Ladislav Svoboda

Gradient elution in liquid chromatography : X. Retention characteristics in reversed-phase gradient elution chromatography

Abstract The reversed-phae chromatographic behaviour of selected barbiturates, alkaloids and substituted alkyluracils on a C 18 bonded phase column was investigated in both isocratic and gradient elution experiments using a binary mobile phase composed of water and methanol. Experimental capacity ratios of sample compounds under isocratic conditions fitted well with the linear relationships of log k ′ versus concentration of methanol in the mobile phase. The approach for the calculation of retention volumes and peak widths in gradient elution chromatography presented earlier was extended to reversed-phase chromatography and verified experimentally. The agreement between the experimental and theoretically predicted values was satisfactory.

Gradient elution in liquid chromatography: XIII. Instrumental errors in gradient elution chromatography

Abstract Instrumental sources of experimental errors in gradient elution liquid chromatography are considered. The performance of the equipment generating the concentration gradient in the low-pressure part has been investigated and it is shown that the equipment is able to reproduce the required ratio of the two components of the mobile phase and to maintain the flow-rate with an error of less than 1%. The deviations from the gradient profile due to the mixing in a reciprocating high-pressure pump are negligible under normal gradient elution conditions.

Separation of phenoxyacid herbicides using liquid column chromatography on chemically bonded phases

Abstract Possibilities for the liquid chromatographic (LC) separation of phenoxyacid herbicides were tested. Two complementary LC systems are suggested for the separation and identification of these compounds. In the first system, an octadecylsilica column is used together with aqueous-methanolic mobile phases containing an inorganic salt or a buffer, such as sodium sulphate or potassium dihydrogen phosphate. The second system makes use of a chemically bonded amino phase and of mobile phases containing acetic acid in water, methanol or other organic solvents and their mixtures. The influence of the mobile phase composition and of the structure of phenoxyacid herbicides on retention and selectivity of separation was investigated. The separation methods suggested can be used in the analysis of commercial herbicide formulations and in environmental analyses.

Silica-coated manganite and Mn-based ferrite nanoparticles: a comparative study focused on cytotoxicity

Magnetic oxide nanoparticles provide a fascinating tool for biological research and medicine, serving as contrast agents, magnetic carriers, and core materials of theranostic systems. Although the applications rely mostly on iron oxides, more complex oxides such as perovskite manganites may provide a much better magnetic performance. To assess the risk of their potential use, in vitro toxicity of manganite nanoparticles was thoroughly analysed and compared with another prospective system of Mn–Zn ferrite nanoparticles. Magnetic nanoparticles of La0.63Sr0.37MnO3 manganite were prepared by two distinct methods, namely the molten salt synthesis and the traditional sol–gel route, whereas nanoparticles of Mn0.61Zn0.42Fe1.97O4 ferrite, selected as a comparative material, were synthesized by a new procedure under hydrothermal conditions. Magnetic cores were coated with silica and, moreover, several samples of manganite nanoparticles with different thicknesses of silica shell were prepared. The size-fractionated and purified products were analysed using transmission electron microscopy, dynamic light scattering, measurement of the zeta-potential dependence on pH, IR spectroscopy, and SQUID magnetometry. The silica-coated products with accurately determined concentration by atomic absorption spectroscopy were subjected to a robust evaluation of their cytotoxicity by four different methods, including detailed analysis of the concentration dependence of toxicity, analysis of apoptosis, and experiments on three different cell lines. The results, comparing two manganese-containing systems, clearly indicated superior properties of the Mn–Zn ferrite, whose silica-coated nanoparticles show very limited toxic effects and thus constitute a promising material for bioapplications.

Modified stepwise method for determining heat capacity by DSC

The methods of heat capacity data determination from differential scanning calorimetry measurements are described. The negative effects increasing uncertainty of heat capacity determination are mentioned. Modified stepwise method was described and verified using molybdenum, copper, and gold standards. Modified stepwise method provides better accuracy of Cp values compared to continuous and stepwise method.

DETERMINATION OF PARTICLE SHAPE AND SIZE DISTRIBUTION OF MODEL TYPES OF NANOMATERIALS

Determination of Particle Shape and Size Distribution of Model Types of Nanomaterials At present, great attention is given to study of preparation and properties of various nanomaterials usable in many applications. They are utilized in varied fields of human activity - eg in electronics, medicine, paint industry etc. Besides the detailed chemical structure, such nanoparticle properties as the shape and size distribution are fundamental to the given application. To measure these parameters various methods are used, e.g. transmission electron microscopy (TEM), atomic force microscopy (AFM), acoustic spectrometry, methods based on the light scattering and X-ray disc centrifuge system.

Thermal transformation of layered zinc hydroxide chloride

Zinc hydroxide chloride, Zn5(OH)8Cl2·H2O, belongs to a special group of layered materials which are used in a wide variety of commercial applications. During the heating, Zn5(OH)8Cl2·H2O undergoes a complex transformation which involves several overlapping stages and highly depends on the experimental conditions. Although it is well established that the thermal transformation of Zn5(OH)8Cl2·H2O leads to the formation of ZnO as final product, there is still no generally accepted mechanism explaining the intermediate stages of this process. This review provides a summary of the studies devoted to this topic complemented by critical data assessment and generalisation of the established information. We hope that the review conveys to the reader state of the art of this problem and provides baseline knowledge required for complete understanding of thermal behaviour of this material.