bluuebunny/crossref_metadata_2025 huggingface dataset:
Glycoprotein Analysis: Using Nuclear Magnetic Resonance
Authors: Leeflang Bas R. , Vliegenthart J.F.G.
Published: September 2006

The majority of proteins are decorated with one or more covalently linked carbohydrate chains, and are thus glycoproteins. These carbohydrate chains may consist of mono‐, oligo‐ or polysaccharides, which can affect the physiological behavior and biological functioning of the glycoprotein. Insight into the structural aspects and characteristics of glycoprotein glycosylation is an important step in unraveling the function of carbohydrate chains in a glycoprotein. In most cases the glycan and protein moieties are cleaved and analyzed separately. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool in this respect. A plethora of NMR techniques are available to obtain NMR parameters such as chemical shift, scalar coupling constants and relaxation and cross‐relaxation properties. From these, both primary structural, three‐dimensional structural and dynamical features can be determined for these molecules. In this article, several aspects of glycoprotein structural studies will be discussed, and a selection of NMR experiments, including experimental conditions, will be presented.
Sample Preparation for Analysis of Chemicals Related to the Chemical Weapons Convention
Authors: Kuitunen Marja‐Leena
Published: September 2006

This article discusses the preparation of environmental samples to be analyzed for chemicals related to the chemical weapons convention (CWC), where analysis takes place on‐site or off‐site by gas chromatography (GC) or liquid chromatography (LC) as an introduction technique to spectrometers or by capillary zone electrophoresis (CZE). The specific sample preparation methods required for analysis by spectroscopic techniques such as Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy are dealt with in separate articles. Preparations of analytical samples from air, aqueous liquid (water), soil, active charcoal, wipe, concrete, paint, rubber, and other polymeric samples for off‐site analysis are presented in section 2, and preparations of analytical samples from aqueous liquid (water), soil, and wipe samples for on‐site analysis, are covered in section 3. Preparations for on‐site analysis are as described in the standard operating procedures (SOPs) of the international organization responsible for verifying the Convention (Technical Secretariat of the Organization for the Prohibition of Chemical Weapons) and those for off‐site analysis are as described in the corresponding recommended operating procedures (ROPs). Section 4 examines the question of quality control (QC) in sample preparation and section 5 the important matter of safety in handling samples containing CWC‐related chemicals. Section 6 reports on the use of the methods in international comparison and proficiency tests.
Biochemical Markers of Acute Coronary Syndromes
Authors: Azzazy Hassan M.E. , Christenson Robert H.
Published: September 2006

The acute coronary syndromes (ACSs) are a continuum of myocardial ischemia ranging from angina, indicating reversible tissue damage, through frank myocardial infarction (MI) with extensive tissue necrosis. The mortality from acute MI in the USA alone is 500 000 deaths per year. New predictors of cardiovascular events, that are easily measurable, are needed to improve diagnostic strategies for treating ACS patients. Cardiac markers, proteins released from the injured myocardium into the circulation, are useful for the diagnosis of MI according to the World Health Organization (WHO) criteria. Troponins I and T have emerged as sensitive, more cardiac‐specific clinical indicators for MI diagnosis and for risk stratification. A new generation of biochemical markers for indicating plaque rupture, platelet reactivity, and early MI offers promise for better assessment of patient risk so that clinicians may intervene to avoid adverse outcomes. Other biochemical markers, including the acute phase reactants and markers of thrombosis, may become useful for identifying a patient's location on the ACS spectrum and consequently the risk of adverse events.

This article describes the spectrum of ACS current and future biomarkers that are closely linked to the progression of cardiac injury from ACS, and various applications of biochemical markers in assessment of reinfarction, reperfusion, perioperative MI, risk stratification, guiding therapeutic intervention, and infarct sizing. Finally, an assessment of the importance of rapid testing, different triage strategies for chest pain patients, and new trends to reduce the overall costs of patient hospitalization are discussed. The recommendations of the National Academy of Clinical Biochemistry for use of cardiac markers are also presented.
Lipid Analysis for Important Clinical Conditions
Authors: Leary Elizabeth Teng , Carlson Timothy H.
Published: September 2006

Lipid analyses are primarily used for determining the risk of diseases resulting from atherosclerosis, including coronary heart disease (CHD), ischemic cerebrovascular disease, and peripheral arterial disease. These disorders are often marked by hyperlipidemia, with increased serum low‐density lipoprotein cholesterol (LDL‐C) and apolipoprotein (Apo) B, but decreased high‐density lipoprotein cholesterol (HDL‐C) and Apo A‐I. For use in risk assessment, serum cholesterol, LDL‐C and HDL‐C cut‐points have been derived from epidemiological data from several nations. The acceptance of these cut‐points, coupled with the remarkable heterogeneity of lipoproteins, has made standardization of cholesterol analytical procedures essential. An international network of laboratories (the Cholesterol Reference Method Laboratory Network (CRMLN)) coordinated by the US Centers for Disease Control (CDC) was formed to address this issue. Thus, several reference methods have been adopted and are used to standardize and certify the commercial reagents for lipid assays for use in the routine clinical laboratory. Other standardization efforts include those by the International Federation of Clinical Chemistry, World Health Organization (WHO) and CDC on Apos or lipoprotein(a) (Lp(a)). In addition to analytical standardization, it is important to standardize preanalytical procedures, and to be aware of potential biological variability.

