Influence of temperature on natural and chemically modified zeolites

Zeolites from Nižny Hrabovec (Slovak Republic) were, modified with solutions of NaOH. The changes of zeolites in the temperature range 20–1200 °C were studied by thermal analysis (DTA, TG, ETA), X-ray analysis and REM analysis. Thermal analysis showed that the process of dehydration started between temperatures 20 and 600 °C, over this temperature the dealumination and structural changes have taken place. X-ray analysis and REM analysis showed the structural changes of natural zeolites and gradual loss of cristallinity of the chemically modified zeolites.     

The influence of a competing eluting ion content on the efficiency of separation of rare-earth metals in displacement complex forming chromatography

The separation of rare-earth metals (REMs) by displacement complex forming chromatography was studied for S-shaped isotherms of the eluting ion with eluted elements. It was found that sodium competing ions, which entered the REM zone, decelerated ion exchange of REMs. The effect increased as the amount of eluting ions entering the zone of elements to be separated grew. Original Russian Text ? O.V. Kharitonov, L.A. Firsova, E.A. Chuveleva, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 6, pp. 1169–1170.     

The intensity of spontaneous surface convection in di-(2-ethylhexyl)phosphoric acid systems

The dependence of the rate of the arising and evolution of spontaneous surface convection (SSC) on various effects during the extraction of rare-earth metals (REMs) with heptane (or toluene) solutions of di-(2-ethylhexyl)phosphoric acid (D2EHPA) (HA) was studied. The intensity of SSC in heptane was higher than in toluene systems. In the same solvent, it was higher for the elements from the cerium subgroup. At low concentrations of a REM salt in the starting aqueous solution, the modulus of the surface rate of liquid flow in the dynamic interphase layer (DIL) was high because low-solubility salt particles experienced sedimentation, and the interphase surface was renewed. It was concluded that, at higher REM concentrations in the aqueous phase, the modulus of the surface flow rate was considerably higher because of the accumulation of LnA₃ and structure formation in the interphase layer. For comparison, we give the moduli of surface flow rates of liquids during the re-extraction of acids in a toluene, HNO₃/water system, in which the rate is higher than in aqueous REM(III) salt/D2EHPA solution in an organic diluent. Original Russian Text ? N.F. Kizim, E.N. Golubina, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 7, pp. 1384–1390.     

Preparation, thermal, spectral and microscopic studies of calcium silicate hydrate–poly(acrylic acid) nanocomposite materials

A series of calcium silicate hydrate (C–S–H)-polymer nanocomposite (C–S–HPN) materials were prepared by incorporating poly(acrylic acid) (PAA) into the inorganic layers of C–S–H during precipitation of quasicrystalline C–S–H from aqueous solution. The as-synthesized C–S–HPN materials were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The XRD analysis of C–S–HPN materials suggest the intermediate organizations presenting intercalation of PAA within C–S–H and exfoliation of C–S–H. The SEM micrographs of C–S–H, PAA and C–S–HPN materials with different PAA contents exhibit the significant differences in their morphologies. The effect of the material’s composition on the thermal stability of a series of C–S–HPN materials along with PAA and C–S–H were studied by TG, DTA and DSC. Three significant decomposition temperature ranges were observed on the TG curves of all C–S–HPN materials.     

Electrochemical discharge performance of Mg-Li based alloys in NaCl solution

Mg–Li–Al–Sn and Mg–Li–Al–Sn–Ce alloys were prepared using a vacuum induction melting method. Their electrochemical oxidation behavior in NaCl solution was investigated by means of potentiodynamic and chronoamperometric measurements. The surface morphology after discharge was examined using scanning electron microscopy. Utilization efficiency was estimated with a mass-loss method. The results indicated that Mg–Li–Al–Sn has a higher discharge current density but lower utilization efficiency than Mg–Li–Al–Sn–Ce. The typical utilization efficiency after continuous discharging at constant potential of −1.0 for 2 h is 65% and 70% for Mg–Li–Al–Sn and Mg–Li–Al–Sn–Ce, respectively. The utilization efficiency decreased with the increase of anodic potential. Both alloys have similar self-discharge rate in NaCl solution at open-circuit potential.     

