Reversed-phase high-performance liquid chromatographic/mass spectrometric method for separation of 4-methylimidazole and 2-acetyl-4-(1,2,3,4-tetrahydroxybutyl)imidazole at pg levels

A high-performance liquid chromatographic/mass spectrometric method (HPLC/MS) has been developed to determine both 4-methylimidazole (4MeI) and 2-acetyl-4-(1,2,3,4-tetrahydroxybutyl)imidazole (THI) in one run. Among three sorbents tested, the best peak shape of 4MeI was achieved on a reversed-phase MetaChem Polaris C18-A at pH 9.5. The sensitivity and the range of UV detection at 215 and 290 nm for 4MeI and THI, respectively, were compared to the parameters achieved by the electrospray ionization mass spectrometric (ESI/MS) detection in the presence of 5 mmol l⁻¹ ammonium hydroxide using selected ion-monitoring (SIM) mode. The on-column limits of detection were 0.147 ng of 4MeI and 0.084 ng of THI using UV detection and 1 pg of 4MeI and 3 pg of THI using ESI/MS detection, respectively. The effect of both ammonium ion concentration and energy of fragmentation on 4MeI and THI ionization is discussed. The method could be applied for a fast and sensitive determination of 4MeI and THI in different biological materials as well as in Class III Caramels.     

Influence of the energy distribution function on thermodesorption

A kinetic model of the desorption process based on the energy distribution function was set up. The influence of known distribution functions, such as those of Dirac, Gauss, Cauchy. Weibull and others, on the kinetics of thermodesorption was investigated. In those cases the energy distribution function is a kinetic parameter. It was shown that the shape and position of the thermodesorption peaks depend on the type of energy distribution function. On the basis of the theoretical kinetic model the dependencies of differential desorption heat upon degree of coverage were calculated. It was shown that the differential desorption heat also depends on the energy distribution function.     

Effect of preparation of sol-gel coatings on the strength of optical fibres

SiO₂, TiO₂, ZrO₂, and TiO₂-ZrO₂ thin coatings were applied by sol-gel method on quartz fibres during the fibre drawing. Durable layers with the thicknesses up to 0.7 m were obtained. The layer smoothness and thickness were determined using electron microprobe analyzer and electron or optical microscopy. In order to investigate a decrease in the strength of sol-gel coated fibres a novel method employing silica capillaries was developed. The fibre strength decrease was explained by the influence of water penetrating as a result of the coating process into the flaws on the fibre surface.     

Flow injection-capillary electrophoresis system with contactless conductivity detection and hydrostatic pressure generated flow. Application to the quantitative analysis of inorganic anions in water samples

A simple and inexpensive flow injection-capillary electrophoresis (FI-CE) system with contactless conductivity detection (CCD) for automated quantitative analysis of chloride, nitrate, and sulfate in various water samples is demonstrated. A glass bottle containing the background electrolyte that is raised above the FI-CE interface generates a pulse-free, highly reproducible flow of the electrolyte through the FI-CE interface. The system operates at a flow rate of 300 microLmin(-1) with an injection volume of only 4 microL. The repeatability of peak areas (n = 18) was better than 0.81% RSD and the sample throughput was 90 samples per hour using the background electrolyte containing 12 mM L-histidine adjusted to pH 4.00 with acetic acid. The limits of detection were better than 125 microgL(-1) and were comparable to those obtained by conventional CE systems with CCD. Various calibration methods for FI-CE system with electrokinetic injection were tested and their suitability for the analysis of anions in real samples was evaluated.     

Limitations of reaction frontal gas chromatography in organic elemental analysis

Summary The basic phenomena affecting the precision and accuracy of reaction frontal GC in organic elemental microanalysis are discussed with special reference to determination of C, H, N, O and S. Attention is paid to the concentration changes occurring during the frontal GC separation, and it is shown that their effect is generally negligible if proper standards and conditions are used.

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Grenzen der Reaktions-Gaschromatographie in der organischen Elementaranalyse

Zusammenfassung Die grundlegenden Vorgänge der frontalen Reaktions-Gaschromatographie und ihr Einfluß auf die Genauigkeit organischer Elementaranalysen, besonders der Bestimmung von C, H, N, O und S wurden erörtert. Besondere Aufmerksamkeit wurde dabei den Konzentrationsveränderungen geschenkt, die während der Trennungsvorgänge auftreten, wobei gezeigt werden konnte, daß deren Wirkung im allgemeinen vernachlässigt werden kann, wenn geeignete Standardproben und Versuchsbedingungen angewendet werden.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Studies on hydrolyzable carbides. XXII: The carbothermal reduction of scandium oxide Sc2O3

The composition of the products of carbothermal reduction of Sc₂O₃ is examined by X-ray diffraction and chemical analysis and by the hydrolysis method. At pressures of 10^–2-1 Pa, the reaction starts in the temperature region of 1 000–1 200°C. The first product is Sc₂OC of NaCl type; at 1 Pa and 1 400–1 500°C this substance is formed quantitatively (according to stoichiometry) within 50–100 h, repeated homogenization, however, is necessary, or else Sc₂OC reacts locally with Sc₂O₃ giving Sc₂O_1+x C_1–x . The lattice parameter of Sc₂OC in the presence of Sc₁₅C₁₉ is 457.6₃pm. At temperatures above 1 500°C, Sc₁₅C₁₉ is incompletely formed by subsequent reaction with carbon. The product melts at cca. 1 800°C; carbon dissolves and the final composition approaches ScC₂. Carbon separates during solidification. The phase fractions in the products are affected by evaporation, the vapour pressures above both Sc₂OC and Sc₁₅C₁₉ being comparable with the pressure requisite for the carboreduction process. The results are discussed with respect to the often ambiguous published data.