In the 1980s and 1990s, significant advances have been made in the procedures for routine analysis of lipids and lipoproteins. The analyses have become much more precise and efficient, frequently performed in automated analyzers using small sample volumes. A variety of enzymatic methods for cholesterol and triglyceride (TG) measurements are in current use. HDL‐C is generally determined after precipitation of low‐density lipoprotein (LDL) and very low‐density lipoprotein (VLDL). LDL‐C is calculated from the difference between total cholesterol (TC), and the sum of HDL‐C and a total TG‐derived estimate of the very low‐density lipoprotein cholesterol (VLDL‐C) (the Friedewald equation). Several direct methods for measurement of LDL‐C and HDL‐C have been introduced with improvement in performance and labor efficiency, Apo B which is associated with LDL in equimolar ratio and Apo A‐I which is associated with high‐density lipoprotein (HDL) may be measured in conjunction with LDL‐C and HDL‐C or used in their place for clinical assessment. Other important lipid measurements include the C and E Apos, Lp(a), TG‐rich remnant lipoproteins, lipoprotein particle size and markers of oxidative stress.
Laboratory Instruments in Clinical Chemistry, Principles of
Authors: Karnik Hemant B.
Published: September 2006

In the last 40–45 years, instruments have evolved from simple analyzers that analyze few analytes in an hour to auto analyzers that analyze hundreds of tests in a fraction of an hour. A historical perspective on the evolution of the instruments, with discussion on the basic principles of their operation, along with the advantages and limitations of methodologies, is provided. Information on standardization, quality control and quality assurance in the clinical laboratory is also included. The article concludes with a brief discussion on the future developments in instrumentation. The material presented in this article is meant as a reference. For detailed information the reader is referred to other books and publications.
Phospholipids of Plasma Lipoproteins, Red Blood Cells and Atheroma, Analysis of
Authors: Ravandi Amir , Kuksis Arnis
Published: September 2006

The large number of lipid classes and great complexity of molecular species present in blood plasma, red cells, platelets and atheromatous lesions requires a combination of analytical techniques for comprehensive analyses, including chemical and enzymatic derivatization of samples. In many instances only partial analyses are required, which can be accomplished by specific analytical techniques. This chapter describes the full spectrum of the methodology ranging from the most basic thin‐layer chromatography (TLC) to the detailed mass spectrometric assays. Traditional sample extraction by liquid–liquid partition is time‐consuming and involves large volumes of solvents. Liquid–solid extraction using adsorbent cartridges is more economical. At the present time total lipid extracts can be effectively assayed for lipid class content and molecular species composition by flow injection tandem mass spectrometry (MS/MS), while a more detailed analysis of complex lipid mixtures is provided by a combination of liquid chromatography with on‐line electrospray mass spectrometry (LC/ESMS). The new techniques permit completion of the analyses in a few hours, where previously several days or weeks may have been required. The soft ionization mass spectrometric techniques have permitted the recognition and detailed analysis of such minor components of blood as the lipid oxidation and glycation products often observed in disease.
Gas Chromatography and Mass Spectrometry in Clinical Chemistry
Authors: Bertholf Roger L.
Published: September 2006

Automated spectrophotometric, electrochemical, and immunochemical analyses have become the mainstays of clinical chemistry and toxicology laboratory services, but their scope is limited. A wide array of clinically relevant analytes demand more sophisticated analytical techniques to provide sensitive and specific assays for diagnostic purposes. Gas chromatography (GC) and mass spectrometry (MS) are becoming cost‐effective alternatives for many of these challenging assays. GC is a robust technique that offers the ability to resolve volatile components of a complex mixture. MS provides structural information that can unambiguously identify a compound. In combination, these two techniques provide qualitative and quantitative answers to many difficult analytical problems. GC and MS applications have been developed for a variety of clinical analytes, and the use of these methods has created new and exciting frontiers for clinical laboratory medicine. Several clinical applications of these analytical techniques will be discussed in this chapter.
Molecular Biological Analyses and Molecular Pathology in Clinical Chemistry
Authors: Lo Y.M. Dennis , Lam Ching‐Wan , Wong Ivy H.N.
Published: September 2006

