bluuebunny/crossref_metadata_2025_split huggingface dataset:
X‐Ray Photoelectron Spectroscopy in Analysis of Surfaces
Authors: Oswald Steffen 
Published: September 2006

AbstractX‐ray photoelectron spectroscopy (XPS) is an analytical technique that uses photoelectrons excited by X‐ray radiation (usually Mg Kα or Al Kα) for the characterization of surfaces to a depth of 2–5 nm. Elemental identification and information on chemical bonding are derived from the measured electron energy and energy shifts, respectively. The use of ultrahigh vacuum (UHV) during analysis requires special sample handling. Depth profiling is possible using ion sputtering.In contrast to the most popular surface analytical technique, Auger electron spectroscopy (AES), nonconducting material can be investigated, little material damage occurs, and the chemical shifts are easier to interpret. However, the lateral resolution of AES (typically 50 nm) is much greater than for XPS (50 µm for standard equipment, down to lower than 3 µm for dedicated instruments). The detection limit (of about 0.1 atom %) is not as low as for mass spectroscopic techniques, but the quantification from XPS peak area measurements is much better, even disclaiming standard sample measurements.This article briefly discusses the principles of the technique, sample requirements, and the typical measuring strategy. Possible information sources (elements, chemical bonding, depth and lateral distributions) are described and their quantification principles are summarized. The main part deals with typical applications relating to several material classes (metals, semiconductors, insulators, polymers) to give a feeling for the effectiveness of the method over a wide range of research and technological problems. A comparison with similar techniques is given as a summary.Technological developments in electronics, nanotechnology, polymers, biotechnology and medicine are all concerned with surface‐related phenomena, suggesting sustained interest in XPS in the foreseeable future.
Background Correction Methods in Atomic Absorption Spectroscopy
Authors: de Loos‐Vollebregt Margaretha T.C. 
Published: September 2006

AbstractAtomic absorption spectroscopy (AAS) is based on the absorption of element‐specific primary source radiation by analyte atoms. If part of the radiation isabsorbed by molecules or lost due to scattering, a higher gross absorbance is measured. The difference between the net absorption of the analyte atoms and the measured gross absorbance is called background absorbance. Background absorption and scattering effects have much more serious effects on the results produced in electrothermal atomization atomic absorption spectroscopy (ETAAS) than flame atomic absorption spectroscopy (FAAS).The amount of incident light deflected or absorbed by nonatomic species must be measured to obtain the correct, net absorbance of the analyte atoms only. Perfect background correction can be obtained only when the background absorbance measurement corresponds exactly in space, time and wavelength with the atomic absorbance measurement. Since exact coincidence of all three parameters is obviously impossible, it is customary to give priority to the equality in space and to make the difference in time and/or wavelength as small as possible. Although molecular absorption and radiation scattering are both broad‐band phenomena, there is no spectral range where constant background attenuation can be guaranteed.In all background correction systems two measurements are made. The total or gross absorbance is measured at the wavelength of the resonance line emitted by the hollow cathode lamp (HCL). The background attenuation is then subtracted from the measured analyte absorbance to obtain the analyte absorbance. There are several ways in which the nonatomic absorption at the resonance wavelength can be estimated, including two‐line background correction, continuum‐source or deuterium lamp background correction, Zeeman background correction, pulsed lamp or Smith–Hieftje background correction and wavelength‐modulation correction methods. The principle of each method, the instrumentation and applications are discussed. Continuum‐source background correction is widely used in FAAS and ETAAS, whereas Zeeman background correction and pulsed lamp background correction are often preferred in ETAAS.
Flame and Vapor Generation Atomic Absorption Spectrometry
Authors: Amos M.D. 
Published: September 2006

