Midinfrared polarization spectroscopy of OH and hot water in low pressure lean premixed flames

The application of midinfrared polarization spectroscopy (mid-IRPS) is demonstrated for sensitive detection of minor molecular species in combustion environments by probing rovibrational transitions. High resolution mid-IRPS spectra of low pressure flames were obtained in the spectral range around 3 microm. Rotational lines of the fundamental vibrational band of the hydroxyl radical (OH) were fully resolved and properly assigned among the abundant hot water lines in the flame mid-IRPS spectra. The high signal-to-noise ratio of the recorded OH lines indicates the feasibility of sensitive mid-IRPS OH detection. This constitutes, to the best of our knowledge, the first reported OH flame detection in the midinfrared spectral range. A simulation of hot water mid-IRPS lines with molecular parameters extracted from the HITRAN/HITEMP database was performed and compared with the observed flame spectra. The proper prediction of the hot water lines may help to clarify the potential spectral interferences associated with minor species measurements.     

Experimental and modelling study of sulfur and nitrogen doped premixed methane flames at low pressure

Laser-induced fluorescence (LIF) has been used to observe NS and NO in methane/oxygen/argon laminar flames at low pressure doped with ammonia and sulfur dioxide. NS profiles as a function of height above the burner have been measured for rich flames. The effect of adding various amounts of sulfur dioxide on the observed NO in the burnt gas region has been investigated for a variety of stoichiometries. The experimental measurements have been compared with PREMIX simulations using a detailed elementary reaction mechanism for nitrogen- and sulfur-containing species in a methane flame. Sensitivity analysis has been employed to highlight the important reactions for NS, NO and SO2. The results demonstrate significant uncertainties in currently best available rate data for important reactions involving sulfur-containing species.     

Unraveling chemical structure of laminar premixed tetralin flames at low pressure with photoionization mass spectrometry and kinetic modeling

This work reports an investigation on laminar premixed flames of tetralin at 30 Torr and equivalence ratios of 0.7 and 1.7. Measurements of the chemical structure including identification and mole fraction measurements of free radicals, isomers, and polycyclic aromatic hydrocarbons (PAHs) were performed using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV‐PIMS). A kinetic model with 296 species and 1 577 reactions was developed and validated against the flame chemical structure data measured in this work. Modeling analysis reveals the key reaction pathways in tetralin decomposition and PAHs formation. The H‐atom abstraction reactions by H, O, and OH are found to control the consumption of tetralin in the lean flame, while those by H play the dominant role in the rich flame. Indene and naphthalene have very high concentration levels in the rich tetralin flame due to the existence of direct formation pathways from the decomposition of tetralin. The two bicyclic PAHs and their radicals play significant roles in the PAHs growth process of tetralin combustion, which results in the high sooting tendency of tetralin compared to those of alkylbenzenes with smaller or same carbon atom numbers.     

Pyrene measurements in sooting low pressure methane flames by jet-cooled laser-induced fluorescence

This paper presents in detail the study we carried out concerning the pyrene measurement by jet-cooled laser-induced fluorescence (JCLIF) in different sooting low pressure methane flames. The aim of this paper is both to demonstrate the potentialities of this technique for the measurement of such moderately sized polycyclic aromatic hydrocarbons under sooting flame conditions and to provide new experimental data for the understanding and the development of chemical models of the soot formation processes. Several concentration profiles of pyrene measured in different sooting flame (various pressure and equivalence ratio) are presented. The validation of the JCLIF method for pyrene measurements is explained in detail as well as the calibration procedure, based on the standard addition method, which has been implemented for the quantification of the concentration profiles. Sensitivity lower than 1 ppb was obtained for the measurement of this species under sooting flame conditions.     

Protein-bound glutathione measurement in cultured cells by CZE with LIF detection