The recent introduction of powerful methods for the analysis of nucleic acids has started a revolution in medicine, opening up a new field of molecular diagnosis. The core technologies of molecular diagnosis involve techniques for the amplification and characterization of nucleic acids. These techniques have enabled the diagnosis of many diseases with unprecedented sensitivity and specificity. As research tools, these methods have increased our understanding of many diseases on a molecular level, with the unraveling of the molecular pathology of many common disorders. Foundation for the rapid and continual development of molecular pathology into the next century has received a boost from the Human Genome Project (HGP), which is expected to be completed over the next few years and which will provide the essential genetic blueprint for future investigations.
Atomic Spectroscopy in Coatings Analysis
Authors: Weldon Dwight G.
Published: September 2006

In atomic spectroscopy, vaporized neutral atoms are detected by measuring either the absorption or emission of light at characteristic frequencies. In atomic absorption (AA) spectroscopy, radiation is absorbed by the atom in the process of exciting an electron from a lower energy state into a higher energy state. In atomic emission (AE) and inductively coupled plasma (ICP) spectroscopy, radiation is released when an electron from an excited energy state relaxes into a lower energy state. The energy required for these transitions occurs in either the visible or ultraviolet region of the electromagnetic spectrum.

Atomic spectroscopy is a very useful technique in the field of coating analysis. It is primarily used for the analysis of metallic constituents, such as certain pigments and coating additives. It is extremely sensitive, and can detect several dozen different elements. It is especially useful in determining whether or not a particular coating contains environmentally hazardous levels of heavy metals, such as lead, cadmium and chromium. Disadvantages of the technique include its inability to determine the chemical form in which the element is present, somewhat laborious sample preparation procedures, and the inability to determine other important constituents of coatings, such as resins and solvents.
Gas Chromatography in Coatings Analysis
Authors: Haken J.K.
Published: September 2006

This work describes the analysis of coating materials using gas chromatography (GC). An element of volatility is necessary for samples to be amenable to the technique and early applications concerned the analysis of solvents and their mixtures. The examination of low molecular weight and volatile components of coatings followed; these included trace or residual products in resins. The resinous or binder components are essentially nonvolatile, and to be amenable to GC a considerable reduction in molecular weight is necessary. This has been achieved by chemical cleavage of condensation systems, with examination of the reconstituted reactants or their derivatives, or by thermal means in the absence of oxygen where pyrolysis provides fragments which may be related to the initial composition. Chemical cleavage was applied to alkyd resins, acrylics, polysiloxanes, polyurethanes and polyethers during the 1960s and while the results were most satisfactory, the time required was considered excessive. Several decades later, some of the problems have been eliminated but the procedures have found little application. Pyrolysis was also introduced at the same time and while the early reports were of low reproducibility, refinements in technique allow reproducible results to be achieved rapidly. The major area of the application of GC to coating materials is pyrolysis, where, in combination with mass spectroscopy (MS), valuable information is achieved in minutes.

Other coating applications of GC include inverse chromatography which has found negligible use and headspace chromatography which is widely used in determining the source of odors or taints in coated food packaging. Special applications of GC include use in forensic science where accelerants used by arsonists are readily detected and also examination and identification of paint flakes by pyrolysis GC/MS. Similarly pyrolysis techniques are used in conservation studies, with the analysis of old paints on art works.
InfraredLIDARApplications in Atmospheric Monitoring
Authors: Orr Brian J.
Published: September 2006

The acronym LIDAR stands for light detection and ranging, an optical analog of RADAR (radio detection and ranging). The conventional version of LIDAR requires a laser transmitter to launch short pulses of coherent light, which are scattered from atmospheric targets of interest back to an optical receiver, with a time delay that is determined by the range of the target. Optical phenomena in the Earth's atmosphere (e.g. Rayleigh scattering, Raman scattering, Mie scattering, refraction, and resonant absorption) contribute to the amplitude of optical signals returning to the receiver and their characteristic wavelength dependence allows us to measure the concentration and velocity distributions of different atmospheric molecules and aerosol particles. LIDAR backscattering in the infrared (IR) region, on which this article concentrates, is well suited to detecting aerosols (as in clouds or industrial particulate emissions). IR DIAL (differential absorption LIDAR), a variant in which two wavelengths are used simultaneously to separate resonant molecular signals from background, enables most molecular species to be monitored by means of their IR absorption spectra. A closely related approach comprises long‐path IR laser absorption, with retro‐reflection from a topographic target (e.g. a strategically located mirror); this sacrifices optical range information but gains sensitivity because it integrates over all molecules in the optical column between the transmitter/receiver and the reflector. Such techniques are vitally dependent on pulsed IR laser technology.
Flame and Graphite Furnace Atomic Absorption Spectrometry in Environmental Analysis
Authors: Sperling Michael
Published: September 2006

