Evaluation of simulant migration of volatile nitrosamines from latex gloves and balloons by HS-SPME-GC-MS

Nitrosamines are a group of carcinogens that have been found in various latex products. Methods have been developed for extraction, concentration and detection of simulant migration of volatile nitrosamines from latex gloves and balloons. After glove samples or balloon samples were treated with artificial sweat and artificial saliva, headspace solid-phase microextraction and gas chromatography with mass spectrometer detection were performed. Eight volatile nitrosamines were extracted by a fused silica fiber coated with carboxen-polydimethylsioxane, and solid-phase microextraction conditions were optimized. The developed method was successfully used to analyze simulant migration of volatile nitrosamines from latex gloves and balloons. The described methods are rapid and simple, with adequate sensitivity and without organic solvent.     

Swelling and Dissolution of Cellulose Part 1: Free Floating Cotton and Wood Fibres in N-Methylmorpholine-N-oxide–Water Mixtures

Summary: Five modes describing the behaviour of cellulose fibres dipped in a chemical have been identified:

• Mode 1: Fast dissolution by disintegration into fragments
• Mode 2: Large swelling by ballooning, and dissolution
• Mode 3: Large swelling by ballooning, and no dissolution
• Mode 4: Homogeneous swelling, and no dissolution
• Mode 5: No swelling and no dissolution

In the case of the behaviour of wood and cotton cellulose fibres in N-methylmorpholine-N-oxide (NMMO) and water mixtures, four domains of water content have been identified. Below 17% of water up to monohydrate (13%), the fibres are disintegrated into rod-like fragments and dissolve (mode 1). In NMMO – water mixtures containing 19–24% water, the cellulose fibres exhibit a heterogeneous swelling by forming balloons (composed of dissolved cellulose holds inside a membrane) separated with non-swollen sections. The whole fibre will completely dissolve (mode 2) in four successive steps (growth of the balloons, burst of the balloons, dissolution of the non-swollen sections and finally dissolution of the membrane). With still greater water contents (25–30%), only the ballooning phenomenon is observed, with a partial dissolution inside the balloon (mode 3). Above 35% of water, the fibres swell homogeneously and are not dissolving (mode 4).     

Swelling and dissolution of cellulose,Part III: plant fibres in aqueous systems

Raw and refined flax, hemp, abaca, sisal, jute and ramie fibres are dipped into N-methylmorpholine N-oxide (NMMO)–water with various contents of water and into hydroxide sodium (NaOH)–water. The swelling and dissolution mechanisms of these plant fibres are similar to those observed for cotton and wood fibres. Disintegration into rod-like fragments, ballooning followed or not by dissolution and homogeneous swelling are all observed as for wood and cotton fibres, depending on the quality of the solvent. Balloons are not typical of wood and cotton and they seem to be present in all plant fibres. Another interesting result is that the helical feature seen on the balloon membrane is not related to the microfibrillar angle. Plant fibres are easier to dissolve than wood and cotton. This is not related to the molar mass of the cellulose chain. Raw plant fibres keeping most its non-cellulosic components do not show the formation of balloons. Patrick Navard is a Member of the European Polysaccharide Network of Excellence (EPNOE)     

Ultrafiltration of non-newtonian fluids

The current study reports on a series of ultrafiltration experiments using newtonian and non-newtonian fluids (pectine, xanthan and polyacrylamide solutions). For non-newtonian pseudoplastic fluids, the shape of the plot of flux versus log(bulk concentration) is different to the linear decline in flux which would occur throughout. Moreover, we observed that the axial velocity exponent decreases with increasing bulk concentration. An empirical equation for the laminar mass transfer coefficient of a pseudoplastic fluid has been proposed which includes a Sieder and Tate type correction factor. The equation is a tool for understanding the decrease in axial velocity exponent with increasing bulk concentration. However, a comprehensive numerical model is necessary to get better agreement between observed and predicted axial velocity exponent and permeate flux.     

