Electrospray and chemical ionization mass spectrometry of di-n-butyl sulfate. Unimolecular chemistry of its protonated form and quantification method by liquid chromatography/electrospray ionization tandem mass spectrometry

Di-n-butyl sulfate (DNBS) has been studied by electrospray (ESI) and chemical (CI) ionization mass spectrometry. The use of methanol as solvent in electrospray ionization allows observation of relatively abundant [DNBS + CH(3)OH + H](+) ions (m/z 243) which upon collision dissociate to [DNBS + H](+) ions (m/z 211). In both ESI and CI experiments, it is found that [DNBS + H](+) ions lead to m/z 113 daughter ions. The composition of this m/z 113 fragment ion and its mechanism of formation have been established by high resolution measurements and CID-MIKE experiments. An 'internal substitution' reaction involving an ion-neutral intermediate is proposed to explain the formation of a [C(8)H(17)](+) ion (m/z 113) by loss of a H(2)SO(4) molecule. Finally, a LC/ESI-MS/MS quantification method is proposed in which a detection limit of di-n-butyl sulfate in the ppm range is obtained. It is suggested that the quantification method might be extended to higher dialkyl sulfates. Copyright 2000 John Wiley & Sons, Ltd.     

X-ray measurements with micro- and nanoresolution at BESSY

Capabilities of the KMC-2 beamline at BESSY for spatially resolved X-ray measurements with micro- and nanometer resolution have been reviewed. A combination of experimental methods of X-ray fluorescence analysis and extended X-ray absorption fine spectroscopy with X-ray standing waves technique was applied for the depth profiling of Si/W/Si layers with sub-nanometer resolution. The investigated layers were placed into the waveguide structure formed by two Au films to increase sensitivity and accuracy of the measurements. In-depth resolution on the order of 1 nm for the structure measurements has been obtained.     

A multiresolution approach for the convergence acceleration of multivariate curve resolution methods

Modern computerized spectroscopic instrumentation can result in high volumes of spectroscopic data. Such accurate measurements rise special computational challenges for multivariate curve resolution techniques since pure component factorizations are often solved via constrained minimization problems. The computational costs for these calculations rapidly grow with an increased time or frequency resolution of the spectral measurements.     

Improved isotopic abundance measurements for high resolution fourier transform ion cyclotron resonance mass spectra via time-domain data extraction

The simultaneous high resolution and accurate mass measurements possible with Fourier transform ion cyclotron resonance mass spectrometry coupled with the gentle ionization of electrospray hold attractions for protein, peptide, and oligonucleotide characterization, including multistage-mass spectrometry measurements for assignment of fragment masses and greater confidence in structural measurements. The detection of cyclotron motion over extended periods of time (in some cases for several minutes) allows higher resolution and mass accuracy. Generally, signal duration has been considered to be limited primarily by background pressure, with ion-neutral collisions leading to the reduction and dephasing of cyclotron motion, causing signal loss. However, recent theoretical work has shown that the ion cloud stability that is a prerequisite for high performance measurements is highly dependent on the electric field generated by the ion cloud, thus giving rise to a minimum number of charges or ions required for extended time-domain signals. The effects of ion population on ion cloud stability and signal duration, and the subsequent effects on resolution and measured isotopic abundances are reported. Individual time-domain signals for bovine insulin isotopic peaks were extracted to allow a comparison of the damping rates for each of these ion clouds and the measured time-domain amplitude maxima are shown to provide a better match with the theoretically predicted isotopic abundances for insulin. These results show that different damping rates of ions of very similar mass, but different ion cloud population sizes, can have dramatic effects on the observed isotopic patterns. Additionally, more accurate, high resolution spectra can be produced by correcting for the effects of the different damping rates that are observed for different ion population sizes.     

Evaluation and improvement of the resolution of voltammetric measurements

Two approaches for estimating and improving resolution in chromatography analyses can be applied successfully to voltammetric measurements. It is shown that the resolution of voltammetric procedures yielding symmetric (or nearly symmetric) current peaks can be described by R = 2DeltaE (p)1.699 (b(1,2,1) + b(1,2,1)) where DeltaE(p) is the difference between the peak potentials of the two analytes, and b(1,2,1) and b(1,2,2) are the peak half-widths. The window diagram approach is used to improve the resolution between neighbouring voltammetric peaks by optimization of the supporting electrolyte composition. The applicability of these approaches to differential-pulse anodic-stripping measurements at the mercury film electrode is demonstrated.     

