bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alkaloids, Pharmaceutical Analysis of
Authors: Gilpin R.K. , Hann C.J. 
Published: September 2006

AbstractAlthough alkaloids are naturally occurring bases, additional generalizations are difficult because they include a wide range of structurally dissimilar compounds. They vary greatly in their chemical and physical properties as well as in their distribution in nature. In some cases certain alkaloids are associated with only a single species of plant, whereas others are more widely distributed between biological groupings of plants, and yet others are found in a wide range of unrelated plants. Likewise, the concentration of a particular compound may be highly localized within a given region of one plant and found predominantly in a different region of another plant. In some cases the levels of an alkaloid may be relatively high and its isolation as a natural product may be economically feasible, whereas in other cases the levels may be extremely low and less commercially desirable. The medicinal use of alkaloids in the form of crude plant extracts has been known for several thousand years and today there are hundreds that have been isolated and characterized. However, very few of them are accepted therapeutically and many of these fit into the broad categories of cinchona, ergot, opium, rauwolfia, tropane, vinca and xanthine alkaloids.
Antibiotics, Pharmaceutical Analysis of
Authors: Gilpin R.K. , Gilpin C.S. , Pachla L.A. 
Published: September 2006

Abstract
An antibiotic is a chemical substance, produced by microorganisms (or recently, synthetic routes) which has the capacity to inhibit the growth of other microorganisms/bacterial agents. The terminology for antibiotics stems from the Latin term of antibiosis and the noun antibiotic was coined by Professor Waksman in 1942. Considered as a single therapeutic class, antibiotics are one of the most diverse groups of medicinal agents. They can be grouped into several subclasses depending on their source, structure and activity. These are the cephalosporins, penicillins, quinolones, streptomyces and tetracycline. In addition to these agents, the sulfonamides and other miscellaneous compounds are also included owing to their antibacterial activity.
Gas and Liquid Chromatography, Column Selection for, in Drug Analysis
Authors: Duff Keith J. 
Published: September 2006

AbstractWithin the realm of pharmaceutical drug analyses, two techniques currently dominate the field. High‐performance liquid chromatography (HPLC) is at the forefront, followed somewhat distantly by gas chromatography (GC). HPLC is more prevalent than GC owing mainly to the heat‐labile nature of the majority of drug substances. Still GC continues to play a very active role. In comparison to HPLC and GC, combined, the frequency of use of other techniques is quite small. Perhaps the major reason for this is that chromatography not only involves qualitative and quantitative detection of targeted species, but also provides a medium for isolating these analytes from potential interfering impurities prior to measurement. The proficiency of this combination is unparalleled by any other blending of means to clean up a sample and detect the target compound. These more prominent techniques are often complementary, although each has its own strengths and limitations. General guidelines are given to assist the chromatographer to elect HPLC and/or GC for a particular separation. Considerations for choosing hardware type and sizes, solid support and bonded phase are presented. Particular emphasis is placed on the latest, which is of primary importance for obtaining rugged methods. The reader is directed towards optimum phase selection based on the compound of interest's functional group type, or by its drug activity classification (e.g. barbiturate, cardiovascular, etc.). Assistance in developing new methods frequently arises when starting with an existing published method for a compound with similar structure. This article provides 514 references for more in‐depth separation information. In addition, background knowledge on bonded‐phase chemistry, chromatographic modes of separation, approaches to chromatographic chiral drug discrimination and processes for developing rugged methods is contributed.
Nuclear Magnetic Resonance Spectroscopy in Pharmaceutical Analysis
Authors: Dawson Brian 
Published: September 2006

Abstract
Nuclear magnetic resonance (NMR) spectroscopy is an extremely powerful tool for the detection, identification and quantification of drugs and related substances. The whole range of one‐dimensional (1‐D) and two‐dimensional (2‐D) NMR techniques is available for performing the required analyses. These NMR methods may be used for routine purposes, such as the confirmation of the identity of the drug or quantification of the amount of drug substance present in a formulation. However, the area where NMR stands out as an analytical tool is in the identification of unknown compounds such as metabolites or drug degradation products. NMR is also used for impurity profiling or determination of the drug's optical purity.
Although NMR has been used for many years to analyze drugs, even the most modern spectrometers lack the sensitivity obtainable by other techniques such as mass spectrometry (MS) or high‐performance liquid chromatography (HPLC). However, NMR is a nondestructive technique which provides essential structural information that cannot easily be obtained from these other methods. Recent advances in technology have allowed the interfacing of NMR instruments with other equipment such as HPLC devices to provide even more robust analytical methodology.
Quantitative Structure–Activity Relationships and Computational Methods in Drug Discovery
Authors: Balaban Alexandru T. 
Published: September 2006