A new mechanistic Parachor model to predict dynamic interfacial tension and miscibility in multicomponent hydrocarbon systems

Widely used traditional Parachor model fails to provide reliable interfacial tension predictions in multicomponent hydrocarbon systems due to the inability of this model to account for mass transfer effects between the fluid phases. In this paper, we therefore proposed a new mass transfer enhanced mechanistic Parachor model to predict interfacial tension and to identify the governing mass transfer mechanism responsible for attaining the thermodynamic fluid phase equilibria in multicomponent hydrocarbon systems. The proposed model has been evaluated against experimental data for two gas-oil systems of Rainbow Keg River and Terra Nova reservoirs. The results from the proposed model indicated good IFT predictions and that the vaporization of light hydrocarbon components from crude oil to gas phase is the governing mass transfer mechanism for the attainment of fluid phase equilibria in both the gas-oil systems used. A multiple linear regression model has also been developed for a priori prediction of exponent in the mechanistic model by using only the reservoir fluid compositions, without the need for experimental measurements. The dynamic nature of interfacial tensions observed in the experiments justifies the use of diffusivities in the mechanistic model, thus enabling the proposed model predictions to determine dynamic gas-oil miscibility conditions in multicomponent hydrocarbon systems.     

Staging during anion-exchange intercalation into [LiAl2(OH)6]Cl.yH2O: structural and mechanistic insights

A series of experiments has been performed to seek more insight into the staging process that occurs during anion-exchange intercalation of some organic carboxylates and phosphonates into the layered double hydroxide [LiAl2(OH)6]Cl.yH2O. High resolution transmission electron microscopy has been employed to gain additional insight into the second-stage intermediates, providing strong evidence that the Rüdorff model of staging is applicable. Small-angle X-ray scattering was used to study the very early stages of the intercalation of succinate into [LiAl2(OH)6]Cl.yH2O: it was observed that the only species present during the reaction were the host, a second-stage intermediate and the first-stage product. The influence of temperature and solvent on the reaction mechanism was investigated. Staging was observed only at low temperatures (T<60 degrees C), and found to be confined largely to aqueous systems. Reactions performed in a 95:5 (v/v) mixture of water and a second non-aqueous solvent such as ethanol, acetone, THF or formamide proceeded via a second-stage intermediate, whereas for those undertaken in 50:50 (v/v) mixtures a direct transformation from host to product was usually observed.     

Spectral line shape in open-source atomic beam laser spectroscopy experiments

The line shape in atomic beam laser spectroscopy experiments has been calculated for an atomic beam emitted from an open filament and propagated into the vacuum under collisionless conditions. It is shown that the activation energy the atoms have to overcome in order to leave the sample leads to significant deviations from the Voigt line shape. The unreliable application of the Voigt profile under the conditions specified above leads to an overestimate of the line width by up to 70%. A modified Voigt profile is given, which has proved a reliable capability to describe the line shape under the above mentioned conditions.     

Metabolic profiling of mouse cerebrospinal fluid by sheathless CE-MS

The need for sensitive analytical technologies applicable to metabolic profiling of volume-restricted biological samples is high. Here, we demonstrate feasibility of capillary electrophoresis (CE) coupled to electrospray ionization mass spectrometry (MS) with sheathless nano-electrospray interface for non-targeted profiling of ionogenic metabolites in body fluids of experimental animals. A representative mixture of the metabolites and body fluids of mice such as cerebrospinal fluid (CSF), urine and plasma were used as examples of low-volume biological samples for method evaluation. An injection volume of only 9?nL resulted in limits of detection between 0.7 and 12?nM for the metabolite mixture. The method allowed the detection of ～350 molecular features in mouse CSF (an injection volume of ca. 45?nL), while ～400 features were observed in mouse plasma and ～3,500 features in mouse urine (an injection volume of ca. 9?nL). The low-volume body fluid samples were analyzed directly after only 1:1 dilution with water, thereby fully retaining sample integrity, which is of crucial importance for non-targeted metabolic profiling. As little is known about the metabolic composition of mouse CSF, we identified a fraction of the molecular features in mouse CSF using accurate mass information, migration times, MS/MS data, and comparison with authentic standards. We conclude that sheathless CE-MS can be used for sensitive metabolic profiling of volume-restricted biological samples.     

