Enzyme-assisted extraction of arsenic species from plant material

Investigations regarding the transfer and metabolism of arsenic species in plants require mild extraction conditions to conserve the original composition of arsenic species. Beside the use of water or water/methanol for extraction of arsenic species from plant samples, enzymes can assist this procedure by digestion of cellulose and other constituents of cell walls, resulting in a faster, more efficient extraction technique which preserves the arsenic species. The investigations presented here were focused on the stability of certain arsenic species in enzymatic solutions, optimal conditions for their chromatographic separation and detection namely by means of ion chromatography–inductively coupled plasma mass spectrometry and improvements with respect to extraction efficiency. With commercially available enzymes and enzyme mixtures, the digestion rate of soluble starch as model cellulose was determined using high-performance anion exchange chromatography–pulsed amperometric detection analysis of glucose as the major digestion product. The most effective digestion rate (80% within 4?h) was obtained with Viscozyme®. This enzyme mixture was applied to extracted arsenic species from algae and terrestrial plant materials. Qualitative and quantitative differences in the results between enzyme-assisted and water extractions were obtained and discussed. The results show that the application of enzymes in mild extraction protocols should be evaluated as an additional step for the identification of As-metabolics in organisms. Careful selection of suitable enzyme mixtures can overcome the disadvantage that extraction efficiency is very organism-specific.     

Random Diophantine inequalities of additive type

Using the Davenport–Heilbronn circle method, we show that for almost all additive Diophantine inequalities of degree k in more than 2k variables the expected asymptotic formula for the density of solutions holds true.     

Monotone nonlinear finite‐volume method for nonisothermal two‐phase two‐component flow in porous media

This article presents a new nonlinear finite‐volume scheme for the nonisothermal two‐phase two‐component flow equations in porous media. The face fluxes are approximated by a nonlinear two‐point flux approximation, where transmissibilities nonlinearly depend on primary variables. Thereby, we mainly follow the ideas proposed by Le Potier combined with a harmonic averaging point interpolation strategy for the approximation of arbitrary heterogeneous permeability fields on polygonal grids. The behavior of this interpolation strategy is analyzed, and its limitation for highly anisotropic permeability tensors is demonstrated. Moreover, the condition numbers of occurring matrices are compared with linear finite‐volume schemes. Additionally, the convergence behavior of iterative solvers is investigated. Finally, it is shown that the nonlinear scheme is more efficient than its linear counterpart. Copyright © 2016 John Wiley & Sons, Ltd.