Simultaneous thermal analysis — Mass spectrometer skimmer coupling system

A mass spectrometer coupling system for simultaneous TG/DSC/DTA-QMS measurements will be introduced that is capable of operation at temperatures up to 2000°C. The coupling is maintained at a temperature very close to that of the sample, minimizing condensation, and features an extremely short gas flow path. The efficiency of this coupling system will be demonstrated through examples from the area of polymers, ceramics, metallurgy and recycling.     

Determination of the partial pressure of single low volatile compounds in mixtures

A new measuring system for the determination of the vapour pressure of single compounds in mixtures is introduced. A coupling system consisting of a quadrupol mass spectrometer and a vapour pressure balance was used for these measurements. Some calibration measurements and investigations of mixtures are discussed.     

Determination of the partial pressure of single low volatile compounds in mixtures

A new measuring system for the determination of the vapour pressure of single compounds in mixtures is introduced. A coupling system consisting of a quadrupol mass spectrometer and a vapour pressure balance was used for these measurements. Some calibration measurements and investigations of mixtures are discussed.     

Aerodynamic mass spectrometry interfacing of microdevices without electrospray tips

A new concept for electrospray coupling of microfluidic devices with mass spectrometry was developed. The sampling orifice of the time-of-flight mass spectrometer was modified with an external adapter assisting in formation and transport of the electrosprayed plume from the multichannel polycarbonate microdevice. The compact disk sized microdevice was designed with radial channels extending to the circumference of the disk. The electrospray exit ports were formed by the channel openings on the surface of the disk rim. No additional tips at the channel exits were used. Electrospray was initiated directly from the channel openings by applying high voltage between sample wells and the entrance of the external adapter. The formation of the spatially unstable droplet at the electrospray openings was eliminated by air suction provided by a pump connected to the external adapter. Compared with the air intake through the original mass spectrometer sampling orifice, more than an order of magnitude higher flow rate was achieved for efficient transport of the electrospray plume into the mass spectrometer. Additional experiments with electric potentials applied between the entrance sections of the external adapter and the mass spectrometer indicated that the air flow was the dominant transport mechanism. Basic properties of the system were tested using mathematical modeling and characterized using ESI/TOF-MS measurements of peptide and protein samples.     

Thermodynamic interaction parameters in polymer solutions and gels

Polymer-solvent interaction parameters are reported for poly(vinyl acetate)-acetone, poly(vinyl acetate)-toluene, and poly(dimethyl siloxane)-toluene systems using different techniques. Results obtained by osmotic deswelling are compared with those from quasi-elastic light scattering and small-angle neutron scattering (SANS). In gels, the latter techniques involve separation of the time-dependent from the static component of the scattered radiation+ Separation is achieved in quasi-elastic light scattering through the heterodyning properties of the light, and in SANS by subtracting an appropriate static structure factor. The interaction parameters obtained by different separation procedures are consistent with measurements using the osmotic method. © 1995 John Wiley & Sons, Inc.     

Micelles of SDS Surfactants in Concentrated NaCl Solutions

We investigated the aggregation behavior of rod-like micelles of sodium dodecyl sulfate (SDS) in concentrated NaCl solution by quasi-elastic light scattering (QLS) and viscosity measurement over a range of temperature (25 °C to 50 °C) and NaCl concentration. The reduced viscosity of aqueous SDS in the presence of NaCl has been measured by an Ubbelohde-type capillary viscometer. We show mean hydrodynamic radius of micelles can be determined from viscosity data. We also determined mean hydrodynamic radius using quasi-elastic light scattering. Micellar size decreases with increasing temperature, whereas it increases with increasing ionic strength. The results of viscosity and dynamic light-scattering measurements are interpreted as the extension of length of rod-like micelles. We compare viscosity and light scattering experimental results.     

