bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sample Preparation for Gas Chromatography
Authors: Torkos Kornél 
Published: September 2006

Abstract
The success of a gas chromatographic analysis mostly depends on the sample preparation procedure. Biological and environmental samples are not suitable for direct analysis. Organic analytes can be separated from matrixes by extraction methods such as gas–solid, liquid–liquid, solid–liquid, purge‐and‐trap, headspace, solid‐phase (SPE), solid‐phase microextraction (SPME), supercritical fluid (SFE) and Soxhlet extractions. These extraction methods are called phase separation methods. Matrix solid‐phase dispersion (MSPD) is a special highly efficient phase separation procedure for biological matrixes such as meat, liver, muscle, vegetables, etc. The aim of the extraction procedure is not only separation of organic analytes from matrixes but also concentration in another phase.
If the organic analytes contain protic (active) hydrogen (alcohols, carboxylic acids, amines, oxo compounds, etc.) some derivatization reactions, such as acylation, alkylation and silylation, need to be carried out first. The aim of the derivatization methods is to increase the sensitivity of detection and thermal stability of the organic analytes. The other aspect of derivatization is to reduce the polarity of the compounds.
Theory of Infrared Spectroscopy
Authors: Turrell George 
Published: September 2006

Abstract
This article is devoted to the fundamentals of infrared spectroscopy. While it is well known that infrared spectroscopy is an extremely important analytical technique, its theoretical basis is not easily assimilated by most analytical chemists. It must be admitted that a certain understanding of abstract concepts, such as those encountered in quantum mechanics, is required. However, with all apologies to the reader, it is the objective here to present the essentials of these ideas, as needed in analytical applications of infrared spectroscopy. It should be noted that most of these principles apply equally to Raman spectroscopy, a subject which is described in other articles.
It is the Born–Oppenheimer approximation that provides the theoretical basis for the analysis of infrared spectra. The rotational and vibrational degrees of freedom of a molecule are specified to allow the spectra of molecules in the gas phase to be interpreted. It is shown that the logical extension of these arguments can be employed in the analysis of the spectra of liquids and crystalline solids.
In later sections, an effort has been made to explain how the basic ideas developed earlier can be applied to the interpretation of the infrared spectra of hydrogen‐bonded molecules, polymers and amorphous systems. A brief description of the notion of characteristic group frequencies, as routinely employed in organic chemistry, has been included to allow the practicing chemist to appreciate the possibilities – as well as the limitations – of this most important approach to the subject. To advance his appreciation of the advantages of infrared spectroscopy in analytical chemistry, the reader should refer to the various applications, as listed at the end of this article.
Microspectroscopy
Authors: Lang Patricia L. 
Published: September 2006

Abstract

The essential features of an infrared (IR) microscope accessory include

reflective optics for focusing, collecting, and imaging transmitted or reflected IR radiation from the sample onto a detector,

one or more variable apertures located in an image plane of the sample which serve to define the area to be recorded, and

a visible light path which is parfocal and collinear with the IR light path so that the sample can be viewed and positioned.

The accessory is coupled to a Fourier transform IR (FTIR) spectrometer by a set of transfer optics from the interferometer into the microscope.

IR microspectroscopy provides the analyst with the capability to perform IR transmission, absorption‐reflection, specular reflection, and diffuse reflection experiments on microscopic samples. Using special microscope objectives or accessories, attenuated total reflection (ATR) and grazing angle reflection experiments can be performed as well. IR microspectroscopy can also be used to map a sample's heterogeneity using a motorized stage in conjunction with a standard mercury cadmium telluride (MCT) detector. Alternatively, spatial and spectral information can be collected simultaneously using a step‐scan interferometer coupled with an IR microscope and a focal plane array (FPA) detector. In either case, the superior contrast attained by functional group imaging and the selectivity found in the mid‐IR region has been shown to be a powerful analytical tool.
However, diffraction ultimately limits the quality of the spectral information obtained using the IR microscope, and its effects may include poor spatial resolution, a reduction in photometric accuracy, and unreliable band intensities. Furthermore, unwanted optical effects from microscopic samples can also affect the quality of the spectrum, and sample preparation techniques must often take into account a sample's thickness, diameter, refractive index, and shape.
Kinetic Determinations: Introduction
Authors: Mottola Horacio A. 
Published: September 2006

AbstractThis introduction opens by discussing the distinction between kinetic and thermodynamic determinations. After defining equilibrium, pseudo‐equilibrium, and dynamic measurements, a historical perspective is given that covers early tests and publications to the present overall scope of kinetic determinations. In closing, a listing of selected bibliography is presented; this follows a short narrative emphasizing that kinetics goes beyond determinations in analytical chemistry.
Data Treatment and Error Analysis in Kinetics
Authors: Baeza‐Baeza Juan J. , Pérez‐Pla Francisco F. 
Published: September 2006

