bluuebunny/crossref_metadata_2025_split huggingface dataset:
Normal‐Phase Liquid Chromatography
Authors: Cooper William T. 
Published: September 2006

Abstract
Normal‐phase liquid chromatography (NPLC) is a technique that uses columns packed with polar stationaryphases combined with nonpolar or moderately‐polar mobile phases to separate the components of mixtures. The rate at which individual solutes migrate through NPLC columns is primarily a function of their polarity. Less polar solutes move the fastest and therefore exit the column and are detected first, followed by solutes of increasing polarity which move more slowly. However, polarity can sometimes play a secondary role relative to a solute's ability to experience a specific interaction with active sites on the stationary phase surface. The importance of these specific solute–stationary phase interactions in NPLC gives it some unique advantages over the more widely practised reversed‐phase liquid chromatography (RPLC) technique. RPLC utilizes nonpolar stationary phases and aqueous‐based polar mobile phases, and the elution order of solutes in a mixture is related to their hydrophobicity, not polarity; more polar solutes move the fastest and appear first, followed by solutes of decreasing polarity. RPLC is useful for separating mixtures in which components differ in molecular weight and/or water solubility. However, NPLC is preferred for many separation problems, including those in which the water solubility of sample compounds is limited. In addition, NPLC is a better technique for separating compounds that differ in the number or character of functional groups and is particularly useful for separating many types of isomers.
Silica Gel and its Derivatization for Liquid Chromatography
Authors: Neue Uwe D. 
Published: September 2006

AbstractIn this article, we review the preparation and use of silica and its derivatives in liquid chromatography (LC). First, the properties of silica that are important for its application in LC are examined, then bonded phases and coated phases based on silica are considered. The current state‐of‐the‐art of the preparation of bonded phases and coated phases is surveyed, and the properties that are relevant for the chromatographer are discussed. Owing to the popularity of reversed‐phase liquid chromatography (RPLC), most of the emphasis is placed on phases used in this technique, but other chromatographic techniques are not ignored. A detailed characterization of reversed‐phase packings is provided.
Artificial Intelligence and Expert Systems in Mass Spectrometry
Authors: Beavis Ronald C. , Colby Steven M. , Goodacre Royston , Harrington Peter de B. , Reilly James P. , Sokolow Stephen , Wilkerson Charles W. 
Published: September 2006

AbstractThis article provides a brief introduction to aspects of mass spectrometry (MS) that employ artificial intelligence (AI) and expert system (ES) technology. These areas have grown rapidly with the development of computer software and hardware capabilities. In many cases, they have become fundamental parts of modern mass spectrometers.Specific attention is paid to applications that demonstrate how important features of MS are now dependent on AI and ESs. The following topics are specifically covered: history, MS data systems, biological applications, artificial neural networks (ANNs), and optimization techniques.
Chemical Ionization Mass Spectrometry: Theory and Applications
Authors: Munson Burnaby 
Published: September 2006

AbstractChemical ionization mass spectrometry (CIMS) is a technique for forming ions of the compound of interest (analyte, A) by ion/molecule reactions from reactant ions of a reagent gas that is generally present in a much greater abundance than the analyte. The reactant ions are generally produced by electron ionization (EI) of the reagent gas. The ions produced by EI often react with the large excess of the reagent gas to form the actual reagent ions that react with the analyte. CIMS is performed with both positively and negatively charged reactant ions. The most common ion/molecule reactions in CIMS are proton transfer (which forms AH+or [A − H]−ions), hydride transfer (which forms [A − H]+ions), charge or electron transfer (which forms A+•or A−•ions), and adduct formation or attachment (which forms [A + R]+or [A + R]−ions). Fragment ions from decompositions of these AH+, A±•, [A − H]±, and [A + R]±ions are frequently observed. The extent of fragmentation can be controlled by the choice of reagent gas used and can be predicted to some extent from ionic thermochemical data. Collisionally stabilized electron capture at high pressures (to form A−•ions) is often classified as chemical ionization (CI). The most common use of CIMS in analytical mass spectrometry is to obtain simplified mass spectra of compounds, often one species spectra, which can be used for quantitative analysis of mixtures. CIMS can be performed with any type of mass spectrometer (quadrupole, magnetic, time‐of‐flight (TOF), Fourier transform ion cyclotron resonance (FTICR), ion trap) and CIMS capabilities are routinely available on many commercial instruments. With ion trap or FTICR mass spectrometers, it is possible to select specific reactant ions. It is generally considered that CI and EI sensitivities are approximately the same in the positive ion mode and that electron capture CI at high pressures for compounds with high electronegativities gives a much greater sensitivity than other EI or CI techniques. CIMS has the same general limitations as electron ionization mass spectrometry (EIMS) on the volatility and thermal stability of the compound being analyzed. However, direct insertion of the sample into the source of the mass spectrometer allows the analysis of relatively involatile and thermally unstable compounds.
Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
Authors: Marshall Alan G. , Hendrickson Christopher L. , Jackson George S. 
Published: September 2006

