bluuebunny/crossref_metadata_2025 huggingface dataset:
Clustering and Classification of Analytical Data
Authors: Lavine Barry K.
Published: September 2006

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

Multivariate 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

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

This 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

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

This 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

Tremendous 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

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

Absorption 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

In 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

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.
Fluorescence in Organized Assemblies
Authors: Hinze Willie L.
Published: September 2006

This article provides an overview of the general properties of organized assembly (ordered media) systems such as aqueous surfactant and bile salt micelles, lipid and surfactant vesicles (liposomes) and cyclodextrins (CDs) and summarizes their utilization to enhance the performance of analytical fluorescence measurements. In many instances, organic molecules and metal complex species, when included within a CD cavity or solubilized and bound to surfactant aggregates, exhibit enhanced fluorescence. This gives rise to improved detectability of such analytes. The altered microenvironment within the organized medium is capable of impeding the interfering action of other species (inorganic or organic) present in the sample matrix. This often can improve the selectivity of the analytical method. These benefits of improved sensitivity and selectivity arise from the compartmentalization, isolation and shielding of the excited singlet state of the guest analyte from quenching and nonradiative decay processes as well as prevent side reactions that otherwise can occur in bulk solution (or sample matrix). In addition, organic solvents or time‐consuming extraction steps can be avoided owing to the increased solubility of the nonpolar organic or inorganic reagents and/or analyte molecules in water in the presence of the organized medium; allowing for the use of an aqueous medium to perform the procedure. The possibility of conducting reactions and forming fluorescent organic or metal chelates in micellar (or other organized) media that are not observed in a bulk homogeneous solvent system serves to expand the scope of chemistries that one can consider using to design/develop new, unique and improved fluorescent assays. Numerous representative examples of fluorescent methods for determination of both organic and inorganic analytes are provided which serve to illustrate the advantages and benefits accrued from the use of the micelles, vesicles, liposomes or CDs in such procedures. Some experimental considerations and cautions to keep in mind when utilizing organized media are also delineated. An extensive reference section is provided so that the interested reader can easily refer to such for more detailed information on these systems and topics.
Near‐infrared Absorption/Luminescence Measurements
Authors: Swamy A.R. , Mason J.C. , Lee H. , Meadows F. , Baars M. , Strekowski L. , Patonay G.
Published: September 2006

The near‐infrared (NIR) region (600–1100 nm) offers several advantages in comparison with the conventional ultraviolet/visible (UV/VIS) region for spectroscopic measurements and detection. The lack of commercial instrumentation impeded the development of NIR techniques for years. The advent of inexpensive photodiodes and diode lasers used widely by the telecommunication industry gave the necessary impetus for development of analytical NIR techniques. This article describes the fundamental properties of NIR fluorophores and absorbers and provides a comparison with conventional UV/VIS dyes. The various analytical applications developed in the past decade that have utilized the advantages offered by this region are described with a particular emphasis on bioanalytical uses.
Absorption and Luminescence Probes
Authors: Acree William E.
Published: September 2006

Absorption and luminescence probes are molecules or ions whose spectral properties depend upon the chemical nature of the solubilizing media in the immediate vicinity of the probe molecule. Probe character is generally evidenced by the appearance of new spectral bands, shifts in the absorption or emission wavelengths, or by changes in emission intensities. Probe molecules have been used to determine solvent polarity and solvent acidity/basicity, pH, microviscosity, temperature and/or presence of specific ions/molecules. When combined with fluorescence lifetime measurements, absorption and luminescence probes can provide additional information regarding diffusion coefficients in probe excimer formation, fluidity in lipid vesicles, and rates of intermolecular collisions in quenching experiments.
Surface Measurements Using Absorption/Luminescence
Authors: Oldham Philip B. , Asanov Alexander N. , Rangnekar Vinay M.
Published: September 2006

The physical and chemical characteristics of surfaces along with the structure and dynamics of molecules near surfaces or interfaces have recently become critically important. Surface measurements have provided important information concerning the properties of the surfaces and the surface/adsorbate interactions. The physical, chemical and biological sciences have benefited tremendously from these studies, with significant developments being made in the areas of diagnostic devices, optical devices, electronic devices and sensors.