Abstract
Methods of data treatment in kinetics are reviewed from a practical viewpoint. The equations to describe the kinetics of chemical reactions and the methodology to obtain the models are presented. Moreover, the integration methods that are needed for the simulation of complex reactions are explained, from the simple first‐order reaction to the complex general mechanism.
However, it is essential to know the main sources of error in data treatment in order to reduce their effects on the results. Stress is put on the analysis of the errors due to the simplification of complex models. The different factors that influence the kinetics of the reaction are reviewed. How to take advantage of the kinetic information contained in the experimental data with an analytical aim is described. Finally, the propagation of errors in the analytical results is studied, reviewing both the simple univariate methods, used to determine one species, as well as the complex multivariate methods devoted to the determination of multicomponent mixtures.
Enzymatic Kinetic Determinations
Authors: Hüttl Regina 
Published: September 2006

AbstractKinetic methods for analytical applications can be divided into noncatalytic and catalytic methods. Enzyme kinetic determinations are a special type of catalytic methods. Enzymatic reactions are used analytically to determine enzyme activities – for instance in the diagnosis of diseases, substrate concentrations in food industry or medicine and concentrations of effectors – for example in trace analysis. Due to the high selectivity of enzymatic analysis the importance of this method in various fields is growing rapidly. The widest use is observed in clinical chemistry and in food chemistry.This article can only give a general survey of the great potential of enzymatic analysis, with references to more detailed literature.Enzymatic reactions are characterized by some special features, explained after the introduction. The theoretical background for kinetic determination is the comprehension of the principles on enzymatic kinetics. In section 3 the simplest mechanism, outlined by Michaelis and Menten and several transformations of this equation will be described. In this section two kinetic parameters, enzyme activity and the Michaelis constant, will be introduced. Section 4 deals with substances, so called effectors, influencing the rate of an enzymatic reaction. Simple mechanisms of these effectors will be shown. The different methods for determination of substrates, enzymes and effectors, illustrated by many examples, are represented in section 5. While substrate concentrations can be determined using both ways, equilibrium or kinetic methods, the determination of enzymes and effectors can only be performed by kinetic approaches. In the last two sections the application of immobilized enzymes in flow systems and biosensor development will be shown.
Uncatalyzed Kinetic Determinations
Authors: Koupparis Michael A. 
Published: September 2006

Abstract
Analytical procedures in which the measurement step (chemical, physical or physicochemical) is influenced by a transient (kinetic) process, can strictly be classified as kinetic method. Thus, the majority of modern analytical methods (continuous‐flow, time‐resolved fluorimetric and chromatographic methods, among others) are kinetic in nature. Nevertheless, the term “kinetic method”, for historical reasons, is incorrectly limited to methods based on direct or indirect measurements of the rate of a chemical reaction, which should be classified as “reaction‐rate methods”. Analytical methods based on signal measurements made under dynamic conditions compete in efficiency with static and equilibrium measurements. The growing development of kinetic methods is due to the need for quantification of microamounts of substances, increasing knowledge of reaction mechanisms, and breakthroughs in instrumentation and data handling and interpretation. The most popular classification of kinetic methods of analysis is based on the chemistry of reactions employed and distinguishes between catalytic (nonenzymatic, enzymatic and electrochemical), and noncatalytic methods. The latter are further categorized into those used to determine a single species or several components in mixtures (differential reaction‐rate methods). This article deals with kinetic methods for the determination of single noncatalytic species. Although the majority of kinetic‐based determinations depend on catalytic systems, some analytical applications using the rate of uncatalyzed reactions are of analytical interest, mainly those involving organic chemical species. Advances in instrumentation: (1) improved signal detection, (2) resolving of problems arising from time measurements especially in fast processes, and (3) availability of automated mixing devices and data processing (error‐compensated methods, curve‐fitting and predictive approaches) establish noncatalytic methods as powerful alternatives to equilibrium methods. The main field of application of noncatalytic reactions is organic analysis, unlike catalytic reactions where a metal ion usually acts as the catalyst.
Affinity Chromatography
Authors: Hage David S. 
Published: September 2006