Protein modification due to S-glutathio(ny)lation, usually a reversible process in intact cells, arises interest as a possible mode of regulatory events that may potentially modify a large number of cellular processes. However, since less than 1% of the total protein is S-thiolated in resting cells, high sensitivity methods are required for its evaluation. We set up a new method by CE with LIF detection that allows to measure all forms of intracellular GSH involved in the process. For total and reduced glutathione, cell lysates were rapidly derivatized by 5-iodoacetoamidofluorescein (5-IAF), a selective reagent which traps thiol groups, thus minimizing auto-oxidation. Derivatized samples were separated in a 47 cmx75 microm id capillary by using 7 mmol/L sodium phosphate at pH 11.6. For the evaluation of S-glutathio(ny)lation, intracellular proteins from cell lysates were precipitated and washed to eliminate free GSH. After protein resuspension with NaOH and reduction treatment with tri-n-butylphosphine (TBP), the freed GSH was dried in a vacuum concentrator and directly dissolved in the derivatization mixture. GSH-IAF adduct was detected in a 6 mmol/L sodium phosphate, 3 mmol/L boric acid, and 75 mmol/L N-methylglucamine run buffer in less than 5 min. The high sensitivity ensured by 5-IAF use and sample concentration, allowed to quantify GSH at levels as low as 5 nmol/L, value suitable for the evaluation of protein S-glutathio(ny)lation. The method suitability was checked both in HUVEC and ECV304 cultured cells.     

High-temperature oxidation chemistry of n-butanol--experiments in low-pressure premixed flames and detailed kinetic modeling

An automated reaction mechanism generator is used to develop a predictive, comprehensive reaction mechanism for the high-temperature oxidation chemistry of n-butanol. This new kinetic model is an advancement of an earlier model, which had been extensively tested against earlier experimental data (Harper et al., Combust. Flame, 2011, 158, 16-41). In this study, the model's predictive capabilities are improved by targeting isomer-resolved quantitative mole fraction profiles of flame species in low-pressure flames. To this end, a total of three burner-stabilized premixed flames are isomer-selectively analyzed by flame-sampling molecular-beam time-of-flight mass spectrometry using photoionization by tunable vacuum-ultraviolet synchrotron radiation. For most species, the newly developed chemical kinetic model is capable of accurately reproducing the experimental trends in these flames. The results clearly indicate that n-butanol is mainly consumed by H-atom abstraction with H, O, and OH, forming predominantly the α-C(4)H(9)O radical (CH(3)CH(2)CH(2)˙CHOH). Fission of C-C bonds in n-butanol is only predicted to be significant in a similar, but hotter flame studied by O?wald et al. (Combust. Flame, 2011, 158, 2-15). The water-elimination reaction to 1-butene is found to be of no importance under the premixed conditions studied here. The initially formed isomeric C(4)H(9)O radicals are predicted to further oxidize by reacting with H and O(2) or to decompose to smaller fragments via β-scission. Enols are detected experimentally, with their importance being overpredicted by the model.     

The determination of gallium by atomic absorption spectrometry in premixed inert gas(entrained air)-hydrogen flames

Gallium can be determined sensitively in premixed argon (entrained air)- and nitrogen (entrained air)-hydrogen flames at 287.4 nm ; sensitivity (for l% absorption) is 0.20–0.24 p.p.m. and calibration graphs are linear up to 10 p.p.m. Many elements and acids interfere, but the addition of magnesium (1000 p.p.m.) as chloride is very effective in eliminating these interferences. This finding was satisfactorily applied to the determination of gallium in some semi-conducting III–V compounds.     

Free-atom formation processes in premixed fuel-rich and stoichiometric oxygen-acetylene flames employed in atomic emission and absorption spectroscopy

Detailed observations on the atomic and molecular absorption and emission spectra of the various zones of premixed oxyacetylene flames are presented. Spatial flame profile data for both the natural flame species and those formed when solutions of metallic salts are nebulized into the flame are interpreted in terms of: (a) the relative concentrations of reactive intermediate and stable species in the various zones; (b) the mechanism of free-atom formation from aerosol droplets; and (c) free-atom depopulation processes. The results of this study clearly show that the striking enhancement in atomic spectra observed in either absorption or emission for many elements in the fuel-rich oxyacetylene flame originate in the favorable chemical environment provided by the interconal zone for the formation and existence of free-atoms.     

Evaluation of atmospheric pressure ionization interfaces for quantitative measurement of sulfonamides in honey using isotope dilution liquid chromatography coupled with tandem mass spectrometry techniques

A comparison was made between electrospray, atmospheric pressure chemical and atmospheric pressure photospray ionizations to evaluate the MS/MS responses of standard sulfonamides and honey spiked samples. The sample preparation entails an acidic hydrolysis followed by a liquid/liquid extraction. Full method validation was realised by LC-APPI-MS/MS. Decision limit and detection capability were calculated for each analyte (at 50 microg/kg) and ranged between 53.6 and 56.9 and 57.5 and 63.2 microg/kg, respectively. Limits of detection and of quantification ranged, respectively, at 0.4-4.5 and 1.2-15.0 microg/kg. Precursor ion scan experiments of m/z 92 were also carried out as a survey experiment, linked with an enhanced product ion scan experiment to potentially identified additional sulfonamides via a library search.     