Atomic absorption spectrometry (AAS) is one of the most often used techniques for the quantitative determination of elements in environmental materials at trace and ultratrace levels. AAS is an optical atomic spectrometric technique based on the measurement of the specific absorption originating from free nonionized atoms in the gas phase. To transfer the analyte to free atoms, different types of atomizer are in use, the flame and the graphite furnace types being the most often used. Typical detection limits of flame atomic absorption spectrometry (FAAS) are of the order of 1–100 µg L−1, making it a perfect tool for the determination of minor and trace elements, at least for contaminated samples. Graphite furnace atomic absorption spectrometry (GFAAS), offering detection limits which are about a factor of 20–200 lower than for FAAS, is the standard method for many trace elements, especially for background values, and for unpolluted samples, such as fresh water and biological materials. AAS in its conventional configuration is a single‐element technique, which has to be used in a sequential mode when more than one element has to be determined. However, there are commercial instruments available that can be used for the determination of 6–8 elements simultaneously.
Hydride Generation Sample Introduction for Spectroscopic Analysis in Environmental Samples
Authors: Narasaki Hisatake
Published: September 2006

The hydride generation (HG) technique using sodium tetrahydroborate(III) (SBH) is applied to atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP/AES), and inductively coupled plasma mass spectrometry (ICP/MS). All the detection limits using the HG technique are less than those for solution nebulization. Chemical speciation in the HG technique is effected by changing the pH of the solution, the cold trap method and various hyphenated techniques. The author used a gas–liquid separator containing a spiral tube to separate efficiently the hydrides from solution. This minimized the consumption of the sample and SBH solutions and of the hydrogen evolution compared with the continuous‐flow method. The author used a high‐resolution ICP/MS instrument which allowed the use of hydrochloric acid in the sample preparation of arsenic and the determination of selenium without its isotopes.
Infrared Spectroscopy in Environmental Analysis
Authors: Visser Tom
Published: September 2006

Infrared (IR) spectroscopy is a universal, versatile analytical technique for the structure elucidation and quantification of a large variety of organic, inorganic and biological samples. The technique is based on the measurement of IR radiation, absorbed or emitted by a sample, as a function of the wavelength in the region 2.5–100 µm, or 4000–100 cm
−1
in wavenumbers. The absorption or emission of IR radiation is related to discrete vibrational and rotational transitions in a molecule and, therefore, represents structural information. The analytical value of IR spectroscopy is based on the fact that the IR bands occur at more or less localized positions in the spectrum which are correlated to the presence of characteristic structural features of the sample under study. This similarity and transferability of spectral characteristics and the corresponding structural features, makes IR a powerful tool for functional group analysis. On the other hand vibrations, and thus the exact peak positions, are sensitive to the local environment which also makes IR spectra unique molecular fingerprints, highly suited for the unambiguous identification of a sample by comparison with reference spectra. Finally, IR spectroscopy obeys Beer's Law and can thus be used for quantitative purposes too.

The major advantage of IR over other spectroscopic techniques is that practically all compounds show absorption/emission and can thus be analyzed both quantitatively and qualitatively. Besides, IR spectroscopy is nondestructive and admits in situ and remote measurement of almost any sample, irrespective the physical state and without elaborate preparations. A broad variety of advanced accessories and technologies, such as IR microscopy, optical fibers, remote sensing, reflection and emission equipment and the combination with gas chromatography (GC), liquid chromatography (LC) and supercritical fluid chromatography (SFC) sampling and measurement techniques are available to tackle a diversity of problems. The absolute sensitivity is about 50–500 picograms, which is sufficient to solve many problems in trace analysis.

IR spectroscopy is used in a broad range of environmental applications. The technique is a viable tool in remote measurements of gases, liquids and solids and as a fast and reliable method for the characterization and indicative structure classification of a wide variety of samples. Besides, IR is widely applied for identification purposes either to confirm results of other techniques or for reasons of quality assurance (QA).
Liquid Chromatography/Mass Spectrometry in Environmental Analysis
Authors: Careri M.
Published: September 2006

On‐line liquid chromatography/mass spectrometry (LC/MS) has become a powerful technique in environmental analysis because of the separation capabilities of liquid chromatography (LC) and the detection and identification potential of mass spectrometry (MS), the characteristics of both methods making coupling very attractive. Among the interfacing systems used to couple LC with MS, those based on the atmospheric pressure ionization (API) offer advantages in terms of sensitivity and capability to analyze highly polar, ionic, heat sensitive and high‐molecular‐weight substances. Further, the on‐line coupling of chromatographic separations with element‐selective detection systems such as inductively coupled plasma mass spectrometry (ICP/MS) is an attractive technique for trace element speciation.

The main advantage of LC/MS lies in its ability to provide qualitative information (including molecular mass and fragmentation pattern) on the detected peaks. In addition, when all the ionization parameters are optimized, quantitative analyses can be carried out and low detection limits (at the ppb level) are obtained performing selective ion detection.