AbstractThis review offers an introduction to the principles and generic applications of Fourier transform ion cyclotron resonance/mass spectrometry (FTICR/MS), directed to readers with no prior experience with the technique. The fundamental Fourier transform ion cyclotron resonance (FTICR) phenomenon is explained from a simplified theoretical treatment of ion behavior in idealized magnetic and electric fields. The effects of trapping voltage, trap size and shape, and other nonidealities are then manifested mainly as perturbations that preserve the idealized ion behavior modified by appropriate numerical correction factors. Topics include: effect of ion mass, charge, magnetic field, and trapping voltage on ion cyclotron frequency; excitation and detection of ion cyclotron resonance (ICR) signals; mass calibration; mass resolving power and mass accuracy; upper mass limit(s); dynamic range; detection limit, strategies for mass and energy selection for multiple mass spectroscopy (MSn); ion axialization, cooling, and remeasurement; and means for guiding externally formed ions into the ion trap. The relationship of FTICR/MS to other types of Fourier transform (FT) spectroscopy and to the Paul (quadrupole) ion trap is described. The article concludes with selected applications, an appendix listing accurate fundamental constants needed for ultrahigh‐precision analysis, and an annotated list of selected reviews and primary source publications describing various FTICR/MS techniques and applications in fuller detail.
Isotope Ratio Mass Spectrometry
Authors: Krouse H. Roy 
Published: September 2006

AbstractWith the separation of two of the three stable isotopes of neon by Sir J.J. Thomson in 1913, mass spectrometers have continued to be the instrument of choice for measuring ratios of isotope abundances. The first magnetic sector mass spectrometer specifically dedicated to this task was designed by A.O. Nier in 1947 and featured simultaneous collection of ion currents. Many diverse instruments have evolved from this design. Decades of development of sample preparation techniques have realized isotope ratio data from many elements in solids, liquids, and gases. Coupling of devices such as gas chromatographs, combustion apparati, and laser probes to mass spectrometers in concert with computer control, have realized features such as unattended operation, compound‐specific isotope analyses and isotopic data spatially resolved over distances of a few micrometers on solid surfaces.Today, applications of isotope ratio mass spectrometry (IRMS) embrace many disciplines with topics such as paleodiets, food adulteration, paleoclimatology, migration of birds and animals, pollutant tracing, ore and oil deposits, meteorology, energy expenditure of animals, including astronauts, and the origin of the universe.
Liquid Chromatography/Mass Spectrometry
Authors: Klink Frederick E. 
Published: September 2006