AbstractQuantitative structure–activity relationships (QSARs) are mathematical equations or other types of functions (such as the weights of connections in artificial neural networks) relating chemical structures to their biological activity. The purpose of QSAR studies is to predict novel structures with either beneficial activity as drugs for human or veterinary medicine (bactericides, antiviral or anticancer drugs, metabolic regulators such as hypoglycemics, hypotensives, etc.), or selective toxicity for various unwanted higher organisms (pesticides such as fungicides, insecticides, acaricides, weed‐killers, etc.). Quantitative structure–property relationships (QSPRs) are similar, but the property may be physical or chemical. The main problems involve:finding a mathematical representation of chemical structures (usually organic molecules), represented either as molecular graphs by their constitution or connectivity without considering the three‐dimensional (3‐D) (stereochemical) factors, or as 3‐D objects including stereochemical information;measuring the biological activities of a series of molecules;finding the QSAR between each type of biological activity and the most convenient molecular descriptors.Physicochemical parameters that are closely related to drug transport and ligand binding include lipophilicity, polarity, polarizability, and electronic influence on hydrogen‐donor and hydrogen‐acceptor binding. The next task is to use the QSAR to predict which novel structures to prepare in order to obtain molecules with the desired biological activity. Then the cycle is usually repeated, because a single pass seldom affords the optimal solution.The main mathematical descriptors and the techniques for obtaining QSARs are reviewed. An important molecular parameter, which may be measured experimentally or computed from the chemical structure, is lipophilicity or hydrophobicity; Hansch (see below) introduced the n‐octanol–water partition coefficient as a measure of this property, which to a large extent determines the ability of molecules to penetrate the lipophilic, bilayer, extra‐ or intracellular membranes. Lipophilicity levels that are too high lead to insolubility in water, i.e. it is difficult to administer the drug orally via the digestive tract. The main constitutional and 3‐D molecular descriptors are described and examples are given. To be statistically valid, correlations must involve orthogonal or orthogonalized descriptors. Linear, multilinear, and nonlinear types of correlations are reviewed. Screening of virtual combinatorial libraries together with high‐throughput combinatorial synthesis and testing provide modern tools for more efficient drug design.
Field Flow Fractionation in Analysis of Polymers and Rubbers
Authors: Ratanathanawongs Williams S. Kim , Benincasa Maria‐Anna 
Published: September 2006

Abstract
Field‐flow fractionation (FFF) was conceived by J. Calvin Giddings in 1966 as a separation and characterization method for macromolecules, colloids, and particulates. Like chromatography, sample migration is caused by differential interaction with a field acting along an axis orthogonal to that of the transport liquid. Unlike chromatography, where separation is achieved by solutes partitioning between mobile and stationary phases, separation in FFF arises from the distribution of sample components in fluid laminae flowing at different velocities in a single phase. The different flow velocities, described by a parabolic profile, arise from the high aspect ratio of the FFF channel. Different types of fields can be used in FFF as long as they interact with some physicochemical property of the sample. The FFF channel design makes it highly suited for analyses of fragile aggregates, high‐molecular‐weight polymers, and gels. In comparison with packed columns, shear rates in the channel and the probability of plugging the channel are low. The ability of thermal FFF to differentiate polymers and latexes of different bulk and surface composition is unique among currently used separation techniques. The FFF family of techniques can provide a great deal of information about the sample but an initial time investment is often required for methods development.
In this article, the fundamental mechanism of FFF is shown at play in the separation and characterization of polymers and rubbers by the two techniques par excellence in this field: flow FFF and thermal FFF.
Infrared Spectroscopy in Analysis of Plastics Recycling
Authors: Eisenreich Norbert , Rohe Thomas 
Published: September 2006