AbstractAffinity chromatography is a type of liquid chromatography that makes use of biological‐like interactions for the separation and specific analysis of sample components. This article discusses the basic principles behind the theory and use of this method. Various factors that are important in the development of an affinity chromatographic system are considered, such as the choice of affinity ligand, support material, immobilization method, and elution conditions. A survey of the different types of affinity chromatography is also presented; this includes bioaffinity chromatography, immunoaffinity chromatography, dye–ligand affinity chromatography, immobilized metal affinity chromatography, and analytical affinity chromatography. In addition, some areas of expected future growth are considered, such as the use of molecular imprints or aptamers as ligands in affinity columns, and the coupling of affinity chromatography with other analytical techniques.
Gradient Elution Chromatography
Authors: Dolan J.W. , Snyder L.R. 
Published: September 2006

Abstract
Elution chromatography can be carried out in either isocratic or gradient modes. In isocratic elution, the mobile‐phase composition is held constant during separation of the sample, e.g. 60% v acetonitrile–water. In gradient elution, the mobile‐phase composition will be varied during sample separation, e.g. changing from 0 to 100% v acetonitrile–water. Gradient elution requires special chromatographic equipment, as well as somewhat greater care on the part of the operator, but it has important advantages for many separations. Thus, in isocratic elution (Figure 1a), sample peaks tend to “bunch up” at the beginning of the chromatogram (often with decreased resolution) and to broaden at the end of the chromatogram (with reduced detection sensitivity). Gradient elution (Figure 1b), on the other hand, provides a more even spacing of peaks, similar widths throughout the chromatogram, and often a shorter run time. For these and other reasons, gradient elution is preferred for the separation of many samples.
Micellar Electrokinetic Chromatography
Authors: Pyell Ute 
Published: September 2006

Abstract
Micellar electrokinetic chromatography (MEKC) is a highly efficient miniaturized separation technique that is performed with the same experimental set‐up that is used with capillary electrophoresis (CE). While the separation principle of CE is based on differences in the electrophoretic mobility of the solutes to be separated (only charged species can be separated), in MEKC separation is also based on differences in the distribution constants between two phases migrating at different velocity due to electrokinetic effects. The second phase is introduced into the separation electrolyte by adding an ionic surfactant (anionic or cationic) at a concentration above the critical micelle concentration (CMC). Aggregates of surfactant monomers (micelles) are present in the separation electrolyte. These aggregates have an electrophoretic mobility and are able to incorporate solutes or interact strongly with species dissolved in the surrounding medium.
MEKC extends the applicability of CE to neutral solutes. In addition, MEKC has been proven to be superior to CE in the separation of very complex mixtures of solutes with similar electrophoretic mobility, because of the various factors that are available for the manipulation of separation selectivity. Currently, MEKC can be regarded as a separation technique with a similar scope to that of reversed‐phase high‐performance liquid chromatography (RPHPLC), having advantages over the latter concerning the efficiency of the separation system, separation speed, cost and tolerance to matrix constituents, as in MEKC no stationary phase is present that can be fouled by irreversible sorption of matrix constituents of the sample. Owing to the small injection volume (a few nanoliters) and small detection volume that is necessary to avoid intolerable instrumental band broadening, current MEKC instrumentation restricts the applicability of MEKC to the determination of those compounds in complex mixtures that are present in concentrations sufficiently high with respect to the limits of detection that can be obtained with such instrumentation.
Reversed Phase Liquid Chromatography
Authors: Lough W. John 
Published: September 2006

Abstract
Reversed‐phase liquid chromatography (RPLC) is an elution procedure used in liquid chromatography (LC) in which the mobile phase is significantly more polar than the stationary phase, e.g. a microporous silica‐based material with chemically bonded alkyl chains. Typically, the mobile phase is a mixture of an aqueous component, often containing a buffer to control pH, and a water‐miscible polar organic solvent. This most frequently used mode of LC is suitable for the analysis of compounds with a very wide range of polarities, using experimental variables such as mobile‐phase pH and ratio of organic to aqueous mobile phase components to manipulate selectivity and retention to separate sample components from one another.
Thin‐Layer Chromatography
Authors: Sherma Joseph 
Published: September 2006

Abstract
In thin‐layer chromatography (TLC), the sample solution is applied as a spot or band on the origin of the layer spread on a support (the plate). After evaporation of the sample solvent, the plate is placed in a sealed chamber containing a solvent chosen as the mobile phase. Development occurs as the mobile phase moves through the layer, and the components of the sample move at different rates to create the separation. The plate is removed from the chamber, and the separated zones are detected by physical or chemical methods, identified by comparison of their migration to standard zones on the same plate, and quantified by visual or instrumental methods based on measurement of zone sizes and intensities. A great variety of compounds can be separated, including organic, inorganic, biological, and chiral. Environmental, pharmaceutical, biomedical, and food samples are among the sample types commonly analyzed by TLC. Advantages of TLC include rapid analysis time because many samples can be analyzed simultaneously, low solvent usage on a per‐sample basis, a high degree of accuracy and precision for instrumental TLC, and sensitivity in the nanogram or picogram range. Coupling of TLC with other analytical methods such as high‐performance liquid chromatography (HPLC), mass spectrometry (MS), and Fourier transform infrared spectrometry (FTIR) provides enhanced opportunities for sample analysis. Disadvantages of TLC include application to only nonvolatile compounds, limited resolution capability (separation numbers or peak capacities of 10–50), and the absence of fully automated systems, although the individual steps of the technique can be automated.
Atmospheric Pressure Ionization Mass Spectrometry
Authors: Tarr Matthew A. , Zhu Junhua , Cole Richard B. 
Published: September 2006

