bluuebunny/crossref_metadata_2025 huggingface dataset:
Supercritical Fluid Extraction of Inorganics in Environmental Analysis
Authors: Ashraf‐Khorassani Mehdi , Taylor Larry T. , Combs Michael T.
Published: September 2006

Supercritical fluid extraction (SFE) of metal ions via in situ chelation and preformed metal chelates using pure or modified CO
2
from several matrices has been accomplished. To understand the extraction results better, the solubilities of different ligands and metal chelates have been measured in supercritical fluids (SFs). In most cases, fluorinated chelates have been found to possess higher solubility in the SF than nonfluorinated ones, which in turn can often enhance extraction efficiency. Metal chelate stability under supercritical conditions plays an important role in the extraction of metals. Also, the matrix has a major effect on extraction efficiency of both hydrated metal ions and metal chelates. In order to obtain sufficient extraction not only should solubility of the metal complex be considered, but also the overall stability of the complex is critical.
Supercritical Fluid Extraction of Organics in Environmental Analysis
Authors: Benner Bruce A.
Published: September 2006

Supercritical fluids (SFs) possess several physical properties that make them attractive substitutes for conventional liquid solvents in analytical‐scale extractions. Molecular diffusivities of SFs are typically a factor of 10 greater (10−4vs 10−5 cm2 s−1) and their viscosities are a factor of 10 lower (10−4vs 10−3 N s m−2) than liquid solvents. These properties improve the rate of mass transfer of a solute from the matrix surface to the bulk extractions fluid – a transfer believed to be the rate‐limiting step of most extractions. Under optimized conditions, the improvements in mass transfer can enable a supercritical fluid extraction (SFE) to be completed in less than 1 h compared to ≥12 h for extractions involving conventional solvent techniques. The typical SFE also generates little solvent waste, compared to traditional extraction methods, but limitations have also emerged with respect to the efficiency of SFE as related to the sample composition (matrix effect). This review will discuss the progress made over the last 20 years in SFE as an alternative technique to liquid solvent extractions of environmental samples for the subsequent measurement of organic constituents.
Trace Organic Analysis by Gas Chromatography with Quadrupole Mass Spectrometry
Authors: Booth Matthew M. , Powell David H.
Published: September 2006

Gas chromatography (GC) with quadrupole mass spectrometry (MS) is one of the most powerful and widely used analytical techniques. This technology combines the high resolving power of GC with the excellent sensitivity and chemical‐structure‐informing power of quadrupole MS. The combination of these two techniques provides both the selectivity and sensitivity needed for qualitative and quantitative analysis of organic analytes at trace levels in a wide variety of matrices.

This article provides an overview of the development and combination of these two technologies. Types of quadrupole mass spectrometers that are commonly coupled to gas chromatographs are discussed. Both electron ionization (EI) and chemical ionization (CI) are reviewed. Sample preparation methods are discussed for air, water, and solids. The different approaches employed for highly volatile and semi‐volatile substances are presented. The use of chemical derivatives to improve sample response and various instrumental analysis considerations are also covered.
Aircraft‐Based Flux Sampling Strategies
Authors: Desjardins R.L. , MacPherson J.I. , Schuepp P.H.
Published: September 2006

One of the essential elements of plant growth is carbon dioxide assimilation and water vapor loss. Measuring the exchange of these gases can provide an accurate picture of plant growth, health, and ultimate yield. This report describes the instrumentation used on the Canadian flux aircraft and the type of data collected for measuring gas exchange over large areas. It presents flux measurements of carbon dioxide, sensible heat (H) and latent heat (LE) using the eddy‐covariance technique. This technique provides the most direct measurements of mass and energy exchange at the land–atmosphere interface. Flux measurements obtained over wetlands near James Bay, the boreal forest in northern Saskatchewan, grasslands in Kansas, agricultural crops in California, and over the city of Fresno in California are presented as examples of the potential of this technique to characterize transfer processes over complex ecosystems. The accuracy of aircraft‐based flux measurements is examined using data obtained with other aircraft during wing‐to‐wing formation flights and with several tower‐based systems during tower fly‐by. Finally, examples of the use of these data for interpreting satellite data and for characterizing the photosynthetic response of a wide range of vegetation are presented.
Chemical‐Sensing Networks: Satellite‐Based
Authors: Hahn John C.
Published: September 2006

This paper addresses preliminary system engineering for a disposable, remote, chemical‐sensing network. This network could interconnect a satellite hub, low‐earth orbiting (LEO) satellites, remote sensors, and a fiber optic (OF) interface that interlinks remote chemical sensors, situated underground in aquifers or directly beneath hazardous chemical/waste sites, with remote transmitter/receivers on the earth's surface. Some critical technical factors: orbital analysis, telemetry, data rates, data structures, digital modulation techniques, antennae selection, remote power considerations, satellite transponder access, and other hardware tradeoffs, are examined in an effort qualitatively to optimize the configuration of a wide area network (WAN). This paper demonstrates the viability of the proposed network, which is suited to the detection of hazardous chemicals in the atmosphere or underground.
Electrochemical Sensors for Field Measurements of Gases and Vapors
Authors: Cox James A. , Holmstrom Scott D.
Published: September 2006

