Acid—base equilibria in the mixed solvent 80% dimethyl sulfoxide—20% water: Part 3. Determination of Acid—Base Indicator Constants

The acid—base constants of ten nitrophenol, sulfonphthalein and phthalein indicators in 80% dimethyl sulfoxide—20% water are reported. The indicators were selected so that their transitional intervals cover a large part of the pH-scale. The relationship between the constants in the mixed solvent and in water is linear: (pK_HI)_SH = 1.48 (pK_HI)_H2O— 1.68.     

Validation of the membrane composition effect on the flow-injection signal profile of chalcogenide-based ion-selective sensors: a model study using electrochemical approach: Hg(II) flow-injection detector case

The membrane composition effect on signal profile of the combined ISE-flow-injection system is examined on the example of Hg(II) flow-injection potentiometric (FIP) detector based on the secondary response to Hg(II) of different thin layer silver chalcogenide membranes, obtained by cathodic electrodeposition at controlled potential. The potential of the electrochemical approach to produce a great diversity of membrane compositions and the possibility for fine tuning of their stoichiometry made it possible to select the stoichiometry with respect to silver (intrinsic defects factor) and the inclusion of dopant (extrinsic defects factor) as the two variable composition parameters. The following membranes have been tested: Ag₂Se_1−xTe_x, Ag₂Se, Ag_2+δSe and Ag_2+δSe_1−xTe_x (δ=0.24). The experimental conditions have been varied in a wide range to include four flow-rates (within the 2.5-6 ml min⁻¹ interval), and three typical carrier compositions to which either Ag(I) or Hg(II) have been added as pilot ions. The results obtained in this study show unambiguously that the membrane composition factors are an important figure of merit, the weight of which in some particular cases can be co-measurable with that of the flow manifold factors. A new important information concerning the active role of the “pilot ion” added to the carrier in controlling the rising part of the signal, through changing the membrane response rate order, is also provided.     

Irregular linear sesquiterpene dilactones from Anthemis auriculata Boiss

Seven new irregular linear sesquiterpene lactones, epi-antheindurolide A (1), epi-antheindurolide A-5,6-oxide (2), 5-hydroxy-5,6-dihydro-6,13-dehydro-epi-antheinduro lide A (3), 5-hydroperoxy-5,6-dihydro-6,13-dehydro-epi-antheindurolide A (4), epi-antheindurolide B (5), 6-hydroxy-5,6-dihydro-4,5-dehydro-epi-antheindurolide A (6) and 6-hydroperoxy-5,6-dihydro-4,5-dehydro-epi-antheindurolide A (7), were isolated from the flowers of Anthemis auriculata Bioss. Their structures were established by spectroscopic techniques. The discussed compounds were found to be stereoisomers of recently reported lactones for A. arvensis.     

Spirodepressolide: an unusual bis-norsesquiterpene lactone from Achillea depressa Janka

A new bis-norsesquiterpene lactone, spirodepressolide (1), has been isolated from the aerial parts of Achillea depressa Janka and its structure determined by spectroscopic methods to have a new 4-methyl-7-methylethyl-spirobicyclo[4,4]nonane skeleton.     

Determination of photolysis constants of some aliphatic amines in the mixed solvent 80% dimethylsulfoxide/20% water and assessment of titration conditions

The pK_b values of some aliphatic amines in 80% dimethylsulfoxide—20% water are reported. The mixed solvent offers worse titration conditions than water for the determination of these bases. The only advantage of using this solvent for titration of bases is its excellent solvating ability.     

Linear bending of star-like pyramids

A family of polyhedra possessing unusual deformation properties is found. On one hand, models of these polyhedra admit free continuous large reversible bending without visible distortions of the material. On the other hand, the polyhedra themselves are rigid and do not admit continuous bending in the sense of the Cauchy definition. The found polyhedra are called model flexors in order to distiguish them from theoretical flexsors of Connelly. Bendings of the models are asymptotically exactly approximated by linear bendings of polyhedra. They represent a nonrigid, soft or slow, loss of stability that corresponds to the loss of stability in small accordingly to Euler. This new phenomenon in mechanics of deformable solid bodies may be considered as an original geometric machine of catastrophe. To cite this article: A.D. Milka, C. R. Mecanique 331 (2003).     

Analysis of Tea for Metals by Flame and Graphite Furnace Atomic Absorption Spectrometry with Multivariate Analysis

The concentrations of iron, zinc, manganese, copper, chromium, nickel, lead, arsenic, and cadmium were determined using flame and graphite furnace atomic absorption spectrometry in nine herbal tea samples. Hawthorn, yarrow, elderflower, and bearberry are herbal teas for which the metal content has been rarely determined. The concentration of cadmium in St John’s wort exceeded the maximum permissible limit of 0.3?mg/kg. The metals were also determined in aqueous extracts following 5, 10, and 20?min of boiling and using different preparations, including acidification with lemon juice. The influence of these factors on metal release was demonstrated using multivariate analyses by redundancy analysis and principal component analysis. The metal release was not considerably affected by the boiling time, while the acidity of the medium was generally positively correlated. For the infusions, arsenic was detected only in acidified mint tea. The extraction efficiencies of metals were determined and classified as highly, moderately, and poorly extractable, with chromium showing largest variations.