Heterodiffusion of chromium and cobalt in liquid iron

The heterodiffusion has been studied by the method of stationary diffusion source. In that method the saturated radioactive vapour of the diffusing element comes into contact with the liquid in which diffusion is being studied. Two variants of that method were applied and the diffusion coefficients of chromium and cobalt in liquid iron were determined, i.e.D _{(Cr→Fe, 1860K)}= =4·9×10^?5cm²/s andD _{(Co→Fe, 1820K)}=5×10^?5cm²/s, respectively. The values of maximum concentration of chromium in Fe-samples after diffusion were of the order of 10^?1 to 10^?2 wt-%, those of cobalt of 10^?4 wt-%. This experimental method is rather simple and the results obtained are in good conformity with other measurements.     

Separation of phenolic acids by capillary electrophoresis with indirect contactless conductometric detection

A new method for the electrophoretic separation of nine phenolic acids (derivatives of benzoic and cinnamic acids) with contactless conductometric detection is presented. Based on theoretical calculations, in which the mobility of the electrolyte co- and counterions and mobility of analytes are taken into consideration, the electrolyte composition and detection mode was selected. This approach was found to be especially valuable for optimization of the electrolyte composition for the separation of analytes having medium mobility. Indirect conductometric detection mode was superior to the direct mode as predicted theoretically. The best performance was achieved with 150 mM 2-amino-2-methylpropanol electrolyte at pH 11.6. The separation was carried out in a counter-electroosmotic mode and completed in less than 6 min. The LODs achieved were about 2.3-3.3 microM and could be further improved to 0.12-0.17 microM by using a sample stacking procedure. The method compares well to the UV-Vis detection.     

Microscale separation methods for enzyme kinetics assays

Miniaturization continues to be one of the leading trends in analytical chemistry and one that brings advantages that can be particularly beneficial in biochemical research. Use of a miniaturized scale enables efficient analysis in a short time and requires very small amounts of samples, solvents, and reagents. This can result in a remarkable decrease in costs of enzyme kinetics studies, especially when expensive or rare enzymes and/or substrates are involved. Free zone electrophoresis is without a doubt the most common microscale separation technique for capillary and on-chip enzyme assays. Progress and applications in this field are reviewed frequently whereas other modes of separation, although successfully applied, receive only marginal interest in such publications. This review summarizes applications of less common modes of separation in capillary or chip formats, namely micellar electrokinetic chromatography, liquid chromatography, gel electrophoresis, isoelectric focusing, and isotachophoresis. Because these techniques are based on separation mechanisms different from those of free zone electrophoresis, they can be, and have been, successfully used in cases where zone electrophoresis fails. Advantages and drawbacks of these alternative separation techniques are discussed, as also are the difficulties encountered most often and solutions proposed by different research groups.     

Application of dilatometric analysis to the study of autoclaved calcium silicate materials

The process of shrinkage of calcium silicate hydrate was investigated by dilatometry up to 350 °C. The properties of this material are based on the formation of C–S–H phases during the reaction at temperatures between 180 and 205 °C and water vapor pressure lower than 16 bars. The main C–S–H phases are 11.3 Å tobermorite and xonotlite. 11.3 Å tobermorite converts to 9.3 Å tobermorite on air at temperatures around 300 °C. The hydrosilicate materials were prepared from quicklime and finely ground sand with different CaO/SiO₂ ratios under different hydrothermal conditions. The reaction time was 24 h. Materials based on xonotlite and tobermorite were produced, and the calcium silicate phases were characterized by XRD and TG/DTA methods. Dilatometry measurements were used to study the effect of heating conditions on sample shrinkage. Dehydration of hydrated calcium silicate minerals occurred during heating. The results show that sample shrinkage is dependent on the type and amount of C–S–H phases, the amount of bound water and formation of 9.3 Å tobermorite. All samples showed shrinkage after heating up to 350 °C, but this change was not irreversible for all samples after cooling to room temperature.

     

Rapid speciation of Se(IV) and Se(VI) by flow injection–capillary electrophoresis system with contactless conductivity detection

A flow injection–capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25 samples per hour using a background electrolyte solution containing 8.75 mM l-histidine (His) adjusted to pH 4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190 g L^–1 and 7.5 g L^–1 for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations.     

