bluuebunny/crossref_metadata_2025 huggingface dataset:
Under‐ and Overdispersion
Authors: Xekalaki Evdokia
Published: September 2006

Very often, in connection with applications, one is faced with data that exhibit a variability, which differs from that anticipated under the hypothesized model. This phenomenon is termedover dispersionif the observed variability exceeds the expected variability orunder dispersionif it is lower than expected.

Such discrepancies between the empirical variance and the nominal variance can be interpreted to be induced by a failure of some of the basic assumptions of the model. These failures can be classified by how they arise, that is, by the mechanism leading to them. In traditional experimental contexts, for example, they are caused by deviations from the hypothesized structure of the population, such as lack of independence between individual item responses, contagion, clustering, and heterogeneity. In observational study contexts, they are the result of the method of ascertainment, which can lead to partial distortion of the observations. In both cases, the observed valuexdoes not represent an observation on the random variableX, but an observation on a random variableYwhose probability distribution (the observed probability distribution) is a distorted version of the probability distribution ofX(original distribution). This can have a variance greater than that anticipated under the original distribution (over dispersion) or, much less frequently in practice, lower than expected (under dispersion).
Valuation of Life Insurance Liabilities
Authors: O'Brien Christopher David
Published: September 2006

Placing a value on life insurance liabilities is not easy. The issues are not new: we can go back to 1864, when the British Prime Minister William Gladstone referred in Parliament to the accounts of the Prudential Assurance Company:

‘As it stands, it presents a balance of £41,000 in favor of the society; but it has been examined by actuaries, and those gentlemen, proceeding upon principles which are no more open to question than a proposition of Euclid, say, that instead of a balance of £41,000 in favor of, there is one of £31,000 against the society’.

In the twenty‐first century we still have debates on how to value the liabilities arising from life insurance policies, notably with the work of the International Accounting Standards Board in its effort to design an international financial reporting standard for insurance contracts, to be used in insurers' accounts.

Key questions are

what are the estimated future cash flows from a life policy? and

what discount rate should be applied to the cash flows to derive a present value?

Closely linked with these questions are

how should the uncertainty about the cash flows be reflected in the valuation? and

how can we ensure consistency of the valuation of the liabilities with the valuation of the insurers' assets?
Value‐at‐Risk
Authors: Dowd Kevin
Published: September 2006

The Value at Risk (VaR) on a portfolio is the maximum loss we might expect over a given period, at a given level of confidence. It is therefore defined over two parameters – the period concerned, usually known as the holding period, and the confidence level – whose values are arbitrarily chosen. The VaR is a relatively recent risk measure whose roots go back to Baumol, who suggested a risk measure equal to μ –
k
σ, where μ and σ are the mean and standard deviation of the distribution concerned, and
k
is a subjective parameter that reflects the user's attitude to risk. The term
value at risk
only came into widespread use much later. The notion itself lay dormant for nearly 30 years, and then shot to prominence in the early to mid 1990s as the centerpiece of the risk measurement models developed by leading securities firms. The most notable of these, Morgan's Risk‐Metrics model, was made public in October 1994, and gave rise to a widespread debate on the merits, and otherwise, of VaR. Since then, there have been major improvements in the methods used to estimate VaR, and VaR methodologies have been applied to other forms of financial risk besides the market risks for which it was first developed.
Workers' Compensation Insurance
Authors: Feldblum Sholom
Published: September 2006

Although some of the earliest workers' compensation systems were in Europe, many countries now have included recompense for worker injury into social welfare programs. Currently the largest system for which employers purchase private insurance for this matter is in the United States, and this will be the focus of this article. Each state has its own system, so some differences among these will be addressed. State workers' compensation systems developed in the early twentieth century to replace negligence liability for workplace accidents and illnesses. The development of workers' compensation rates by class and state sparked the emergence of the Casualty Actuarial Society (CAS) in 1914.
Magnetic Resonance Angiography
Authors: Yuan Chun
Published: September 2006