In environmental analysis, universal, selective and sensitive methods are needed to afford the assay of a wide variety of target and nontarget substances. Even though gas chromatography/mass spectrometry (GC/MS) is extensively applied to the analysis of organic contaminants in several matrices, LC/MS offers major advantages over GC/MS for analyzing polar, nonvolatile and thermolabile compounds. Ultraviolet (UV) or diode‐array detector (DAD) are commonly used to perform detection in high‐performance liquid chromatography (HPLC). However, UV‐based detection methods for HPLC have several disadvantages deriving from nonspecific detection and lack of sensitivity. A more reliable identification is sometimes possible using DAD for certain compound classes, e.g. nitrophenols, in environmental samples; however, structural information is lacking for some classes of pollutants, among which are some pesticides, because their UV spectra are often almost identical. Using unspecific LC detectors, detection may be complicated by false‐positive results; in such cases, MS has proved to be an extremely valuable technique for unequivocal identification of micro‐contaminants in a variety of environmental samples.

This overview discusses recent instrumental developments concerning mass analyzers of the mass spectrometers and on‐line sample treatment procedures, with emphasis on the environmental field. Among the environmental applications of LC/MS, methods for the analysis of pesticides, polycyclic aromatic hydrocarbons (PAHs), dyes, surfactants, inorganic and organometallic compounds in environmental samples are discussed.
Organic Analysis in Environmental Samples by Electrochemical Methods
Authors: Naranjo‐Rodríguez Ignacio , Hidalgo‐Hidalgo de Cisneros José Luis
Published: September 2006

Concern for the environment is not limited to ecological aspects, but encompasses matter such as the origin and the effects of pollutant discharges, the evaluation of environmental programs, quality control and quality assurance related to analytical precedures, and the analysis of the content of environmental matrices – both inorganic and organic – in order to control and evaluate environmental pollution. Thus, it is right to say that analytical chemistry has an important role to play in environmental analysis.

A large number of analytical methods are used in environmental analysis. Some are widely used in environmental programs, and are reference/standard/official methods for the analysis of a great variety of compounds.

However, there is no single universal procedure that can be applied to the analysis of any chemical species in any environmental matrix, and for any in situ/remote measurement.

Electrochemical (EC) methods are widely used to investigate environmentally significant compounds, both organic and inorganic. EC research covers all important branches of environmental analysis, such as in situ/remote measurements, flow systems, combined applications with a separation technique, (bio)sensors for selective analysis, and monitoring and control procedures.

This article discusses the application of these EC methods to the study of organic compounds occurring in environmental water and waste samples.
Organometallic Compound Analysis in Environmental Samples
Authors: Ebdon Les , Fisher Andy
Published: September 2006

Many organometallic species exist in the environment and these may range from being completely nontoxic, e.g. the arsenic compound arsenobetaine, to exceptionally toxic, e.g. methyl mercury. Compounds of intermediate toxicity, such as the arsenic species dimethylarsinic acid and monomethylarsonic acid also exist. Determining the chemical form or speciation of samples is vital in environmental impact assessment as it affects bioavailability and mobility in the environment. Speciation analysis usually comprises a number of analytical steps. Sampling and sample storage are critical and must be performed in such a way that ensures a representative sample whilst preventing changes in speciation or losses of some of the more labile species. Sample preparation normally requires the extraction of the species of interest from the sample materials. This may be achieved in a number of ways that are discussed in detail in the relevant section. Sample cleanup and derivatization methods that may be required if gas chromatographic methods of analysis are to be used are also discussed. The actual sample analysis stage is discussed in detail and this concentrates mainly upon different chromatographic techniques coupled with assorted atomic spectrometric methods of detection. This is because these so‐called “coupled” techniques are used for the majority of speciation analyses. Other nonchromatographic methods of sample introduction to atomic spectrometric detection, such as hydride generation (HG), are also discussed together with techniques including more conventional detectors for the chromatographic techniques (such as ultraviolet (UV)/visible, fluorescence, flame ionization detectors (FIDs), electrochemical detectors, etc.), electrochemical methods, nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. In addition to obtaining quantitative data, techniques such as NMR and IR spectroscopy may be used to obtain structural information on individual species.