Interlayer water molecules in vanadium pentoxide hydrate. 8. Dynamic properties by quasi-elastic neutron scattering

The dynamics of water molecules in the layered vanadium pentoxide hydrate, V(2)O(5).nH(2)O, were studied by quasi-elastic neutron scattering (QENS) measurements. Heterogeneity of the dynamic properties was confirmed by alpha-relaxation model analysis. Translational diffusion of monolayer and double-layer water molecules is by site-to-site diffusion and is reduced relative to that of bulk water. Water molecules lose their mobility markedly and solidify with decreasing temperature. However, mobile water remains at 253 K. Rotational diffusion coefficients are unaffected by confinement and are very similar to the bulk values determined at temperatures in the range 253-298 K. The dynamic speed characterized by QENS is much faster than that expected from the data determined by deuterium NMR (DNMR) measurements at low temperatures.     

Inelastic neutron scattering spectra of the hydrogen tungsten bronze H0.4WO3

Inelastic neutron scattering spectra of metallic H_0.4WO₃ show only the vibrations that would be expected of a metal hydroxide. The diffusion coefficient of the proton could not be detected from quasi-elastic scattering with the best available neutron spectrometer setting an upper limit to its value of 10^?7 cm²/sec. Both these results confirm that this material is correctly described as a hydroxide.     

A novel direct coupling of simultaneous thermal analysis (STA) and Fourier transform-infrared (FT-IR) spectroscopy

Evolved gas analysis (EGA) from thermal analyzers such as thermogravimetry (TG) or simultaneous thermal analysis (STA) which refers to simultaneous TG–DSC is well established since it greatly enhances the value of TG or TG–DSC results. The sensitive and selective FT-IR technique is in particular useful for the analysis of organic molecules but also for infrared active permanent gases evolved during most decomposition processes. The coupling interface between thermal analyzers and FT-IR spectrometers usually consists of heated adapters and a flexible, heated transfer line. In this work, a novel direct coupling of an STA instrument and an FT-IR spectrometer without a transfer line is presented. A very small FT-IR spectrometer is directly mounted on top of the STA furnace leading to a compact and fully integrated STA–FT-IR coupling system. The possibilities and the value of simultaneous STA–FT-IR measurements are demonstrated for organic, biomass, and ceramic samples in the temperature range between room temperature and about 1,500 °C. Various samples from the field of inorganics and organics—especially polymers—were furthermore measured showing the advantages of the direct STA–FT-IR coupling compared to state-of-the-art STA–FT-IR coupling using a heated transfer line: we found that the time delay caused by the volume of the transfer line itself is rather negligible whereas a significantly better correlation between gas detection and TG results was observed in case of some highly condensable decomposition gases. Aspects of quantification of evolved gases are furthermore discussed as well as the known nonlinearity of FT-IR detection at higher gas concentrations.     

Fibre optic coupler as a detector for microfluidic applications

A new construction of a fibre optic coupler is presented in the paper. Two polymer optical fibres were used to build a coupler in which coupling efficiency of optical power depends on the refractive index of liquid delivered to a microchannel formed by the fibres. The coupler was tested as a detector in saccharose concentration measurements, and was used in absorbance measurements. A red light emitting diode and a spectrometer were used as a light source and a photodetector, respectively. Experiments confirmed that the coupler can be used for the real time monitoring of the changes in the refractive index of a saccharose solution exhibiting repeatable changes in the signal, with no hysteresis. Absorbance tests were performed with a solution of bromothymol blue at different pH.     

New TA-MS coupling system with increased sensitivity for low volatile materials

The quantitative transfer of condensable gases and vapours from a thermal analysis instrument to a quadrupole mass spectrometer presents technical and physical problems, particularly at high temperatures. This paper describes a new orifice system for coupling a simultaneous TG-DTA unit with a quadrupole mass spectrometer, able to measure quantitatively the vapour pressures of iodine, selenium, tellurium, lead, silver, etc. up to 1200°C. In designing the new two-stage orifice system the laws for gas flow dynamics were considered. A new high temperature furnace guarantees both small temperature gradients within the system and optimal flow conditions (1). The paths for released vapours, i.e. distances between sample, orifices and MS analyser, have been kept as short as possible. The measurements reported demonstrate the greatly increased sensitivity of the new system, particularly necessary when analysing metal vapours.     