Structure of adsorbed polyelectrolyte monolayers investigated by combining optical reflectometry and piezoelectric techniques

Polyelectrolyte monolayers on solid substrates are studied with optical reflectivity and the quartz crystal microbalance (QCM). In particular, we investigate the adsorption of anionic poly(styrene sulfonate) (PSS) on amino-functionalized silica as well as cationic poly(allylamine hydrochloride) (PAH) and poly-L-lysine (PLL) on bare silica. By comparing the dry and wet masses measured on identical substrates with these two techniques, we obtain information on the layer thickness and water content of these layers. Monolayers typically feature an adsorbed dry mass of about 0.1-2 mg/m(2), a layer thickness of 0.5-2 nm, and a water content of 20-50%. One finds that the layer thickness increases with increasing concentrations of monovalent salts and polyelectrolytes.     

Induction and measurement of glassy-state relaxations by vapor sorption techniques

Recent gravimetric studies of the sorption of organic vapors by poly(vinyl chloride) and polystyrene powders have demonstrated several features which promise to be generally useful in studying the structure and properties of the glassy state. The uptake of vapor can be significantly altered by prior thermal or vapor treatment of the polymer, apparently reflecting changes in the microvoid content or free volume of the polymer. Fickian sorption in sufficiently fine powders proceeds to equilibrium in a few minutes. Upon exposure of a polymer powder to an appreciable pressure of vapor, both a rapid Fickian sorption and a slower, relaxation-controlled sorption are observed. Superposition of these processes leads to widely varied sorption kinetics; a model comprising Fickian diffusion and first-order relaxation terms accurately describes the data and allows estimation of equilibrium and rate constants for both processes. After prolonged exposure, removal of a swelling vapor induces a slow reconsolidation of the polymer structure; this deswelling relaxation can be monitored by the decreasing amounts of vapor sorbed in repeated brief exposures to low vapor pressures, and can also be described by a first-order relaxation model. In this regard, the penetrant vapor serves as a molecular probe, monitoring glassy-state relaxation occurring in the absence of penetrant. The same, presumably true equilibrium is ultimately reached both by swelling from a low free-volume state and by consolidation from a preswollen state of high free volume. The rates of both swelling and consolidation relaxations appear to be retarded by the presence of low concentrations of vapor in the polymer, suggesting that vapor molecules may preempt some of the free volume required for relaxation.     

Zipper and layer-by-layer assemblies of artificial photosystems analyzed by combining optical and piezoelectric surface techniques

Quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) were used to study zipper and layer-by-layer multilayer assemblies of artificial photosystems based on naphthalenediimides (NDIs) attached to an oligophenylethynyl (OPE-NDI) or p-oligophenyl (POP-NDI) backbone in dry and wet state. For the most interesting OPE-NDI zipper, one obtains for the dry film a monolayer thickness of 1.85 nm and a density of 1.58 g/cm(3), while the wet film has a larger monolayer thickness of 3.6 nm with a water content of 36%. The dry thickness of a monolayer in OPE-NDI zippers corresponds to about one-half of the length of the OPE scaffold in agreement with the proposed structure of the zipper. The low water content of the OPE-NDI films confirms their compact structure. The dry monolayer thickness of the POP-NDI films of 1.45 nm is smaller than that for the OPE-NDI films, which is probably related to a tilt of the POP scaffolds within the adsorbed layer. The POP-NDI films swell in water much more substantially, suggesting a much more open structure. These features are in excellent agreement with the better photophysical performance of the OPE-NDI assemblies when compared to the POP-NDI films.     

LIF, LEI, RIMS etc. — New promising techniques in elemental micro- and trace analysis

Summary The application of laser spectroscopy in spectrochemistry requires excitation and detection schemes different from the estabolished optical spectrochemical methods. The most promising techniques developed in laser spectrochemistry are described and the analytical figures of merits are discussed. The very low absolute detection limits of the laser methods are required if trace elements have to be measured in microsamples.     