Sensors that utilize signals produced by redox of a targeted species (analyte) at an electrode under controlled potential, the conductance changes produced by contact of a chemical species with an electrolyte, or a change in the equilibrium potential of an electrode upon contact with an analyte are being employed in studies of gaseous samples of environmental, biomedical, and industrial interest. Changes in the work function of chemically modified field effect transistors (FET) also is a strategy related to both conductivity and potentiometry. Electrochemical sensors are fundamentally advantageous over other types in that they directly convert information from the chemical to the electrical domain, rather than requiring another transducer. Yet, few have found commercial application. The common types that are employed for field measurements of gaseous samples include devices to quantify oxygen, hydrogen sulfide, sulfur dioxide, oxides of nitrogen, hydrogen cyanide, hydrogen chloride, and chlorine. The limitation is not sensitivity; by this measure electrochemistry is among the best of the analytical measurement methods. Amperometric sensors accrue selectivity by control of the electrode potential along with control of the process by which the analyte partitions from the gas to the electrolyte. The latter is the primary means by which conductivity and potentiometry systems achieve sensitivity. These methods are not as selective as those in which a chemical reaction is incorporated in the sensor. The most selective electrochemical sensors employ an enzymatic reaction as part of signal production, but these are applicable to only a few analytes, such as alcohols, of importance in the gas phase.
Field‐Based Analysis of Organic Vapors in Air
Authors: Berkley Richard E.
Published: September 2006

Volatile organic compounds (VOCs) exist in the vapor phase in ambient air at partial pressures ranging from less than 1 part per billion to a few parts per million. Some of them are toxic and potentially harmful to the environment and to human health. The threshold concentrations at which individual compounds become harmful is often not well defined, and less is known about mixtures. Accurate assessment of health risk requires analytical methods that are accurate, affordable, convenient, fast, and sensitive enough to detect each compound at a concentration below the threshold of harmful effect. The usual approach to identification and quantitation of them has been to collect samples and submit them to laboratory analysis. United States Environmental Protection Agency (USEPA) Method TO‐14 is a standard procedure for analyzing a group of 41 potentially harmful nonpolar and semipolar organic compounds, which is in widespread use and has been found to detect and measure target compounds reliably under most conditions. However, more rapid delivery of data is often needed, and samples can deteriorate during storage pending analysis. Alternative analytical methods that produce immediate data are needed. Analysis of samples at the time and place of collection has seldom been done because of the lack of suitable equipment and the vicissitudes of operating it under field conditions. Portable or field‐deployable gas chromatographs (PGCs) have, with cause, been regarded as less accurate than laboratory equipment, and a perception remains that analyses done in the field are less useful than those done in the laboratory. In fact, laboratory‐ and field‐based analyses each have inherent advantages and disadvantages, and using them together can finesse the disadvantages of both. A high‐speed gas chromatograph (GC) using a time‐of‐flight mass spectrometer (TOFMS) detector can mitigate the problem of delayed data.
Mobile Mass Spectrometry Used for On‐Site/In Situ Environmental Measurements
Authors: Matz Gerhard , Schröder Wolfgang , Kotiaho Tapio
Published: September 2006

The potential of mass spectrometry (MS) and gas chromatography/mass spectrometry (GC/MS) techniques for on‐site analysis of compounds in a variety of matrixes such as air, water, soil and surfaces is discussed. The fundamental principles of operation including different mass separation procedures, modes of injection and separation methods for mixtures are presented here with a special emphasis on equipment suitable for measurement in the field. Commercially available systems as well as prototypes are described in detail. The power of MS and/or GC/MS analyses on‐site compared with conventional methods carried out in the laboratory is demonstrated in a detailed review of the literature dealing with measurement campaigns and experiences when applying mobile MS and GC/MS. In conclusion, mobile mass spectrometers have reached a high standard of quality and the operational areas in which they are utilized are likely to increase considerably in the future.
Solid‐State Sensors for Field Measurements of Gases and Vapors
Authors: Dickert Franz L. , Lieberzeit Peter A.
Published: September 2006

Remote and in‐field analysis is developing into a crucial aspect of modern analytical chemistry. Chemical sensors, which are small measuring devices consisting of a recognition layer, a transducer and the measurement electronics, have proven to be highly suitable tools for this purpose. Although usually they are constructed for the detection of very limited amounts of chemical compounds and often do not reach the detection limits of modern analytical instruments, they show very desirable advantages: the systems are easy to operate, mostly rugged, small, good value and can be manufactured by established technological methods. Due to their size and ruggedness they can even be operated in harsh environments and often they can be constructed to be suitable for remote measurements, where several sensors are interrogated by a central analytical site.