Reversible voltage-induced assembly of au nanoparticles at liquid/liquid interfaces

The voltage-induced assembly of mercaptosuccinic acid-stabilized Au nanoparticles of 1.5 +/- 0.4 nm diameter is investigated at the polarizable water/1,2-dichloroethane interface. Admittance measurements and quasi-elastic laser scattering (QELS) studies reveal that the surface concentration of the nanoparticle at the liquid/liquid boundary is reversibly controlled by the applied bias potential. The electrochemical and optical measurements provide no evidence of irreversible aggregation or deposition of the particles at the interface. Analysis of the electrocapillary curves constructed from the dependence of the frequency of the capillary waves on the applied potential and bulk particle concentration indicates that the maximum particle surface density is 3.8 x 10(13) cm(-2), which corresponds to 67% of a square closed-pack arrangement. This system provides a unique example of reversible assembly of nanostructures at interfaces, in which the density can be effectively tuned by the applied potential bias.     

Disubstituted polyacetylene brushes grown via surface-directed tungsten-catalyzed polymerization

Disubstituted polyacetylene brushes were grown from modified silicon and quartz surfaces using a transition metal-catalyzed polymerization technique employing tungsten hexachloride/tetraphenyl tin (WCl6/Ph4Sn). The substrate surfaces were initially functionalized with terminal alkyne functional groups by using an alkyne-functionalized silane, O-(propagyloxy)-N-(triethoxysilylpropyl) urethane, as a surface coupling agent. Surface polymerization of 5-decyne under microwave irradiation at 150 degrees C for 30 min was performed on the functional surfaces to produce surfaces consisting of grafted poly(1,2-dibutylacetylene) brushes. The alkyne-functionalized and polymer-coated surfaces were characterized using surface contact angle measurements, film thickness measurements, atomic force microscopy, and X-ray photoelectron spectroscopy, and fluorescence spectrometer measurements were performed to analyze the surfaces at each step of the modification process. This simple technique demonstrates a novel way of synthesizing a poly(1,2-dibutylacetylene) brush layer on silicon substrate, and it has future potential in the fabrication of selectively functionalized surfaces on the nanoscale via this new synthetic approach.     

Development of a pre-concentrator-thermo-desorber/micro-gas chromatograph/mass spectrometer coupling for on-site analyses of emissions of volatile organic compounds from landfills

The development and use of a pre-concentrator-thermo-desorber/micro-gas chromatograph/mass spectrometer (μTD/μGC/MSD) coupling for the on-site analysis of VOCs in landfill gases are presented. The coupling has the advantage of analysing compounds with two detectors operated in series: the TCD (of the μGC) initially analyses the gas without destroying it, and then the MSD identifies the compounds. Due to the TCD response, the results were quantified with reference to toluene. The reliability of the analytical chain for quantitative analysis was validated by sampling two gaseous standards, including the EPA TO14 mixture, containing 39 compounds. With the OV1?μGC column, 24 compounds were identified and 16 correctly quantified. The repeatability of the measures estimated by their standard deviation was in the order of 1–2%. The detection limit was evaluated at 0.1?ppbv, for a 40?min pre-concentration on the Tenax of the μTD. The results of VOC analyses in the air of a landfill site obtained with the μTD/μGC/MSD coupling show its potential for on-site analyses: immediate results, high sensitivity, no storage for the samples, and measurements of pollution peaks.     

H＋对水溶液中脱氧胆酸钠聚集体的影响

运用pH滴定、傅立叶变换红外光谱、紫外可见光谱、激光光散射谱、ICP和元素分析等方法研究了H＋的加入对水溶液中脱氧胆酸钠（NaDC）聚集体的影响.结果表明,浓度大于cmc的NaDC水溶液具有一定的缓冲能力,NaDC浓度越高,缓冲能力越大;随溶液中H＋浓度的增加,首先形成质子化胶团,质子化胶团通过酸盐结构的氢键作用使NaDC初级胶团长大,形成较大的高级胶团,甚至形成凝胶体,最终形成HnNam(DC)n＋m沉淀.     

