Simple chamber for temperature-controlled planar chromatography

This article describes a construction of a simple developing device designed for temperature control of thin-layer chromatographic plates. The plates can be developed by the ascending technique under temperature gradient or non-gradient conditions. Saturated or unsaturated chamber conditions can be easily selected. The effects that give rise to pseudo-non-linear Van't Hoff plots, e.g. a temperature irregularity inside the chamber or heat evolving during solvent adsorption near the migrating front of the mobile phase are minimized. The preliminary temperature-retention studies show that the device is suitable for temperatures ranging from -20 to 60 degrees C. Using a binary mobile phase mixture (methanol-water, 70:30, v/v) the velocity of the mobile phase front on the HPTLC RP-18W plates at different temperatures was investigated. Under these conditions the retention profiles of four natural estrogens (estetrol, estriol, 17beta-estradiol and estrone) were examined. The application of the described device for temperature-retention studies is also discussed.     

Crystallization of gels and glasses made from hot-pressed gels

Silica gels were prepared by two different methods: (1) destabilization of a silica hydrosol (gel 1); (2) hydrolysis and polycondensation of a tetra-methoxysilane (gel 2). The crystallization of the gels was then studied as a function of the temperature by means of X-ray diffraction. It was evident that the crystallization was strongly influenced by the amount of alkali oxides present in the gel. It is effectively the concentration of akali impurities which could explain the lower temperature of crystallization necessary for gel 1 compared with that of gel 2. During the crystallization of the gel containing Na₂O the crystalline phase of silica which appears first is the cristobalite; with Li₂O it is quartz. The effect of additives such as boric anhydride was studied. This oxide was found to reduce the tendency of the gels to crystallize. The glasses of the system SiO₂B₂O₃ obtained by the hot-pressing of the gels confirmed this phenomenon. Above 10 mol% B₂O₃ it was impossible to crystallize the gels and the glasses of this system under two hours.     

Modelling of ζ-potential of the montmorillonite/electrolyte solution interface

The electrokinetic potential (ζ-potential) is calculated using the combination of the Poisson-Boltzmann equation and the Surface Complexation Models for energetically heterogeneous surface. This approach gives negative values of ζ for the whole pH region, which is in agreement with the published results of ζ-potential measurements. Moreover, the correct changes of ζ-potential values for different types of montmorillonite are observed. It is shown that electrokinetic properties of the considered systems are not as sensitive to surface heterogeneity as the adsorption isotherms and surface charge densities. As it was shown in our previous paper [P. Zarzycki, F. Thomas, J. Colloid Interface Sci. 302 (2006) 547-559], the presented model predicts parallel titration curves for reasonably small equilibrium constants of exchange processes. Here, we show further development of this model in order to predict ζ-potential.     

Supercritical fluctuations in the B2O3PbOAl2O3 system

A small-angle X-ray diffraction study of the supercritical region of the B₂O₃PbOAl₂O₃ immiscibility surface is presented. This is the first time that diffraction methods have been applied to the study of critical opalescence in a system of oxides at high temperatures. Debye's theory is shown to be applicable and, from the spectra correlation lengths and the range of molecular interactions l is calculated. The topography of the supercritical region is determined and the relationship between l and the main interatomic distances in the melt discussed.     

Predictive tracking of an object by a pan–tilt camera of a robot

Nonlinear Dynamics - Moving-object tracking using a pan–tilt camera setup is quite a well-known task in robotics. However, the presented research addresses specific properties of the tracked...