AbstractAtomic absorption spectrometry (AAS) is a means of specific analysis for most of the metallic and metalloid elements. It achieves its specificity from the highly selective absorption, by free atoms of the analyte, of atomic emission of the same element at characteristic wavelengths. In its simplest form of application the free atoms of the analyte are created by aspiration of a solution of the sample to be analysed into a suitable flame, flame atomic absorption spectrometry (FAAS). The other principal means employed for the production of atoms (atomization) are graphite furnace atomization (GFAAS) and vapor generation atomization (VGAAS). Sample volumes of a few milliliters are normally needed for FAAS and VGAAS, but smaller volumes are needed for GFAAS. For most of the approximately 65 elements amenable to measurement by AAS, detection limits are from parts per billion to parts per million by flame methods and from parts per trillion to parts per billion levels by GFAAS and VGAAS. FAAS is inherently simple and rapid to use, whereas GFAAS and VGAAS are less rapid. The instrumentation used for AAS is relatively inexpensive Since all of these methods generally require the sample to be in solution form, the need for dissolution may be seen as a limitation in some cases. In the most common instrumentation employed, elements are only measured one at a time. It follows that for the determination of many elements in a large group ofsamples the method must be seen to be slow by comparison with multielement techniques such as inductively coupled plasma mass spectrometry (ICPMS) and inductively coupled plasma atomic emission spectrometry (ICPAES). However, the equipment costs involved for these techniques are generally higher and they are more complex to employ.
Glow Discharge Optical Spectroscopy and Mass Spectrometry
Authors: Steiner Robert E. , Barshick Christopher M. 
Published: September 2006

AbstractGlow discharge (GD) sources provide analytically useful gas‐phase species from solid samples. These sources can be interfaced with a variety of spectroscopic and spectrometric instruments for both quantitative and qualitative analysis. Optical (atomic absorption spectroscopy, AAS; atomic emission spectroscopy, AES; atomic fluorescence spectroscopy, AFS; and optogalvanic spectroscopy) and mass spectrometric (magnetic sector, quadrupole mass analyzer, QMA; quadrupole ion trap, QIT; Fourier transform ion cyclotron resonance, FTICR; and time‐of‐flight, TOF) instrumentation are well suited for coupling to the GD.The GD is a relatively simple device. A potential gradient (500–1500 V) is applied between an anode and cathode. In most cases the sample is also the cathode. A noble gas (e.g. Ar, Ne, Xe) is introduced into the discharge region prior to power initiation. When a potential is applied, electrons are accelerated toward the anode. As these electrons accelerate they collide with gas atoms. A fraction of these collisions are of sufficient energy to remove an electron from a support gas atom, forming an ion. These ions are, in turn, accelerated toward the cathode. These ions impinge on the surface of the cathode, sputtering sample atoms from the surface. Sputtered atoms that do not redeposit on the surface diffuse into the excitation/ionization regions of the plasma where they can undergo excitation via a number of collisional processes.GD sources offer a number of distinct advantages that make them well suited for specific types of analyses. These sources afford direct analysis of solid samples, thus minimizing the sample preparation required for analysis. The nature of the plasma also provides mutually exclusive atomization and excitation processes that help to minimize the matrix effects that plague so many other elemental techniques. Unfortunately, the GD source functions optimally in a dry environment, making analysis of solutions difficult. These sources also suffer from difficulties associated with analyzing nonconducting samples.In this article, the principles of operation of the GD plasma will first be reviewed, with an emphasis on how those principles relate to optical spectroscopy and mass spectrometry. Basic applications of the GD techniques will next be considered. These include bulk analysis, surface analysis, and the analysis of solution samples. The requirements necessary to obtain optical information will be addressed following the analytical applications. This section will focus on the instrumentation needed to make optical measurements using the GD as an atomization/excitation source. Finally, mass spectrometric instrumentation and interfaces will be addressed as they pertain to the use of a GD plasma as an ion source.
Laser Ablation in Atomic Spectroscopy
Authors: Russo Richard E. , Mao Xianglei , Borisov Oleg V. , Liu Haichen 
Published: September 2006