Preparation and activity measurement of some low pressure methanol synthesis catalysts

Summary In the present study, twenty four catalysts for low pressure methanol synthesis were prepared according to a pre-designed research program consisting of three stages. In each stage, applying the experimental design techniques, a number of catalysts were synthesized by the co-precipitation method, using different proportions of metal salts solutions. The activities of the catalysts were determined applying a laboratory scale continuous packed bed reactor. It was noted that the calcinations temperature, ageing time and molar ratio of metal nitrates to precipitant, had the highest effects on the activity of the catalysts.     

Simultaneous measurement of vapor diffusion and solubility coefficients in polymers by frequency response techniques

An experimental technique for the simultaneous measurement of solubility and diffusion coefficients in polymers by frequency response techniques has been developed. A sample of polymer suspended from an electrobalance is exposed to a permeating gas whose pressure is being varied sinusoidally at ultra-low frequencies. The phase angle and amplitude of the weight changes are measured as a function of the frequency of the pressure wave. It is shown that in the linear range the diffusivity coefficient for polyethylene–ethane calculated from the phase angle lag and the Henry's law solubility and the diffusivity obtained from the amplitude ratios are in excellent internal agreement and also agree with values obtained from transient measurements.     

Preparation of nonwoven polyimide/silica hybrid nanofiberous fabrics by combining electrospinning and controlled in situ sol-gel techniques

A controlled in situ sol-gel synthesis combined with the electrospinning technique and postspun imidization was applied in the fabrication of polyimide/silica hybrid nonwoven nanofiberous fabrics with excellent thermal and mechanical performance. The nanofiberous fabrics were prepared by electrospinning of the solution of tetraethoxysilane (TEOS) and polyamic acid (PAA). The different silica contents in the fabrics were achieved by varying the amount of TEOS while fitting the solid content of PAA. The final polyimide/silica fabrics was obtained after imidization of PAA and gelation of silica phase simultaneously accomplished through a step-wise heating process. Some specific IR techniques and other characterizations indicated the successful incorporation of the silicon dioxide (SiO₂) into the PI matrix and the relatively even distribution of the SiO₂ in the fabrics. An increase of 133 °C in the decomposition temperature and 4-fold enhancement of the ultimate tensile strength were achieved for the hybrids with a 6.58 wt.% of SiO₂ content, compared to the pure PI fabric. The excellent performance could be attributed to the good compatibility between the polyimide and silica, and good adhesion among the fibers, which resulted from the controlled TEOS hydrolysis and the simultaneous imidization and gelation process.     

Thermodynamic study of aqueous solutions of polyelectrolytes of low and medium charge density without added salt by direct measurement of osmotic pressure

A special block osmometer has been constructed and applied to a systematic study of poly (vinyl alcohol and vinyl sulphate ester) (PVS) sodium salts in dilute and moderately concentrated salt free aqueous solutions. In order to avoid surely ionic contamination all parts of the equipment that can contact with the polyelectrolyte solutions were made of different kinds of plastics and glass. The pressure range spans from (50 to 1.3 · 10⁵) Pa. The measuring system was found to be appropriate for determination of the molar mass of water soluble polymers, too. Above a certain analytical density of dissociable groups (ADDG) an ion size dependent transition was observed on the reduced osmotic pressure vs. concentration curves. The analysis of the osmotic pressure data has clearly revealed that the dependence of the degree of dissociation on ADDG calculated at zero polyelectrolyte concentration contradicts to ‘ion condensation’ theory. With increasing polyelectrolyte concentration the degree of dissociation decreased rather steeply but at very low concentrations sharp maximums appeared due either to the change in conformation of these charged macromolecules, or formation of dynamic clusters induced by salting out of neutral parts of the macromolecules by the ionized groups. The applicability of the scaling concept as well as the many possible ways of characterization of non-ideality of polyelectrolyte solutions will be discussed in detail.     

Overcoming hydrolytic sensitivity and low solubility of phosphitylation reagents by combining ionic liquids with mechanochemistry

Ionic liquids have been used in combination with ball milling on a range of chlorophosphoramidite reagents to phosphitylate nucleosides and 2-deoxynucleosides. The enhanced stability offered by the ionic liquid mediated processes combined with efficient mass transfer induced by ball milling has enabled excellent yields to be obtained even when using small dialkyl amino groups as well as the more commonly used diisopropylamino protection.