bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffraction in Particle Size Analysis
Authors: Novales Bruno
Published: September 2006

The diffraction techniques for particle size analysis are based on the measurement of the angular distribution of light diffracted by particles situated in the path of a light beam. These techniques have been used for many years to measure the size of small particulates but the calculation to generate a particle size distribution is so complex that it is only in the last 15 years with the development of small, inexpensive, and powerful computers that these techniques have become so popular. The complete theory describing the diffraction of light by a spherical particle was described by Mie in 1908 and is able to predict the electromagnetic field at any point in space. This theory is adequate for particles with diameters of the same order as the wavelength of the incident light. Some other models have been presented. The most commonly used are based on the Fraunhofer diffraction theory. Light‐scattering techniques have obvious advantages for particle size analysis as compared to other methods. They are faster than mechanical techniques, nonintrusive, nondestructive and do not require large amounts of sample. These techniques can be performed on dry powders or on suspended particles in a liquid or in a gas. The operating range of light diffraction techniques is from 20 µm to several millimeters. This article presents the main theoretical aspects of light diffraction by particles. Also, a brief description of a diffraction particle sizer is given with some practical recommendations. Problems related to particle size analysis by light diffraction are examined. Some other light‐scattering methods (photon correlation spectroscopy, single particle scattering, Doppler techniques) are also presented.
Electrozone Sensing in Particle Size Analysis
Authors: Figueiredo M. Margarida
Published: September 2006

Particle sizing is a rapidly growing field, not only because of its importance in a great variety of technological applications but also due to its outstanding relevance to numerous areas of scientific research.

The currently available instruments to measure particle‐size distributions are many and varied, the results often being dependent on the measuring technique used. It is thus essential to understand the physical principles behind each technique in order to make an adequate choice.

Electrozone sensing, a widely used method of particle‐size analysis, constitutes the main topic of this paper. A general description of its operating principle is provided, followed by some practical considerations mainly concerning sample preparation and the selection of electrolyte solutions and aperture tubes. Being a technique that requires prior calibration, emphasis is placed on the calibration procedures. The section dedicated to the measurement of special materials also reviews some recent improvements of this technique. Finally, a list of commercially available equipment is supplied, together with its most relevant features.
Field‐Flow Fractionation in Particle Size Analysis
Authors: Janča Josef
Published: September 2006

Field‐flow fractionation (FFF) is an analytical methodology suitable for the separation and characterization of macromolecules within a wide range of molar masses, and for particles in submicrometer and micrometer ranges. The separation is based on the action of effective physical or chemical forces across the separation channel. The field forces interact with the separated species and concentrate them at the appropriate position inside the channel. The resulting concentration gradient induces an opposite diffusion flux. This process leads to a quasi‐steady‐state distribution of the affected sample components across the channel. The velocity of the longitudinal flow of the carrier liquid also varies across the channel. A parabolic flow velocity profile is usually established inside the channel. The components of the separated sample are transported in the longitudinal direction inside the channel at different velocities, depending on the transverse positions of the zones of the sample components within the flow of the carrier liquid.

The separation is performed in one liquid phase. This is of fundamental importance for the fractionation and particle size analysis of biological samples, which can be sensitive to the type and intensity of the interaction with the surfaces and can denaturate. Steady‐state inside the channel is usually reached within a short time due to a small channel thickness. The simplicity of the channel construction permits an accurate description of the separation processes.

The field strength can be controlled over a wide range. Many operational variables in FFF can be manipulated during the experiment by suitable programming.