Devices being used include optical fibers, field effect transistors (FETs), electrochemical cells (be they potentiometric or amperometric) and mass‐sensitive components of all kinds. The chemically‐sensitive coatings range from bare transducer surfaces to dyes reacting with analyte or sterically‐specific binding sites (host–guest complexes etc.). A seeming drawback is the fact that only few sensors react specifically towards one defined component but normally show a sensitivity pattern towards chemically‐related substances. By using an array of several components followed by modern methods of data evaluation (such as neural networks) a group of analytes can be detected and characterized simultaneously. This article introduces device and recognition layer principles as well as covering field sensors published during the last one and a half decades based on all the different kinds of transducers and sensor layers. Some of the devices (such as the lambda probe) are already marketed, others are developed to a stage where field measurements have already been carried out, but which are not market‐ready.
Atomic Spectroscopy in Food Analysis
Authors: Baker Scott A. , Miller‐Ihli Nancy J.
Published: September 2006

Since food is the primary source of essential elements for humans, the accurate and precise analysis of food materials is critical. The methods best suited to meet this task are atomic spectroscopic methods such as atomic absorption, atomic emission, and elemental mass spectrometry (MS). Methods commonly used in the generation of food composition data include flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma atomic emission spectrometry (ICP/AES), and more recently, inductively coupled plasma mass spectrometry (ICP/MS). FAAS and ICP/AES offer similar detection limits (DLs) (ng mL−1levels), whereas, GFAAS and ICP/MS can provide sub‐ng mL−1detection capability. The choice of a method often depends on detection capability, but ease of use, speed of analysis, and cost must be considered. ICP/AES and ICP/MS offer the advantage of providing simultaneous multielement measurements, making them well suited for the analysis of large numbers of elements in food samples. If one or a few elements are to be determined, less expensive atomic absorption spectrometry (AAS) methods might be more suitable. The most critical stage in the development of analytical methods is sample preparation. Samples can be prepared using numerous procedures, but the most useful for a wide range of analytes and sample matrices are based on dry ashing or wet ashing of the sample. In addition to total element determinations, speciation measurements are important to determine the exact form of the element that is present in the sample. Since the bioavailability of an element is dependent on its chemical form (speciation), the development of reliable methods for identification and quantification of trace element species is critical. The coupling of chromatographic separation and atomic spectroscopic detection has proven useful for elemental speciation measurements.
Dietary Fiber Analysis as Non‐Starch Polysaccharides
Authors: Englyst Hans N. , Quigley Michael E. , Hudson Geoffrey J.
Published: September 2006

The original hypothesis on fiber, that a diet with a high content of unrefined plant foods was linked to a low incidence of Western diseases, has been largely confirmed. The plant cell wall encapsulates and thus controls the release of nutrients, including free sugars and starch, from the plant tissue and thereby influences the glycemic response. This ability to influence digestion and absorption, and thus the physiological effects of other nutrients, is an important property of dietary fiber. The other main properties of a high‐fiber diet are increased fermentation and fecal bulk, and binding of potentially toxic substances, e.g. lectins, thus affecting large gut physiology and health. Naturally high‐fiber diets have low contents of fat and sodium, and are a good source of vitamins and minerals. The national dietary guidelines recommend a diet rich in fruit, vegetables and whole‐grain cereals, and thus naturally rich in plant cell‐wall material, the major constituents (approximately 90%) of which are nonstarch polysaccharides (NSP). Food labeling for dietary fiber should help the consumer in the choice of the recommended unfortified, high‐fiber diet. Analysis of NSP represents a good measure of endogenous plant cell‐wall material for most plant foods and NSP values thus provide a very good marker for a high‐fiber diet.

The Englyst procedure for the measurement of dietary fiber as NSP involves enzymatic hydrolysis of starch, precipitation of NSP in ethanol, acid hydrolysis of the NSP and measurement of the released constituent sugars by gas–liquid chromatography (GLC), high‐performance liquid chromatography (HPLC) or colorimetry. Values for total, soluble and insoluble NSP may be obtained using any of the end‐point techniques. The detailed information obtained from the chromatographic methods, which identify and quantify the individual constituent sugars, is particularly useful in studies of the relation between intakes of NSP and health; values for the constituent NSP sugars have been published for a wide range of foods.
Electrophoresis and Isoelectric Focusing in Food Analysis
Authors: Cancalon Paul F.
Published: September 2006

Electrophoresis is based on the differential migration of charged components in an electric field. Until recently, gel electrophoresis and particularly sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) were the main electrophoretic techniques used in food analysis. Recently, capillary electrophoresis (CE) has become widely adopted for the monitoring of many food components.