Method validation is as important for speciation analysis as it is for any other analysis. This may be achieved using mass balance data, the analysis of certified reference materials (CRMs) or using completely independent analysis techniques. The text gives an overview of all stages of the analysis, highlighting potential pitfalls and areas of uncertainty.
Sample Preparation Techniques for Elemental Analysis in Aqueous Matrices
Authors: Marín Sergio R.
Published: September 2006

The reliability of results obtained from chemical analysis of environmental samples is related to the sample collection and preparation techniques. A succession of stages is required to obtain a result that is both accurate and representative of the initial material. The task begins by taking the appropriate precautions during collection of the liquid and solid samples, and during their later shipment to the laboratory. The environmental conditions in the laboratory where the sample will be prepared are important, as is the quality of the apparatus, containers, glassware, and reagents that are usually used. The preparation of solid waste samples requires the selection of appropriate digestion procedures, apparatus that is of high enough quality to resist the aggressiveness of some inorganic acids, and convenient systems of security for the procedures that are carried out. The information produced by the laboratory should have a high degree of reliability. For this reason, the procedures used usually permit the results obtained to be guaranteed. The more important procedures include the use of certified reference materials (CRM) and participation in interlaboratory programs. Some organizations, for example the United States Environmental Protection Agency (USEPA), have developed and distributed procedures for environmental sample preparation, which are used by many laboratories as normalized methods of reference.
Underground Fuel Spills, Source Identification
Authors: Lavine Barry K. , Moores Anthony , Ritter Jason
Published: September 2006

Water samples from underground wells or aquifers contaminated by middle distillate fuels exist in one of two forms. Either the water sample collected from the well shows a layer of floating fuel, or the sample contains the dissolved hydrocarbons from the leaking fuel. In the worst case scenario, that of a floating fuel, the fuel layer is collected and analyzed by gas chromatography (GC). The GC profile of the fuel layer is then compared with the GC profile of the different candidate fuels to determine the fuel type of the leaking material. Usually, the gas chromatograms are compared visually, in order to obtain the best match. However, this approach to data analysis is subjective and is not always persuasive in a court of law. Visual analysis of gas chromatograms also has the drawback that it cannot take into account the influence of weathering on the overall GC profile of the fuel.

Pattern recognition (PR) methods offer a better approach to the problem of matching the gas chromatograms of jet fuels because these methods involve less subjectivity in the interpretation of the data. PR methods can identify fingerprint patterns in GC data characteristic of fuel type, even if the fuel samples have been subjected to a variety of conditions. Hence, discriminants can be developed that are relatively insensitive to the changes in the overall GC profile data of the original fuel due to contamination, analytical error, or weathering.
Volatile Organic Compounds in Groundwater, Probes for the Analysis of
Authors: Patterson B.M. , Davis G.B. , McKinley A.J.
Published: September 2006

An automated system using a semipermeable polymer tubing [volatile organic compound (VOC) probe] coupled to an electrochemical sensor has been used for monitoring of VOCs in groundwater. The system operates by purging a VOC probe, which is in contact with groundwater, with gas at a low flow rate. The gas concentration of VOCs exiting the VOC probe can then be related to an external aqueous concentration according to Henry's law. The system enables semicontinuous in situ monitoring of total VOC concentrations in gaseous and aqueous environments.

The in situ VOC probes provided a reliable monitoring technique under long‐term (between 1 and 3 months) aggressive and dynamic field conditions. The probes provided data that were comparable to conventional techniques without the labor‐intensive sample collection and processing associated with conventional techniques, such as purge and trap or microextraction. Only the total VOC concentration can be determined using the electrochemical sensor; however, coupling the VOC probe to a gas chromatograph does enable compositional analysis to be determined.
Lipid Analyses in Food
Authors: Marini Domenico
Published: September 2006

The term lipid encompasses a great host of compounds (e.g. fatty acids (FAs), mono‐, di‐ and triglycerides), that are almost ubiquitously present in foods; their characterization and quantification is then of importance for an analytical chemist.

The first step for an accurate analysis is sample preparation: choosing an appropriate solvent or phases can isolate one particular class of lipid from a sample [a good separation of classes can be accomplised by thin‐layer chromatography (TLC)]; obviously, the sample pretreatment will be governed by the determinations to follow. Indeed, nowadays, there is a host of techniques, mainly chromatographic, for lipid analysis. TLC is a rapid way to gather information about the sample (presence of conjugated double and triple bonds, free FAs and of oxygenated FAs), particularly with the development of modified normal phases. For example, silica gel can be impregnated with boric acid, which inhibits isomerization of mono‐ and diglycerides, or it can be treated with silver ions [argentation, for silver ion thin‐layer chromatography (Ag‐TLC)] used for resolution of unsaturated FAs. Gas chromatography (GC) and high‐performance liquid chromatography (HPLC) are the most common techniques actually employed, because of their versatility (many parameters can be changed, e.g. stationary and mobile phases, detector) and to their capacity to be hyphenated (coupled with another measuring device). Particularly, the advent of the light‐scattering detector has allowed greater reproducibility in the HPLC of lipids. Mass spectrometry (MS) is often coupled with GC. However, coupling MS with another MS (MS/MS or tandem MS) is useful for the determination of the structure of long‐chain FAs with improved selectivity and sensitivity. Finally, nuclear magnetic resonance (NMR) is able to identify functional groups, even in mixtures, and is a valid aid for the elucidation of structures with double bonds (DBs) by interpretation of the coupling patterns.

