bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas Chromatography/Mass Spectrometry
Authors: Palmer Peter T. 
Published: September 2006

AbstractGas chromatography/mass spectrometry (GC/MS) is perhaps the most widely used analytical technique for the analysis of complex mixtures. The power of this technique stems from the “marriage” of two powerful techniques into a hyphenated method. Gas chromatography (GC) is used to separate the components of a mixture based on their differing affinities for the stationary phase on the column. Mass spectrometry (MS) serves not only to detect and quantify the various species eluting off the column but also provides definitive information as to their identity. The most common GC/MS instruments employ a gas chromatograph with a split/splitless injector, capillary column, and either a quadrupole or quadrupole ion trap as a mass analyzer. A high degree of automation and a powerful data system are required for handling the large amounts of three‐dimensional (3‐D) data (time, mass‐to‐charge ratio, and intensity) that can be generated. The technique typically requires that the analytes in question have sufficient volatility to be amenable to GC. It is very sensitive, with detection limits typically in the picogram or even sub‐picogram range. It can be highly selective and allows for incredible flexibility with respect to the type and quality of the mass spectral data; the user may choose from a number of ionization modes and scan modes, and control mass range and mass resolution, and many other experimental parameters. Analysis speeds are relatively slow due to the time required for adequate chromatographic separation, but can be reduced to an order of a few minutes using fast GC techniques. GC/MS instrumentation is usually intended for benchtop operation in the laboratory, although a number of field‐portable instruments have been developed. The technique requires significant user expertise, knowledge of various means for compound identification and quantitation, and instrument tuning, maintenance, and upkeep.
High‐Resolution Mass Spectrometry and Its Applications
Authors: Jennings Keith R. 
Published: September 2006

Abstract

With the exception of the
12
C isotope of carbon which has a mass arbitrarily set equal to exactly 12 Da, all isotopes have unique nonintegral masses. The elemental composition of a sample can therefore often be inferred from an accurate measurement of the relative molecular mass of the sample. This requires that the mass resolving power (RP) of the instrument in use must be sufficiently high for the peak on which the mass measurement is based to be resolved from peaks arising from other components of closely similar mass. For samples of relative molecular mass below 500, an RP of 20 000 is often adequate, but for samples such as peptides and proteins an RP of several hundred thousand is often required.

The modes of operation, strengths and weaknesses of the several different types of mass analyzer currently available for the production of mass spectra of sufficiently high resolution are reviewed. Particular emphasis is placed on the use of mass spectrometry in the detection and identification of samples of biological origin for which its high sensitivity and specificity of information provided are of great importance. This article concludes with a brief review of the uses of high‐resolution mass spectrometry, in which the difficulties encountered in working with samples of very high relative molecular mass are discussed and an account is presented of the information to be gained from time‐dependent studies of H/D interchange at high resolution.
Inorganic Substances, Mass Spectrometric in the Analysis of
Authors: Taylor Howard E. 
Published: September 2006

Abstract
Mass spectrometry is an analytical technique used to measure the composition of a substance by isolating specific analyte components according to their individual atomic or molecular mass‐to‐charge ratios. Inorganic mass spectrometry is specifically used to determine the elemental and isotopic composition of the material being analyzed. The techniques are capable of the measurement of a range of concentrations from major components to ultratrace constituents.
Several instrumental approaches are used to separate and measure the abundance of component ions formed from the sample. These techniques include electron ionization mass spectrometry (EIMS), inductively coupled plasma mass spectrometry (ICPMS), thermal ionization mass spectrometry (TIMS) and spark source mass spectrometry (SSMS). These techniques utilize a variety of mass spectrometers including ion trap, quadrupole, magnetic sector and time‐of‐flight mass analyzers, depending on the type of sample being analyzed and the desired quality of the results. Often sample introduction techniques can be utilized to enhance the capabilities for solving specific analytical chemistry problems.
Secondary Ion Mass Spectrometry as Related to Surface Analysis
Authors: Hanton Scott D. , Cornelio Clark Paula A. 
Published: September 2006