A comparison of three solvent-free techniques coupled with gas chromatography for determining trihalomethanes in urine samples

The analysis of volatile organic compounds in samples of biological fluids characterized by complex matrices is highly challenging. This paper presents a comparison of the results obtained in this field using three solvent-free techniques: thin-layer headspace with autogenous generation of liquid sorbent (TLHS) and membrane separation of the trace substances (pervaporation, PV), both of which are coupled to direct aqueous injection gas chromatography–electron capture detection (TLHS–DAI–GC–ECD and PV–DAI–GC–ECD), as well as conventional static headspace analysis followed by GC analysis with ECD detection (HS–GC–ECD). Basic validation parameters of the HS–GC–ECD, TLHS–DAI–GC–ECD and PV–DAI–GC–ECD procedures were calculated for water and urine samples. The calibration curves for all procedures were linear within the concentration range examined. The intermediate precisions of the procedures were good and reached about 10% (for all analytes) for HS–GC–ECD and TLHS–DAI–GC–ECD. The poorest results were obtained for PV–DAI–GC–ECD: about 20% for all analytes. The lowest method detection limits were obtained for the TLHS–DAI–GC–ECD procedure: below 0.0022 μg/L for all analytes. The enrichment factors did not differ significantly between water and urine samples, indicating little or no matrix effect in all procedures.     

Synthesis, thermal and structural characterization of nanocomposites for potential applications in construction

Several calcium silicate hydrate (C–S–H)-polymer nanocomposite (C–S–HPN) materials have been prepared by incorporating poly(acrylic acid) (PAA) into the inorganic layers of C–S–H during precipitation of quasicrystalline C-S-H from aqueous solution. The synthetic C–S–HPN materials were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS), thermogravimetry (TG), differential thermogravimetry (DTG) and differential scanning calorimetry (DSC). The XRD peaks of C–S–HPN materials suggest the intermediate organizations presenting both intercalation of PAA and exfoliation of C–S–H. The SEM images of C–S–H and C–S–HPN materials with different PAA contents exhibit the significant differences in their morphologies. Effects of the material compositions on the thermal stability of series of C–S–HPN materials along with PAA and C–S–H has been studied by TG, DTG and DSC. Three significant decomposition temperature ranges were observed on the TG curves of all C–S–HPN materials.     

The effect of the relative content and accumulation of the competing displacer ion on the efficiency of separation of rare-earth metals in complex formation displacement chromatography with the use of various retaining ions

The separation of rare-earth metals (REMs) by complex formation displacement chromatography with the use of various retaining ions (Cu, Ni, Zn, Co) and nitrile triacetate as an eluent was studied. In the series Ni, Zn, Co, the displacer concentration in the REM zone decreased, while the efficiency of separation increased, and the competing ion was accumulated in the system. With copper used as a retaining ion, the accumulation factor of the competing ion was absent, and the separation of REMs was more effective, in spite of a higher concentration of the competing ion in the zone of the elements to be separated. Original Russian Text ? O.V. Kharitonov, L.A. Firsova, E.A. Chuveleva, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 7, pp. 1374–1376.     

Simultaneous GC-MS quantitation of acids and sugars in the hydrolyzates of immunostimulant, water-soluble polysaccharides of basidiomycetes

