Comparison of quantitative analytical methods in headspace gas chroamtography of residual solvents

Summary The aim of this work was to compare quantitative methods used for headspace gas chromatographic analysis of residual solvents in standard aqueous solutions and to apply the methods to the analysis of medicines. We found that all three quantitative methods (external standard, ESTD; internal standard, ISTD; and standard addition, ASTD) enable determination of the total amount of solute in the equilibrated system by analysis of defined volumes of headspace gas. The results showed that the ISTD method is more precise than ESTD and ASTD when there is no strong interaction between the residual solvents and the pharmaceutical base material. When, however, there is a strong polarpolar interaction between them, the ESTD and ISTD methods give worse results than the ASTD method, because the ASTD method can eliminate the matrix effect. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Structure-Stability Study of Cyclodextrin Complexes with Selected Volatile Hydrocarbon Contaminants of Soils

The association constants for the inclusion compounds of various hydrocarbons (linear alkanes, cycloalkanes, aromatics) with different cyclodextrins (CDs) in aqueous solution have been determined using static headspace gas chromatography (SHSGC). The structure-stability relationship was examined.     

Metal transition complexes of tridentate Schiff base ligands derived from 2-hydrazinopyridine: synthesis,spectroscopic characterization and X-ray structures

Transition Metal Chemistry - Mononuclear complexes of 1-(pyridin-2-ylmethylidene)-2-(pyridin-2-yl)hydrazine (HL1) and 1-(pyridin-2-yl)-2-(1-(pyridin-2-yl)ethylidene)hydrazine (HL2),...     

Synthesis, spectroscopic studies and crystal structure of (Et4N)(SnMe3)7(HAsO4)4 · 2H2O

On allowing tetraethylammonium dihydrogen arsenate dihydrate to react with trimethyltin chloride, the title compound has been obtained and characterized by infrared, Mössbauer and NMR techniques. Its crystal structure has been determined and consists of layers containing both corner sharing AsO₄H tetrahedra and trans-O₂SnC₃entities. It contains large cavities in which tetraethylamonium cations are located.     

Mathematical modeling of methane flow in a borehole coal mining system

Safety in coal mining is greatly increased by the drainage of the methane content of coal seams through boreholes, simultaneously producing significant energy. The design of suitable drainage technology is based on the mathematical modeling of methane flow in coal seams. In the calculation of the methane pressure, the new mathematical model presented in this paper considers both the sorption phenomenon of methane depending upon the methane pressure and the fact that the variation in methane pressure can create a change in the stress condition of the rock and, as a consequence of this, a change in the permeability of the coal. The new mathematical model can be used for the numerical simulation of the flow processes in coal seams and methane drainage technology can be designed more accurately.     

Absolute line intensities for oxirane in the 11.4 μm spectral region

Absolute individual line intensities of numerous transitions of the fundamental ν₁₅, ν₁₂ and ν₅ bands of oxirane (ethylene oxide, cyc-C₂H₄O) have been measured in the 750–950 cm^?1 region using eight high-resolution Fourier transform spectra recorded at 0.002 cm^?1 resolution and various pressures. These line intensities were least-squares fit using a theoretical model which takes into account the vibration–rotation interactions linking the upper state rotational levels and, therefore, accurate rotational expansions of the transition moments of the ν₁₅, ν₁₂ and ν₅ vibrational bands were derived. Using the coefficients obtained in the fitting, a line list has been generated and used to perform comparisons with the present measurements. Also, comparisons with measurements taken at medium–low resolution of the ν₁₅/ν₁₂/ν₅ system show excellent agreement.     

Phenolic profile of edible honeysuckle berries (genus lonicera) and their biological effects

The current status of research on polyphenolic compounds in the berries of edible honeysuckle and their biological effects, including recommended utilization, are reviewed. The major classes of phenolic compounds in the blue berried honeysuckle are flavonols (quercetin, rutin, quercitrin) and flavanes (proanthocyanidins, catechins) and anthocyanins. Cyanidin-3-glucoside and cyanidin-3-rutinoside are considered as major anthocyanidins in edible honeysuckle berries. Such a high level of antioxidant activity in the berries of different species of the genus Lonicera is especially due to the high level of polyphenolic compounds, especially anthocyanins. These berries seem to be prospective sources of health-supporting phytochemicals that exhibit beneficial anti-adherence and chemo-protective activities, thus they may provide protection against a number of chronic conditions, e.g., cancer, diabetes mellitus, tumour growth or cardiovascular and neurodegenerative diseases.     

Effect of Reynolds number on heat transfer and flow for multi-oxide nanofluids using numerical simulation

A numerical simulation model for laminar flow of nanofluids in a pipe with constant heat flux at the wall has been built to study the effect of Reynolds number on heat transfer and pressure loss. The investigation was performed for metallic oxide and multi-oxide nanoparticles suspended in water. The thermal conductivity and dynamic viscosity were measured for a range of temperature (10–60 °C) and volume fraction of multi-oxide nanofluid. Comparison of the thermal conductivity for monocular oxide and multi-oxide nanofluids reveals a new way to control the enhancement in nanofluid conductivity. The numerical results obtained were compared with existing well-established correlations. The predictions of the Nusselt number for nanofluids are in agreement with the Shah correlation, and the deviation in the results is less than 1 %. It is found that the pressure loss increases with the Reynolds number, nanoparticle density, and volume fraction for multi-oxide nanoparticles. However, the flow demonstrates enhancement in heat transfer which improves with increasing Reynolds number of the flow.     

Synthesis and Crystal Structure of La(NO<Subscript>2</Subscript>)(SO<Subscript>4</Subscript>)(H<Subscript>2</Subscript>O)

Abstract Single crystals of new open-framework lanthanide sulphate nitrite La(NO₂)(SO₄)(H₂O) has been synthesized, in the presence of 2,6-diformyl-4-chlorophenol. His structure has been determined by X-ray diffraction data: the complex crystallizes in the tetragonal system, space group P4₃, with a = 7.0028(2) (?), b = 7.0028(2) (?), c = 11.8341(4) ?, V = 580.34(3) ?³, Z = 4, D _c = 3.582 Mg m⁻³. The three-dimensional (3D) framework of this compound is built up by the linkages of lanthanide atoms and the oxygen atoms of the sulphate and nitrite groups. The lanthanum atom is 9-fold coordinated. The structure is unfamiliar in lanthanide chemistry and this compound represents the first example of nitrite lanthanide sulphate complex. Graphical Abstract An unfamiliar structure in lanthanide chemistry represented by the first example of nitrite lanthanide sulphate complex is described.