Differential dynamical effects of macromolecular crowding on an intrinsically disordered protein and a globular protein: implications for in-cell NMR spectroscopy

In-cell NMR provides a valuable means to assess how macromolecules, with concentrations up to 300 g/L in the cytoplasm, affect the structure and dynamics of proteins at atomic resolution. Here an intrinsically disordered protein, alpha-synuclein (alphaSN), and a globular protein, chymotrypsin inhibitor 2 (CI2) were examined by using in-cell NMR. High-resolution in-cell spectra of alphaSN can be obtained, but CI2 leaks from the cell and the remaining intracellular CI2 is not detectable. Even after stabilizing the cells from leakage by using alginate encapsulation, no CI2 signal is detected. From in vitro studies we conclude that this difference in detectability is the result of the differential dynamical response of disordered and ordered proteins to the changes of motion caused by the increased viscosity in cells.     

Complementary DSC and dilatometric investigation of M-PTFE pyrotechnic compositions

Results of high thermal resolution microcalorimetric and dilatometric measurements performed on reducer — polytetrafluoroethylene (M-PTFE) pyrotechnic compositions have been discussed. The materials were selected for the study because of their behaviour in combustion tests. Two complementary thermal properties, i.e. the specific heat and coefficient of linear thermal expansion (CLTE), have been analysed in detail. The specific heat was obtained from DSC measurements performed from −20 to 375°C. Measurements of CLTE and linear expansion were carried out from −40 to 270°C. In both cases the measurements were performed on thermocycling with the high thermal resolution preserved. A special attention has been paid to a two-stage phase transition occurring just below the room temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

溶剂化金属原子浸渍法制备高分散负载型催化剂——Ⅸ.K-Fe/硅沸石催化剂的XRD、TEM、XPS和磁测定表征

用溶剂化金属原子浸渍(SMAI)法和普通浸渍(CI)法两种不同的方法制备了组成相同的K-Fe/硅沸石催化剂。TEM,XRD,XPS和磁测定结果表明,SMAI K-Fe/硅沸有催化剂中铁的分散度和还原度都大于CI催化剂,SMAI催化剂中金属颗粒直径小于4nm,具有超顺磁性,而CI催化剂中金属颗粒较大,表现铁磁性。两种方法制备的催化剂反应前后金属的状态发生明显的改变,对CO+H_2反应的催化性质不同。     

PREPARATION OF Au/SULFONATED POLYSTYRENE CATALYSTS FOR LOW-TEMPERATURE CO OXIDATION*

Supported An catalysts for low-temperature CO oxidation were prepared by solvated motal atom impregnation(SMAI) and conventional impregnation (CI). X-ray photoelectron spectroscopy (XPS) investigations indicated that theelemental gold in all the samples was in the metallic state. XRD measurements showed that the mean diameters of Auparticles prepared by SMAI were smaller than those prepared by CI with the same gold content. Catalytic tests showed thatthe SMAI catalyst had higher CO oxidation activity than the CI catalyst with the same compositions. Both SMAI and CIcatalysts exhibited high activity in low temperature CO oxidation. Full CO conversion was obtained at 323--383K.     

Absolute photoabsorption oscillator strengths by electron energy loss methods: the valence and S 2p and 2s inner shells of sulphur dioxide in the discrete and continuum regions (3.5–260 eV)

Absolute photoabsorption oscillator strengths (cross-sections) for the valence shell discrete and continuum regions of sulphur dioxide from 3.5 to 51 eV have been measured using high resolution (0.05 eV FWHM) dipole (e,e) spectroscopy. A wide-range spectrum, covering both the valence shell and the S 2p and 2s inner shells, has also been obtained from 5 to 260 eV at low resolution (1 eV FWHM), and this has been used to determine the absolute oscillator strength scale using valence shell TRK (i.e., S(0)) sum-rule normalization. The present measurements have been undertaken in order to investigate the recently discovered significant quantitative errors in our previously published low resolution dipole (e,e) work on sulphur dioxide (Cooper et al., Chem. Phys. 150 (1991) 237; 150 (1991) 251). These earlier measurements were also in poor agreement with other previously published direct photoabsorption measurements. We now report new absolute photoabsorption oscillator strengths using both high and low resolution dipole (e,e) spectroscopies. These new measurements cover a wider energy range and are much more consistent with the previously published direct photoabsorption measurements. The accuracy of our new measurements is confirmed by an S(−2) dipole sum-rule analysis which gives a static dipole polarizability for sulphur dioxide in excellent agreement (within 3.5%) with previously reported polarizability values. Other dipole sums S(u) (u=−1,−3 to −6,−8,−10) and logarithmic dipole sums L(u) (u=−1 to −6) are also determined from the presently reported absolute oscillator strength distributions.     

