Determination of total carbon and total organic carbon from volatile air pollutants

Summary The method developed based on the determination of TC and TOC in the form of the total amount of CO₂ requires application of the proper techniques for the final determination of CO₂. The possibility of using a stream of carrier gas at a convenient flow-rate for desorbing quantitatively CO₂ concentrated on a molecular sieve permits use of a wide variety of known analytical techniques for the final determination of CO₂. Various methods were compared on the basis of both absolute and calibration measurements. The absolute methods chosen were gravimetric (classical or an automated version based on application of a gravimetric automat and automatic recording balance), thermogravimetric analysis and coulometry. The calibration methods included thermal conductivity, the flame-ionization detector (after conversion of CO₂ into methane) and infrared absorption. Usefulness of the methods was evaluated on the basis of comparative statistical analysis of experimental data with respect to precision (Snedecor'sF-test and Bartlett'sU ²-test) and accuracy (Student'st-test).

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Zusammenfassung Das entwickelte Verfahren zur Bestimmung des TC- und TOC-Gehaltes in Form der gesamten Menge CO₂ erfordert die Anwendung geeigneter Analysentechniken zur Endbestimmung dieser Verbindung. Die Möglichkeit einer Desorption des am Molekularsieb angereicherten CO₂ in einem Gasstrom mit geeignetem Durchfluß erlaubt zur Endbestimmung von CO₂ die Anwendung einer Reihe verschiedener Analysenverfahren. Die Anwendbarkeit verschiedener, auf Absolutverfahren und auch auf relativen Messungen beruhender Methoden wurde vergleichend untersucht. Die folgenden Methoden zur CO₂-Bestimmung wurden gewählt: die Gravimetrie (klassische oder automatisierte unter Einsatz eines Wägeautomaten und einer registrierenden Waage), die Thermogravimetrie und die Coulometrie. Von den relativen Methoden wurden die Thermokonduktometrie, der Flammenionisationsdetektor (nach Umsetzung von CO₂ zu Methan) und das IR-Absorptionsmeßverfahren geprüft. Die Anwendbarkeit der Methoden wurde mit Hilfe statistischer Prüfverfahren beurteilt, wobei die Präzision (SnedecorsF-Test und BartlettsU ²-Test) und die Genauigkeit (Studentst-Test) der erhaltenen Analysenwerte verglichen wurden.

     

Use of isothermal microcalorimetry in pharmaceutical preformulation studies

Excipient compatibility of a new chemical entity was assessed using an isothermal microcalorimeter. Mixtures of an active pharmaceutical ingredient with a primary amine group and excipients were prepared in a 1:1 ratio and compatibility monitored by exposing to 50, 60 and 70°C in presence of 200 mL of water. The new chemical entity, a primary amine, reacted with reducing sugars such as lactose and resulted in a brown discoloration. This reaction is the Maillard type condensation reaction between amines and reducing sugars. The rate of reaction was dependent on the temperature with rapid degradation at higher temperatures. No other incompatibility was apparent between the primary amine and other excipients This revised version was published online in July 2006 with corrections to the Cover Date.     

Working conditions of a Clark-type sensor with a polyethylene membrane in the presence of vapours of chlorine derivatives of methane

The indications of a Clark-type electrochemical sensor with a polyethylene foil used as a membrane are noticeably changed if vapours of chlorine derivatives of methane (CCl₄, CHCl₃, CH₂Cl₂) are present in the atmosphere examined and the sensor has been calibrated in an atmosphere from which those vapours were absent. The sensitivity of the sensor increases and tends to deviate from linearity. The increase is more profound, when the number of chlorine atoms within a molecule of the vapour increases, the partial pressure of the vapour increases and the temperature of the atmosphere examined decreases. If the vapours affect the membrane for a long time, the response time decreases. If the membrane is freshly subjected to the influence of the vapours, a longer period of time is needed to reach a stable indication corresponding to the partial pressure of oxygen actually observed.     

Prediction of Retention in Liquid-Solid Chromatography with Ternary Mobile Phases

The method for the prediction of capacity factors in ternary mobile phases is presented. The adsorption mechanism of retention is considered. The simple theoretical equations are proposed for mobile phases for which the ratio of mole fractions of the weaker solvents remains fixed. The relations between parameters characterizing retention in ternary and binary mobile phases are discussed. The theoretical model is verified for numerous solutes and different mobile phases.     