Changes of organic acids and phenolic compounds contents in grapevine berries during their ripening

Changes of total content of phenolic substances, alteration in total titratable acidity and differences in tartaric acid content in grapes of four white (Müller-Thurgau — MT, Pinot Blanc — Rulandské bílé in Czech, RB, Sauvignon (Sg), and Muscat Ottonel — Mu?kát Ottonel in Czech, MO) and two blue (Dornfelder — Df and Blue Frankish — Frankovka in Czech, Fr) grapevine varieties throughout their growth, ripening and maturing (July–November). Potentiometric titration was applied for the determination of total titratable acids in grapes (expressed as tartaric acid equivalents in g L^?1). A spectrophotometric method according Rebelein based on the formation of a colored complex of ammonium metavanadate and tartaric acid was used for determination of tartaric acid in green juice made by pressing unripe grapes. A spectrophotometric method based on reduction of phosphomolybdato-tungsten complex in alkaline solution using Folin-Ciocalteau reagent was applied for determination of total content of phenolic substances (TCP).

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Interaction of porphyrins with a dendrimer template: self-aggregation controlled by pH

The interaction between self-aggregated porphyrins such as 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and 5,10,15,20-tetrakis(4-phosphonatophenyl)porphyrin (TPPP), and a generation 5 (G5) PAMAM dendrimer template is governed by minute differences of porphyrin acido-basic properties. While at neutral pH both monomeric TPPS and TPPP form complexes with G5, decreasing pH did not lead to porphyrin ring protonation (pK(a) approximately 5) but rather to the preferential formation of H-aggregates (probably H-dimers), most likely due to protonation of the G5. Upon further acidification of the solution, this face-to-face orientation of the porphyrin units is being converted to edge-to-edge aligned J-aggregates with a tightly defined structure. This process starts by protonation of the porphyrin ring at pH below 2.3 and 2.8 for TPPS and TPPP, respectively. The AFM imaging of porphyrin/G5 nanostructures obtained at pH 0.7 shows the formation of long nanorods of TPPS with partially aggregated G5 and small aggregates of TPPP connected to individual G5 molecules.     

Capillary electrophoretic studies of acid-base properties of sanguinarine and chelerythrine alkaloids

Capillary zone electrophoresis with UV detection was used for determination of dissociation constants of alkaloids sanguinarine and chelerythrine. Despite the limited solubility of the uncharged forms of the alkaloids resulting in insufficient analytical signal at higher pH the reliable dissociation constants were obtained when acidified samples containing low amount of the alkaloid were injected into the capillary. The precipitation of the alkaloid in the capillary induced by injecting sample of low pH into the background electrolyte of higher pH does not affect the mobility of the alkaloid if its concentration injected exceeds the solubility only to a small extent. Dissociation constants (pK(R+)) of sanguinarine and chelerythrine calculated to 8.3 +/- 0.1 and 9.2 +/- 0.1, respectively, are relevant to Good buffers of ionic strength of 30 mM.     

Supercritical fluid extraction as a tool for isolation of monoterpenes from coniferous needles and walnut-tree leaves

Several monoterpenes, i.e., (+)-α-pinene, (−)-camphene, sabinene, (−)-β-pinene, myrcene, R-(+)-limonene, (−)-bornylacetate, (−)-trans-caryophyllene and a-humulene were identified and determined by gas chromatography-mass spectrometry (GC-MS) in needles of Pinaceae (Picea abies, P. omorika, P. pungens, P. Breweriana, Pinus nigra, P. mungo turra, P. black, P. sylvestris, Abies pinsapo, A. holophylla, A. Bronmuelleris, A. alba, Larix Kaempferi L. decidua) and tree-leaves of Juglandaceae (Juglans regia, J. nigra, J. sieboldiana var. Cordiformis) families. Supercritical fluid extraction (SFE) was found to be very useful for their isolation at optimised conditions (needles/leaves: pressure 20/30 MPa, temperature 80/130°C, time of extraction 60/60 min, modifier chloroform/chloroform). Their seasonal distribution, evaluation of differences in concentrations and relative amounts in different trees and their varieties grown in different localities were evaluated.      

Immobilization of porphyrins in poly(hydroxymethylsiloxane)

Three tetracationic porphyrins differing in the position of charged nitrogen atoms on the peripheral substituents — 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP4), 5,10,15,20-tetrakis(N-methylpyridinium-2-yl)porphyrin (TMPyP2), 5,10,15,20-tetrakis(4-trimethylammoniophenyl) porphyrin (TMAPP), and hydrophobic 5,10,15,20-tetraphenylporphyrin (TPP), were immobilized by adsorption and encapsulation in poly(hydroxymethylsiloxane) (PHOMS). The so prepared porphyrin-PHOMS composites were characterized by porosimetry, scanning electron microscopy, fluorescence and diffuse reflectance UV-VIS spectroscopy. It was found that porphyrins are immobilized in the PHOMS matrix in the free base monomer form Their irradiation produced singlet oxygen O₂(¹Δ_g) with the lifetime of 10–30 μs.