Angiography generally refers to any imaging method that can visualize blood vessels. Magnetic resonance angiography (MRA) is a class of magnetic resonance (MR) imaging techniques that create blood vessel images. During the past decade, there has been a tremendous amount of development and refinement in MRA techniques, making MRA a powerful tool in the diagnosis of cardiovascular disease. In most of the cases, MRA techniques are applied noninvasively, without the use of ionizing radiation. The inherent advantages of MR imaging (noninvasive, flow sensitive, high soft tissue contrast, and flexible imaging approaches) make it ideally suited to the study of the vasculature in almost any part of the human body. MRA presents a wide spectrum of techniques for the study of flowing blood: different methods for high spatial resolution, high temporal resolution, velocity sensitization, flow quantification, and visualizing pulsatility. This article addresses the basic principles of MRA and describes its applications.
Magnetic Resonance Imaging, Functional
Authors: Richter Wolfgang
Published: September 2006

Functional magnetic resonance imaging (FMRI) is an analytical method for measuring brain activity while it occurs. FMRI was first demonstrated in 1992, but it has since become the most popular neuroimaging method. Its temporal resolution is of the order of seconds and hence superior to positron emission tomography (PET). Its spatial resolution is on the order of millimeters which makes it superior to both PET and electrophysiological methods such as electroencephalography (EEG). Furthermore, FMRI is noninvasive in the sense that no external contrast agent has to be used. FMRI contrast is based on the intrinisic blood oxygenation changes that occur at the site of brain activity in response to a specific task. The exact mechanism that links activity and signal change is currently not well understood and is an area of active research.

FMRI is subject to many experimental difficulties, however. A vexing problem is that of physiological (heartbeat and breathing) and gross motion. Gross motion is often coupled to the presentation of the stimulus and hence especially prone to producing artefactual activation. The analysis of the experimental data is not a standard procedure at present. While past research has generally used paradigmatic methods of analysis (hypothesis testing), nonparadigmatic (data driven) methods like fuzzy clustering analysis (FCA) or independent component analysis (ICA) have become important tools.

A more complete understanding of the physiological mechanisms leading to the activation signal, and a better grasp of the proper statistical treatment of the data, are likely to increase the power of FMRI even further.
Multinuclear Magnetic Resonance Spectroscopic Imaging
Authors: Richards Todd L.
Published: September 2006

Magnetic resonance spectroscopic imaging (MRSI) is a technique for producing spatially resolved maps or images of different chemicals that are found in the body or tissue. These chemicals may be naturally inherent or may be introduced by injection, but they must be detectable by the magnetic resonance (MR) process (i.e. they must have nuclei that have a magnetic moment, and are mobile enough to give a free‐induction decay (FID)). The MRSI technique is based on many of the same principles that are used for conventional magnetic resonance imaging (MRI) and also uses much of the same equipment as MRI. This chapter focuses on multinuclear applications of MRSI such as phosphorus‐31, carbon‐13, fluorine‐19, sodium‐23, xenon‐129, helium‐3, and boron‐11. The MRSI method is an important technique for noninvasive measurement of biochemical and physiological changes in health and disease.
Optical Coherence Tomography
Authors: Fercher A.F.
Published: September 2006

Optical coherence tomography (OCT) is a technique with which to peer inside a body noninvasively. Tissue structure defined by tissue absorption and scattering coefficients, and the speed of blood flow, are derived from the characteristics of light remitted by the body. Singly backscattered light detected by partial coherence interferometry (PCI) is used to synthesize the tomographic image coded in false colors. A prerequisite of this technique is a low time‐coherent but high space‐coherent light source, usually a superluminescent diode or a multimode semiconductor laser. This limits the wavelengths to the red and near‐infrared (NIR) region from about 600 nm to 1300 nm, the so‐called therapeutic window, where absorption (μ

a

 ≈ 0.01 mm
−1
) is small enough. Transverse resolution in OCT is diffraction limited, as in conventional imaging; depth resolution is limited by the coherence length of the light. Both figures are of the order of micrometers. Velocity resolution is of the order of 0.1 mm s
−1
. A few instruments are commercially available. At present, OCT is mainly used in the medical field, in particular in ophthalmology. Owing to the high transmissivity of ocular media, the depth penetration is considerable. Corresponding applications in dermatology are somewhat hindered by the strong scattering of epidermic tissue (μ

