Study of the fate of nitrogen in organic compounds

Summary The closed-flask combustion products of some nitrogen compounds were studied. The percentage of nitrogen oxides formed (expressed as nitrate-nitrogen) was determined. Combustion of these samples, after mixing with inorganic oxidants, in a stream of oxygen was also investigated. Trials for the application of the oxygen-flask method for the microdetermination and detection of nitrogen in many organic compounds are reported.

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Zusammenfassung Die aus einigen Stickstoffverbindungen bei der Verbrennung im sauerstoffgefüllten Kolben entstehenden Produkte wurden untersucht. Der Anteil an Stickstoffoxiden (ausgedrückt als Nitratstickstoff) wurde bestimmt. Ebenso wurde auch die Verbrennung dieser Substanzen im Sauerstoffstrom bei Gegenwart anorganischer Oxydantien untersucht. Über Versuche, die Kolbenmethode zum Nachweis und zur Bestimmung des Stickstoffs in vielen organischen Verbindungen anzuwenden, wurde berichtet.

     

Spectrographic determination of trace elements in cement

Summary A simple straight-forward spectrographic method is extended to the analysis of cement to cover elements of general interest to cement industry and to non-metallic materials. A d.c. arc of 9 amperes at 220 volts is used to determine the elements Mg, Sr, Ba, V, Nb, and Mn with reasonable detection limits using the visible region of the Hilger spectrograph. The sensitivity of the method is satisfactory and the precision is unusually good for a routine quantitative analysis.

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Zusammenfassung Obwohl im Schrifttum eine Reihe von Untersuchungen über die spektrochemische Bestimmung von Spurenelementen in Silicaten und Zement vorliegt, ergeben sich bei der praktischen Anwendung dieser Analysenvorschriften Schwierigkeiten.Im vorliegenden Verfahren war der Verzicht auf die Veraschung der Mischung der spektralanalytischen Proben mit Graphit deshalb notwendig, weil einige Elemente, wie z.B. Mg, Sr, Ba, V, Nb, Cr und Mn, auf direktem Weg im Zement quantitativ bestimmt werden. Die Nachweisempfindlichkeit beträgt etwa 10 ppm für die meisten Elemente mit einem mittleren Fehler von 3,0–8,0%.

     

Response behavior of sodium-selective electrodes modified by surface attachment of the anticoagulant polysaccharides heparin and chondroitin sulfate

Two different polysaccharides with anticoagulant activities, heparin and chondroitin sulfate, were used to modify the surface of sodium-selective electrodes based on asymmetric cellulose triacetate (CTA) membranes. The membranes were formulated with sodium ionophore X, anionic additive, and o-nitrophenyl octyl ether. The response behavior of the surface-modified sodium electrodes was compared with that of control CTA, as well as poly(vinyl chloride) (PVC)-based sodium-selective electrodes. It was found that the selectivity coefficients obtained with the surface modified CTA membrane electrodes were slightly higher than those of the control, but in the case of heparin-modified electrodes they still met the requirements for analysis of sodium in physiological fluids within an error of <1%; the corresponding error for chondroitin sulfate-modified electrodes was also <1% except for the case of potassium ion in which the error was 1.3%. Likewise, it was found that other response characteristics, such as detection limit, linear range, slope of the response plot, selectivity pattern, and response time were comparable in both the control and the polysaccharide-modified electrodes. Therefore, the surface modification does not significantly alter the response behavior of the sensors.     

Acetate- and thiol-capped monodisperse ruthenium nanoparticles: XPS, XAS, and HRTEM studies

Monodisperse ruthenium nanoparticles were prepared by reduction of RuCl3 in 1,2-propanediol. The mean particle size was controlled by appropriate choice of the reduction temperature and the acetate ion concentration. Colloidal solutions in toluene were obtained by coating the metal particles with dodecanethiol. High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XANES and EXAFS for the Ru K-absorption edge) were performed on particles of two different diameters, 2 and 4 nm, and in different environments, polyol/acetate or thiol. For particles stored in polyol/acetate XPS studies revealed superficial oxidation limited to one monolayer and a surface coating containing mostly acetate ions. Analysis of the EXAFS spectra showed both oxygen and ruthenium atoms around the ruthenium atoms with a Ru-Ru coordination number N smaller than the bulk value, as expected for fine particles. In the case of 2 nm acetate-capped particles N is consistent with particles made up of a metallic core and an oxidized monolayer. For 2 nm thiol-coated particles, a Ru-S bond was evidenced by XPS and XAS. For the 4 nm particles XANES and XPS studies showed that most of the ruthenium atoms are in the zerovalent state. Nevertheless, in both cases, when capped with thiol, the Ru-Ru coordination number inferred from EXAFS is much smaller than for particles of the same size stored in polyol. This is attributed to a structural disorganization of the particles by thiol chemisorption. HRTEM studies confirm the marked dependence of the structural properties of the ruthenium particles on their chemical environment; they show the acetate-coated particles to be single crystals, whereas the thiol-coated particles appear to be polycrystalline.     