AbstractLaser ablation (LA) is a unique technique to transform a solid sample into vapor‐phase constituents, which then can be chemically analyzed by atomic spectroscopy. Ablation brings many exciting capabilities to the field of chemical analysis, primarily because of the laser‐beam properties. The ability to analyze directly any solid samplewithout sample preparation and minimal sample‐quantity requirements are just some of the unique capabilities. This article discusses current issues related to using LA in atomic spectroscopy. A general introduction to LA sampling is presented along with a comparison with other solid sampling techniques. The critical issues for all analytical techniques are calibration, accuracy, and sensitivity. Techniques that have been demonstrated to address these analytical characteristics and define these parameters for LA are investigated in detail. Finally, many unique applications are described, ranging from dating geological materials to providing crime‐scene evidence. Most of these applications could not be performed without the use of a laser beam. The inductively coupled plasma (ICP) will be emphasized in this article because it is currently the most prevalent excitation and ionization source for chemical analysis using LA.
Clustering and Classification of Analytical Data
Authors: Lavine Barry K. 
Published: September 2006

Abstract
Clustering and classification are the major subdivisions of pattern recognition techniques. Using these techniques, samples can be classified according to a specific property by measurements indirectly related to the property of interest (such as the type of fuel responsible for an underground spill). An empirical relationship or classification rule can be developed from a set of samples for which the property of interest and the measurements are known. The classification rule can then be used to predict the property in samples that are not part of the original training set. The set of samples for which the property of interest and measurements is known is called the training set. The set of measurements that describe each sample in the data set is called a pattern. The determination of the property of interest by assigning a sample to its respective category is called recognition, hence the term pattern recognition.

For pattern recognition analysis, each sample is represented as a data vector

x

= (x
1
, x
2
, x
3
, x

j

, …, x

n

), where component x

j

is a measurement, e.g. the area a of the jth peak in a chromatogram. Thus, each sample is considered as a point in an n‐dimensional measurement space. The dimensionality of the space corresponds to the number of measurements that are available for each sample. A basic assumption is that the distance between pairs of points in this measurement space is inversely related to the degree of similarity between the corresponding samples. Points representing samples from one class will cluster in a limited region of the measurement space distant from the points corresponding to the other class. Pattern recognition (i.e. clustering and classification) is a set of methods for investigating data represented in this manner, in order to assess its overall structure, which is defined as the overall relationship of each sample to every other in the data set.
Multivariate Calibration of Analytical Data
Authors: Wold Svante , Josefson Mats 
Published: September 2006

AbstractMultivariate calibration (MVC) is a methodology for using multiple signals, for instance a digitized spectrum, to determine the levels of concentrations of chemical compounds in analytical samples. MVC can also be used to determine other properties of interest, for instance viscosity, particle size distribution, energy content, or taste. MVC is made in two phases. In the first, the “training” or “calibration” phase, samples with known concentration (property) values and their signal profiles are used to develop a model of their relationship, a multivariate standard curve. In the second phase, this model is used with new samples to determine their concentration (property) values from their signal profiles.
Chemiluminescence, Electrogenerated
Authors: Bard Allen J. , Debad Jeff D. , Leland Jonathan K. , Sigal George B. , Wilbur James L. , Wohlstadter Jacob N. 
Published: September 2006

Abstract

Electrogenerated chemiluminescence (ECL) is the process in which electrogenerated species undergo electron transfer reactions to form excited states that emit light. Many molecules have the potential to produce ECL, however Ru(bpy)
3
2+
(bpy = 2,2′‐bipyridine) is the most common emitter used for analytical applications. Application of a voltage to an electrode in the presence of an emitter induces light production and allows for the detection of the emitter at very low concentrations. Advantages over other analytical methods include low backgrounds, precise spatial and temporal control over the emission, and the possibility of signal amplification. Commercial systems exist that use ECL to detect numerous clinically relevant analytes with high sensitivity using a variety of assay formats.
Ion‐Selective Electrodes: Fundamentals
Authors: Young Vaneica 
Published: September 2006

