Cold on-column – solvent split injection with a three-way press-fit device

In a previous paper we described the possibilities of cold on-column – sample split injection achieved by means of an inexpensive and simple three way press-fit device [1]. The same arrangement is proposed here for cold on-column – solvent split injection in which specific elimination of the solvent, without loss of any other sample components, is achieved by opening the splitting tube (or better, in this case, the early solvent vapor exit) during solvent elution, and then closing it during elution of the sample's other components. Discrimination between solvent and other sample components is achieved by means of a retention gap, a retaining precolumn, and an early vapor exit. The technique enables both selective enrichment of a sample, in order to record satisfactory mass and infrared spectra of minor components, and injection of large volumes (up to 100 μl) of dilute solutions which cannot be concentrated because of component volatility. Details of the assembly and tuning the system are given, together with some examples.     

Characterisation of natural polysaccharides (plant gums) used as binding media for artistic and historic works by capillary zone electrophoresis

The monosaccharide constituents of plant gums were separated by capillary electrophoresis at pH 12.1 and detected with indirect UV absorbance. The plant gums investigated were gum arabic, gum acacia, gum tragacanth, cherry gum and locust bean gum (carob gum). The monosaccharides obtained after hydrolysis with 2M trifluoroacetic acid and lyophilisation of the hydrolysate were arabinose, galactose, mannose, rhamnose, xylose, fucose, and glucose, and the two sugar acids galacturonic and glucuronic acid, in accordance with the literature. They were separated in a background electrolyte consisting of NaOH to adjust the pH, 20 mM 2,6-pyridinedicarboxylic acid as chromophore for detection and 0.5 mM cetyltrimethylammonium bromide as additive to reverse the electroosmotic flow. Based on their electropherograms, the plant gums could be identified by their typical composition (depicted in a decision scheme) as follows: a peak of glucuronic acid, together with that of rhamnose, is indicative for gum arabic. Peaks of galacturonic acid and fucose point to gum tragacanth. Locust bean gum shows a major peak for mannose (with the concomitant galactose peak in ratio 4-1), whereas a glucuronic acid and a mannose peak together with a prominent arabinose peak indicates cherry gum. The method was applied to identify the plant gums in samples like watercolours and in several paint layers like gum tempera or those with egg white or drying oils as additives. Artificial aging experiments of thin layers of gum arabic on paper or glass carried out with UV-A radiation (366 nm) did not result in changes of the saccharide patterns, in contrast to the simultaneously conducted aging of a drying oil layer.     

Stochastic perturbation in meteorology

We illustrate recent developments of dynamical meteorology and climate studies that have been approached by means of stochastic differential equations. In particular, we present stochastic dynamics reasoning in climate theory, wave excitation and dynamic initialization of meteorological fields. A few possible future developments are also indicated.     

A computer simulation of model discotic dimers

We set up a model for discotic liquid crystal dimers and study, by means of Monte Carlo simulations, their phase behaviour and self–assembling properties, in comparison with the simpler monomeric case. Each discotic dimer is described by two oblate Gay–Berne ellipsoids connected by a flexible spacer, modelled by a harmonic “spring” of three different lengths. We find that dimerization in general yields produces a significant change on the phase behaviour, with an increase of the columnar–nematic transition temperature, a widening of the nematic region and the apparent suppression of the crystalline phase in favour of the columnar phase up to very low temperatures. Longer spacers prove to ease the formation of columns and to increase the orientational order. Contribution to the Fernando Bernardi memorial issue.     

Assessment of the Arsenic Removal From Water Using Lanthanum Ferrite

The catalytic performance of a perovskite-type lanthanum ferrite LaFeO₃ to remove arsenic from water has been investigates for the first time. LaFeO₃ was prepared by citrate auto-combustion of dry gel obtained from a solution of the corresponding nitrates poured into citric acid solution. Kinetic studies were performed in the dark with As(V) and in the dark and under UV-C irradiation at pH 6–7 with As(III) (both 1 mg L⁻¹), and As : Fe molar ratios (MR) of 1 : 10 and 1 : 100 using the LaFeO₃ catalyst. As(V) was removed from solution after 60 min in the dark in 7 % and in 47 % for MR=1 : 10 and MR=1 : 100, respectively, indicating the importance of the amount of the iron material on the removal. Oxidation of As(III) in the dark was negligible after 60 min in contact with the solid sample, but complete removal of As(III) was observed within 60 min of irradiation at 254 nm, due to As(III) photooxidation to As(V) and to As(III) sorption to a minor extent. Morphological and microstructural studies of the catalyst complement the catalytic testing. This work demonstrates that LaFeO₃ can be used for the removal of As(III) from highly arsenic contaminated water.