s

 ≈ 10
2
 mm
−1
). As OCT provides images with a resolution comparable to conventional histology, but in real time, it can be used as a biopsy technique in a wide range of biological systems to detect diseases. These include the tomographic imaging of the internal microstructure of in vitro atherosclerotic plaques, the tomographic real‐time diagnostics for intraoperative monitoring, and in microsurgical intervention. Optical biopsy based on OCT also provides diagnostic information by differentiating the architectural morphology of urological tissue, gastrointestinal tissue, and respiratory tissue.
Photodynamic Therapy
Authors: Röder Beate
Published: September 2006

Photodynamic therapy (PDT) is an effective treatment of different types of cancer, virus infections, skin diseases and others using photosensitizers (PSs) which are nontoxic in the dark but become phototoxic following activation by low energy light. The PS is applied topically or systemically and should be selectively accumulated in the target tissue. The molecular mechanism of the therapy is the photodynamic effect: following light absorption energy is transferred from the PS to molecular oxygen generating singlet molecular oxygen (1O2) which causes direct or indirect photodamage of the target tissue.

In clinical therapy with first generation PSs like Photofrin®typically fluences of around 100 J cm−2of red light are used. The light doses vary in dependence on the treated disease. Using PSs of second generation with very strong absorption in the red region like the very efficient m‐tetrahydroxyphenylchlorin (m‐THPC), smaller fluences, typically around 10 J cm−2, are required. According to the different optical properties and the efficiency of selective accumulation of PS in the target tissue, the drug doses vary from 1–5 mg (first generation PS) to 0.1 mg (second generation PS) per kilogram body weight.

PDT is a very efficient method for the treatment of minor diseases, blood cancer, inoperable diseases like some types of bladder, brain or lung cancer, and breast carcinoma metastases. The side effects are less than in the case of chemo‐ or radiotherapy. The most common side effect is skin photosensitization. The strength of this effect depends on the PS used and also on the patients' skin type. Most of the new second generation PSs cause no or only weak skin phototoxicity. The therapeutic radius is limited by the penetration depth of the used light (in the order of some millimeters to centimeters). The method will not be very successful for the treatment of large solid tumors.
Two‐Dimensional Vibrational Correlation Spectroscopy in Biomedical Sciences
Authors: Ozaki Yukihiro , Noda Isao
Published: September 2006

Two‐dimensional (2‐D) vibrational correlation spectroscopy offers a new opportunity for analyzing vibrational spectra. In the 2‐D approach, spectral peaks are spread over the second dimension, thereby simplifying the visualization of complex spectra consisting of many overlapped bands, and enhancing spectral resolution. Correlation peaks appearing in the synchronous and asynchronous maps represent in‐phase and out‐of‐phase variation tendencies of corresponding band intensities, respectively. 2‐D correlation spectroscopy is very useful in unraveling infrared (IR), near‐infrared (NIR), and Raman spectra of biological molecules and biomedical materials. For example, it has a powerful deconvolution ability for highly overlapped amide I, amide II, and amide III bands of proteins, enabling these bands to be assigned to various secondary structures. 2‐D NIR correlation spectroscopy provides new insights into the hydration of proteins, and can also be used to investigate the order of perturbation‐dependent structural changes.
Fluorescence‐Based Biosensors
Authors: Brennan John D.
Published: September 2006

Biosensors, as defined by Biosensors and Bioelectronics, are analytical devices “incorporating a biological material, a biologically derived material or biomimetic intimately associated with or integrated within a physicochemical transducer or transducing microsystem”. Fluorescence‐based biosensors are those devices that derive an analytical signal from the fluorescence emission process. Such biosensors may be used for a wide variety of tasks, including: detection of compounds of biomedical,
1
environmental
2
or defense interest,
3
on‐line monitoring for process control,
4
monitoring of foodstuffs,
5
selective detection of compounds undergoing a chemical separation,
6
and screening of drug compounds.
7
Advantages of such devices include:
8
high selectivity; rapid response times; reusability; amenability to remote analysis; and immunity from electrical interferences. The selective nature of the complexation between the biomolecule and the analyte, combined with the small size of the device and the advantages of total internal reflection (TIR)‐based spectroscopy,
9
also results in an ability to measure analytes in complex matrixes. Such samples may include highly scattering systems such as milk or whole blood,
10
or relatively inaccessible locations such as groundwater wells, or even intracellular environments.
11

