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) methods were used to study the behavior of sulforaphane (SFR). To established electrochemical properties of SFR methyl-, ethyl-, 2-chloroethyl-, propyl-, butyl- and tert-butyl-isothiocyanates were examined at gold electrode. Optimal measurement parameters were established and stock solutions developed. The electrode activity of the studied compounds (cathodic peak E(p)=-0.6 V) was found to be primarily due to the oxidation of the isothiocyanate group. By the EQCM method it was found that during the reduction of SFR the mass of the electrode systematically increased in successive scans by ca. 120 ng per scan and in the mixture of SFR and Zn(2+) ions ca. 350 ng. Formation of SFR complexes with Zn(2+) ions was confirmed by EQCM and UV methods. Cyclic voltammetric method has been elaborated for SFR determination and compared with UV method.
Silica in Soils1
Publisher Summary Silica in free and combined forms is a dominant component of the solid material of many soils, and dissolved silica is commonly a major solute of soil solutions. Breakdown of primary silicates, translocation of silica in solution, and deposition of secondary silica-containing substances are involved in the development of soils. Ions essential for the growth of plants are released to the soil solution as silicates weather, and these ions may be held against leaching at exchange sites on other silicates. Silica is absorbed in appreciable quantities by some plants and is returned to the surface of the soil as the plants decay. The nature and transformations of silica and silicates in soil are, thus, fundamental to an understanding of many aspects of soil and plant sciences.