Abstract

Many important processes such as catalysis, corrosion, and adhesion depend on the elemental and molecular composition of the surface or interfacial region. The focus of this article is specifically surface applications of secondary ion mass spectrometry (SIMS). Conceptually, SIMS is a very simple technique consisting of a primary ion bombardment step, an energy transfer step, a particle desorption step, and an ion detection step. SIMS experiments are carried out in either a dynamic or a static mode. The two modes are distinguished on the basis of ion dose. Dynamic SIMS uses high primary ion beam doses and is generally used for elemental depth profiling. Static SIMS uses low primary ion beam doses (≤1 × 10
12
ions cm
−2
) and is generally used for the chemical characterization of surfaces. The major advantages of SIMS include high sensitivity (parts per million detection limits for some elements), the ability to obtain molecular information, isotopic analysis, lateral characterization (imaging), and analysis of low‐atomic‐number elements such as H and Li. These characteristics combine to make SIMS a very powerful analytical tool. The key disadvantages of SIMS are that the instrumentation is relatively expensive and that the data can be complex. Related analytical techniques for surface analysis include X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Scanning Auger Microscopy (SAM), and laser desorption mass spectrometry (LDMS).
Chemical Shifts in Nuclear Magnetic Resonance
Authors: Van Bramer Scott E. 
Published: September 2006

Abstract

This article explains a variety of methods used to calculate
13
C and proton (
1
H) chemical shifts for alkanes, alkenes, aromatic compounds, and cyclic compounds. Additivity rules, which account for the effect of different functional groups, are used to calculate chemical shifts for a wide range of compounds. Example calculations are provided for each rule, to clarify the use and for comparison with experimental results. The chemical shifts calculated with these rules are typically accurate to ±10 ppm for
13
C nuclear magnetic resonance (NMR) and ±0.5 ppm for
1
H‐NMR.
Nuclear Magnetic Resonance Instrumentation
Authors: Neiss Thomas G. 
Published: September 2006

Abstract
A nuclear magnetic resonance (NMR) spectrometer is composed of a magnet, a sample probe, a transmitter and receiver, and a computer for instrument control and display of results. Magnets used in NMR spectroscopy are predominantly superconducting solenoid systems, in which a wire coil is immersed in liquid helium to render it superconducting. An electric current is passed through the coil and produces a static magnetic field proportional to the size of the current. The magnet has an open bore that has shim coils to compensate for imperfections in the magnetic field and in the sample probe coils. Liquid samples with a deuterated solvent are placed inside this coil.

An array of high‐power radiofrequency (RF) transmitter channels is also necessary to perturb the nuclear spin distribution from equilibrium through the use of strong RF pulses. A transmitter comprises an RF source, a phase modulator for determining pulse phases during an experiment, an amplitude controller and a solid‐state amplifier capable of pulses of up to several hundred watts. An excitation pulse tilts the net nuclear magnetization away from its equilibrium orientation parallel to the magnetic field axis, although it continues to precess around this axis. The precession induces a voltage in the probe coil that is tuned to the resonance frequency of the observed nucleus. One of the transmitters is part of a channel (known as a lock channel) that is dedicated to the detection of
2
H nuclei in deuterated solvents and is used to stabilize the magnetic field and permit the adjustment of field homogeneity. For both the observe and lock channels a high fidelity preamplifier and receiver are used to amplify and detect the signal and then route it to an analog‐to‐digital converter (ADC) and a noise filter system before converting it to a stored data file on a computer as a free induction decay (FID) signal. Software on the computer performs a Fourier transformation of the FID signal to convert the time base‐data into a frequency spectrum for interpretation.
Quadrupole Couplings in Nuclear Magnetic Resonance, General
Authors: Man Pascal P. 
Published: September 2006

