Mineral mediated isotope fractionation of soil water.

RATIONALE: The ability to recover the isotopic signature of water added to soil samples that have previously been oven-dried decreases with the increasing presence of silt and clay. The effects on the isotopic signature of water associated with physicochemical soil properties are not yet fully understood, for either hydration or dehydration of soil samples. METHODS: The soil sample chemistry and the crystallinity of minerals were measured by X-ray fluorescence and X-ray diffraction. The organic carbon and the cation-exchange capacity were also determined. Water of known isotopic signature was used to spike an oven-dried substrate and subsequently extracted by cryogenic vacuum extraction at a temperature of 105°C. In addition, the soils were oven-dried at 205°C and water extractions were also performed at 205°C. The isotopic signatures of the water samples were determined by cavity-ring-down spectrometry. RESULTS: The isotope effects caused by the cryogenic vacuum extraction method applied to soils with elevated clay content were reduced. First, by increasing the extraction temperature to 205°C, we improved the precision of the cryogenic vacuum extraction method and the recovery of the known isotopic signature of the spike water. Secondly, the post-correction of data based on the physicochemical soil properties and a common extraction temperature of 105°C improved the measurement trueness. CONCLUSIONS: The isotopic signature of soil water is influenced by mineral-water interaction. During the hydration of clay, different minerals deplete free water in heavy isotopes. The extracted soil water (dehydration water) gathered from clay-rich soils is generally more depleted in the heavy isotopes than the spike water, making results obtained for different soil types difficult to compare. Isotope effects observed at the mineral-water interface highlight potential explanations for eco-hydrological separation of water pools. Copyright © 2016 John Wiley & Sons, Ltd.

The variable charge of dioctahedral smectites.

One of the most important properties of smectites is the cation exchange capacity resulting both from the structural permanent charge and the pH depending variable charge. The variable charge, in turn, mainly results from the edge aluminol groups (in the case of dioctahedral smectites). The permanent charges can be calculated using the layer charge density; the variable charges, however, were rarely quantified accurately. The present study was conducted to (i) test and compare different methods for the measurement of the variable charge of dioctahedral smectites (mainly montmorillonites), (ii) characterize the range of differences of the variable charge of smectites from different deposits, and (iii) identify the reason for different variable charge values. Considering a 0.1×0.1 µm montmorillonite particle, a variable charge of 8 meq/100 g (about 10% of the CEC) was calculated. Two CEC (Cu(trien)) based methods provided slightly larger values. These values ranged from 2% to 14% between pH 4 and 6 and from approximately 10% to 30% between pH 4 and 9. With the potentiometric titration method, even larger values for the variable charge were determined (15-35%). Interestingly, both the CEC based methods and the titration method provided comparable trends. Accordingly, any of these methods is suitable to distinguish materials with larger or lower variable charge. One of the reasons for the differences of the variable charge of different bentonites is the variable chemical composition of the smectites, particularly the structural Mg content. Further reasons may be the roughness of the edge surface (not considered in the calculation) and the submicron particle size distribution, which are both difficult to determine.

N(2)-BET specific surface area of bentonites.

The specific surface areas (SSA(N2BET)) of 36 different bentonites had larger values for Ca(2+)/Mg(2+) bentonites than for Na(+) bentonites. This trend could not be explained by the different d(001) values nor by the different microstructures. The investigation of Cu-triene-exchanged smectites, which on drying at 105 degrees C still had a d(001) value accounting for approximately 13A, proved that the SSA(N2BET) of low-charged smectites increased more than that of high-charged smectites. This could be explained by: (i) more space between the permanent charge sites in the case of low-charged smectites and (ii) the fact that the layers of Cu-triene smectites do not collapse at 105 degrees C. In contrast the SSA(N2BET) of Ca(2+)-exchanged bentonites could not be related to the layer charge density (LCD) as in the case of the Cu-triene-exchanged bentonites which is probably due to the varying number of collapsed layers. In conclusion, the SSA(N2BET) of bentonites which is known to be largely variable is probably determined by microporosity resulting from the quasi-crystalline overlap region and accessible areas of the interlayer. The number of layers per stack and the microstructure are supposed to play a subordinate role. The larger SSA(N2BET) of Ca/Mg bentonites compared to Na bentonites probably can be explained by the larger space between the charges in the case of the presence of divalent cations.

[Numerical studies of the effect of prosthetic implants on the strain energy density distribution in the femur]. / Numerische Untersuchungen zum Einfluss einer prothetischen Versorgung auf die Strain-Energy-Density-Verteilung im Femur.

In this study the distribution of the strain energy density (SED) in the natural femur as well as changes of it due to the implantation of an artificial hip joint has been investigated. Because of recently published theoretical considerations the volume related SED was used to describe the respective biomechanical loading situation completely. By means of parameter variation different load cases were simulated. The calculated SED-distributions were compared with the respective results of the natural femur. Thus, the known reasons of failures of hip joint prostheses has been proofed numerical. It was shown that the SED is a suitable mechanical parameter to simulate bone remodeling after hip joint replacement.

Lipid interference in the determination of the concentration of haemoglobin in plasma using the ACA SX analyzer.

In comparison to a triple wavelength procedure, the dual wavelength method for the determination of plasma haemoglobin concentration using the ACA analyzer showed considerable interference with hypertriglyceridaemic (triacylglycerols > 2.3 mmol/l) plasma. By addition of isolated human lipoprotein fractions to normotriglyceridaemic plasma, chylomicrons were identified as a major source of interference with the ACA plasma haemoglobin method, whereas VLDL was without effect up to a triacylglycerol concentration of 5.7 mmol/l. Airfuge ultracentrifugation proved to be a reliable means for removal of interfering lipid. We conclude that the extent of lipid interference with the ACA plasma haemoglobin method is highly dependent on the type of lipoprotein present. An accurate measurement of plasma haemoglobin concentrations in non-fasting plasma can only be ensured after lipid removal through airfuge ultracentrifugation.