Accurate analytical results can be obtained from FFF by correct treatment and interpretation of the experimental data. If the relationship between the retention parameters and the characteristics of the separated particles is known, or can be predetermined by using an appropriate calibration procedure, the characteristics of an unknown analyzed sample can be evaluated quantitatively. The particle size distribution (PSD) of the analyzed sample then is determined from a fractogram.
Light Scattering, Classical: Size and Size Distribution Characterization
Authors: Berry Guy C.
Published: September 2006

The use of classical, or time‐averaged, light scattering methods to characterize the size and size distribution of macromolecules in dilute solutions or particles in dilute dispersions is discussed. The necessary scattering relations are presented systematically, starting with three cases at infinite dilution: the scattering extrapolated to zero angle, the scattering at small angle, and the scattering for arbitrary angle, including the inversion of the scattering data to estimate the size distribution. The relationships needed to effect an extrapolation to infinite dilution from data on dilute solutions are also discussed. These are followed by remarks on light scattering methods, and the concluding sections give examples for several applications. The Rayleigh–Gans–Debye (RGD) approximation is usually appropriate in the scattering from dilute polymer solutions and is also adequate for the scattering from dilute dispersions of small particles. The approximation is assumed when appropriate, but more complete theories are introduced where necessary, as in the use of the Mie–Lorentz theory for large spherical particles.
Sieving in Particle Size Analysis
Authors: Dishman Karla L.
Published: September 2006

Sieve analysis is used to obtain the particle size distribution of a solid material by determining the amount of powder retained on a series of sieves with different sized apertures. A sample is added to the top of a nest of sieves arranged in decreasing size from top to bottom. As the sieves are vibrated, the sample is segregated onto the different sized sieves. The weight of sample retained on each sieve is then used to determine the particle size distribution as well as the mean diameter of the sample.
Turbidimetry in Particle Size Analysis
Authors: Kourti Theodora
Published: September 2006

The size of particles in a suspension can be estimated by measuring the turbidity of the suspension. Turbidity measures the attenuation of a beam of light traveling through the suspension caused by the scattering and absorption of light by the particles. The amount of scattering and absorption depends on the size of the particles and their concentration in the suspension. Most of the reported applications in the literature use turbidimetry for the estimation of the particle size distribution (PSD) or an average size for particles with diameters ranging from 0.035 to 50 µm. Turbidimetric techniques are low cost, experimentally simple, fast, nondestructive and require no calibration. They are robust methods with very good reproducibility and can be used either off‐ or on‐line, in a laboratory or a plant environment. They have been used for particle or droplet size determination in a variety of diverse systems such as latex particles, silver bromide sols and cow's milk. Most of the time common ultraviolet/visible (UV/VIS) spectrophotometers are utilized for the turbidity measurements. Certain modifications may be necessary on these instruments depending on the size of the particles. The turbidity of the suspension is measured and the size of the particles or the PSD is estimated utilizing light scattering theory. For spherical isotropic homogeneous particles and absence of multiple scattering this theory is well established. The extension to nonspherical and inhomogeneous particles is a field of active research yielding numerous publications.

A controversy existed in the literature regarding the capability of turbidimetry to provide the full PSD but has now been resolved. For polydisperse suspensions, for certain combinations of particle sizes and optical properties, the method cannot provide the full PSD, but only an average of the PSD. This limitation is simply a result of the light scattering patterns and it is expected theoretically. In some cases it can be overcome by simply altering the optical properties of the suspension (i.e. choosing the proper wavelengths for the turbidity measurements or a medium with a different refractive index to suspend the particles). To make the best use of the method and interpret the results in a meaningful way one should be aware of this limitation and work with it. When this is done, excellent results can be achieved. The advantages of the method and a good knowledge of its capabilities make it a very robust choice for many applications. The numerous reports from the successful application of the method are a testimony to this.
Velocimetry in Particle Size Analysis
Authors: Farrell Patrick V.
Published: September 2006

Velocimetry in particle size analysis encompasses the range of issues and methods used to measure particle velocities consistent with particle size measurement systems. Particle size may be measured simultaneously or consecutively with the velocity measurements described in this article. This article will present some issues that should be considered in selection of a velocity measurement technique. Three examples of commonly used particle velocity methods will be discussed as illustrations of possible approaches. For each of these examples, a brief discussion of advantages and limitations of the methods will also be presented.
Capillary Electrophoresis in Peptide and Protein Analysis, Detection Modes for
Authors: Weber Paul L.
Published: September 2006