Determination of Carcinogenic and Allergenic Dyestuffs in Toys by LC Coupled to UV/Vis Spectrometry and Tandem Mass Spectrometry

A comprehensive analytical method based on LC coupled with ultraviolet–visible spectrometric detection and tandem mass spectrometry has been developed for the determination of sixteen carcinogenic and allergenic dyestuffs in toys. Various toy samples, including textiles, leathers, woods, paper, aqueous liquids, solid toy materials such as crayons, modeling or play clay, balloons and temporary tattoos were ultrasonically extracted with ethanol. Quantitative analysis was carried out after chromatographic separation with a mobile phase of acetonitrile-tetrahydrofuran-citrate buffered tetrabutylammonium hydroxide mixture under gradient elution. The mean recoveries at three spiked levels were between 88.6 and 104.7, with the relative standard deviations from 1.6 to 6.7%. The intra-day reproducibility ranged from 1.7 to 3.9% and inter-day reproducibility ranged from 3.0 to 5.8%. The identities of the dyestuffs were further verified by LC-tandem mass spectrometry. The method was successfully applied to the investigation of different toy components.     

The dynamics of water evaporation from partially solvated cytochrome c in the gas phase

The study of evaporation of water from biological macromolecules is important for the understanding of electrospray mass spectrometry experiments. In electrospray ionization (ESI), electrically charged nanoscale droplets are formed from solutions of, for example, proteins. Then evaporation of the solvent leads to dry protein ions that can be analyzed in the mass spectrometer. In this work the dynamics of water evaporation from native cytochrome c covered by a monolayer of water is studied by molecular dynamics (MD) simulations at constant energy. A model of the initial conditions of the process is introduced. The temperature of the protein drops by about 100 K during the 400 picoseconds of the simulations. This sharp drop in temperature causes the water evaporation rate to decrease by about an order of magnitude, leaving the protein with 50% to 90% of the original water molecules, depending on the initial temperature of the simulation. The structural changes of the protein upon desolvation were considered through calculations of the radius of gyration and the root mean square (RMS) of the protein. A variation of 0.4 A in the radius of gyration, together with an RMS value of less than 3 A, indicates only minor changes in the overall shape of the protein structure. The water coordination number of the solvation shell is much smaller than that for bulk water. The mobility of water is high at the beginning of the simulations and drops as the simulation progresses and the temperature decreases. Incomplete desolvation of protein ions was also observed in recent experiments.     

Experimental and modeling study of Newtonian and non-Newtonian fluid flow in pore network micromodels

The in situ rheology of polymeric solutions has been studied experimentally in etched silicon micromodels which are idealizations of porous media. The rectangular channels in these etched networks have dimensions typical of pore sizes in sandstone rocks. Pressure drop/flow rate relations have been measured for water and non-Newtonian hydrolyzed-polyacrylamide (HPAM) solutions in both individual straight rectangular capillaries and in networks of such capillaries. Results from these experiments have been analyzed using pore-scale network modeling incorporating the non-Newtonian fluid mechanics of a Carreau fluid. Quantitative agreement is seen between the experiments and the network calculations in the Newtonian and shear-thinning flow regions demonstrating that the 'shift factor,'alpha, can be calculated a priori. Shear-thickening behavior was observed at higher flow rates in the micromodel experiments as a result of elastic effects becoming important and this remains to be incorporated in the network model.     

Determination of concentration profiles from diffusion experiments in liquid monotectic alloys by AAS

To study the transport behaviour in monotectic melts diffusion experiments have been carried out in the liquid homogeneous phase of aluminium-indium alloys. The penetration curves from mass transport experiments in capillaries with a ratio length/diameter >25 have been measured by Atomic Absorption Spectroscopy (AAS). The optimized quantitative measurement procedure for Al and In, the working parameters in the concentration range 0–50 mg/l and the observed interferences are described. By exact adjusting of sample and standard solutions, the concentrations of both elements have been determined with relative standard deviations less than 1%.     