The specific behavior of macromolecules at or near surfaces, interfaces, and membranes is currently of primary interest in the biological sciences. Important applications include: adsorption of blood proteins on biomaterials in thrombogenesis research; the binding to and triggering of living cells by hormones, neurotransmitters and antigens; cell adhesion to various surfaces; the mechanism of electron transport in mitochondrial and photosynthetic membranes; and also reaction rate enhancement with membrane receptors by nonspecific adsorption and surface diffusion of ligands. However, investigation of biomolecular behavior at surfaces and interfaces remains a difficult task. Most of the common analytical methods available for investigation of surfaces either lack the extent of surface selectivity required or demand relatively harsh sample handling that severely limits the biological relevance of any results obtained. This article specifically describes ultraviolet/visible (UV/VIS) absorption and photoluminescence techniques applicable to analysis of surfaces or thin films.
Data Reduction in Gas Chromatography
Authors: Eiceman G.A. , Gardea‐Torresdey J.
Published: September 2006

The data obtained from a gas chromatographic measurement provide the user with details on both the quantitative and the qualitative composition of the sample. This information is displayed in the chromatogram from which information also can be gleaned concerning the performance and quality of the measurement. Quantitative determinations require attention to the relative response of the detector. The assignment of identity of individual constituents is possible in a formal sense only with authentic standards and mass spectra though retention times or indices can be indicators of identity. These aspects of data reduction have been understood for several decades and chemical information can be extracted from a chromatogram with ease and convenience.

In recent years, advanced chemometrics methods have been applied to chromatographic data with intrinsic advantages for probing patterns and trends too subtle or too complex for simple inspection of chromatograms. These methods are rooted in tools such as multivariate analysis and neural network analysis. Such methods are being developed in the area of natural products analysis.
Hyphenated Gas Chromatography
Authors: Coleman W.M. , Gordon Bert M.
Published: September 2006

Hyphenated gas chromatography (GC) refers to not only the coupling of a GC to information‐rich detectors but also the coupling of the gas chromatograph to automated sample preparation techniques. Examples of information‐rich detectors include mass and infrared spectrometers, whereas automated sample preparation techniques include solid‐phase microextraction (SPME), large‐volume injection (LVI), purge and trap (PT), headspace (HS), and gas chromatographic approaches. The gas chromatographic approach involves the wedding of two gas chromatographs and is commonly referred to as multidimensional gas chromatography (MDGC). The union of the automated sample preparation techniques with MDGC and information‐rich detectors affords the capability for quantitative and qualitative analysis of a wide variety of sample matrices for analytes at parts per billion (ppb) concentrations. However, not every hyphenated configuration is worth considering, and careful matching of the hyphenated approaches is essential to obtain the maximum analytical benefits.
Instrumentation of Gas Chromatography
Authors: Eiceman G.A.
Published: September 2006

Instrumentation for gas chromatography (GC) comprises well‐defined components, each of which contributes to the overall chromatographic performance. Most of these components have reached a mature level of technical development after nearly 50 years of development. Nonetheless, advances are occurring in an evolutionary, not revolutionary, manner with sample handling and in refinements of detectors. One area of dramatic advance in GC instrumentation is the development of small, sophisticated, portable gas chromatographs. Each component of a gas chromatograph (columns excepted) is discussed below where principles and recent developments are emphasized.
Liquid Phases for Gas Chromatography
Authors: Snow Nicholas H.
Published: September 2006

In gas chromatography (GC) the liquid phase, also called the stationary phase, provides the medium in which the separation occurs. The magnitude of separation is given by the relative strengths of intermolecular interactions between analyte and stationary phase molecules, thus numerous liquids have been used over the years. The stationary phase can be coated onto a solid support and packed into a tube (packed column GC), or coated onto the wall of a capillary (capillary GC). Today, most GC analyses are performed using capillary columns.
Spectral Data, Modern Classification Methods for
Authors: Mallet Yvette L. , Coomans Danny H. , de Vel Olivier
Published: September 2006