Capillary electrophoresis (CE) is a highly efficient separation technique which achieves high resolution with low sample consumption. Crucial to any separation technique are detection modes capable of giving useful data about separated analytes, including both quantitative and qualitative information. A variety of general detection modes for CE have been developed, most based on similar systems used in high‐performance liquid chromatography (HPLC), but only some are useful in the analysis of peptides and proteins. Modes which are selective for certain spectral or chemical properties of these analytes are often employed. The absorption of ultraviolet/visible (UV/VIS) light as well as fluorescence (Fl) fit into the former category while electrochemical (EC) detection falls under the latter. The development of mass spectrometry (MS) as a detection mode for peptide and protein analysis may be the ideal choice since a great deal of qualitative information can be obtained and used for identification and structural characterization. By definition, CE involves separation in a “micro” environment, a capillary, and this places certain demands on the performance of the detection system and perhaps the greatest challenge is that of sensitivity.
Capillary Electrophoresis/Mass Spectrometry in Peptide and Protein Analysis
Authors: Tomlinson Andy J. , Naylor Stephen
Published: September 2006

The focus of this article is to describe the developments of capillary electrophoresis (CE) on‐line with detection by mass spectrometry (MS) for the analysis of peptides and proteins. Following a brief introduction in which we discuss the increasing role of the mass spectrometer for characterizing these important biomolecules, we present a historical overview of capillary electrophoresis/mass spectrometry (CE/MS). The latter discussion describes the experiments that allowed the connection of CE with MS, through developments to increase the volumes of analyte solutions that can be analyzed, to the current investigations of microfabricated chips that bring CE/MS towards a nano‐scale technology. We also consider the technical aspects of CE/MS, which include how to inject analyte mixtures into the capillary, ways to improve the concentration sensitivity of the technique, the optimal capillary surface technology to use, and considerations of buffer compositions that are compatible with on‐line MS detection. Other practical issues, including the physical connection between the CE and MS components, along with sample preparation and sequencing peptides by this technology are also reviewed. In the final section, the future of CE/MS is contemplated, with particular emphasis on the current developments of nanotechnologies that include the interfacing of microchip‐based CE with MS.
F
ourier Transform Infrared Spectroscopy in Peptide and Protein Analysis
Authors: Fabian Heinz , Schultz Christian P.
Published: September 2006

Infrared (IR) spectroscopy is one of the two forms of vibrational spectroscopy, the other being Raman spectroscopy. IR spectroscopy measures absorptions of vibrating molecules and yields information about molecular structures and structural interactions. The development of computerized Fourier transform infrared (FTIR) techniques has opened up new dimensions in biological IR spectroscopy owing to the increase in achievable signal‐to‐noise ratios, wavenumber accuracy, and data aquisition rates, and the ability to perform measurements with strongly absorbing samples. High‐quality FTIR spectra can be obtained with relative ease and rapidly with very small amounts of sample in a variety of environments. Measurements of proteins in aqueous solution are almost routine now, and can be performed under equilibrium and nonequilibrium conditions. There are many IR absorption bands characteristic of peptide groups and amino acid side‐chain groups from which information on protein structures can be obtained. The information provided by FTIR spectroscopy may be a global one or highly specific for a single vibrating chemical group. In some cases, the usefulness of the method is limited by difficulties in extracting the structural information contained in the IR absorption bands.
Gel Electrophoresis in Protein and Peptide Analysis
Authors: Kaplan Batia
Published: September 2006

Gel electrophoresis is a widely used method in biochemical research; a number of different forms of gel electrophoresis have been developed and applied to the analysis of proteins and peptides. The most popular form is polyacrylamide gel electrophoresis (PAGE), in which proteins are separated within a gel matrix on the basis of differences in their charge density and/or relative molecular mass (Mr). Polyacrylamide gel is also widely used as a media for the generation of pH gradients in an isoelectrofocusing (IEF) technique, where separation of proteins is due to their differences in isoelectric point (pI). Two‐dimensional (2D) electrophoresis is an extremely powerful separation technique, allowing differentiation of proteins on the basis of their pI in IEF, and their Mrin sodium dodecyl sulfate (SDS)/PAGE. Agarose gels are rarely used today in the electrophoretic analysis of proteins; their utility is mainly restricted to the immunoelectrophoretic techniques, which allow the characterization of proteins by their migration in gel and immunological properties.