Summary The simultaneous quantitation of acids and sugars as their trimethyl silyl (TMS) derivatives has been extended in order to identify and quantitate the simple acid and sugar constituents in the hydrolyzates of various immunostimulant, water-soluble polysaccharides obtained from various Basidiomycetes, such as Armillariella mellea, Auricularia auricula-judae, Coriolus versicolor, Flammulina velutipes, Fomes fomentarius, Ganoderma applanatum, Ganoderma lucidum, Pleurotus ostreatus, Schizophyllum commune, Trametes hirsuta. Optimum hydrolysis conditions, performed with 2 M trifluoroacetic acid (TFAA) for five hrs, proved the presence of several sugars and acids with maximum recovery. (i) the total sugar/sugar alcohol content of polysaccharides varied between 20- and 65% and consisted of arabitol (0.01–10.2%), arabinose (0.09–1.3%), ribose (0.2–1.8%), fucose (0.3–1.2%), mannitol (0.01–5.3%), sorbitol (0.01–0.05%), galactiol (0.04%), fructose (0.08–0.8%), galactose (0.9–29%), glucose (10–53%), uronic acids (0.14–3.7%), sucrose (0.03–2%), trehalose (0.2–1%), cellobiose (0.01–0.6%), maltose (0.2–1.9%), other disaccharides (0.2–8%). (ii) The total of acids varied from 1.5 to 30% including o-phosphoric (1.3–19%), malic (0.08–4.7%), citric (0.08–4.7%), isocitric; (3%) and C₁₆−C₁₈ fatty acids (1–6%).     

Thermal degradation and smoke suspension of cotton cellulose modified with THPC and its lanthanide metal complexes

Complexes of cell–THPC–urea–ADP with transition metal ion Co²⁺ and lanthanide metal ions such as La³⁺, Ce⁴⁺, Nd³⁺ and Sm³⁺ have been prepared. The thermal behavior and smoke suspension of the samples are determined by TG, DTA, DTG and cone calorimetry. The activation energies for the second stage of thermal degradation have been obtained by following Broido equation. Experimental data show that for the complexes of cell–THPC–urea–ADP with the metal ions, the activation energies and thermal decomposition temperatures are higher than those of cell–THPC–urea–ADP, which shows these metal ions can increase the thermal stability of cell–THPC–urea–ADP. Moreover, these lanthanide metal ions can more increase thermal stability of samples than do the transition metal ion Co²⁺. The cone calorimetry data indicate that the lanthanide metal ions, similar to transition metal Co²⁺, greatly decrease the smoke, CO and CO₂ generation of cell–THPC–urea–ADP, which can be used as smoke suppressants.     

Thermal degradation of poly(lactic acid) measured by thermogravimetry coupled to Fourier transform infrared spectroscopy

Thermogravimetric (TG), differential thermal analysis (DTA) and thermal degradation kinetics, FTIR and X-ray diffraction (XRD) analysis of synthesized glycine–montmorillonite (Gly–MMT) and montmorillonite bound dipeptide (Gly–Gly–MMT) along with pure Na–MMT samples have been performed. TG analysis at the temperature range 25–250 °C showed a mass loss for pure Na–MMT, Gly–MMT and Gly–Gly–MMT of about 8.0%, 4.0% and 2.0%, respectively. DTA curves show the endothermic reaction at 136, 211 and 678 °C in pure Na–MMT whereas Gly–MMT shows the exothermic reaction at 322 and 404 °C and that of Gly–Gly–MMT at 371 °C. The activation energies of the first order thermal degradation reaction were found to be 1.64 and 9.78 kJ mol⁻¹ for Gly–MMT and Gly–Gly–MMT, respectively. FTIR analyses indicate that the intercalated compounds decomposed at the temperature more than 250 °C in Gly–MMT and at 250 °C in Gly–Gly–MMT.     

Modification and re-validation of the ethyl acetate-based multi-residue method for pesticides in produce