AbstractNuclear magnetic resonance (NMR) spectroscopy is continually finding new applications. It enables the local symmetry to be probed at the atomic scale using the nuclear spins I of the compound under investigation. The nuclear spin is either a half‐integer (or odd) number or an integer (or even) number. The nuclei in the periodic table can be divided into two parts – spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclei and spin larger than$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclei. The spin larger than$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclei are called quadrupole nuclei because they possess an electric quadrupole moment which interacts with the electric‐field gradient (EFG) generated by its surroundings. By extension, their spins are called quadrupole spins. Spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclei are not sensitive to the EFG. Of the nuclei that possess a spin, 6% have integer quadrupole spins and 66% have half‐integer quadrupole spins.This article focuses on the half‐integer quadrupole spins ($\def\tovr#1#2{{\scriptstyle{#1\over #2}}} {\hbox{I}} = \tovr{3}{2},\ \tovr{5}{2},\ \tovr{7}{2}$, and$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{9}{2}$) in single crystals and in powder compounds. Most of these spins are observable. As they are multi‐energy‐level systems (the number of energy levels is 2I + 1), multiple quantum (MQ) transitions occur during excitation of the spin system by a radiofrequency (RF) pulse sequence. As a result, quantum mechanical concepts are needed for an understanding of the spin dynamics and for interpretation of the results. In particular, the choice of pulse sequence and the experimental conditions, such as pulse duration, pulse strength, and phase cycling in the pulse sequence, depend on the strength of the EFG surrounding the nuclear spin.
Quadrupolar Nuclei in Solid‐State Nuclear Magnetic Resonance
Authors: Freude Dieter 
Published: September 2006

AbstractSolid‐state nuclear magnetic resonance (NMR) spectroscopy is mostly applied to1H or13C nuclei with the nuclear spin$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} I = \tovr{1}{2}$, but about 100 of 130 NMR isotopes have$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} I > \tovr{1}{2}$, and the electric quadrupole interaction strongly broadens the NMR signal in the solid‐state powder spectra. The perturbing effect of the electric quadrupole interaction is reduced at the higher magnetic fields which are available at present. In addition, approaches of the solid‐state NMR traditionally used in the study of spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclei have been adapted for use with quadrupolar nuclei, and some techniques, e.g. double‐rotation (DOR) and multiple‐quantum transition in combination with fast spinning [multiple‐quantum magic‐angle spinning (MQMAS)], were recently developed for quadrupolar nuclei with half‐integer spins.This article describes the basic theory, the line shape for first‐ and second‐order quadrupole broadened spectra with and without magic‐angle spinning (MAS) of the powder, the most important experimental techniques for the study of quadrupolar nuclei with half‐integer spins such as DOR, dynamic‐angle spinning (DAS), MQMAS, echo and nutation techniques, and some recent developments in deuterium NMR. Electric field gradient and chemical shift data for the most commonly studied quadrupolar nuclei with half‐integer spins,27Al,23Na, and17O, and a few references to recent solid‐state NMR studies of some other quadrupolar nuclei are given.
Scalar Couplings in Nuclear Magnetic Resonance, General
Authors: Lee Jo Woong 
Published: September 2006

Abstract
Indirect spin coupling refers to the magnetic interaction operative between a pair of magnetic nuclei in a molecule that is mediated by bonding electrons. The anisotropic part of this interaction averages out to zero when the internuclear vector connecting the two nuclei randomly changes its orientation in the isotropic fluid state as does the direct magnetic dipolar interaction between the same pair of nuclei which operates through space. The isotropic part, which is usually called the scalar spin coupling, survives such random modulations of the internuclear vector in the fluid state to give rise to splitting of the nuclear magnetic resonance (NMR) lines which would otherwise represent a mere collection of individual absorption lines corresponding to the chemical shift of each constituent spin. Adequate analysis of the multiplet structure of the NMR spectrum arising from a given set of nuclear spins can provide knowledge of the scalar coupling between each pair of nuclear spins which in turn yields a wealth of information on molecular structure as well as molecular processes occurring in the system.
Solid‐State Nuclear Magnetic Resonance: Spin‐1/2 Nuclei Other than Carbon and Proton
Authors: Wu Gang 
Published: September 2006