This article provides a brief history of gel electrophoresis and describes the principles of major electrophoretic techniques. The utility of gel electrophoresis in different fields of biochemical research is also demonstrated. Topics included are analytical and small‐scale preparative separations of complex proteins samples; determination of molecular mass of the electrophoretically separated proteins and polypeptides; electrophoretic micropreparation of a protein sample for its further immunochemical, enzymatic, and chemical analysis; study of protein interactions with different ligands; examination of protein unfolding and its quaternary structure. The advantages and limitations of the described techniques are discussed.
High‐Performance Liquid Chromatographic Separations and Equipment in Peptide and Protein Analysis, Miniaturization of
Authors: Nice E.C. , Catimel B.
Published: September 2006

The use of short narrow‐bore (2.1‐mm i.d.), microbore (1‐mm i.d.) or capillary (<1‐mm i.d.) columns allows the recovery of purified proteins and peptides in reduced volume at concomitantly increased concentration compared with larger bore columns. Additionally, sample detection is correspondingly improved for concentration‐dependent detectors. Sample volumes are not limiting: large sample volumes can be loaded on to interactive supports (e.g. reversed‐phase (RP), ion‐exchange (IEX), hydrophobic interaction (HI), affinity) under appropriate mobile phase conditions (trace enrichment). Suitable instrumentation requires careful consideration with regard to minimized pre‐ and postcolumn dead volumes, accurate gradient formation at low flow rates, detector flow cell geometry and sample recovery. These techniques are ideally suited for the purification of trace protein or peptide components in bulk biological samples prior to application to highly specific and sensitive downstream analytical techniques (e.g. microsequence analysis, mass spectrometry (MS), biosensor analysis, biological assay). They also facilitate the recovery of low levels of material following chemical or enzymatic modification (e.g. radioiodination, enzymatic semi‐synthesis, chemical derivatization). The techniques can also be applied to the development of large‐scale processes, whereby multidimensional purification protocols can be rapidly developed using minimum amounts of sample, solvent and column packing materials and then scaled up appropriately.
High‐Performance Liquid Chromatography/Mass Spectrometry in Peptide and Protein Analysis
Authors: Shen Tun‐Li
Published: September 2006

Since the 1970s, high‐performance liquid chromatography/mass spectrometry (HPLC/MS) has gone through many stages of development. The main technical challenge has been the coupling of liquid chromatography (LC) systems with mass spectrometers. Soft ionization techniques that have contributed to HPLC/MS for peptide and protein study include fast atom bombardment (FAB), matrix‐assisted laser desorption/ionization (MALDI), and electrospray ionization (ESI). Among these techniques, FAB was developed first and used extensively in the 1980s; it lacked the sensitivity of the other two more recent techniques. MALDI and ESI are comparable in terms of sensitivity and the types of biomolecules that can be analyzed. However, MALDI has the slight advantage of being more tolerant to salts and able to analyze complex mixtures. On the other hand, the ability of ESI to interface mass spectrometry (MS) directly with LC makes it extremely useful for protein and peptide analysis. Another advantage that ESI offers is its ability to produce multiply charged protein ions, which allows the observation of large proteins with mass analyzers of limited mass range. In this article we discuss the experimental parameters that are important in HPLC/MS and the considerable progress made in ESI source design and capillary HPLC/MS.