Such rapid development is due to several factors, but especially to speed and versatility. Most often separation can be performed in a few minutes with minimal sample preparation. A new method can be started by filling the capillary with the proper buffer, and new modular instruments can be rapidly fitted with the appropriate detector. Various CE procedures have been developed since the introduction of this technique. Capillary zone electrophoresis (CZE), the basic CE method, consists of a capillary tubing of fused silica with a diameter of 50–150 µm. The tube is filled with a buffer and subjected to an electric field, and under these conditions the positive charged species migrate toward the cathode at a rate determined by their mass‐to‐charge ratios. However, a net movement of the buffer toward the cathode, electroosmotic flow (EOF), is generated within the tube by the ionized capillary wall silanol groups. As a result, all the molecules present in the buffer proceed toward the cathode, the neutral molecules migrate as a single group, and each negative species moves toward the cathode at a rate determined by the difference between the EOF and its anodic attraction. The other main CE techniques are micellar electrokinetic chromatography (MEKC), where an anionic surfactant is added to the buffer to form negatively charged micelles, isotachophoresis (ITP), in which the sample is sandwiched between electrolytes of high and low mobility and the analytes migrate in order of decreasing mobility, and isoelectric focusing (IEF), which is one of the main techniques used in protein gel electrophoresis: amphoteric electrolytes are allowed to migrate in a capillary where they form a pH gradient. In such a gradient, proteins move until they reach their isoelectric point (pI). Many detection techniques have been applied to CE, including direct and indirect ultraviolet (UV) absorption, fluorescence, electrochemical detection and even mass spectrometry (MS).

Most food components can be examined with these techniques, particularly proteins, ions, organic acids, sugars and various plant chemicals.
Enzyme Analysis and Bioassays in Food Analysis
Authors: Powers J.R.
Published: September 2006

The objectives for carrying out analysis of food products include food safety, food quality, meeting regulatory requirements and the control of food processes. Biological entities used in food analyses include enzymes, microbes and antibodies. Based on categories of food analysis general principles of enzyme, immunological and whole organism (microbial) analyses are described. Applications of the use of enzymes for substrate analysis, with examples of their application, are presented. A brief description is given of the use of enzymes as preparative tools in food analysis and of biosensors that use enzymes as elements. Immunological analysis applicable to food systems is given with an emphasis on applications related to food safety. Microbial assays used in food analysis are described including vitamin analysis and protein quality.
Liquid Chromatography in Food Analysis
Authors: Nollet L.M.L.
Published: September 2006

This article gives a general overview of the possibilities for use of the HPLC (high‐performance liquid chromatography) technique in food analysis. Different methods of sample preparation, cleanup and, if necessary, derivatization techniques are discussed.
Sample Preparation for Food Analysis, General
Authors: Lichon Michael J.
Published: September 2006

Sample preparation is the obtaining and manipulation of representative portions of a whole prior to subjecting it to any particular analysis. This includes all steps from design and implementation of sampling from the whole, bulk matrix, or population, in such a manner as to represent the whole (or some determinable aspect of the whole), reduction of particle size, mixing, drying, weighing, dilution, and any number of physical or chemical manipulations prior to analysis. These may include apportionment, storage, digestion, extraction, cleanup separation, and derivatization. While the purpose of these essential steps is to enhance precision and accuracy in determining an analyte concentration relating to the whole, each step adds inherent errors to the result. Furthermore, they may contribute to the contamination and deterioration of the sample relative to the original whole. The consistent use of observation, documenting, replication of test portions, recoveries and reference materials should highlight problem areas. These may be reduced, or at least quantified, using the skill of the professional analyst.
Sample Preparation, Headspace Techniques
Authors: Chaintreau Alain
Published: September 2006

Among sample preparation techniques used prior to gas chromatography (GC), headspace sampling (HS) offers many advantages as it only collects vapors that are directly compatible with GC. The main variants are: (1) collection of a fraction of the HS (static headspace, SHS), (2) gas stripping of volatiles from a solution and subsequent trapping in an adsorbent (purge and trap headspace, P&THS), (3) collection and trapping of volatiles from a whole HS in equilibrium with a liquid (static and trapped headspace, S&THS), (4) partition of volatiles between a sample, its HS, and an adsorbent fiber (headspace solid‐phase microextraction (HSSPME)). For each one, a design and some guidelines for qualitative and quantitative use are given, as well as the equation giving the theoretical recovery. Performances are compared between HS techniques and others such as simultaneous distillation extraction (SDE).

A special section is devoted to the timesaving hyphenation of HS to detectors without chromatographic separation like HS‐sensor array and headspace sampling mass spectrometry (HSMS).