Measuring local pH in electrochemistry

Localized pH measurements are important in various areas of electrochemistry, from corrosion to bio-electrochemistry and electrocatalysis. Different techniques are available to perform these measurements and offer numerous possibilities in terms of spatial and temporal resolution, sensitivity, and precision. In this brief review we present the recent progress made and summarize the main techniques available for localized pH measurements in electrochemistry such as scanning probe techniques (SECM, SICM, SIET), laser (confocal) fluorescence microscopy, rotating ring-disc electrode (RRDE) voltammetry, and infra-red spectroscopy, among others.     

Quantitative elastic recoil detection (ERD)

Elastic recoil detection with heavy ions is a well suited method to measure depth profiles of light and medium heavy elements in thin films. Due to known Rutherford scattering cross sections and stopping powers of ions in matter, measurements can be quantified with an accuracy of about 1%. The transformation of energy spectra to quantitative elemental depth profiles, however, is generally a non trivial task and therefore a transofrmation algorithm has been developed based on a similar one for RBS analysis and realised in the program KONZERD. The transformation procedure allows a fast conversion from raw spectra to concentration profiles for classical ERD measurements as well as for high resolution measurements with a depth resolution better than 1 nm.     

Characterizing the resolution and accuracy of a second-generation traveling-wave ion mobility separator for biomolecular ions

High-accuracy, high-resolution ion mobility measurements enable a vast array of important contemporary applications in biological chemistry. With the recent advent of both new, widely available commercial instrumentation and also new calibration datasets tailored for the aforementioned commercial instrumentation, the possibilities for extending such high performance measurements to a diverse set of applications have never been greater. Here, we assess the performance characteristics of a second-generation traveling-wave ion mobility separator, focusing on those figures of merit that lead to making measurements of collision cross-section having both high precision and high accuracy. Through performing a comprehensive survey of instrument parameters and settings, we find instrument conditions for optimized drift time resolution, cross-section resolution, and cross-section accuracy for a range of peptide, protein and multi-protein complex ions. Moreover, the conditions for high accuracy IM results are significantly different from those optimized for separation resolution, indicating that a balance between these two metrics must be attained for traveling wave IM separations of biomolecules. We also assess the effect of ion heating during IM separation on instrument performance.     

Resolution of two-way data: theoretical background and practical problem-solving. Part 1: theoretical background and methodology

This paper reviews recent progress in the resolution of two-way data obtained from hyphenated instruments. Special emphasis is placed on the solution of practical problems. Methods for estimating the number of chemical components both statistically and visually (the first step in solving the resolution problem) and methods for resolving the pure profiles (the second step in solving the resolution problem) are discussed in detail. To deal with real-world problems, pitfalls in the chemometric analysis of the two-way data from the instrumental measurements are also pointed out. Applications of methods for solving some difficult practical problems in environmental chemistry, pharmaceutical chemistry, and physical chemistry will be discussed in the second part of this paper.     

Resolution of two-way data: theoretical background and practical problem-solving Part 1: Theoretical background and methodology

This paper reviews recent progress in the resolution of two-way data obtained from hyphenated instruments. Special emphasis is placed on the solution of practical problems. Methods for estimating the number of chemical components both statistically and visually (the first step in solving the resolution problem) and methods for resolving the pure profiles (the second step in solving the resolution problem) are discussed in detail. To deal with real-world problems, pitfalls in the chemometric analysis of the two-way data from the instrumental measurements are also pointed out. Applications of methods for solving some difficult practical problems in environmental chemistry, pharmaceutical chemistry, and physical chemistry will be discussed in the second part of this paper.     