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Untersuchung hydrolysierbarer Carbide, XXII. Die karbothermische Reduktion von Scandiumoxid

Zusammenfassung Zur Untersuchung von Produkten der karbothermischen Reduktion von Scandiumoxid wurden sowohl röntgenographische und chemische Analyse als auch die hydrolytische Methode verwendet. Bei 10^–2 bis 1 Pa beginnt die Reaktion im Temperaturintervall von 1 000–1 200°C. Das erste Reaktionsprodukt ist das Scandiumoxidcarbid Sc₂OC von NaCl-Typ, das quantitativ (der Stöchiometrie entsprechend) bei 1 400–1 500°C und 1 Pa in 50–100 Stunden entsteht. Eine wiederholte Homogenisierung ist allerdings notwendig, damit es zu keiner lokalen Reaktion zwischen Sc₂OC und Sc₂O₃ kommt, bei der dann die Phase Sc₂O_1+x C_1–x entsteht. In Gegenwart von Sc₁₅C₁₉ ist der Gitterparameter von Sc₂OCa=457.6₃pm. Über 1 500°C führt eine weitere Reaktion mit Kohlenstoff zu einer nicht ganz vollendeten Bildung von Sc₁₅C₁₉. Bei cca. 1 800°C schmilzt das Reaktionsprodukt bei gleichzeitiger Auflösung von weiterem Kohlenstoff und die Zusammensetzung nähert sich der Formel ScC₂, beim Erstarren fällt der Kohlenstoff wieder aus. Die Verteilung der Phasen im Produkt wird von der Verdampfung beeinflußt, da die Dampfdrucke von Sc₂OC und Sc₁₅C₁₉ mit dem zum Karboreduktionverlauf notwendigen Druck vergleichbar sind. Die erhaltenen Ergebnisse werden in Relation mit den nicht eindeutigen Angaben in der Literatur diskutiert.

     

Speciation of chromium (III) and chromium (VI) by capillary electrophoresis with contactless conductometric detection and dual opposite end injection

A sensitive, rapid and inexpensive capillary electrophoretic method for the determination of Cr(III) and Cr(VI) species is presented. The method is based on the dual opposite end injection principle and contactless conductometric detection. The sample containing cationic and anionic species is injected into the opposite ends of the separation capillary and after the high voltage is applied, the analytes migrate towards the capillary center, where the cell of a contactless conductivity detector is placed. The method does not require any sample pretreatment, except dilution with deionized water. The separation of Cr(III), Cr(VI) and other common inorganic anions and cations is achieved in less than 4 min. The parameters of the separation electrolyte solution, such as pH and concentration of L-histidine, were optimized. Best results were achieved with electrolyte solution consisting of 4.5 mM L-histidine, adjusted to pH 3.40 with acetic acid. The detection limits achieved for Cr(III) and Cr(VI) were 10 and 39 microg.L(-1), respectively. The repeatability of migration times and peak areas was better than 0.3% and 2.8%, respectively. The developed method was applied to the analyses of rinse water samples from the galvanic industry. The results for the determination of Cr(III) and Cr(VI) were in good agreement with the results obtained by certified differential spectrophotometric method using diphenylcarbazide (CN 83 0520-40) and with the results for the total chromium concentrations determined by electrothermal atomic absorbance spectrometry (ET-AAS) and inductively coupled plasma-mass spectrometry (ICP-MS).     

On uniform continuity of the spectral radius in Banach algebras

We investigate relations between different forms of subadditivity and submultiplicativity of the spectral radius. In particular, we prove that if the spectral radius is uniformly continuous on a Banach algebra, then the algebra is commutative modulo the radical; this confirms a conjecture raised by the second author in [7].     

MoS2/WS2‐Graphene Composites through Thermal Decomposition of Tetrathiomolybdate/Tetrathiotungstate for Proton/Oxygen Electroreduction

MoS₂ and WS₂ have been prepared on a conductive graphene support by thermal reduction of tetrathiotungstate/tetrathiomolybdate and graphite oxide. Whereas the catalytic properties towards hydrogen evolution are strongly influenced by the Magnéli phases formed as a byproduct during the synthesis, the catalytic activity towards oxygen reduction of these composite materials is not affected by this phenomenon and these materials exhibit high catalytic activity towards this industrially important reaction.     

GC/MS of terpenes in walnut-tree leaves after accelerated solvent extraction

Terpenes, e. g. (+)-alpha-pinene, (-)-camphene, (-)-(-pinene, myrcene, R-(+)-limonene, eucalyptol, (+/-)-linalool, (-)-bornyl acetate, (-)-trans-caryophyllene, and alpha-humulene were determined in leaves of walnut trees from the Juglandaceae family (walnut tree, royal (J. regia L.), black (J. nigra L.), and Siebold (J. sieboldiana, var. Cordiformis Lam.) using gas chromatography with mass spectrometric detection. Terpenes were repeatedly (3 cycles, 5 min each) extracted from leaves of walnut trees by accelerated (pressurized) solvent extraction (ASE) 150 bar and 120 degrees C. The efficiency of ASE extraction was superior to that of steam distillation, solvent extraction according to Soxhlet, sonication, and extraction by agitation. Differences in relative concentrations and distribution of terpenes were studied in dependence on the species of walnut tree and on different locations.