Main HS applications in various areas (food, environment, health and biosciences) since the late 1980s are illustrated. In addition, HS appears to be a unique tool to measure thermodynamical constants of volatiles characterizing their partitioning between phases and their interactions with a nonvolatile matrix.
Fluorescence in Forensic Science
Authors: Menzel E. Roland
Published: September 2006

Emission spectroscopy, which in the forensic science context historically has meant (carbon) arc spectroscopy, is occasionally still employed in paint examination and some other trace evidence areas, but has largely been replaced by atomic absorption (AA), Fourier transform infrared (FTIR), gas chromatography/mass spectrometry (GC/MS) and other analytical techniques. Notwithstanding its intrinsically very high sensitivity, molecular fluorescence spectroscopy is not utilized as a general technique of forensic analysis either, because spectra tend to be broad and featureless. Fluorescence spectral examination may occasionally be used in areas such as document examination, specifically for ink differentiation in instances of document alteration, but fluorescence spectra as such tend to pertain primarily to the arena of research. This is not to say, however, that the photoluminescence phenomenon is not exploited in criminalistics, the examination of articles of physical evidence recovered from the crime scene. Indeed, it is widely and effectively employed in tagging or labeling modalities and via the inherent fluorescence itself of trace evidence. Fluorescence‐based approaches to authentication of currency and passports, identification of valuables, origin specification of gun powders and explosives, surveillance, and so on, are less directly pertinent to forensic science. These areas of fluorescence tagging will thus not be dealt with in detail. In criminalistics, photoluminescence is today the mode par excellence for ultrasensitive latent fingerprint detection. It is also employed in detection of body fluids, visualization of fibers, ink discrimination, and so on. Thus, the focus in this article will be on visualization and imaging. We begin, however, with discussion of the basic molecular photoluminescence phenomenon and description of some useful spectroscopic measurements, namely luminescence and excitation spectra, and luminescence lifetime determination by time‐gated and phase‐resolved techniques. These set the stage for the latest advances in photoluminescence visualization in physical evidence processing, with emphasis on fingerprints, the most prominent photoluminescence application in forensic science.
Atomic Spectroscopy for Forensic Applications
Authors: Grant Diana M. , Peters Charles A.
Published: September 2006

Forensic science is a discipline that evolved from the interaction between law enforcement and the scientific community. The typical operating budget of laboratory facilities created to support law enforcement is often far below what is necessary for practical modernization. Hence, routine analyses that require low maintenance and can be readily performed with practical experience were quickly instituted as standard procedures in many such laboratories. As an example, atomic absorption (AA) spectroscopy has served the forensic community for over 40 years and continues to work effectively for such diverse applications as gunshot powder residue analysis and toxicological examinations in suspected heavy metal poisoning cases.

These and other traditional forensic applications have also utilized other forms of spectrochemical analysis such as neutron activation. The advantage of the various forms of atomic spectroscopy over these other methods lies in the practical considerations of accessibility and cost as much as in sampling requirements and detection limits. From well established AA methods to the increasing number of forensic applications being developed for laser ablation/inductively coupled plasma mass spectrometry (LA/ICPMS), modern atomic spectroscopy has proven itself to be a compelling and evolving tool in the investigation of forensic evidence.
Capillary Ion Electrophoresis in Forensic Science
Authors: Ferslew Kenneth E. , Hagardorn Andrea N.
Published: September 2006

Electrolyte concentrations can be determined in biological specimens by a number of analytical techniques including flame emission spectrophotometry, atomic absorption spectrometry, high‐performance liquid chromatography (HPLC), and potentiometry with an ion‐specific electrode. Capillary ion electrophoresis (CIE) is an adaptation of free zone capillary electrophoresis to a particular electrophoretic analysis of highly mobile low‐molecular‐weight ions.

Vitreous humor electrolyte and nitrogenous compound concentrations are often used to determine potential antemortem disease states or the time interval between time of death and time of autopsy (postmortem interval). Potassium ion concentration in the vitreous humor increases after death, and determination of its concentration in vitreous humor is often used to estimate the postmortem interval.

Lithium ion is considered valuable in the treatment of certain types of mania and major endogenous depression and is even used in the treatment of cluster headaches. The optimum dosage is best determined by monitoring serum lithium concentrations. Lithium toxicity can occur with elevated serum lithium concentrations and repeated measurement every 3 h of serum lithium concentrations is recommended for intoxicated patients to differentiate acute poisoning from chronic toxicity and to determine the best course of therapy.

The development of the CIE methodology reported herein offers a different qualitative and quantitative analytical technique to detect these ions in biological fluids and tissues. Application of CIE analysis for detection and quantitation of potassium and lithium ions in biological fluids and tissues commonly collected and analyzed in clinical and forensic toxicology is described.
Scanning Electron Microscopy in Forensic Science
Authors: Basu Samarendra
Published: September 2006