AbstractSolid‐state nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique with a wide range of applications in chemistry, biochemistry and materials science. Solid‐state NMR is amenable to studies of molecular systems that are not suitable either for liquid‐state NMR because of insolubility or for single‐crystal diffraction techniques because of poor crystallinity. Therefore, solid‐state NMR provides a natural connection between liquid‐state NMR and single‐crystal diffraction techniques. Furthermore, solid‐state NMR is the best way of studying the anisotropic nature of nuclear magnetic properties, thus potentially yielding more complete information about molecular structure and chemical bonding. This article provides an overview of the fundamental principles of solid‐state NMR with selected examples of chemical applications. Emphasis is placed on the fundamental information and practical aspects of solid‐state multinuclear NMR experiments for the following spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclei:15N,29Si,31P,77Se,113Cd,199Hg,117Sn,195Pt,207Pb,57Fe,89Y,109Ag and183W. A brief introduction to the second‐order quadrupolar effect on spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$NMR spectra is also provided.
Solution Nuclear Magnetic Resonance: Spin‐1/2 Nuclei Other than Carbon and Proton
Authors: McGregor Mike 
Published: September 2006

AbstractThere are 22 spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclei other than hydrogen and carbon, some with more than one spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$isotope. Four of these,15N,19F,29Si and31P, have been of major importance in chemistry and nuclear magnetic resonance (NMR) and are the subject of an extensive literature. Many spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclides have had more specialized uses, such as3H,77Se,109Ag,113Cd,119Sn,125Te,129Xe,195Pt,205Tl, and207Pb. A few have been of limited use, generally due to poor sensitivity:57Fe,89Y,103Rh,169Tm,171Yb,183W,187Os and199Hg.Spin‐$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$nuclei generally produce sharp spectral lines, which may allow a wealth of fine structure from spin–spin coupling to be observed. This coupling, along with chemical shift information and dipolar coupling information (nuclear Overhauser effect (NOE)) are used in a variety of ways to obtain structural information and solve chemical problems.After a brief discussion of analytical techniques, the history, experimental practices, physical properties, relaxation properties, chemical shift referencing, applications and literature references for each nuclide are presented.
Z
eeman Interaction in Nuclear Magnetic Resonance
Authors: Dybowski Cecil 
Published: September 2006

Abstract
The Zeeman interaction is the physical phenomenon underlying the coupling of magnetic moments to magnetic fields. Its effects are detected in the features of spectra of samples taken while the sample is immersed in a magnetic field. Specifically, the features of nuclear magnetic resonance (NMR) spectra depend strongly on the coupling of nuclear spins to various sources of magnetic field.
Elastic Recoil Detection Analysis
Authors: Trocellier Patrick 
Published: September 2006

AbstractIn 1976, a Canadian group described in detail for the first time a new ion beam analytical method based on the elastic recoil of target nuclei collided with high energy heavy incident ions. In this case 25–40‐MeV35Cl impinged on a multilayer C or Cu (backing)/LiF or LiOH/Cu (30–150 nm)/LiF or LiOH and H, Li, O and F recoiled atoms were detected. These exemplified the main characteristics of elastic recoil detection analysis (ERDA): its sensitivity to depth distribution and its ability to detect light elements in heavy substrates. In 1979, the use of megaelectronvolt energy4He beams permitted the use of ERDA to be extended to depth profiling of hydrogen isotopes in the near surface region of solids.ERDA has rapidly been revealed to be an excellent alternative to resonant nuclear reaction spectrometry for hydrogen determination in solids. Despite its less advantageous performance with respect to its lower depth resolution, lower analyzable depth, comparable sensitivity and more restricting irradiation and detection geometry, some ERDA features have made its development in ion beam analysis (IBA) laboratories worldwide easier; these are simultaneous access to1H and2H depth distributions, access to single‐ended Van de Graaff accelerators compared with tandem or cyclotrons, the ability to be combined with Rutherford backscattering spectrometry (RBS) and a less damaging effect on the investigated targets compared to those generated by heavy ions.The development of detection devices and the analytical capabilities offered by high‐energy heavy ion‐induced ERDA in material sciences for profiling light, medium and large mass number elements give this method a wide area in which to progress as illustrated by discussions at ion beam‐related technique conferences.
Nuclear Reaction Analysis
Authors: Demortier Guy 
Published: September 2006