A major concern which arises from the classification of spectral data, such as near‐infrared (NIR) spectra, is that the number of variables often exceeds the number of cases. In this instance each spectrum represents a case or observation, and each variable corresponds to the wavelengths at which a response (e.g. reflectance) is measured. Classification refers to the process of assigning a spectrum whose class identity is unknown into one of several predefined classes. There are two main strategies for combating the high‐dimensional (i.e. more variables than cases) scenario. One strategy is to use a high‐dimensional classifier, that is, one which is suited to the ill‐posed nature of the data. The second strategy is to reduce the number of variables by a feature extraction method and supply the variables to a low‐dimensional classifier, one which is suited to high observation‐to‐variable ratios. This article presents two high‐dimensional classification methods – regularized discriminant analysis (RDA) and penalized discriminant analysis (PDA). The low‐dimensional classifiers used include Bayesian linear discriminant analysis (BLDA), Bayesian quadratic discriminant analysis (BQDA), RDA and flexible discriminant analysis (FDA). Common stepwise selection routines are employed to investigate the effectiveness of the wavelet transform as a feature extraction technique. This includes implementation of the local discriminant bases (LDBs) algorithm and the adaptive wavelet algorithm (AWA).
Emission Spectroscopy, Infrared
Authors: Keresztury Gábor
Published: September 2006

Infrared emission spectroscopy (IRES) is a branch of experimental infrared (IR) spectroscopy that can be considered as an alternative to the more commonly used IR absorption or reflection techniques for observing vibrational transitions in molecular systems. While these methods provide spectral data that are similar regarding their information content (structural, analytical), IRES may have definite advantages (or drawbacks) depending on the object to be studied.

This article aims at giving an up‐to‐date account of the theory, instrumentation and laboratory practice of IRES. Following an introduction to the principles and nature of thermal radiation, the governing laws of IRES are outlined and analyzed in some depth, with the aim of defining the conditions for obtaining analytically meaningful IR emission spectra. Spectral distortions concomitant with the measurement of condensed‐phase samples and other sources of error are pointed out along with the procedures devised for their elimination. Various methods of excitation of thermal radiation and the instrumentation most often used in laboratory measurements of IR emission spectra are described, with emphasis on modern Fourier transform (FT) techniques and with an outlook to special applications like remote sensing and process monitoring. Attention is given to data manipulation and presentation of emission spectra in relation to quantitative evaluation of spectral data. Recent advances in sample handling techniques, for example allowing the measurement of optically thick samples or thin surface layers, are also reviewed, while reference is given to the original sources of literature in the field.
Gas Chromatography/Infrared Spectroscopy
Authors: Le Quéré Jean‐Luc
Published: September 2006

Gas chromatography/infrared (GC/IR) spectroscopy coupling combines the separation power of high‐resolution gas chromatography (HRGC) to the highly specific identification technique, infrared (IR) spectroscopy, based on the absorption of IR radiation by the molecules. Relying on different molecular properties, IR is an excellent complement to mass spectrometry (MS) in structural analyses. For volatile compounds, the coupling of gas chromatography/mass spectrometry (GC/MS) has been the universal basic technique for a long time. The advantages of Fourier transform infrared spectrometry (FTIRS) allowed the coupling of gas chromatography (GC) to an FTIR (Fourier transform infrared) spectrometer, ending with a powerful tool, gas chromatography/Fourier transform infrared spectrometry (GC/FTIRS). The first device developed to interface a gas chromatograph to an FTIR spectrometer was a flow‐through gas cell, known as the light pipe (LP), delivering vapor‐phase IR spectra of eluting solutes. Two other cryogenic devices which allowed mobile‐phase elimination by trapping the compounds eluting from the GC at sub‐ambient temperature have been developed: the matrix isolation (MI) interface operating at 11 K and the direct deposition (DD) window operating at 77 K. Each of these three types of interface has advantages and drawbacks that are discussed in terms of sensitivity and specificity. Some selected applications in selected domains of analytical chemistry, i.e. environment, flavor and fragrances, pheromones and fatty acids, are presented and discussed again in terms of sensitivity and specificity according to the interface type used. Finally some concluding remarks on technique developments for GC/FTIRS and related techniques combining chromatography with IR spectroscopy are given.
Infrared Reflection–Absorption Spectroscopy
Authors: Hollins Peter
Published: September 2006