Abstract
The atmospheric pressure ionization (API) techniques serve to transform neutral analytes into ionic species that may then be analyzed by mass spectrometry (MS). Ionization takes place under ambient pressure (∼1 atm), and formed ions are subsequently directed into the low‐pressure regions of the mass spectrometer for mass analysis. The API techniques have offered notable successes in enabling ionization of nonvolatile compounds contained in solution that are not amenable to “classical” mass spectrometric ionization techniques such as electron ionization and conventional chemical ionization. Under favorable API conditions, neutral analytes may be converted to ionic forms in extremely high efficiencies approaching 100%. Fundamental aspects and applications of the two most widely used API techniques, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), are discussed at length in this article.
Discrete Energy Electron Capture Negative Ion Mass Spectrometry
Authors: Laramée James A. , Cody Robert B. , Deinzer Max L. 
Published: September 2006

Abstract
Standard electron capture negative ion mass spectrometry (ECNIMS) has long been known as a sensitive and selective method for the analysis of molecules with positive electron affinities. Applications of this technique for the analysis of environmental contaminants, particularly of halogenated compounds such as polychlorobiphenyls (PCBs), are common. However, the requirement for a moderating gas in the ion source to lower the energy of the electrons into the range required for resonance electron capture generates new experimental variables that are difficult to control. Differences in the moderating gas pressure cause changes in the electron energy distribution and in the resulting ion abundances, whereas small fluctuations in temperature often cause major differences in ion abundance ratios. Even more serious are the uncontrollable reactions between ions, molecules, and radicals within the high‐pressure ion source region that give unpredictable spurious product ions, making spectral interpretation difficult and leading to wide variations of negative ion spectra from different instruments. Because of these difficulties, the advantages in sensitivity and specificity of ECNIMS for analysis of electronegative compounds often have been unrealized.
Better results can be obtained by having direct control over the electron energies. Control over electron energies can be achieved using a trochoidal electron monochromator, which allows the operator to tune to or scan a range of electron energies necessary for resonance electron capture. With this device some of the inherent difficulties encountered with ECNIMS can be avoided and reliable spectra for a broader range of compounds becomes possible. The ability to tune to a desired electron energy or to scan over a range of electron energies makes another dimension of analytical information available for identifying compounds. Quadrupole and sector instruments have been equipped with electron monochromators and the results are very promising. A clear advantage of these units is the reproducibility of the data they produce, the potential for three‐dimensional spectra for easier interpretation of the results, and the availability of a new dimension of analytical information. These instruments have not shown the sensitivity inherent in the ECNIMS method. Improvements of about two or three orders of magnitude in sensitivity will be required before these instruments can compete with existing technology for trace analysis of environmental residues or other electron‐capturing compounds. An improvement in the sensitivity of this magnitude is well within reasonable expectations and it should not be long before gas chromatography/electron monochromator mass spectrometry (GC/EMMS) becomes a standard technique for detecting environmental compounds, explosives and substances of abuse.
Electron Ionization Mass Spectrometry
Authors: Watson J. Throck 
Published: September 2006

Abstract

Electron ionization (EI) is the basis for one of the most effective mass spectrometric means for identification of a given organic compound. The identification is based on an indication of the molecular weight (MW) coupled with a fragmentation pattern that serves as a chemical fingerprint for the compound. Of the many ionization techniques available in mass spectrometry, EI is one of the most harsh in terms of promoting fragmentation of the molecular ion. The analyst can take advantage of this extensive fragmentation by using some of the fundamental principles of organic mechanistic chemistry and physical chemistry for the purposes of rationalizing the fragmentation pathways that characterize various structural features in an organic molecule. Four basic mechanisms of fragmentation are considered in this chapter; most of them operate on an odd‐electron ion, although some pathways will be applicable to even‐electron ions as well. The multiplicity of peaks that represent a given ion allows one to estimate the elemental composition of an ion. This information on composition, coupled with a rationalization of a given fragmentation pathway, often enables the structure of a given organic compound to be deduced.
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