Abstract
Liquid chromatography/mass spectrometry (LC/MS) is the combination of high‐performance liquid chromatography (HPLC) and mass spectrometry (MS) into a single, continuous‐flow analytical system. HPLC separates analytes from their matrix and from one another in a flowing system on a time basis. These separated analytes are removed from the solvent stream and introduced to the MS system through one of several types of available interfaces which facilitate ionization of the analyte molecules. MS is an analytical technique which separates these analyte ions on the basis of their mass‐to‐charge ratio (m/z). Data collected from LC/MS is a series of mass spectra taken over time as the chromatographic effluent exits the column and is analyzed by the mass spectrometer. The three interface types in common usage are particle beam (PB), atmospheric pressure chemical ionization (APCI) and electrospray interface (ESI). These interfaces differ in the characteristics of the mass spectra that they produce, the types of chemical compounds for which they are best suited and the interferences to which they are subject. With the combined capability of two of these interfaces, APCI and ESI, LC/MS is able to address nearly any type of organic molecule from small molecules to biological macromolecules. ESI has ushered in a revolution in biochemical research on large molecules although the technology itself is not completely understood and is subject to a variety of interferences. APCI is limited to smaller molecules and is most at home in routine use for very high‐throughput drug and metabolite analyses. The PB interface, although not as flexible as the other two, is able to produce electron ionization (EI) spectra which can be searched against standard, commercial libraries. ESI and APCI are not able to produce EI spectra but, through the use of collisionally activated dissociation (CAD), are able to produce usable spectra in both single‐stage and tandem mass spectrometry (MS/MS).
Tandem Mass Spectrometry: Fundamentals and Instrumentation
Authors: de Hoffmann Edmond 
Published: September 2006

AbstractTandem mass spectrometry (MS/MS) is a methodology which allows selection of ions of a given mass, fragmentation of these ions and detection of the fragments. It requires the use of dedicated instruments of different types. Some of them allow repetition of the ion selection step to fragment fragments further.This methodology allows structural information on pure compounds or on components of mixtures to be obtained. It also allows highly selective and sensitive detection of target compounds or of compound classes, even from complex mixtures. It is widely used in environmental analysis, pharmaceutical research, biotechnology, forensic science and toxicology, clinical analysis, organic synthesis, process control and many other areas.
Parameters, Calculation of Nuclear Magnetic Resonance
Authors: Jameson Cynthia J. 
Published: September 2006

AbstractThe fundamental parameters that reproduce a nuclear magnetic resonance (NMR) spectrum in gases, liquids, and solids are the four tensor quantities: the NMR chemical shift of the nucleus, the indirect nuclear spin–spin coupling, the nuclear electric quadrupole coupling, and the direct dipolar coupling tensors. The first three are intimately related to the local electronic structure at the nucleus and the chemical bonds connecting the nuclei. On the other hand, the direct nuclear spin dipole–dipole interaction depends directly and entirely on the third power of the inverse of the direct through‐space distance between two nuclei, whether bonded or otherwise. In gases and in liquids where free tumbling of the molecules bearing the nuclear spins leads to isotropic averaging of these quantities, only the isotropic average values, the average of three components along the principal axes of the chemical shift and the indirect spin–spin coupling tensors determine the observed frequencies in the NMR spectrum. In the solid state, restricted motion permits the tensors to manifest all the components, whether the sample is a polycrystalline powder, an amorphous solid, or a single crystal. Theoretical calculations of the NMR chemical shift, indirect spin–spin coupling, and nuclear quadrupole coupling parameters, using quantum mechanical methods, permit the prediction of NMR spectra and provide the physical basis for the relationship between the parameters and molecular electronic structure, which may include local electronic structure (electronic distribution in the immediate vicinity of the nucleus and neighboring bonds), local molecular geometry, bond connectivities, stereochemical structure, as well as subtleeffects of the chemical environment, such as contributions from remote parts of the molecule, tertiary and secondary structure, crystal packing, solvent effects, and isotopic substitution.
Relaxation in Nuclear Magnetic Resonance, General
Authors: Canet Daniel , Mutzenhardt Pierre 
Published: September 2006

AbstractRelaxation phenomena in nuclear magnetic resonance (NMR) govern the recovery of nuclear magnetization after it has been taken from its equilibrium state (i.e. along the static magnetic field direction). Various interactions, leading to local fluctuating magnetic fields, are responsible for the timescale of these phenomena. By themselves, these interactions yield valuable dynamic and structural information. Conversely, the influence of relaxation on the quantitative aspect of NMR spectra has to be assessed prior to any experiment aiming at using NMR as an analytical tool. This implies an evaluation not only of the relaxation parameters but also of indirect relaxation processes such as the nuclear Overhauser effect (NOE).
Two‐Dimensional Nuclear Magnetic Resonance of Small Molecules
Authors: Pedersen Henrik 
Published: September 2006