In the study of natural and synthetic peptides, HPLC/MS has been used to separate, characterize, and sequence the peptides being investigated. In protein analysis, HPLC/MS is most useful in characterizing protein post‐translation modification such as glycosylation and phosphorylation. We discuss specific HPLC/MS methods for detecting glycopeptides and phosphopeptides during chromatographic separation by monitoring marker ions: Hex
+
(m/z 163), HexNAc
+
(m/z 204), NeuAc
+
(m/z 292), HexHexNAc
+
(m/z 366) for glycopeptides, and PO
2
−
(m/z 63), PO
3
−
(m/z 79) for phosphopeptides. Another important application of HPLC/MS is in proteomic analysis. Here, the most significant development in the last decade has been the implementation of MS as the primary analytical technique to identify proteins separated by two‐dimensional polyacrylamide gel electrophoresis (2D/PAGE). Additionally, the need to identify gel‐separated proteins has promoted various MS‐based protein database search strategies. These include peptide mass mapping using proteolytic peptide masses for database search, and using peptide fragmentation data obtained from tandem mass spectrometry (MS/MS) to search protein sequence databases. Finally, we examine the recent advance in integrating HPLC/MS and database search strategy in proteomic analysis.
Hydrophilic‐Interaction Chromatography in Peptide and Protein Analysis
Authors: Jenö Paul
Published: September 2006

Hydrophilic‐interaction liquid chromatography (HILIC) has been introduced as a highly efficient chromatographic technique for the separation of a wide range of solutes. A hydrophilic stationary phase is eluted with a hydrophobic mobile phase whereby retention of solutes increases with the hydrophilicity of solutes. Bound solutes are eluted by decreasing the hydrophobicity of the mobile phase. Mixed mode effects based on hydrophilic and ionic interactions can also be exploited by proper selection of the stationary and the mobile phase. Typically, the order of elution is the opposite of that obtained by reversed‐phase chromatography (RPC). HILIC is particularly interesting for solutes which are difficult to chromatograph on conventional reversed‐phase materials. This review focuses on the application of HILIC to the separation of amphipathic α‐helical peptides, the analysis of protein glycosylation, phosphorylation, and acetylation, and to the removal of detergents from membrane proteins.
Matrix‐Assisted Laser Desorption/Ionization Mass Spectrometry in Peptide and Protein Analysis
Authors: Lewis J. Kathleen , Wei Jing , Siuzdak Gary
Published: September 2006

Matrix‐assisted laser desorption/ionization mass spectrometry (MALDIMS), first introduced in 1988 by Hillenkamp and Karas, has become a widespread analytical tool for peptides, proteins and most other biomolecules. In MALDI (matrix‐assisted laser desorption/ionization) analysis, the analyte is first co‐crystallized with a large molar excess of a matrix compound, usually an ultraviolet (UV)‐absorbing weak organic acid, after which laser radiation of this analyte–matrix mixture results in the vaporization of the matrix which carries the analyte with it. The matrix therefore plays a key role by strongly absorbing the laser light energy and causing, indirectly, the analyte to vaporize. The matrix also serves as a proton donor and receptor, acting to ionize the analyte in both positive and negative ionization modes, respectively. The efficient and directed energy transfer during a matrix‐assisted laser‐induced desorption event provides high ion yields of the intact analyte and allows for the measurement of compounds with high accuracy and subpicomole sensitivity. The ability to generate such accurate information can be extremely useful for protein identification and characterization. For example, a protein can often be unambiguously identified by the accurate mass analysis of its constituent peptides (produced by either chemical or enzymatic treatment of the sample). This article discusses basic MALDI concepts and instrumentation and focuses on applications in the field of peptides and proteins, specifically on the utility of MALDI in protein identification, protein structural studies, and as a clinical assay.
Molecular Modeling in Peptide and Protein Analysis
Authors: Kuczera Krzysztof
Published: September 2006