Phase separation in perfluorosulfonate ionomer membranes

The extent of phase separation in Nafion® perfluorosulfonate ionomer membranes has been studied by small-angle neutron scattering (SANS). These polymers, which consist of a perfluorocarbon main chain and a sulfonate-containing side group, can absorb up to 30% by weight of water. Previous studies have shown that clustering of water occurs, forming particles in the size range observable by SANS. The current study is concerned with the fraction of water molecules which participate in the clustering and the chemical composition of the phases present. Experiments have been made on melt-quenched samples which have no fluorocarbon crystallinity. The analysis is based on isotopic replacement experiments in which SANS measurements are made on samples hydrated with mixtures of H₂O and D₂O. Values of the small-angle x-ray scattering (SAXS), mean-square electron density fluctuation, and mass density are used as additional criteria. It is shown that at high water content (more than 15% absorption by weight), a two-phase model can explain the data with a majority (>60%) of the water molecules in one phase and most (>90%) of the perfluorocarbon in the other phase; a sample hydrated to a lower extent (8% by weight) shows deviations from the two-phase model. These results are consistent with the scattering behavior at large angles observed by SAXS.     

Structure of AOT reverse micelles under shear

Reverse micelles in the AOT/water/isooctane system, at various water contents (W(0)), were studied using rheometry and small angle X-ray scattering (SAXS) experiments under static conditions and under shear. The SAXS analysis confirmed the spherical shape of the micelles at low water content and revealed a transition into elongated micelles at higher water content. A population of spherical micelles was found to coexist with the cylindrical ones, even above the percolation threshold. The shape transformation was correlated with a viscosity leap observed in the rheometry measurements. Reverse micelles at low water content under shear act as a Newtonian fluid, without any detectable shape changes. In contrast, reverse micelles at high water content behave as a shear thinning fluid. SAXS measurements at high water content under shear force have shown that the shear forces induced alignment of the cylindrical micelles in the flow direction, without any other changes in the micelle dimensions. The anisotropy parameter, a measure of the degree of the spatial order, was found to increase with increasing water content and shear rate.     

Considerations on the ideal sample shape for Total Reflection X-ray Fluorescence Analysis

Total Reflection X-ray Fluorescence analysis (TXRF) is widely used in semiconductor industry for the analysis of silicon wafer surfaces. Typically an external standard is used for the calibration of the spectrometer. This is sensitive to errors in quantification. For small sample amounts the thin film approximation is valid, absorption effects of the exciting and the detected radiation are neglected and the relation between sample amount and fluorescence intensity is linear. For higher total sample amounts deviations from linearity have been observed (saturation effect). These deviations are one of the difficulties for external standard quantification.A theoretical determination of the ideal TXRF sample shape is content of the presented work with the aim to improve the calibration process and therefore the quantification.The fluorescence intensity emitted by different theoretical sample shapes was calculated, whereby several parameters have been varied (excitation energy, density, diameter/height ratio of the sample). It was investigated which sample shape leads to the highest fluorescence intensity and exhibits the lowest saturation effect. The comparison of the different sample shapes showed that the ring shape matches the ideal TXRF sample shape best.     

Method development and validation for the determination of biogenic amines in soy sauce using supercritical fluid chromatography coupled with single quadrupole mass spectrometry

Biogenic amines have been reported in many foods such as fish, meat, and soy sauce. The consumption of foods containing high concentrations of biogenic amines has been associated with health hazards. In this study, a green and efficient method using supercritical fluid chromatography coupled with single quadrupole mass spectrometry was developed for determination of biogenic amines in soy sauce. The chromatographic and mass spectrometry conditions were systematically optimized in terms of selectivity and peak shape. Nine biogenic amines were well separated within 25 min on a Cosmosil 5HP column using 5% (v/v) water and 0.2% (v/v) ammonia solution in methanol as mobile phase additives at a backpressure of 120 bar and temperature of 40°C. The established method was fully validated regarding the linearity, sensitivity, precision, and accuracy. The limits of detection and limits of quantification ranged from 0.03 to 10.50 μg/mL and 0.10 to 23.1 μg/mL, respectively. The relative standard deviations for intra‐ and interday precisions were all lower than 9.36% and the recoveries ranged from 75.82 to 99.63% and 80.10 to 99.89% for two levels of standards spiked in soy sauce, respectively. Finally, the established method was successfully applied to the quantitative analysis of biogenic amines in soy sauce.     