Continuous wave cavity ring-down spectroscopy measurement of NO2 mixing ratios in ambient air

The performance of a continuous wave diode laser based cavity ring-down (CRD) spectrometer is demonstrated for retrieval of NO2 mixing ratios in ambient air. Measurements are made at wavelengths around 410 nm, a region free from other spectroscopic interferences, and the instrument is shown to be capable of quantitative and precise NO2 mixing ratio determinations without any requirement for calibration. The minimum concentration of NO2 that can be measured by the spectrometer is estimated to be 0.1 ppbv (parts per billion by volume) in 50 s at atmospheric pressure. Using dynamic dilution of a standard NO2 sample, the performance of the spectrometer has been validated for NO2 measurements over the range of 0.2 to 80 ppbv. NO2 measurements performed directly on laboratory air are compared with data obtained with a calibrated chemiluminescence instrument and shown to be in excellent agreement.     

Detection of soil pollution by hydrocarbons using headspace-mass spectrometry and identification of compounds by headspace-fast gas chromatography-mass spectrometry

The direct coupling of a headspace sampler with a mass spectrometer is proposed as a screening tool for the rapid detection of soil pollution by hydrocarbons from petroleum and derivatives. The samples are subjected to the headspace generation process, with no prior treatment, and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of the sample analysed. Suitable treatment of the signal by chemometric techniques allows unequivocal characterisation of the different types of sample. The use of fast gas chromatography with a mass spectrometer detector coupled to the headspace sampler allows identification of the major hydrocarbons present in the mineral and organic polluted samples, interpretation of the results obtained, and demonstrates the analytical potential of headspace-mass spectrometry coupling.     

Explanation of spin-lattice relaxation rates of spin labels obtained with multifrequency saturation recovery EPR

Electron paramagnetic resonance (EPR) pulsed saturation recovery (pSR) measurements of spin-lattice relaxation rates have been made on nitroxide-containing fatty acids embedded in lipid bilayers by Hyde and co-workers. The data have been collected for a number of spin-labeled fatty acids at several microwave spectrometer frequencies (from 2 to 35 GHz). We compare these spin-lattice relaxation rates to those predicted by the Redfield theory incorporating several mechanisms. The dominant relaxation mechanism at low spectrometer frequencies is the electron-nuclear dipolar (END) process, with spin rotation (SR), chemical shift anisotropy (CSA), and a generalized spin diffusion (GSD) mechanism all contributing. The use of a wide range of spectrometer frequencies makes clear that the dynamics cannot be modeled adequately by rigid-body isotropic rotational motion. The dynamics of rigid-body anisotropic rotational motion is sufficient to explain the experimental relaxation rates within the experimental error. More refined models of the motion could have been considered, and our analysis does not rule them out. However, the results demonstrate that measurements at only two suitably chosen spectrometer frequencies are sufficient to distinguish anisotropic from isotropic motion. The results presented demonstrate that the principal mechanisms responsible for anisotropically driven spin-lattice relaxation are well understood in the liquids regime.     

Interpretation of quasi-elastic light scattering measurements from moderately concentrated solutions

The autocorrelation functions of elastic and quasi-elastic light scattering measurements of polystyrene ($\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{= 670,000}$) in toluene at 20° and cyclohexane at 35° at concentrations up to 0·07 g cm^?3 are examined employing a scattering law that includes both the self and distinct part of the time-dependent pair correlation function. By taking the convolution approximation of Vineyard, it is shown that within experimental accuracy both terms are governed by the translational diffusion coefficient.     

Characterization of carbofuran photodegradation by-products by liquid chromatography/hybrid quadrupole time-of-flight mass spectrometry

The structural elucidation of by-products arising from carbofuran photodegradation using a high-pressure UV lamp has been investigated by liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) employing a quadrupole time-of-flight mass spectrometer. Exact mass measurements of the [M + H]+ ions of the by-products and of product ions allowed the elemental formulae and related structures of seven photodegradation by-products (resulting, respectively, from photo-Fries rearrangement, hydroxylation of the benzene ring, oxidation of the 2,3-dihydrobenzofuran ring, cleavage of the carbamate group, hydrolysis of the ether group and the newly observed radical coupling and decarboxylation processes) to be determined confidently. Accurate mass measurements of product ions allowed ambiguities to be removed concerning neutral losses having the same nominal mass, namely CO and C2H4, allowing the fragmentation patterns to be rationalized.