This article describes the theoretical background and practical applications of classical molecular mechanics and molecular dynamics (MD). Following a brief historical outline of molecular modeling, the concept of the molecular potential energy function is introduced and the basic algorithms of molecular mechanics: energy minimization, normal mode analysis, MD and Monte Carlo (MC) simulations are defined. The advantages of molecular modeling methods – speed of calculations and detailed microscopic insight – are described. The shortcomings – approximate nature and difficulties with conformational sampling – are also analyzed. A number of modern approaches aimed at improving the reliability of computer simulations are briefly presented, including advanced energy optimization methods, treatment of long‐range forces and accelerated conformational exploration. Examples of applications of molecular modeling methods to study of various aspects of structure, dynamics and function of peptides and proteins are presented. A brief exposition of the relationship between molecular modeling and some fundamental experimental techniques, such as X‐ray crystallography, neutron scattering, nuclear magnetic resonance (NMR), fluorescence and vibrational spectroscopies is provided. Finally, an outline of future directions of modeling studies is suggested.
Peptide Diastereomers, Separation of
Authors: Scriba Gerhard K.E.
Published: September 2006

Diastereomeric peptides, isomers in which one or more of the chiral centers have been converted to the opposite configuration (R or S), often possess different biological activities and/or conformational properties. Therefore, the separation and determination of diastereomeric peptides is particularly significant to the pharmaceutical industry for quality control of peptide synthesis and stability as well as for regulatory requirements. Diastereomers differ in their physicochemical properties which can be utilized for their determination by numerous techniques. In contrast to many other methods such as optical rotation, circular dichroism, differential scanning calorimetry, infrared (IR) spectroscopy, or nuclear magnetic resonance (NMR) spectroscopy only chromatographic techniques and capillary electrophoresis (CE) allow the sensitive and simultaneous identification and quantification of peptide diastereomers.

The current chapter will cover the analytical scale separation of peptide diastereomers by chromatographic methods, including paper chromatography (PC), thin‐layer chromatography (TLC), gas chromatography (GC), and high‐performance liquid chromatography (HPLC) as well as CE. HPLC is currently the predominant method for peptide diastereomer separations. However, due to the high resolving power particularly for polar compounds CE has been applied to the separation of diastereomeric peptides in recent years. This article will cover methods employing achiral stationary phases or buffers without chiral additives for the separations. Moreover, only examples of diastereomeric peptides containing natural amino acids will be discussed.
Surface Plasmon Resonance Spectroscopy in Peptide and Protein Analysis
Authors: Salamon Zdzislaw , Tollin Gordon
Published: September 2006

This chapter presents a detailed overview of the theoretical basis of surface plasmon resonance (SPR) spectroscopy, emphasizing both principles and practical considerations such as thin‐film designs for SPR devices which can be employed in characterization of biological materials, including peptides and proteins. It is demonstrated that the analysis of the resonance spectrum yields structural parameters of anisotropic films of interacting biomolecules, including distribution of mass, long‐range molecular order, and molecular conformational changes. Binding parameters, including binding affinities and rate constants, can also be determined. A summary is presented of different techniques for biomolecule immobilization on SPR‐generating surfaces applicable in peptide and protein analysis.
Chiral Pesticides and Polychlorinated Biphenyl Congeners in Environmental Samples, Analysis of
Authors: Garrison Arthur W.
Published: September 2006

Over 25% of pesticides and other toxic organic pollutants are chiral, as are 19 of the 209 polychlorinated biphenyl (PCB) congeners; that is, they exist as two mirror image species called enantiomers (PCB enantiomers are called atropisomers). The enantiomers of a chiral compound have identical physical and abiotic chemical properties, but usually differ in biological properties such as microbial degradation, uptake and transport across membranes, metabolism rate, and toxicity. Chirality in the environment has become recognized as an important phenomenon since the mid‐1980s, and related research has centered on the need to understand the environmental fate and effects of pesticides and PCBs. This article provides a brief background on chiral chemistry in general and the importance of chirality in the drug industry, followed by a summary of examples of the enantioselectivity of pesticide and PCB occurrences and degradation in the environment as gleaned from the scientific literature. The main emphasis is on the analysis of these compounds, with the primary focus on chiral separations. Chiral separations are generally performed by gas chromatography (GC) or high‐performance liquid chromatography (HPLC) using chiral columns, or, to a lesser extent, by capillary electrophoresis (CE) using cyclodextrin (CD) or other chiral selectors in the run buffer. Summaries of these three separation methods are provided, with figures giving examples of pesticide and PCB enantiomeric separations. Finally, to show the usefulness of these separation methods, applications to several environmental chemistry problems involving chiral pesticides and PCBs are described and illustrated.
High‐Performance Liquid Chromatography Methods in Pesticide Residue Analysis
Authors: Hogendoorn Elbert A.
Published: September 2006