AbstractPlastics recycling recovers valuable materials to save natural resources which are limited in the long term. Reprocessing of the materials requires the identification of the various types of polymers. Difficulties in applying physical separation techniques led to the modification of methods of chemical analysis which have to be operated fast and reliably under harsh industrial environments favoring infrared (IR) methods.In general, the plastic products to be handled can be separated into two main fractions. Domestic wastes contain only five relevant polymers in large quantities. Technical products use a broad variety of polymers containing fillers and additives, e.g. flame retardants, which also have to be identified to allow economic recycling.Solid samples absorb IR radiation strongly, and the fundamental vibrations of the molecules are especially intense. The near‐infrared (NIR) spectral range with the overtone and combination bands is appropriate for analyzing bulky materials in reflection and transmission modes. The plastics from domestic wastes can be reliably identified by the first overtone of the CH bands between 1600 and 1800 nm. Extending this wavelength range to 1000 nm, technical non‐black plastics can also be treated. In the case of black plastics, which are often used in audio and video appliances, the mid‐infrared (MIR) spectral range has to be applied, owing to the reduced penetration depth of radiation into these materials. Also, larger amounts of additives such as plasticizers and flame retardants can be analyzed.The identification of plastics from household waste requires fast scanning techniques in the millisecond range, especially if many samples are to be taken for one identification on movement. Mainly acousto‐optic tunable filter (AOTF) spectrometers or grating spectrometers with diode arrays can be applied. Germanium (Ge) and indium gallium arsenide (InGaAs) detectors with extended wavelength sensitivity cover the spectral range of interest. The movement excludes Fourier transform infrared (FTIR) spectrometers with e.g. indium antimonide (InSb) and mercury cadmium telluride (HgCdTe) diodes, but its application to technical plastics is possible because these pieces are heavier and can be identified in a fixed position.Identification for recycling means a qualitative analysis. Simple algorithms such as those forming the differences of normalized spectra are sufficient for comparing measured with stored spectra. The performance of microprocessors also allows the application of more complex algorithms such as multivariate analysis or even neural networks. The use of NIR spectroscopy in industrial recycling started with application to sorting systems for plastics from household wastes or hand‐held sensors for cable recycling. The MIR technique still suffers from its sensitivity to harsh industrial environments and has been used only rarely and needs further development.
Infrared Spectroscopy in Analysis of Polymer Crystallinity
Authors: Mallapragada Surya K. , Narasimhan Balaji 
Published: September 2006

AbstractThis article provides a comprehensive review of the application of infrared (IR) spectroscopy in the analysis of polymer crystallinity. A brief description of the theory behind the analysis of orientation in polymers using IR spectroscopy is followed by a comparison of various sampling methods for Fourier transform infrared (FTIR) spectroscopy. These include transmission, attenuated total reflectance (ATR), external reflection, diffuse reflectance, photoacoustic and emission spectroscopic techniques. Various modes of measurement, such as polarized IR measurements, deuteration and rheo‐optical measurements to obtain more information from IR spectra and make the interpretation of spectra easier, are also discussed. The use of IR spectroscopy in analyzing both semicrystalline polymers and liquid crystalline polymers is presented. In the case of semicrystalline polymers, applications involve measuring phase transformations, chain conformation/packing, degree of crystallinity, crystallization kinetics, isomer ratios and chain alignment during mechanical treatment. In the case of liquid crystalline polymers, IR spectroscopy has been used to analyze molecular orientation, segmental mobility, photo‐induced reorientation and phase characterization/transformations. A comparison of IR measurements with other techniques used to analyze crystallinity in polymers such as X‐ray diffraction (XRD), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) spectroscopy, Raman spectroscopy and neutron scattering has been presented.
Infrared Spectroscopy in Analysis of Polymer Degradation
Authors: Edge Michele 
Published: September 2006

AbstractInfrared (IR) spectroscopy locates the spectral position (frequency) and intensity of absorbed (or emitted) radiation arising from molecular transitions between quantum states associated with the vibrations and rotations of specific chemical groups. Using this technique both qualitative and quantitative information can be obtained on changes in the composition of polymers during degradation. The use of mathematical data‐processing techniques and instrumental attachments has enabled considerable progress to be made in this field,1–3where changes to the composition of the polymer structure are invariably complex. In conventional IR spectroscopy the light is dispersed and each wavelength is examined separately, whereas the main advantage of Fourier transform infrared (FTIR) spectroscopy is that the signal is multiplexed and each point of an interferogram contains information on all the wavelengths present, enabling all frequencies to be determined simultaneously. The increased speed and higher signal‐to‐noise ratio of FTIR spectroscopy is the prime advantage in the analysis of complex materials. The use of computational software to obtain difference or derivative spectra enhances the dynamic range. This is of particular value when monitoring polymer degradation, where the main interference is from the nondegraded structure of the polymer. The main disadvantage of IR spectroscopy in identifying and quantifying the functional group changes that take place during polymer degradation is that broad and rather featureless bands are frequently produced. As a consequence it is necessary to resolve individual components by subjecting the sample to a prior chemical treatment, or by the use of coupled instrumentation.
Coupled Liquid Chromatographic Techniques in Molecular Characterization
Authors: Kilz Peter , Pasch Harald 
Published: September 2006