Infrared reflection–absorption spectroscopy (IRAS, IRRAS) is an optical technique used to study thin (often submonolayer) films adsorbed on reflective substrates such as metals. Experimentally, it involves measuring the change in the reflectance spectrum of the substrate that accompanies adsorption. In order to maximize sensitivity, the reflection is usually performed at grazing incidence. On metal surfaces, the process is subject to an overriding selection rule which states that only those vibrational modes that have a component of their dipole change perpendicular to the surface can be detected: application of this metal surface selection rule (MSSR) often yields important information about adsorption geometry. Other advantages of the technique include its high sensitivity (<10
−4
monolayers in favorable instances), its ability to operate under high ambient pressures where other primarily electron‐based surface spectroscopies cannot be utilized, and the ease with which its results can be correlated with those from other vibrational spectroscopies, both surface‐ and bulk‐sensitive. A significant current disadvantage is the difficulty in studying low‐wavenumber vibrations, but this is being overcome by the development of more intense far‐infrared sources. Various acronyms for the technique have been employed – IRAS, IRRAS and Reflection–Absorption Infrared Spectroscopy (RAIRS) have all enjoyed wide currency. The last of these is perhaps the most widely used and is the form advocated by the International Union of Pure and Applied Chemistry (IUPAC).1, 2 Accordingly, it will be adopted in this article.
Quantitative Analysis, Infrared
Authors: Cadet Frédéric , de la Guardia Miguel
Published: September 2006

In this article, after reviewing the different mathematical methods used in quantification we will describe and discuss their respective advantages and inconveniences. First of all, different examples of applications of infrared (IR) spectroscopy, used with or without other analytical chemistry methods, will be presented. Some examples of direct quantitative analysis in food analysis will be reviewed: lipids (measurement of unsaturation degrees, lipids determination), carbohydrates, proteins (secondary structures, quantitative analysis). We will also focus on original examples of the use of IR spectroscopy combined with enzymes.

Secondly, some examples of Fourier transform infrared (FTIR) analysis coupled with other analytical methods are reviewed in the following fields: FTIR quantification in pharmaceuticals, petroleum, paints and other industrial products and in the fields of health, environment, and trace compounds analysis.

Finally, we will discuss the limitations and perspectives of IR spectroscopy for quantitative analysis. It appears that the most significant developments in the field of quantitative analysis will most probably come through progress in chemometrics and flow analysis (FA) (automation).
Vibrational Spectroscopy for the Analysis of Geological and Inorganic Materials
Authors: Busca Guido , Resini Carlo
Published: September 2006

The vibrational spectroscopies are those producing the entire (or part) vibrational spectrum of a sample, i.e. the collection of transition energies between its vibrational states. The simplest way to cause vibrational excitation is to allow the chemical species in its vibrational ground state to absorb an energy quantum from electromagnetic radiation of an appropriate energy, i.e. in the medium infrared (IR) or in the far infrared (FIR) regions. Transmission–absorption IR spectroscopy comprises the analysis of the quanta that are actually absorbed by a polyatomic chemical species and those that are not absorbed (so are transmitted). Other IR techniques relate to the analysis of the radiation that is emitted, diffused, or reflected by the sample. Another way to obtain part or all of the vibrational spectrum of a chemical species is to look at the inelastic scattering of beams other than IR radiation. Raman spectrometry is the analysis of the ultraviolet (UV), visible or near infrared (NIR) radiation that is scattered inelastically by the sample. Inelastic neutron scattering (INS) is the analysis of the energy of formerly monochromatic neutron beams after inelastic scattering by the sample. Analyses of the number and energies of the vibrational transitions of the sample, detected by each technique, yield information on the geometric (molecular and crystallographic) structure of the sample and on the strength and nature of the chemical bonds it contains.
Biopolymer Chromatography
Authors: Huber Christian G.
Published: September 2006