Performance of radar absorbing materials by waveguide measurements for X- and Ku-band frequencies

In this work, samples consisting of an elastomeric matrix containing different kinds of active materials in particulate form were prepared for reflectivity measurements. The materials individually used in weight contents of 80% in polychloroprene matrix were: carbonyl-iron (CI) and doped ferrite powders. The microwave reflectivity levels were determined from the magnetic and dielectric properties of the elastomeric composites obtained from scattering data, by fitting the samples in a waveguide, for measurements in the frequency range from 8 to 16 GHz. Better microwave absorption for X-band was obtained for CI while doped ferrite absorbed at higher frequencies (Ku-band).     

SMAI和CI法制备的Ni—Ag／SiO2催化剂的结构与催化性质研究

应用溶剂化金属原子浸渍（ＳＭＡＩ）法和普通浸渍（ＣＩ）法制备了金属含量相同的ＳｉＯ２负载Ｎｉ－Ａｇ双金属催化剂。ＸＲＤ和磁测定结果表明ＳＭＡＩ催化剂中Ｎｉ和Ａｇ的粒度均小于金属含量相同的ＣＩ催化剂，ＳＭＡＩ催化剂中Ｎｉ和Ａｇ未形成合金，而ＣＩ催化剂中Ｎｉ和Ａｇ形成了合金。ＳＭＡＩ和ＣＩ催化剂都具有超顺磁性。研究了这些催化剂在甲苯加氢反应的催化性质，结果表明与组成相同的普通浸渍法催化相比，ＳＭＡＩ催     

Combined Application of Picosecond Transient Absorption and Emission Measurements in Studies of Radical-Ion Pair Dynamics

Abstract— Much of the emphasis in the development of methods for time-resolved measurements is on increasing experimental time resolution. Equally important, however, is the establishment of methods to apply existing techniques to problems of increasing complexity. Here we describe the application of a combination of picosecond absorption and emission measurements to solve a complex kinetic problem in organic photophysics, namely, the dynamics of interconverting radical-ion pairs. Although fairly routine, the emission measurements require higher time resolution and the absorption measurements require higher signal-to-noise ratios than are often achieved. In the first part of this paper we describe the ways in which these experimental requirements have been met. Next, the radical-ion pair kinetic problem and its solution are described. Finally, we discuss some future directions for the techniques as they relate to studies of radical-ion pair dynamics.     

Characterization of subcritical water oxidation with in situ monitoring and self-modeling curve resolution

In this paper, a subcritical water oxidation (SBWO) process was monitored using self-modeling curve resolution (SMCR) of in situ UV-Vis measurements to estimate time-dependant composition profiles of reactants, intermediates and products. A small laboratory scale reactor with UV-Vis fiber-optic probes and a flow cell was used to demonstrate the usefulness of SMCR for monitoring the destruction of model compounds phenol, benzoic acid, and aniline in a dilute aqueous solutions. Hydrogen peroxide was used as the oxidizing reagent at moderate temperature (150-250 °C) and pressure (60-90 atm) in a single phase. By use of in situ monitoring, reaction times were easily determined and conditions for efficient oxidations were easily diagnosed without the need for time consuming off-line reference measurements. For selected runs, the destruction of the model compound was confirmed by gas chromatography and chemical oxygen demand (COD) measurements. Suspected intermediate oxidation products were easily detected by the use of UV-Vis spectrometry and self-modeling curve resolution, but could not be detected by gas chromatography.     

Rate Constants and Activation Energies for Gas‐Phase Reactions of Three Cyclic Volatile Methyl Siloxanes with the Hydroxyl Radical

Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second‐order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D₄), decamethylcyclopentasiloxane (D₅), and dodecamethylcyclohexasiloxane (D₆) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140‐mL gas‐phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D₄ and D₅ with the OH radical are 1.9 × 10^?12 (95% confidence interval (CI): (1.7–2.2) × 10^?12) and 2.6 × 10^?12 (CI: (2.3–2.9) × 10^?12) cm³ molecule^?1 s^?1, respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D₆ is 2.8 × 10^?12 (CI: (2.5–3.2) × 10^?12) cm³ molecule^?1 s^?1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D₅ were 33% higher than for D₄ (CI: 30–37%), whereas the rates for D₆ were only 8% higher than for D₅ (CI: 5–10%). The activation energies of the reactions of D₄, D₅, and D₆ with OH were not statistically different and had a value of 4300 ± 2800 J/mol.