Abstract

The article deals with practical aspects in obtaining two‐dimensional (2‐D) nuclear magnetic resonance (NMR) spectra of small molecules [molecular weight (MW) < 1000]. This includes the choice of parameters for acquisition and processing and the required and optional instrument hardware. Examples of 2‐D experiments are given with emphases on robustness and ease of use. The pulse sequences are given in schematic form together with suggestions for basic parameters and the phase cycle. The experiment examples include homonuclear and heteronuclear experiments with direct and indirect detection. Also the use of pulsed field gradients (PFGs) is exemplified. 2‐D NMR on spin‐

$\def\tovr#1#2{{\scriptstyle{#1\over #2}}} \tovr{1}{2}$

nuclei other than
1
H and
13
C is exemplified by
19
F and
15
N experiments. Experiments on gel‐phase samples under magic angle conditions are mentioned briefly.
Charged Particle Activation Analysis
Authors: Strijckmans Karel 
Published: September 2006

Abstract
Charged particle activation analysis (CPAA) is an analytical method for elemental analysis. It is based on charged particle (CP) induced nuclear reactions producing radionuclides, that are identified and quantified by their characteristic decay radiation. CPAA allows trace element determination in the bulk of a solid sample, as well as characterization of a thin surface layer, i.e. determination of mass thickness or composition.
Advantages of CPAA are: (1) good precision, (2) low detection limit, (3) outstanding accuracy, (4) absolute, i.e. reference method, (5) independent, i.e. based on a totally different principle than more common methods for elemental analysis (atomic/optical emission and mass spectrometry), and hence not subject to the same systematic errors, (6) traceability, (7) not subject to surface contamination for trace element determination in the bulk, (8) if instrumental analysis is not possible it is not subject to reagent blank errors, and (9) errors due to nonquantitative yield (and even nonreproducible yield) can be corrected for. Disadvantages of CPAA are its inherent complexity and costs, it is not suitable for liquid samples, and heating occurs during irradiation. Speciation, depth profiling, or scanning is not possible.
This article covers (1) the principles on the slowing down of CPs in matter, nuclear reactions, and interferences; (2) experimental details concerning irradiation and activity measurement; (3) conceptual and experimental procedures and data handling, from the problem to the final result; (4) perspectives. References to relevant databases are made. A systematic overview of all possible CPAA applications is beyond the scope of this article.
Cyclic Activation Analysis
Authors: Hou Xiaolin 
Published: September 2006

Abstract
Cyclic activation analysis (CAA) is a method of activation analysis for elemental analysis in which a sample is irradiated, decayed, counted, then irradiated again, and this process is repeated for a number of cycles, the spectra from each counting being summed to give a final total spectrum. By this process, the counts of a short‐lived nuclide of interest are considerably increased and the analytical sensitivity of elements is significantly improved. The most commonly used CAA method is cyclic neutron activation analysis (CNAA) by irradiation with thermal, epithermal, and fast neutrons produced from a nuclear reactor, accelerator, or isotopic neutron source. A nuclear reactor can supply a very high neutron flux and is most often used for this purpose. At least 20 elements which produce short‐lived nuclides (half‐life less than 100 s) by thermal neutron bombardment, and also more than 10 elements which produce nuclides with half‐lives of 100–600 s can be determined by thermal and epithermal neutron CAA. This technique has been widely applied in biological, environmental, geological, and industrial studies, and the most often measured elements include Se, F, Pb, Hf, Sc, O, Ag, and Rh.
The advantages of CAA, as compared with conventional activation analysis, include significant improvements of the detection limits, analytical precision, and accuracy for the elements by using short‐lived nuclides, short experimental time, increased number of samples per unit time, a capability for the estimation or confirmation of the half‐lives of short‐lived nuclides and determination of the degree of homogeneity of samples. However, the application of CAA is limited by the number of elements determined, because only some of the elements determined by conventional activation analysis can be determined by this method. In addition, dead time and pile‐up are serious problems in CAA and must be corrected. The principle, selection of optimum experimental conditions, detection limit, and analytical precision of CAA, and also the dead time and pile‐up corrections, are discussed in this article.
Elemental Analysis by Isotope Dilution
Authors: Bahrainwala T.M. , Turel Z.R. 
Published: September 2006