Abstract
Nuclear reaction analysis (NRA) is one among the numerous analytical techniques involving the irradiation of a material with energetic particles. In NRA methods we exclude any remnant radioactivity together with interactions leading to the scattering of the incident particle only: this last procedure leads to RBS (Rutherford backscattering spectroscopy) and ERD (elastic recoil detection).
In NRA the nature of the emitted particle used as an analytical signal is obviously different from that of the incident one. In order to avoid permanent radioactivity, the energy of the projectile is maintained at a sufficiently low value (below 6 MeV, easily available using a small accelerator). Consequently, due to the large coulomb barrier around heavy nuclei, only light nuclei may be easily identified (atomic mass less than or equal to 30).
After discussing the kinematics and fundamentals of the interactions, we present examples of applications in material sciences, archaeological and biological materials.
PIXE
(Particle‐Induced
X
‐Ray Emission)
Authors: Mandò P.A. 
Published: September 2006

Abstract
Particle‐induced X‐ray emission (PIXE) is the most popular among the ion beam analysis (IBA) techniques, which are based on the use of the specimen to be analyzed as a target for a beam of accelerated particles. The detection of the radiation induced by the beam bombardment is then used to discriminate and quantify the presence of the different elements in the specimen. In PIXE, what is exploited is in particular the X‐rays emitted from the target, whose energies are characteristic of the emitting atomic species. After a general, simple description of the main features of PIXE, with a short historical overview and a brief comparison to other X‐ray fluorescence (XRF) techniques, the article covers in greater depth all the specific aspects of this “nuclear” technique. The basic aspects of X‐ray emission from the atoms are first recalled; then, the extraction of quantitative compositional data from thin and thick specimens is explained, and a discussion is given of the excellent performance of PIXE in terms of minimum detection limits (MDLs), and of the factors affecting them. A technical description then follows of how proper beams for PIXE are produced and of the experimental set‐ups commonly used, with particular emphasis on the external‐beam arrangements. The X‐ray detector characteristics, the electronics for constructing the energy spectra, and the software processes for their deconvolution, leading to the extraction of quantitative data, are then briefly described. The last section surveys the main analytical applications of PIXE in various fields (environmental monitoring, biomedicine, earth sciences, cultural heritage), with no intent of exhaustiveness but rather with the purpose of focusing on when and why PIXE may be particularly suitable in each of them.
Radiochemical Neutron Activation Analysis
Authors: Heydorn Kaj 
Published: September 2006

AbstractRadiochemical neutron activation analysis (RNAA) is a method for trace‐element determination based on the measurement of an indicator radionuclide, chemically separated from a neutron‐activated sample. Unlike instrumental neutron activation analysis (INAA) the RNAA is therefore not a nondestructive method, and at the same time the amount of work put into the analysis of each sample makes RNAA much more expensive than INAA. This is the cost that has to be paid for determining selected elements at much lower concentrations and superior accuracy, while maintaining matrix independence and most of the other excellent characteristics of INAA. One of these characteristics is the small self‐shielding during irradiation with neutrons, which opens the possibility of analyzing also large samples without any pretreatment.Particularly for the lowest levels of trace elements RNAA provides several important advantages over alternative analytical methods:the absence of a reagent blank, andthe corresponding insensitivity to contamination after activationthe controlled addition of carrier to avoid losses by adsorption etc., andthe corresponding possibility of determining chemical yield or recovery.When carefully and thoughtfully carried out, RNAA qualifies as a so‐called definitive method, one of the reasons being its direct traceability to a comparator of the pure element to be determined.