In situ sensing of the middle atmosphere with balloonborne near-infrared laser diodes

Since 1997, two near-infrared laser diode sensors have been developed with the support of the CNES, the French space agency, to provide in situ data of H(2)O, CH(4) and CO(2) in the middle atmosphere. The realized instruments were flown from stratospheric balloons within the framework of European campaigns for the study of stratospheric ozone and water vapor and were involved in the validation of the ODIN and ENVISAT satellites. In this paper, we describe the developed laser probing technique, we report atmospheric measurements and finally we discuss future perspectives, particularly the in situ laser sensing of the lower atmosphere of Mars and the implication of the laser hygrometers in balloon campaigns at mid-latitudes and tropical regions to investigate the sources and sinks of stratospheric H(2)O.     

Crystallization of condensation droplets on a liquid surface

Highly ordered microporous two-dimensional membranes have been obtained from polymer solutions (Widawski et al. (1994) Nature 369: 397–399). Recently, a mechanism for the formation of such membranes was proposed, involving water vapour condensation (induced by the rapid evaporation of the volatile solvent) onto the surface of solutions and the formation of floating water droplets. Unfortunately, the droplets growth process was not observed, and consequently only qualitative information was reported. In the present paper, results of light-scattering experiments with this system are reported. The formation of water droplets growing at the surface of the solution has been observed and the evolution with time of the mean droplet radius has been found to be described by a power law with an exponent of 1/3, proving that no coalescence processes occur. This particular behaviour is attributed to the precipitation of the polymer at the water/solution interface and to the formation of a mechanically resistant polymer layer encapsulating each droplet. In this way, water droplets behave like solid particles, allowing compact sheets to be formed. The presence of important surface currents is believed to promote the formation of “polycrystal” and “monocrystal” patterns. Received: 4 January 1999 Accepted in revised form: 15 February 1999     

Effect of the shape of human erythrocytes on the evaluation of the passive electrical properties of the cell membrane

The possible influence of the cell shape on the derivation of the passive electrical parameters of a biological cell membrane is discussed in light of two different models which describe the cell as a shelled ellipsoidal particle and as a biconcave disk obtained by the revolution of the Cassini oval, respectively. Whereas within the first model, the Laplace equation can be solved analytically, in the second one a numerical algorithm based on the boundary element method has been employed. We have compared the results obtained by these two different models in the case of normal human erythrocyte cell membrane, using radiowave dielectric spectroscopy measurements. Our findings show that, although in principle the cell shape might deeply affect the evaluation of the passive electrical parameters of the cell membrane, in the case of the erythrocyte shape modelled by the Cassini curve, only small deviations are evidenced in comparison to the values derived, as usually done in the dielectric spectroscopy of biological cell suspensions, from an ellipsoidal model analysis. This result gives further support to the reliability of the data reported in the literature based on an ellipsoidal shape erythrocyte model.     

A chemical test of the principle of critical point universality: the solubility of nickel (II) oxide in isobutyric acid + water near the consolute point

A mixture of isobutyric acid + water has an upper consolute point at 38.8 mass?% isobutyric acid and temperature near 26?°C. Nickel (II) oxide dissolves in this mixture by reacting with the acid to produce water and nickel isobutyrate. The solubility of nickel (II) oxide in isobutyric acid + water has been measured as a function of temperature at compositions, 25, 38.8, and 60 mass?% isobutyric acid. For values of the temperature, T, which were at least 2 K in excess of the liquid-liquid phase transition temperature, the measured values of the solubility, s, lie on a straight line when plotted in van't Hoff form with ln?s versus 1∕T. The slope, (?ln?s∕?(1∕T)), of the line is negative indicating that the dissolution reaction is endothermic. When the temperature was within 2 K of the phase transition temperature, however, (?ln?s∕?(1∕T)) diverged toward negative infinity. The principle of critical point universality predicts that when excess solid nickel (II) oxide is in dissolution equilibrium with liquid isobutyric acid + water, (?ln?s∕?(1∕T)) should diverge upon approaching the consolute point along the critical isopleth at 38.8 mass?% isobutyric acid. As determined by the sign of the enthalpy of solution, the sign of this divergence is expected to be negative. Not only do our experiments confirm these predictions, but they also show that identical behavior can be observed at both 25 and 60 mass?% isobustyric acid, compositions which lie substantially to either side of the critical composition.