The important role of high‐performance liquid chromatography (HPLC) in pesticide residue analysis (PRA) is presented. Based on the experience and view of the author, a number of reliable and robust liquid chromatography (LC) approaches and methods have been selected to highlight the favorable features of this technique in this field of analysis.

Reversed‐phase liquid chromatography (RPLC) with ultraviolet (UV) detection mode is most widely adopted, owing to its ability to perform efficient separation of very polar to apolar pesticides and the universal character of the detection mode. Therefore, a large part will deal with reversed‐phase liquid chromatography/ultraviolet (RPLC/UV) applications showing its excellent separation performance and detectability of compounds not directly amenable to gas chromatography (GC).

Another important feature of RPLC is the possibility of including sample pretreatment steps such as sample concentration and/or cleanup in the analytical procedure. The very good compatibility with aqueous samples or extracts easily permits RPLC on‐line sample loading (trace enrichment) by means of column switching, allowing fully automated procedures. It will be shown that, depending on whether the first column is a low‐ or a high‐resolution column, two different modes of column switching, solid‐phase extraction (SPE) to LC and LC to LC, are adopted in the determination of pesticides. The type of columns and materials, the advantages and the application range of both column‐switching modes is discussed in detail. Attention will be paid to method development including both the straightforward trial‐and‐error approach and more systematic method development procedures.

The more selective/sensitive detection modes, fluorescence detection (FD) and mass spectrometry (MS) as applied in pesticides residue analysis will be discussed with emphasis on the increasing importance of MS for identification and quantification of polar pesticides in various types of samples.

Finally, the use of LC methods involving normal‐phase liquid chromatography (NPLC), low‐resolution RPLC and gel permeation chromatography (GPC), will demonstrate the powerful sample pretreatment feature of LC prior to gas chromatographic analysis.
Immunochemical Assays in Pesticide Analysis
Authors: Dankwardt Andrea
Published: September 2006

Immunochemical assays (immunoassays, IAs) are biochemical assays which work according to the law of mass action. They are based on the recognition of an antigen (Ag) or a hapten by antibodies (Abs). Abs are serum glycoproteins of the immunoglobulin (Ig) class and are produced by the vertebrate immune system against foreign material of high molecular mass. The result of the binding reaction between the Ab and an analyte is usually made visible by means of enzymatic, chemiluminescent, fluorescent or radioactive markers. According to the label used IAs can be classified into enzyme immunoassays (EIAs), radioimmunoassays (RIAs), fluorescence immunoassays (FIAs) or chemiluminescent immunoassays (CLIAs). The measuring range of most IAs for pesticides is in the parts per trillion to lower parts per billion range. A lot of samples can be analyzed within a short time, while only low sample volumes are necessary. In many cases (water, some liquid food samples) no extraction step and no cleanup are necessary. Not all assays are completely specific to one single compound. Cross‐reactivities of the Abs with haptens similar to the analyte can be observed. In some cases, matrix effects may occur, especially with soil or colored food extracts. Therefore, validation of the assays for the matrix of interest should be carried out. As IAs are usually targeted at a single analyte or a group of analytes, multianalyte approaches using Ab arrays or a combination of immunochemical techniques with liquid chromatography (LC) are pursued.
Multiclass, Multiresidue Analysis of Pesticides, Strategies for
Authors: Lehotay Steven J.
Published: September 2006