Scanning electron microscopy is providing increasingly definitive solutions to criminal problems since its commercial debut in 1965. This has been due to the ability of the scanning electron microscope (SEM) to simultaneously produce several electron probe‐induced signals from the specimen, which generate readily interpretable images of surface topography and material composition. The successful applications of these signals are determined by sample preparation and instrumental parameters. No other microbeam technology combines high resolution (2–5 nm) of the topographic (secondary) electrons with large depth of field for three‐dimensional viewing. The SEM is indeed ideal for stereomicroscopy. The versatility of the SEM stems from its additional capability to process each specimen signal by various contrast enhancement methods, such as line scanning, deflection modulation (DM), area mapping, etc. These methods allow an intuitive, stylistic, and synthetic analysis of the image and are ideal for quality control analysis. Digital SEMs have pioneered in automated image processing and unattended search and analysis of particulates. The combined SEM and energy‐dispersive X‐ray microanalysis (EDX) is the most definitive technique in testing for gunshot residue (GSR) particles, collected by the glue‐lift technique. In the analyses of other trace evidence, such as hair and fibers, in physical matching, and in nondestructive elemental analysis of physical evidence, the SEM/EDX is the most efficient of all microbeam technologies. From firearms, bullet wounds and human bones, to plants, pollen and fungi, the list of criminal evidence examined by SEM/EDX is endless. However, the SEM/EDX is not ideal for quantitative analysis of elements present as traces (<1% w/w). The SEM lacks the three‐dimensional sectioning abilities of scanning beam confocal microscopes. The imaging capabilities of the SEM surpass these limitations. The SEM is, therefore, a major tool in forensic research and investigation.
Aerosols and Particulates Analysis: Indoor Air
Authors: Branisteanu Radu
Published: September 2006

This article is intended to provide information and directions needed in the assessment of indoor aerosols, both in industrial and nonindustrial environments. Section 2 of this material is dedicated to basic explanations needed to understand the scope and directions of the analysis of aerosols in indoor air. It comprises brief considerations about the deposition of particulates in human airways, the characteristics of the particles and aerosol classification. Section 3 describes some widespread types of aerosols found in occupational and domestic environments. The characterization comprises considerations upon chemical composition, size, shape and the influence upon human health. Methods of analysis are also mentioned. Section 4 describes the factors that influence the sampling and storage of aerosols. Section 5 deals with applications of aerosol analysis in industrial hygiene. Sampling, sample preparation and analyse are exemplified on three selected compounds: metallic species, polycyclic aromatic hydrocarbons (PAHs) and silica. Alternative methods for specific applications are presented. Section 6 refers to home and office environments and approaches strategies used for indoor air quality (IAQ) assessment and the analysis of bioaerosols. Section 7 addresses the air standards and their influence upon analytical methodology and instrumentation. Section 8 comprises a brief discussion regarding differences encountered in aerosol analysis in industrial and nonindustrial environments.
Carcinogens, Monitoring of Indoor Air
Authors: Peterson Max R.
Published: September 2006

Carcinogens in indoor air include radioactive radon, a variety of organic compounds, several inorganic species, asbestos fibers, and a large number of chemical species associated with suspended particulate matter (SPM). Within these categories, carcinogens may be grouped byeither chemical class and physical properties or by the methods used to measure them. Generally, measurement methods within a category are at least similar if not identical.

A typical measurement method includes procedures for sampling a known volume of air in a way that quantitatively collects the species of interest, transferring collected samples to a laboratory, and measuring species of interest in the samples using an appropriate validated analysis method. The sampling location may be in the breathing zone of a person (to measure personal exposure) or at a specific location in a building or room (to measure potential for exposure at that location). A sample may be collected very quickly (to obtain a snapshot of carcinogen concentration at a specific time) or very slowly over a period of hours, days, or weeks (to obtain an integrated or average carcinogen concentration).

The analysis method is essentially independent of the sampling location and sampling time, but collection of an adequate quantity of the species of interest is crucial. In general, radon is measured as radiation emitted from the sample; organic compounds are measured using gas or liquid chromatography with an appropriate detector; carcinogenic inorganic species are measured using atomic absorption spectroscopy (AAS) or atomic emission spectroscopy (AES); asbestos fibers are visually counted at high magnification; and particles are extracted with a solvent to quantitatively remove the species of interest, which are then measured using one of the organic or inorganic methods described above. Concentrations of the species of interest can then be calculated by dividing the quantity of each species measured in the collected sample by the volume of air sampled.
Metals in Blood and Urine: Biological Monitoring for Worker Exposure
Authors: Ullucci Paul A.
Published: September 2006

Biological monitoring uses sophisticated analytical techniques for the accurate and precise determination of metals in blood and urine. This provides occupational health professionals with the means to monitor worker exposure to toxic metals. For metals such as lead, cadmium, and mercury, good correlations have been found between the level of the metal in blood and/or urine and health impairment.

Analytical techniques such as graphite furnace atomic absorption spectroscopy (GFAAS) and inductively coupled plasma mass spectrometry (ICP/MS) have been widely used to determine metals in biological samples. Since metals may exist in different forms in blood and urine, chromatographic separation combined with spectroscopic detection has been used to determine metal species. Biological monitoring is an example of how modern analytical chemistry has provided the tools needed to protect the health of workers.
DNAMolecules, Properties and Detection of Single
Authors: Long Zhifeng
Published: September 2006