AbstractThis article begins with an introduction to ion‐selective electrodes (ISEs). The classification protocol based on the most recent International Union of Pure and Applied Chemistry (IUPAC) recommendations is given. The historical development of ISEs is summarized, starting with the pH electrode. For the inorganic cations and anions, a periodic table “time‐line” is given. Recent history has seen the rise of polymer membrane ISEs, which are important in clinical analysis. The historical section concludes with a brief look at these ISEs. The general theory of the potential generation process is explained, and then aspects of the potential generation process that are specific for the different classes of ISEs. A short review of the instrumentation needed to make the measurements is given, followed by an overview of the latest commercially available instrumentation. One aspect of ISE research is the development of selective probes for determining the analyte content of individual cells. This requires miniaturization, and this has been achieved by the development of microelectrode ISEs. An overview of this area is given. Finally, some recent developments that represent the directions of research in the ISE field are given. Included are the development of sensors for patient monitoring, the development of ISE sensor arrays, and the development of more sophisticated electronic and mathematical methods of data analysis.
Organic Electrochemical Mechanisms
Authors: Andrieux Claude P. 
Published: September 2006

Abstract
The determination of electrochemical mechanisms by electrochemical techniques is very efficient in organic electrochemistry. In contrast to the electrochemistry of small molecules and ions, the electron transfers on organic compounds are mainly outer‐sphere electron transfers following a Marcus–Hush law. Hence these fast electron transfers open up the possibility of obtaining kinetic limitation by the associated homogeneous chemical reactions.
The classical methods for these determinations are stationary techniques such as rotating disk electrode voltammetry (RDEV) and polarography but also more powerful methods, involving large‐amplitude transient methods: linear sweep voltammetry (LSV), cyclic voltammetry (CV) and double‐step chronoamperometry (DSC) allow the time window to be extended to thousands of microseconds; 1 µs can be reached with the use of ultramicroelectrodes. When the chemical reaction is the rate‐determining step, the response, i.e. current as a function of time (or potential), provides information about the nature of this reaction and in many case allows the measurement of its rate constant. Characteristic behaviors are detailed for the principal chemical reactions preceding (C + E) or following (E + C) the electron transfer.
Organic electrochemical mechanisms often involve several electron transfers. The influence of homogeneous electron transfers is underlined in particular for two‐electron reductions or oxidations and also in redox catalysis. The possibility of an electron transfer concerted with a chemical reaction is characterized. Some examples of mechanisms and kinetic determinations are given in the field of widely used organic electrosynthetic processes.
Pulse Voltammetry
Authors: Carter Michael T. , Osteryoung Robert A. 
Published: September 2006

AbstractThis article covers fundamentals and applications of pulse voltammetry. These techniques use a train of timed potential pulses to perturb the electrode–solution interface. Electron transfer reactions are driven at the electrode surface during each pulse. Current flowing as a result of electron transfer is measured at specified times during the pulse. Popular pulse voltammetric methods include normal pulse voltammetry (NPV), reverse pulse voltammetry (RPV), square wave voltammetry (SWV) and differential pulse voltammetry (DPV). Pulse voltammetry generally provides improved signal‐to‐noise ratio (S/N) and a decreased lower limit of detection (LLD) compared with continuous electrolysis methods such as cyclic voltammetry (CV), by controlling the extent of electrolysis prior to current measurement and discrimination against background processes. A concise discussion of the basic concepts behind thevarious pulse voltammetric methods is presented, followed by method‐specific discussions of the most popular methods. Instrumentation and practical experimental considerations are covered. Finally, a discussion of selected illustrative applications of pulse voltammetry to analysis and other chemical problems is presented, demonstrating the use of these techniques as a laboratory tool.
Selective Electrode Coatings for Electroanalysis
Authors: Klein Lee J. , Peters Dennis G. 
Published: September 2006