Strategies for multiclass, multiresidue analysis of pesticides depend on several factors that all derive from three fundamental considerations: (1) the need for the results; (2) the form and composition of the matrix; and (3) the time, resources, and technology available to the analyst. First, the need for the data dictates the quality assurance (QA)/quality control (QC) guidelines and the desired analytical figures of merit, such as limits of detection (LOD) and the accuracy and precision of the results. These needs also contribute to the choice of pesticide analytes, which sets the polarity range for the analysis. No single method can determine all pesticides in diverse matrices, so an overall strategy is often used to compartmentalize a series of approaches in order best to detect the targeted pesticides in an effective and efficient process. Second, the various types of matrices that are commonly analyzed for pesticide residues may affect the sample preparation approach employed in the analytical strategy. Common matrices for pesticide analysis consist of solids, liquids, and gases in applications associated with food, agricultural, environmental, and other sample types. Varying degrees of pesticide–matrix interactions in different materials require more or less stringent extraction procedures to separate the pesticides from the sample. Sample preparation in multiclass, multiresidue strategies frequently utilizes liquid–solid, liquid–liquid and other partitioning processes including those, such as pressurized fluid extraction (PFE), in which pressure and temperature of different fluids are controlled. Extracts often require cleanup to remove interfering co‐extracted matrix components prior to analysis. A variety of cleanup techniques based on a number of partitioning processes, such as liquid chromatography (LC), may be employed in an on‐line or off‐line fashion. Lastly, the sample extract is usually further separated and analyzed using one or more techniques. The majority of pesticides are analyzed by gas chromatography (GC) with mass spectrometry (MS) and/or element‐selective GC detectors. High‐performance liquid chromatography (HPLC) is often used in the analysis of thermally labile pesticides that are not amenable to GC analysis. Other alternatives for analysis of certain pesticide include capillary electrophoresis (CE) and immunoassays. Fundamentally, a high degree of selectivity helps in generating excellent analytical results, but the wide polarity range of analytes in multiclass, multiresidue methods (MRMs) for pesticides necessitates a great deal of effort to attain a high degree of selectivity. Trade‐offs and compromises are omnipresent in multiclass, multiresidue analysis of pesticides, and a host of strategies are available depending on how the analytical chemist prioritizes the analytical and practical considerations.
Organophosphorus Pesticides in Water and Food, Analysis of
Authors: Lacorte Sílvia , Barceló Damià
Published: September 2006

The purpose of this article is to provide an overview of the main characteristics of organophosphorus pesticides (OPPs), such as their physicochemical characteristics, sources, fate and distribution in the environment. It covers regulatory compliance from the Commission of the European Communities (CEC) and the United States National Pesticide Survey (USNPS), regarding the maximum permissible levels of the most toxic and persistent OPPs and their transformation products (TPs) in water. This article also describes the analytical methods currently used to monitor pesticides and their degradation products in water and food matrices. A major part concerns sample preparation techniques and includes traditional liquid–liquid extraction (LLE) and novel techniques based in automated solid‐phase extraction (SPE), either on‐line or off‐line. New sorbent materials, their applications and the parameters involved in the extraction are described. Chromatographic methods used for their determination are discussed in detail. Much emphasis has been given to gas chromatography (GC) and liquid chromatography (LC) coupled to mass spectrometry (MS) as a confirmation technique and mass spectral information on several pesticides has been included. The final section is devoted to method validation, with the aim of providing a basis and a framework of information for quality assurance (QA) and interlaboratory calibration studies.
Diesel Fuels Analysis
Authors: Hsu Chang S.
Published: September 2006

Diesel fuels are analyzed for their physical properties and chemical composition to address various issues including their performance, storage stability, evaluation of refinery process efficiency and product quality, and assessment of environmental impact. Various methods of physical property measurement, performance tests, contaminant analyses, and analytical techniques for chemical composition are described.
Alkaloids, Pharmaceutical Analysis of
Authors: Gilpin R.K. , Hann C.J.
Published: September 2006

Although 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

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

Within 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

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

Quantitative 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.