Technological advances have created more DNA detection systems with more power than ever before. By amplifying the target or its molecular counterpart, the probe, very minute amounts of DNA can be detected or even sequenced. Different technologies give rise to different DNA detection systems. Each system has its merits and limitation. In many applications, detection sensitivity is the parameter of interest. This article first gives an outline of different DNA detection systems and their sensitivities and limits. It then describes how to achieve and prove one‐copy sensitivity. Finally, it discusses the testing strategy, supported by statistics to increase detection confidence. Although the limit of detection (LOD) can be improved with better technology and instrument, the highest sensitivity is set by probability laws. To detect one‐copy of a DNA molecule, one needs to understand the properties of single.
DNAProbes
Authors: Tyagi Sanjay
Published: September 2006

Hybridization of nucleic acid probes has been a key technique used in the exploration of the molecular biology of the cell. Use of this technique is now expanding into the field of clinical diagnostics for the detection of pathogens and genetic disorders. In a hybridization assay, a labeled nucleic acid probe of a particular sequence is used to detect the presence of a target nucleic acid sequence. The fundamental principals that guide the design of the nucleic acids hybridization probes and assays are reviewed in this article. New improvements that simplify the implementation of these assays and enhance their sensitivity are discussed. Coupling of hybridization with amplification of nucleic acids in vitro, which results in extremely sensitive detection of specific nucleic acids, are also described.
Optical Mapping in Genomic Analysis
Authors: Aston Christopher , Schwartz David C.
Published: September 2006

Optical mapping is a system for the construction of ordered restriction maps from single deoxyribonucleic acid (DNA) molecules. DNA molecules bound to derivatized glass surfaces are cleaved with restriction enzymes and imaged by fluorescence microscopy. Cut sites are visualized as gaps between cleaved DNA fragments, which retain their original order. Optical mapping offers advantages over electrophoretic methods of restriction enzyme analysis, which require separate techniques for separating cleaved DNA fragments and determining fragment order. Furthermore, small amounts of DNA are required for optical mapping analysis. By determining the existence of these sequence‐specific cut sites and the distances between them, a precise landmark map of the DNA sequence can be constructed. Prokaryote and eukaryote DNA can be mapped. Maps can be constructed from both cloned DNA and genomic DNA. Restriction maps can be constructed for whole genomes by overlapping maps derived from individual molecules. Such maps provide a useful scaffold for accurate alignment of sequence contigs generated by a shotgun sequencing approach and a means of comparing populations and strains.
PNAand Its Applications
Authors: Ray Arghya , Nordén Bengt
Published: September 2006

In recent years, there has been considerable interest in developing gene‐targeting drugs. Synthetic molecules that bind effectively with high sequence specificity to a desired target in a particular “destined” gene sequence are of major interest in medicine and molecular biotechnological research. They show hope for the development of gene therapeutic agents, high‐precision diagnostic devices for genetic analysis and convenient tools for nucleic acid manipulations. Peptide nucleic acid (PNA) is a nucleic acid analog in which the sugar–phosphate backbone of natural nucleic acid has been replaced by a synthetic peptide backbone usually formed from N‐(2‐aminoethyl)glycine units resulting in an achiral and uncharged mimic. It is chemically stable and, in contrast to nucleic acids and peptides, is naturally resistant to hydrolytic (enzymatic) cleavage and thereby not expected to be degraded by cell extracts or inside a living cell. It is capable of sequence‐specific recognition of DNA and RNA obeying a Watson–Crick hydrogen bonding scheme and the hybrid complexes exhibit extraordinary thermal stability and unique ionic strength effects. It also recognizes duplex homopurine sequences of DNA to which it binds by strand invasion, forming a stable PNA·DNA–PNA triplex with a looped‐out DNA strand. This potential synthetic mimic of DNA, since its discovery in 1991, has attracted great attention within medicinal chemistry and molecular biology and also various other fields such as organic and physical chemistry because of its interesting chemical and physical properties. It has been regarded to have great potential for both diagnostic and pharmaceutical applications. In vitro studies have shown successful attempts to use PNA as an inhibitor for both transcription and translation of specific genes. This holds promise for using PNA for antigene and antisense therapy. However, the most exciting use of PNA, as an antisense or antigene drug, requires an efficient and safe method to deliver PNA into living cells, a problem that still remains to be solved.
Polycyclic Aromatic Compounds Mapping
Authors: Chakravarti Dhrubajyoti
Published: September 2006

Polycyclic aromatic compounds (PACs) induce tumors by reacting with specific sequences of the initiating oncogene. The resulting DNA damage is converted into oncogenic mutation by in situ mutagenesis during repair or replication. The analysis of PAC/DNA reaction specificity is crucial for understanding the molecular biology of tumor initiation.