AbstractThe measurement of extremely small traces of materials, which cannot be determined by normal analytical techniques, becomes possible and even relatively rapid and simple if the element can be made radioactive by the action of neutrons or charged particles. Nuclear techniques possess exceptional advantages in having extraordinary sensitivity, selectivity in detection and determination, speed and simplicity.One of the nuclear techniques applied in trace and ultratrace analysis is isotope dilution analysis (IDA) which was first introduced by Hevesy and Hobbie in 1932. The great advantage of the method lies in the fact that it can be used even when the procedure involves loss of material or does not allow a complete separation of the element or compound. The isotope dilution method has found several applications in the determination of geological ages, fission yields and other problems in nuclear physics and chemistry.Various techniques involved in IDA such as substoichiometry, liquid chromatography (LC) and radiometric titration are discussed along with the application of this technique to the estimation of elements in complex matrices as reported in the literature.
Particle‐Induced γ‐Ray Emission
Authors: Mutsaers P.H.A. , de Voigt M.J.A. 
Published: September 2006

Abstract
Particle‐induced γ‐ray emission (PIGE) is commonly applied for quantitative analysis of materials. γ‐Rays, characteristic of the elements, are emitted after nuclear reactions. These reactions are induced by particle beams (e.g. protons) from accelerators. The reaction conditions and probabilities are explained, as well as the γ‐ray properties and probabilities of emission. Knowledge of those parameters enables concentrations of elements to be deduced from the γ‐ray spectra, which under certain conditions are also depth dependent. Therefore the samples must be small and flat. The experimental set‐up and procedures are given together with a table with the most intense proton reactions and the energies of the emitted γ‐rays. Various examples are given to illustrate the method in different applications.
Prompt γ‐Neutron Activation Analysis
Authors: Oliveira Carlos , Salgado José , Carvalho Frederico G. 
Published: September 2006

Abstract
Prompt γ‐neutron activation analysis (PGNAA) is a multielemental analytical technique based on the detection of γ‐rays emitted by excited nuclei following neutron radioactive capture or neutron inelastic scattering. The accumulated count rate relative to the γ‐ray energy characteristic of a certain isotope depends on its concentration. Measurements take place during sample irradiation. The technique can provide accurate information on the elemental composition of materials in a broad range of cases: raw materials, mineral exploration, contaminants, detection of forbidden products, such as drugs and explosives, inspection of containers and applications in health care. Among the main advantages of the PGNAA technique are: faster results; nondestructiveness; flexible sample requirements; bulk sample analysis; in situ application by direct on‐line measurement; detectable unique signatures for most elements; improved accuracy for short‐lived elements; low residual activity. On the other hand, the most significant limitations are: higher detection limits (DLs) as compared with delayed γ‐neutron activation analysis (DGNAA); longer irradiation times; single (one‐cycle) sample irradiation; impracticability of enhancing a specific isotope contribution by radiochemical or physical (half‐life) separation techniques; requirement for relatively larger samples.
Rutherford Backscattering Spectroscopy
Authors: Kimura Kenji 
Published: September 2006

AbstractRutherford backscattering spectroscopy (RBS) is one of the most powerful techniques for measuring elemental depth profiles. It allows quantitative and nondestructive analysis with a reasonable depth resolution. In conventional RBS (combination of 1–4 MeV He ions with a silicon surface‐barrier detector), the typical depth resolution is about 10 nm and the typical mass resolution is about 1 u for light elements (mass numberM < 20) and about 20 u for heavy elements (Mca. 200). Sensitivity of 100 ppm can be easily obtained for heavy elements in light hosts although analysis of light elements in heavy hosts is difficult. In the present article, physical concepts which RBS relies on are briefly introduced. Some examples of analyses are demonstrated and several advanced techniques which have been developed to improve capabilities of the conventional RBS are discussed.