Dehydrogenation of ethylbenzene with nitrous oxide in the presence of mesoporous silica materials modified with transition metal oxides

The novel mesoporous templated silicas (MCM-48, SBA-15, MCF, and MSU) were used as supports for transition metal (Cu, Cr, or Fe) oxides. The catalysts were synthesized using the incipient wetness impregnation, and characterized by low-temperature N2 sorption, DRIFT, photoacoustic IR spectroscopy, UV-vis diffuse reflectance spectroscopy, and temperature-programmed desorption of ammonia. It was shown that the preparation method used results in different distributions and dimensions of the transition metal oxide clusters on the inert support surface. The prepared catalysts were tested in the reaction of oxidative dehydrogenation of ethylbenzene in the presence of nitrous oxide. The iron-containing catalysts showed the highest catalytic activity. The presence of isolated Fe3+ was found to be the most important factor influencing the ethylbenzene conversion. The undesirable effect of the increase in selectivity toward CO2 was observed for the samples with the highest concentrations of acidic surface sites.     

Infrared matrix isolation and quantum chemical studies of the nitrous acid complexes with water

The 1:1 and 2:1 complexes between water and trans- and cis-isomers of nitrous acid have been isolated in argon matrices and studied using FTIR spectroscopy and DFT(B3LYP) calculations with a 6-311++G(2d,2p) basis set. The analysis of the experimental spectra indicate that 1:1 complexes trapped in solid argon involve very strong hydrogen bond in which acid acts as the proton donor and water as the proton acceptor. The perturbed OH stretches are −248, −228 cm⁻¹ red shifted from their free-molecules values in complexes formed by trans- and cis-HONO isomers, respectively. The calculated spectral parameters for the two complexes are in good agreement with experimental data. The calculations also predict stability of two more 1:1 weakly bound complexes formed by each isomer. In these the water acts as the proton donor and one of the two oxygen atoms of the acid as the acceptor. The experimental spectra demonstrate also formation of 2:1 complex between water and trans-HONO isomer in an argon matrix. The performed calculations indicate that the complex involves a seven-membered ring in which OH group of HONO forms very strong hydrogen bond with the oxygen atom of one water molecule and nitrogen atom acts as a weak proton acceptor for the hydrogen atom of the second water molecule of the water dimer. The observed perturbations of the OH stretch of trans-HONO (750 cm⁻¹ red shift) is much larger than that predicted by calculations (556 cm⁻¹ red shift); this difference is attributed to strong solvation effect of argon matrix on very strong hydrogen bond.     

Homo- and hetero-nuclear chromium(III) complexes with natural ligands. Part 2. Oxo- and hydroxo-bridged chromium(III)/vanadium(V) species

Six new heteropolynuclear chromium(III)/vanadium(V) complexes with natural ligands: glycine, glutaminic, nicotinic and asparginic acids, have been isolated and physicochemically characterised. The complexes have been analysed using spectroscopic (diffuse reflectance u.v.–vis., i.r.), magnetic methods and by FAB mass spectra. Spectral analyses with the digital filter and band deconvolution methods are presented. Additionally, preliminary toxicity studies have been performed.     

Isotachophoretic determination of carboxylic acids in biodegradation samples

In the current study a method of isotachophoretic separation of selected carboxylic acids was developed. The method was used for the determination of carboxylated oligo(ethylene glycol)s and their degradation products in biodegradation tests of PEG 250 DA [a mixture of dicarboxylated oligo(ethylene glycol)s]. Two tests were performed in the studies: the Organization for Economic Cooperation and Development (OECD) screening test and the river water die-away test. Both the biodegradation tests proved relatively fast biodegradation of the studied compounds. In the OECD screening test the biodegradation was faster than in the river water die-away test which can be ascribed to a higher concentration of bacteria in the biodegradation liquor. The minimal sample pretreatment and relatively low cost of analysis by the isotachophoretic method used here make it a good alternative to existing methods of carboxylic acids analysis.     

Microanalysis of Volatile Organic Compounds (VOCs) in Water Samples – Methods and Instruments

Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants. Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages of these techniques are discussed and novel developments are also taken into consideration.     

The classification of differential structures on quantum 2-spheres

Exterior algebras of differential forms on quantum 2-spheresS _qc ² ,q[–1, 1]/{0},c[0, ] (c=0 forq=±1), are classified. In the definition of exterior algebras we assume the invariance w.r.t. the action of the quantumSU(2) group and dimensionality conditions (which imply that we deal with two-dimensional manifolds). The exterior algebras exist only forc=0 and are unique in that case. The corresponding generalized directional derivatives are provided.