The ethyl acetate-based multi-residue method for determination of pesticide residues in produce has been modified for gas chromatographic (GC) analysis by implementation of dispersive solid-phase extraction (using primary–secondary amine and graphitized carbon black) and large-volume (20 μL) injection. The same extract, before clean-up and after a change of solvent, was also analyzed by liquid chromatography with tandem mass spectrometry (LC–MS–MS). All aspects related to sample preparation were re-assessed with regard to ease and speed of the analysis. The principle of the extraction procedure (solvent, salt) was not changed, to avoid the possibility invalidating data acquired over past decades. The modifications were made with techniques currently commonly applied in routine laboratories, GC–MS and LC–MS–MS, in mind. The modified method enables processing (from homogenization until final extracts for both GC and LC) of 30 samples per eight hours per person. Limits of quantification (LOQs) of 0.01 mg kg⁻¹ were achieved with both GC–MS (full-scan acquisition, 10 mg matrix equivalent injected) and LC–MS–MS (2 mg injected) for most of the pesticides. Validation data for 341 pesticides and degradation products are presented. A compilation of analytical quality-control data for pesticides routinely analyzed by GC–MS (135 compounds) and LC–MS–MS (136 compounds) in over 100 different matrices, obtained over a period of 15 months, are also presented and discussed. At the 0.05 mg kg⁻¹ level acceptable recoveries were obtained for 93% (GC–MS) and 92% (LC–MS–MS) of pesticide–matrix combinations.     

Thermal, spectral and AFM studies of calcium silicate hydrate-polymer nanocomposite material

A non-ionic polymer (poly(vinyl alcohol) (PVA)) has been incorporated into the inorganic layers of calcium silicate hydrate (C–S–H) during precipitation of quasicrystalline C–S–H from aqueous solution. C–S–H and a C–S–H-polymer nanocomposite (C–S–HPN) material were synthesized and characterized by X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS), ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR) and ¹³C cross-polarization nuclear magnetic resonance (¹³C CP NMR) spectroscopy, atomic force microscopy (AFM), thermal conductivity, thermogravimetric analysis (TG) and differential thermal analysis (DTA). Thermal conductivity of PVA, C–S–H and C–S–HPN material was studied in the temperature range 25–50°C. C–S–HPN materials exhibited the highest thermal conductivity at 25 and 50°C. The thermal conductivity increases from 25 to 50°C are 7.03, 17.46 and 14.85% for PVA, C–S–H and C–S–HPN material, respectively. Three significant decomposition temperature ranges were observed on the TG curve of C–S–HPN material.     

Synthesis of Amido- and Diamidophosphites with Polyfluoroalkyl Substituents

Bis(polyfluoroalkyl) chlorophosphites and polyfluoroalkyl dichlorophosphites react easily with secondary amines (from –40 to –22°C, 1–3 h, CH2Cl2) in the presence or absence of triethylamine to form the corresponding bis(polyfluoroalkyl) diorganylamidophosphites or bis(diorganylamido) polyfluoroalkyl phosphites in the yield of up to 74%. Bis(polyfluoroalkyl) diorganylamidophosphites were also synthesized from diorganylamidodichlorophosphites and polyfluoroalkanols (–25 to –22°C, 2 h, Et3N–CH2Cl2) with a yield of 56–60%.     

Relationships among the transition elements

As part of a series of contributions on patterns in the periodic table, the relationships among the transition metals are examined here in a systematic manner. It is concluded that the traditional method of categorizing transition elements by group or by period is not as valid as by using combinations thereof. From chemical similarities, it is proposed that the transition metals be considered as the [V–Cr–Mn] triad; the [Fe–Co–Ni–Cu] tetrad; the [Ti–Zr–Hf–Nb–Ta] pentad; the [Mo–W–Tc–Re] tetrad; and the [Ru–Os–Rh–Ir–Pd–Pt–Au] heptad. Silver does not fit neatly in anywhere and is better linked with thallium.     

Thermal decomposition properties of 1,2,4-triazole-3-one and guanidine nitrate mixtures

1,2,4-triazole-3-one (TO) and guanidine nitrate (GN) have the potential to be used as alternative gas-generating agents. To obtain a better understanding of thermal decomposition properties of TO/GN mixtures, sealed cell differential scanning calorimetry, thermogravimetry–differential thermal analysis–infrared spectroscopy (TG–DTA–IR), and thermogravimetry–differential thermal analysis–mass spectrometry (TG–DTA–MS) were carried out. The endothermic peak and onset temperatures of TO/GN mixtures were lower than those of individual TO and GN. TG–DTA–IR and TG–DTA–MS showed that the mass of TO/GN mixtures decreased with heat generation and N₂ evolved as the major gas during thermal decomposition. The interaction between TO and nitric acid from the dissociation of GN is proposed for the thermal decomposition of TO/GN mixtures.     

Slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of Cr, Cd and Pb in plastics

Ultrasonic slurry sampling electrothermal vaporization dynamic reaction cell inductively coupled plasma mass spectrometry (USS–ETV–DRC–ICP–MS) for the determination of Cr, Cd and Pb in several plastic samples, using NH₄NO₃ as the modifier, is described. The influences of the instrumental operating conditions and the slurry preparation technique on the ion signals are investigated. A reduction in the intensity of the background at signals corresponding to chromium masses (arising from matrix elements) was achieved by using NH₃ as the reaction cell gas in the DRC. The method was applied to determine Cr, Cd and Pb in two polystyrene (PS) samples and a polyvinyl chloride (PVC) sample using two different calibration methods, namely standard addition and isotope dilution. The results were in good agreement with those for digested samples analyzed by ultrasonic nebulization DRC–ICP–MS. The precision between sample replicates was better than 17% with the USS–ETV–DRC–ICP–MS method. The method detection limits, estimated from standard addition curves, were about 6–9, 1–2 and 8–11 ng g⁻¹ for Cr, Cd and Pb, respectively, in the original plastic samples.     

Synthesis and Electrochemical Behavior of Some 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles

Summary. 1H-3-Methyl-4-ethoxycarbonyl-5-(benzylidenehydrazino)pyrazoles are key intermediates in obtaining various heterocyclic systems including pyrazolotriazoles. We present the voltammetric behavior of these compounds in nonaqueous media, with the following para substituents grafted on the benzene ring: –N(CH₃)₂, –OH, –OCH₃, –F, –Cl, –CF₃, –NO₂, as well as of the novel compounds with –Br, –I, and –SCH₃ in the para position, in order to elucidate the influence of the various substituents on the mechanism of anodic oxidation.     

Molecular structure of basic oligomeric building units of heparan-sulfate glycosaminoglycans

This study reports in detail the results of systematic large-scale theoretical investigations of the acidic dimeric structural units (D–E, E–F, F–G, and G–H) and pentamer D–E–F–G–H (fondaparinux) of the glycosaminoglycan heparin, and their anionic forms. The geometries and energies of these oligomers have been computed using HF/6–31G(d), Becke3LYP/6–31G(d), and Becke3LYP/6–311+G(d,p) methods. The optimized geometries indicate that the most stable structure of these units in the neutral state is stabilized via a system of intramolecular hydrogen bonds. The equilibrium structure of these species changed appreciably upon dissociation. Water has a remarkable effect on the geometry of the anions studied. Because of high negative charge, the solvent effect also resulted in an appreciable energetic stabilization of biologically active anionic forms of these glycosaminoglycans. The stable energy conformations around glycosidic bonds found for dimers and pentamer investigated are compared and discussed with the available experimental X-ray structural data for the structurally related heparin-derived pentasaccharides in cocrystals with proteins.     

FTIR study of the sol–gel synthesis of cementitious gels: C–S–H and N–A–S–H

The study explored the compatibility between the main product of Portland cement hydration and the main product of the alkali activation of fly ash: C–S–H and N–A–S–H gels, respectively. Both gels were synthesized with laboratory reagents at different pH values. Blends of the two were synthesized as well, using the sol–gel procedure. All the gels were characterized with Fourier transform IR spectroscopy (FTIR). The gels synthesized with this procedure were shown to precipitate together with a silica-rich gel. In addition, the pH level was found to play a determinant role in both C–S–H and N–A–S–H gel synthesis. The C–S–H gel is the major phase formed at pH > 11 and N–A–S–H gel for pH > 12. The results relating to the joint synthesis of the two (C–S–H and N–A–S–H) gels were not conclusive. Technique used for the characterization failed to differentiate between them in the blended material.