Each analytical method relies on appropriate sample preparation (e.g. methylation for the GC analysis of FAs) and a critical approach to evaluate its usefulness.
Chiroptical Spectroscopy in Drug Analysis
Authors: Brittain Harry G.
Published: September 2006

Many pharmaceutical compounds contain one or more centers of dissymmetry, thus presenting a unique series of regulatory and compendial requirements. The regulatory authorities are well acquainted with the fact that one given enantiomer or diastereomer of a drug entity may possess more efficacy (or fewer side effects) than its mirror image. Consequently, unless a compelling argument exists for the marketing of a racemate, it is more appropriate to develop enantiomerically pure therapeutic agents. Although most often characterized using chiral chromatography, these molecules can be effectively studied using the various techniques of chiroptical spectroscopy. Techniques that have been found to be very useful for such work include polarimetry (i.e. circular birefringence), optical rotatory dispersion (ORD), and circular dichroism (CD). At present, regulatory authorities remain fixated on the use of polarimetry to establish enantiomeric identity and purity, but as their awareness grows so will an acceptance of the more sophisticated chiroptical techniques. In this article, the principles underlying each chiroptical effect are briefly outlined and the application to problems of pharmaceutical interest is illustrated through the inclusion of appropriate examples.
Microspectrophotometry in Forensic Science
Authors: Ziȩba‐Palus Janina
Published: September 2006

Infrared microspectrophotometry is a combination of two techniques – optical microscopy and infrared (IR) spectrometry – which supply specific information about the composition and structure of a given material. The equipment used is a Fourier transform infrared (FTIR) spectrometer connected on line with an optical microscope.

The microscope allows observation of a sample in white light at relatively high magnification; this allows its morphology and microstructure to be established, and facilitates selection of the area which will subsequently be subjected to IR spectrometric analysis. The microscope also permits use of polarized light in investigations.

The spectrometer enables analysis of a sample with a chosen measuring technique – transmission or reflection – with the aim of determining the chemical composition of the sample. It also supplies information about its microstructure and orientation.

This method is particularly useful in the analysis of trace amounts of various substances secured as material evidence in court cases, and in analysis of the homogeneity of the sample, identification of inclusions and contaminants on the surface, and detection of structural defects.

A specific advantage of this method is its ability to unambiguously photograph and record marked and measured areas of the sample and minimize the process of preparing the sample for analysis.

Furthermore, IR microspectrophotometry gives the rare opportunity of studying small crystals or areas in the oriented materials by using polarized IR radiation, both by the transmission and the reflection technique.

Its fundamental drawback is that the physical nature of the microsample may influence the precision of the photometric measurements and cause distortion of the spectra (artefacts) obtained. Furthermore, because only a small area is studied the heterogeneity of the sample and the amount of contaminants may significantly influence the results of spectrometric measurements.

Microspectrophotometry in the ultraviolet/visible (UV/VIS) range is a combination of photometric measuring techniques and optical microscopy. It allows comparison of the color of very small samples of various materials, such as single fibers, tiny amounts of paint, traces of ink or ball‐point pen ink on a forged document in an objective way, independently of the sharpness and quality of the observers's vision. It yields immediate information about spectral differences existing between two samples of similar color, which are indistinguishable by use of the optical microscope. Additionally, using appropriate software to analyze the results of microspectrometric measurements, it enables precise measurement of a color, and – applying the theory of colors – gives a color a defined numerical value; this facilitates communication between experts working with this method. The equipment consists of an optical microscope with a spectrometer for analysis in the visible and ultraviolet range, connected to a microcomputer via an analog‐to‐digital converter.
Direct Reading Instruments for the Determination of Aerosols and Particulates
Authors: Pui David Y.H. , Chen Da‐Ren
Published: September 2006

Solid and liquid particles suspended in a gas are referred to as aerosols. The suspending medium can be air, or some other gases, such as argon, nitrogen, helium, etc. Aerosols have found numerous scientific and technical applications. Beneficial applications include pharmaceutical aerosols for medical inhalation therapy or diagnosis, industrial aerosols for coating wave guides, refractories, gas sensors and semiconductors, as well as particles ofmodern materials for forming advanced ceramics, optical and optoelectronic devices, cosmetic products, paint pigments, and catalysts. Harmful effects of aerosols include atmospheric aerosols that contribute to urban air pollution and global radiation balance, dust particles ingested by engines causing premature failure of the equipment, and particles deposited on semiconductor wafers causing device failure and product yield loss.