Twin comprehensive two-dimensional gas chromatographic system: concept and applications

A twin GC x GC system has been designed which enables the analysis of a sample by means of two different and independent column combinations simultaneously. Both combinations are incorporated in the same oven, using the same temperature programme, and are fed using a 50:50 column-entrance-split. It is demonstrated that, employing combinations of a conventional non-polar x polar and a reversed-type polar x non-polar column set, the information content is as high, and the analytical performance is as good as when using two separate GC x GC systems. That is, there is an appreciable gain of time and a reduction of costs without any loss of quality. The general usefulness of performing, and comparing two mutually different GC x GC runs is further illustrated with FAMEs in olive oil, and pollutants in a sediment sample.     

Vibrational spectral studies of L-citrullinium perchlorate

Infrared and Raman spectra of L-citrullinium perchlorate crystals have been recorded at room temperature. The vibrational assignments of the observed wavenumbers are proposed on the basis of group theoretical analysis. The presence of carbonyl group indicates that the molecule exists in the ionic form. The shifting of stretching and bending wavenumbers indicates the presence of extensive hydrogen bonding in the crystal. The anion fundamentals however continue to be degenerated. This suggests that its symmetry is not affected in the crystal.     

Solvent and substituent effects on spectroscopical changes of some diazoaminobenzene derivatives

A series of diazoaminobenzene derivatives (seven) in which the substituents have a wide range of electronic characters are set out to understand the involvement of the substituent identity in controlling the changes in their electronic absorption spectra. The interactions between the diazoamino group and the different groups account for some spectral shifts. The UV-vis spectrum of each compound is measured in several solvents with wide variations of solvent polarity parameters to examine the role of the chemistry of the solvent in these spectroscopical changes. The electronic transitions are assigned and the solvent induced spectral shifts are analyzed in relation to the different solute-solvent interaction mechanisms using computational chemistry. The regression analysis is applied for correlating the different parameters. The results help to assign the solute-solvent interactions and the solvatochromic potential of the investigated compounds. It is concluded that the electronic character of the substituent and the chemical nature of the solvent are the major factors for the observed solvatochromism.     

Chemometric approach to evaluate the parameters affecting electrospray: application of a statistical design of experiments for the study of arginine ionization

The effects of different experimental parameters on arginine electrospray ionization have been investigated with response surface modelling design. This chemometric technique allows a study of the effects of selected experimental variables and their interactions on the response of an experiment by performing a limited number of analyses. Six variables were studied: methanol content in the liquid phase, formic acid concentration, electrospray voltage, orifice voltage, mobile phase flow rate, and sheath gas flow rate. Signal abundance and signal-to-noise ratio of the protonated molecule and the protonated dimer were measured from the electrospray mass spectra and these four responses were tested by the design. The factor that exhibits the greatest influence on MH+ abundance is shown to be the liquid flow rate whereas the formation of protonated dimer is mainly controlled by the percentage of methanol in the mobile phase. A strong synergic effect of methanol content and formic acid concentration in the liquid has also been demonstrated in the study of noise level. Moreover, the capabilities of the multicriteria optimization method have been demonstrated through a successful prediction of a set of optimal experimental conditions.     

Determination of antihypertensive mixtures by use of a chemometrics-assisted spectrophotometric method

A simple multivariate calibration method for analysis of two types of hypotensive mixture is described. The mixtures are composed of chlorthalidone with atenolol or chlorthalidone with both amiloride hydrochloride and atenolol. The components of the mixtures result in substantial spectral overlap—between 87.5 and 91.0%. Resolution of the mixtures under investigation has been accomplished mainly by using CLS and PCR methods. The components in each mixture have been simultaneously determined in three commercial dosage forms with high accuracy and without interference from commonly encountered excipients and additives. Good recoveries were obtained with both synthetic mixtures and commercial tablets. The results obtained were compared with those from pharmacopeial methods and found to be in good agreement. The results obtained from CLS and PCR were also compared with those obtained from a ¹D spectrophotometric method.     

The Fibonacci sequence modulo π, chaos and some rational recursive equations

In this paper, we provide the closed form solution to the inter-related equations Both of these equations were suggested as open problems in the book by Kocic and Ladas [V.L. Kocic, G. Ladas, Global Behavior of Nonlinear Difference Equations of High Order with Applications, Kluwer Academic, Dordrecht, 1993]. We also give the closed form solution to the equations studied by X. Li and D. Zhu [X. Li, D. Zhu, Two rational recursive sequences, Comput. Math. Appl. 47 (2004) 1487–1494].