The sequence specificity of PAC/DNA reactions has been analyzed by various methods. These methods detect different types of DNA‐damage lesions. For example, alkali‐labile lesions can be mapped by a chemical procedure (piperidine treatment) and bulky stable adducts can be mapped by a photochemical method (laser‐induced strand scission). Biochemical studies have identified several enzymes that act on damaged DNA and can be used for mapping the location of PAC/DNA reactions. For example, DNA lesions block the processive bypass of various enzymes (DNA polymerases, RNA polymerases and exonucleases), whereas some endonucleases (UvrABC exinuclease, S1 nuclease and apurinic/apyrimidinic (AP) endonuclease) make lesion‐specific incisions. Therefore, the sites of PAC reactions with DNA are mapped by treating PAC‐damaged DNA with these enzymes to generate lesion‐specific DNA strand breaks that are resolved by denaturing polyacrylamide gel electrophoresis. More recently, various polymerase chain reactions (PCRs) have been developed for mapping the sequence preferences of PAC/DNA reactions in vivo. These techniques include ligation‐mediated polymerase chain reactions (LMPCRs), single‐strand ligation polymerase chain reactions (SSLPCRs) and terminal transferase‐dependent polymerase chain reactions (TTDPCRs). In these methods, the PCR is used to amplify gene‐specific DNA fragments generated by chemical or enzymatic DNA lesion processing.
Restriction Landmark Genomic andcDNAScanning
Authors: Kawai Jun , Hayashizaki Yoshihide , Okazaki Yasushi , Suzuki Harukazu , Watanabe Sachihiko
Published: September 2006

Restriction landmark genomic scanning (RLGS) is a method for the high‐speed survey of the presence or absence of restriction landmarks throughout a genome. RLGS also provides for the measurement of the copy number of restriction landmarks based on the concept that restriction enzyme sites can serve as landmarks. RLGS employs direct end‐labeling of the genomic DNA digested with a restriction enzyme and high‐resolution, two‐dimensional electrophoresis. Compared with the conventional technologies for detecting the genes, such as Southern blot analysis and polymerase chain reaction (PCR), RLGS has the following advantages even though it needs specially designed instruments: (1) high‐speed scanning ability – thousands of restriction landmarks can be scanned simultaneously; (2) applicability to any organism – RLGS employs direct labeling of restriction enzyme sites, not a hybridization procedure; (3) a spot intensity that reflects the copy number of the restriction landmarks; and (4) the ability, by using a methylation‐sensitive enzyme, to screen the methylated state of genomic DNA.

RLGS is a very useful system not only for genome mapping, but also in a variety of biological and medical fields, such as cancer research and the growth and development of various organisms throughout all stages of the life cycle. RLGS can also be applied for the visualization of mRNAs [restriction landmark cDNA scanning (RLCS)]. In one procedure, RLCS can scan the expression of several hundred mRNAs.
RNA
Tertiary Structure
Authors: Westhof Eric , Auffinger Pascal
Published: September 2006

Ribonucleic acids are negatively charged polymers assembled from four different types of monomers. Each monomer is made of an invariant phosphorylated sugar to which is attached one of the four standard nucleic acid bases; the pyrimidines uracil and cytosine, and the purines guanine and adenine. The first level of organization is thus the sequence of bases attached to the sugar–phosphate backbone. In salty water, the RNA molecules fold back on themselves via Watson–Crick base pairing between the bases (A with U, G with C or U) leading to double‐stranded helices interrupted by single‐stranded regions in internal loops or hairpin loops. The enumeration of the base‐paired regions or helices constitutes a description of the second level of organization, the secondary structure. The methods available to deduce the secondary structure of an RNA molecule are mainly of three types: the phylogenetic approach, the theoretical prediction, and chemical/enzymatic methods. The secondary structure of an RNA molecule is experimentally accessible and its content measurable. Under appropriate conditions, structured RNA molecules undergo a transition to a three‐dimensional (3D) fold in which the helices and the unpaired regions are precisely organized in space. This folding process usually depends on the presence of divalent ions, such as magnesium ions, and on the temperature. The tertiary structure is the level of organization relevant for biological function of structured RNA molecules.
Sequencing Strategies and Tactics inDNAandRNAAnalysis
Authors: Azhikina Tatyana L.
Published: September 2006

Sequencing procedures are aimed at the determination of sequences of monomer units constituting linear biopolymer molecules. In the particular case of nucleic acids the monomer units are DNA or RNA residues. The present article reviews several sequencing strategies: different approaches (random or systematic sequencing) as well as their combinations giving the best results for long‐range sequencing applicable to long and unique DNA fragments, including entire genomes, up to the Homo sapiens genome size; massive sequencing of relatively short fragments such as RNAs, complementary DNAs (cDNAs), etc.; and comparative sequencing of related DNA fragments originating from various individuals or different species.

Although particular sequencing approaches may involve different ways of DNA treatment (chemical, enzymatic, or physical), they are all based on the same idea: a labeled molecule is cut to obtain a set of fragments all having one common end, other ends being different owing to the statistical character of the nucleic acid chain cleavage. The fragments obtained are then separated according to their lengths.

The primary structure of nucleic acids is a key not only to physical and chemical properties of the molecules but also to the biological (genetic) information therein, including structures of genes and proteins, the ways of gene regulation and cell response to different signals. This is a great advantage over other physical, chemical, or biological methods of DNA/RNA analysis. However, sequencing in itself is usually insufficient to predict unambiguously the biological properties and functions of the encoded products.