AbstractTremendous strides have taken place in recent years in our ability to modify electrodes chemically to enhance their selectivity and sensitivity for electroanalyses. Four different categories of selective electrode coatings have been chosen for discussion in this article: self‐assembled monolayers (SAMs); polymer coatings; Langmuir–Blodgett films; and immobilized enzymes. Each of these chemical modifications is discussed in terms of the necessary materials, the methods of preparation and characterization, and some examples of analytical applications.
Ultraviolet and Visible Molecular Absorption and Fluorescence Data Analysis
Authors: Neal Sharon L. 
Published: September 2006

Abstract
This article is a survey of the data analysis methods that have been applied to ultraviolet (UV) and visible molecular absorbance and fluorescence measurements. The section after the Introduction reviews the principles of the most widely used types of absorbance and fluorescence measurements. These include steady‐state, dynamic and multidimensional measurements. After a brief description of absorption and fluorescence instruments, three classes of data analysis methods for molecular absorbance and fluorescence are described: regression methods, decay analysis and matrix factorization methods. Result validation, software alternatives and future developments are discussed in short sections at the end of the article. A short matrix algebra primer is provided as an appendix to the article.
Detectors, Absorption and Luminescence
Authors: Acree William E. 
Published: September 2006

AbstractAbsorption and luminescence detectors convert radiant energy directly into an electrical signal or into another physical quantity, such as heat or resistance, which is subsequently converted into an electrical signal. Detectors are subdivided into three main categories depending upon their mode of operation. Thermal detectors sense the change in temperature that results from the absorption of incoming radiation. Photon detectors, on the other hand, respond to incident arrival rates rather than to photon energies. Multichannel detectors are arrays of multiple thermal detectors or arrays of multiple semiconductor detectors. Detectors of the third category permit simultaneous detection of dispersed radiation over a broad spectral wavelength region. Absorption and luminescent detectors are components in UV (ultraviolet)‐visible, infrared (IR) and atomic absorption spectrophotometers and in fluorescence, phosphorescence, Raman and atomic emission spectrometers.
Fluorescence Imaging Microscopy
Authors: Lemasters John J. 
Published: September 2006

AbstractIn fluorescence microscopy, an optical microscope creates a magnified image of the fluorescence and phosphorescence of specimens excited by light. Autofluorescence is the intrinsic fluorescence of a specimen, which is often weak. To enhance fluorescence, tags are added, such as fluorescently labeled antibodies which precisely localize specific molecular components. Living cells and tissues may be labeled with a variety of parameter‐indicating fluorophores to measure ion concentrations, electrical potentials and specific chemical species. Thick living specimens create problems of superimposition and haze from out‐of‐focus fluorescence, but advances in confocal fluorescence microscopy and multiphoton fluorescence microscopy now permit successful fluorescence imaging of thickliving specimens with submicrometer three‐dimensional resolution.
Fluorescence Lifetime Measurements, Applications of
Authors: Bright Frank V. , Pandey Siddharth , Baker Gary A. 
Published: September 2006

Abstract

Over the years, the emissive characteristics (spectral, temporal, and polarization) of fluorophores have been widely used to probe the local environments of fluorescent centers. Fluorescence lifetime and rotational reorientation time measurements, in particular, offer a means to elucidate subtle features when examining, for example, complex systems involving environmental heterogeneity, energy transfer, quenching pathways, or excited state reactions. Further, because fluorescence occurs on the nanosecond (10
−9
s) timescale, competing or perturbing kinetic processes like collisional quenching, solvent relaxation, energy transfer, and rotational reorientation can affect the fluorescence. Thus, a carefully chosen fluorophore can serve as an internal nanosecond or faster stopwatch of environmental fluctuations.

This article is divided into a brief introduction, a short discussion on instrumentation, and several sections on various applications of excited state fluorescence measurements.