Abstract
Complex polymers are distributed in more than one direction of molecular heterogeneity. In addition to the molar mass distribution (MMD), they are frequently distributed with respect to chemical composition, functionality, and molecular architecture (see Size‐exclusion Chromatography of Polymers). For the characterization of the different types of molecular heterogeneity it is necessary to use a wide range of analytical techniques. Preferably, these techniques should be selective towards a specific type of heterogeneity. The combination of two or more selective analytical techniques is assumed to yield multidimensional information on the molecular heterogeneity.
The present review presents the fundamental ideas of combining liquid chromatography (LC) with other analytical techniques in multidimensional analysis schemes (see Size‐exclusion Chromatography of Polymers; Gas Chromatography in Analysis of Polymers and Rubbers; Field Flow Fractionation in Analysis of Polymers and Rubbers). The capabilities and limitations of different coupling techniques are discussed and a number of relevant applications are given. It is shown that multidimensional structural information can be obtained when different chromatographic techniques are combined. Another approach is the hyphenation of LC with information‐rich detectors. These detectors include molar mass‐sensitive detection systems, such as on‐line viscometry (VISC) and light scattering (LS). Information on the chemical composition of complex polymers can be obtained when spectroscopic techniques, like Fourier transform infrared (FTIR) (see Infrared Spectroscopy in Analysis of Polymer Structure–Property Relationships), nuclear magnetic resonance (NMR) or mass spectrometry (MS) are coupled to LC.
The basics and applications of multidimensional LC are addressed rather extensively. A brief introduction to different separation mechanisms is given and the particular requirements for the first and second dimensions are discussed. In conclusion, state‐of‐the‐art examples for on‐line coupled two‐dimensional (2‐D) chromatography are demonstrated, and future developments are reviewed.
Nuclear Magnetic Resonance, Solid State in Analysis of Polymers and Rubbers
Authors: Mirau Peter A. 
Published: September 2006

Abstract
Solid‐state nuclear magnetic resonance (NMR) has emerged as one of the premier methods for polymer characterization in the solid‐state. High‐resolution spectra can be obtained with cross‐polarization and magic‐angle sample spinning using equipment that is commonly available on modern NMR spectrometers. Information about the chain structure, conformation, dynamics, intermolecular interactions and the morphology can be obtained by measuring the chemical shifts, line shapes and relaxation times. New experiments have been developed to filter the NMR response such that the spectrum from aparticular component can be measured. The resolution has been increased with the development of multidimensional NMR methods for measuring the structure and dynamics. Solid‐state NMR experiments can provide the link between the chemical structure and the macroscopic properties of polymers.
Pyrolysis Techniques in the Analysis of Polymers and Rubbers
Authors: Wampler Thomas P. 
Published: September 2006

Abstract

Pyrolysis is defined as a chemical degradation reaction induced by thermal energy only,
1
and analytical pyrolysis is the study of materials based on the results of such reactions. Since the overall result of a pyrolysis reaction is the production of small molecules from larger ones, it is extensively utilized in the analysis of polymers, especially as a sample introduction tool since it permits the application of techniques such as gas chromatography (GC) to such macromolecules by breaking them into fragments which are compatible with the technique. Interpretation of the results of a pyrolytic analysis depend on an understanding of the degradation mechanisms involved, which reflect relative bond strengths within the macromolecule. Since specific polymers are chemically different from each other, the degradation products they make are different, providing characteristic information about the original macromolecule. Analytical pyrolysis, coupled with GC, mass spectrometry (MS), gas chromatography/mass spectrometry (GC/MS), Fourier transform infrared (FTIR) spectroscopy and other techniques, has been used in the study of a wide range of polymer types, including polyolefins, vinyl polymers, polyurethanes, acrylics, rubbers, polyamides and polyesters.

Analytical laboratories employ one of a variety of pyrolysis techniques (microfurnace, resistively or inductively heated filament) interfaced to a detection instrument (GC, MS, FTIR) to create an analytical system. These combined systems have strengths and weaknesses based on the limitations of the individual components and must be optimized for a particular analysis. Systems have been devised which permit the routine analysis of such difficult materials as cured and cross‐linked paints and rubbers, textile fibers, filled composites, laminates, dried adhesives, copolymer systems, coatings and packaging. Practical applications are found in laboratories charged with the analysis of forensic evidence, museum artifacts, ink, paper, lubricants, automobile tires, clothing, varnish, wood products, furniture and food containers.
Temperature Rising Elution Fractionation and Crystallization Analysis Fractionation
Authors: Monrabal Benjamin 
Published: September 2006

Abstract
Temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF) are separation techniques for the characterization of semicrystalline polymers in terms of chemical composition. TREF has become a powerful tool for preparative polymer fractionation and for the analysis of the chemical composition distribution (CCD) in polyolefins. CRYSTAF, a more recent technique and with a simple hardware design, provides a faster approach for the analysis of the CCD. Both TREF and CRYSTAF separate according to the crystallizability of the polymer molecules, which is influenced by tacticity or the comonomer incorporation into the chain. TREF and CRYSTAF are becoming specially relevant in the characterization of the new and complex polyolefins made with combinations of homogeneous and heterogeneous catalysts.