Aerosols and particles can be analyzed by collecting them on a filter or a sampling surface for subsequent microscopic, gravimetric, or chemical analyses. The collection by the samplers gives an integrated sample and a time averaged concentration over a period of hours or days. Direct reading instruments carry out the sampling and analysis within the instrument and the property of interest can be obtained in near real‐time. Direct reading instruments are available to cover particles in the size range of 0.002 to 100 µm. These instruments have fast time response and can follow rapid changes in both particle size and concentration. Good counting statistics can also be obtained because repeated measurements can be performed in a short time. However, these instruments usually rely on indirect sensing techniques and more calibration efforts are usually required.
Spectroscopic Techniques in Industrial Hygiene
Authors: Wang Jin , Siegel Paul D. , Lewis Daniel M. , Vo Evanly , Wallace William E. , Ashley Kevin , Stettler Lloyd E.
Published: September 2006

Over the past few decades the pace of change in spectroscopic techniques has been remarkable. Spectroscopic techniques are emerging as important, powerful, and versatile tools in determining exposure levels of hazards generated in working environments. Occupational safety and health studies employ spectroscopic techniques to analyze hazardous chemicals, biomarkers, and particulate matters of exposure. In comparison with many traditional detection techniques such as gravimetric methods, spectrometric techniques are much more sensitive, selective and accurate. The major spectroscopic techniques used in industrial hygiene include mass spectrometry (MS), scanning electron microscopy (SEM), X‐ray microanalysis (XM), atomic spectrometry (AS), ultraviolet/visible (UV/VIS) photometry, fluorescent spectrometry (FS), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy (RS). Interest in using MS in industrial hygiene is driven by its value in understanding basic physical, chemical, and biological processes related to workers' exposure to occupational hazards, and in devising new methodologies to monitor exposures. SEM has become particularly useful in the study of pneumoconioses and workplace environmental particles since being complemented with energy dispersive X‐ray (EDX) analysis and automated image analysis capabilities. SEM and EDX have been used extensively to characterize particles found in lung tissues. Atomic spectrometric methods are used widely for occupational health evaluation of inorganicmetals. The development of inductively coupled plasma atomic emission spectrometry (ICPAES) techniques has become increasingly attractive, and has been applicable to analysis of nearly all the elements. FTIR and Raman spectroscopies are employed to detect highly toxic gas and vapor mixtures. Additionally, field‐portable methods for monitoring airborne workplace contaminants and toxins have received increasing attention. To date, highly specific, selective, and sensitive spectroscopic technologies have allowed for the development of novel methodologies and new indicators for exposure characterization. Assessment of actual body burden of chemicals, which are more directly related to potential adverse occupational health effects, can be accomplished. The major spectroscopic techniques and their applications to industrial hygiene are described in this article.
Filtration in Particle Size Analysis
Authors: Droppo Ian G.
Published: September 2006

Filtration is defined as the separation of solid particles from a liquid or gas by passing the suspension through a porous, fibrous or granular substance. In science and industry, filtration is commonly used for the concentrating and/or removal of particulate matter or for the separation of particles into size classes for subsequent physical, chemical or biological analysis. Separation of particles into multiple size classes is often required for the assessment of particle size. There are many different types of filters available (e.g. fibrous, membrane, polycarbonate) for particle characterization through filtration. The type of filter to be used for particle size characterization is dependent on a number of considerations such as sample (particle) characteristics, collection efficiency, pore size and structure and analytical compatibility. Filtration has the advantage of being one of the few techniques which allow for the physical separation of particles into different size classes for distribution or chemical–biological analysis. If appropriate precautions are taken to minimize sample perturbations (e.g. select appropriate filter for the application, filter in the field, avoid overloading a filter, ensure a low flow rate and stir if possible), a reasonably accurate estimate of particle size can be obtained. Generally, errors associated with filtration arise from filter clogging and when attempting to characterize flocculated/aggregated particles. The basic nature of a suspended aggregate (i.e. fragile, plastic, high water content) means that it is likely to be broken up or created owing to the often tortuous nature of filtration, or be deformed on the surface or within the filter owing to pressure effects. This has implications if optical image analysis of the filter is to be used for particle size analysis as the true particle morphology and size will have been altered. In such an instance, if only a grain size distribution is required, it is suggested that optical image analysis be employed in conjunction with a plankton chamber settling technique rather than with filtration.
Ultrasonic Measurements in Particle Size Analysis
Authors: McClements David Julian
Published: September 2006

The particle size distribution and concentration of a colloidal dispersion can be determined by measuring its ultrasonic velocity and/or attenuation coefficient as a function of frequency and then using a suitable mathematical model to interpret the spectra. Ultrasonic spectroscopy can be used to analyze particle sizes between about 10 nm and 1000 µm, and is suitable for application to concentrated systems (often up to 50 wt%). This technique has considerable advantages over many alternative technologies because it can be applied to systems that are optically opaque without the need of any sample preparation.