Biopolymers are biological macromolecules including peptides, proteins, nucleic acids, and polysaccharides whose physical and chemical properties differ considerably from those of small molecules. Biopolymer chromatography is a branch of liquid chromatography which is adapted to the specific requirements of biopolymers in order to obtain rapid and high‐resolution chromatographic separations of these molecules. Because of the low diffusion coefficients of biopolymers, special stationary phase configurations and surface modifications are necessary to permit sufficiently fast mass transfer kinetics between the mobile and stationary phase. Exploiting different molecular properties of the biopolymers, such as size, charge, hydrophilicity, hydrophobicity, the ability to form complexes with metal ions, or biological function, the most popular liquid chromatographic modes for biopolymer separation are size‐exclusion, ion‐exchange, normal‐phase, reversed‐phase, ion‐pair reversed‐phase, metal‐interaction, and affinity chromatography.

Because of their large size and the multitude of different functional groups present in biopolymers, more than one mechanism may be responsible for interaction with the stationary phase, resulting in enhanced selectivity due to mixed‐mode interactions. Adsorption at multiple sites results in very steep elution isotherms as a function of the mobile phase solvent strength. Therefore, elution with a gradient of increasing solvent strength is usually applied in biopolymer chromatography. The choice of a suitable chromatographic environment is of special importance ifthe native confirmation of a biopolymer, which is essential for its biological activity, is to be preserved for subsequent experiments. Generally, conditions that come close to the physiological environment are most appropriate.

The most important detection techniques for biopolymers are ultraviolet/visible absorbance detection, fluorescence detection, electrochemical detection, mass spectrometry, and low‐angle laser light scattering photometry. Miniaturization and multidimensional separation together with mass spectrometric detection allow the routine separation and identification of femtomole–attomole amounts of hundreds to thousands of different biopolymers contained in complex mixtures of biological origin.
Ion Chromatography
Authors: Pietrzyk Donald J.
Published: September 2006

Ion chromatography (IC), which is an important methodology within high‐performance liquid chromatography (HPLC), is a chromatographic separation/detection strategy that is applied to the determination of inorganic and organic analyte anions and cations. The methodology consists of three main components: (1) a low‐capacity ion‐exchange column, where the separation occurs; (2) a suppressor system, which reduces conductivity due to the mobile phase electrolyte; and (3) a conductivity detector, which is used to detect the analyte ions. Anionic analytes are separated on an anion‐exchange column and analyte cations are separated on a cation‐exchange column. IC, which is routinely applied in water, environmental, health, and food analysis, is a rapid, sensitive, and accurate method for the trace determination of complex mixtures of analyte ions, particularly analyte anions, where no other method offers similar advantages and scope of application.

Today, the term IC defines a broader group of methodologies applicable to the separation of analyte ions and now also defines the following strategies. Nonsuppressed IC of analyte anions and cations is possible. In addition, analyte ions can be separated with an ion interaction reagent (ion pair reagent) as a mobile phase additive and a reversed stationary phase column rather than an ion‐exchange column; this is often called ion interaction chromatography (IIC). Ion exclusion chromatography (IEC), which is a separation of weakly dissociated acid and base analytes on an anion exchanger, is also an important methodology within the field of IC.
Normal‐Phase Liquid Chromatography
Authors: Cooper William T.
Published: September 2006

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

In 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

This 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

Chemical 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

This 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

With 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

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

Tandem 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.