The key limitation of such devices mainly centers around the poor stability of biological compounds, which can lead to a substantial drift in instrument response over time. There is also the potential for interferences related to biological autofluorescence, and the analyte‐dependent sensitivity and limit of detection (LOD) for sensors, which rely on the nature of both the protein and the fluorescent probe utilized. Finally, in cases where immunological reagents are used, the devices can show a lack of reversibility, and may operate only as a “one‐shot” screen, without the potential for continuous, quantitative analysis.
Infrared Spectroscopy of Biological Applications
Authors: Stuart B.H.
Published: September 2006

Infrared (IR) spectroscopy has proved to be a powerful tool for studying biological molecules and the application of this technique to biological problems is continually expanding, particularly with the advent of Fourier transform infrared (FTIR) spectroscopy in recent decades. One of the great advantages of IR spectroscopy is that virtually any sample in virtually any state can be studied. Liquids, solutions, pastes, powders, films, fibers, gases and surfaces can all be examined with a judicious choice of sampling technique. Biological systems such as proteins, peptides, lipids, biomembranes, carbohydrates, pharmaceuticals, foods and both plant and animal tissues have all been successfully characterized using IR spectroscopy.
1–4

IR spectrometers have been commercially available since the 1940s. At that time the instruments relied on prisms to act as dispersive elements, but by the mid 1950s, diffraction gratings had been introduced into dispersive machines. The most significant advances in IR spectroscopy, however, have come about with the introduction of Fourier transform spectrometers. This type of instrument employs an interferometer and exploits the well established mathematical process of Fourier transformation. FTIR spectroscopy has dramatically improved the quality of IR spectra and minimized the time required to obtain data. Also, with improvements to computers in recent years, IR spectroscopy has made great strides.
Nuclear Magnetic Resonance of Biomolecules
Authors: Evans Jeremy N.S.
Published: September 2006

Nuclear magnetic resonance (NMR) spectroscopy exploits a property of the nucleus known as nuclear spin, which exhibits angular momentum and as such generates a local magnetic field that can be influenced by a larger static external field. In the presence of a large external magnet, the nuclear spins align with the field, with a slight excess opposed to the field. That small excess can be flipped to alignment with the field in the presence of a radiofrequency (RF) pulse of appropriate frequency. Relaxation of those spins back to the ground state results in emission of RF radiation whose frequency is an indication of the local electron density of the molecule in which the spin resides. Such information can ultimately be directly related to molecular structure. NMR spectroscopy is unique in that it can be used to image the whole human body at one extreme, and determine the three‐dimensional (3D) structure of a biomolecule within the body at the other extreme. The principal advantages of NMR are that: (i) the complete molecular structure can be determined; (ii) the technique spans all principal states of matter (solid, liquid, gas); (iii) the method is nondestructive and can be used noninvasively, as in a clinical setting. The principal disadvantages of NMR are that: (i) the technique is very insensitive (typically samples below 50 µM are difficult to study, although recent advances in nanoprobe and cryprobe technology are rapidly revising these numbers); (ii) in liquids there are molecular weight limits of around 50 kDa – although there are new methods being developed that may have a significant impact on this; (iii) in solids only limited structural information can be obtained to date.
Disaccharide, Oligosaccharide and Polysaccharide Analysis
Authors: Blackwood Anne D. , Chaplin Martin F.
Published: September 2006

Disaccharides, oligosaccharides and polysaccharides form a very diverse and complex family of biologically important macromolecules. In order to discover their structure it is necessary to determine not only monosaccharides present and their linkage positions and sequence, but also the anomeric configuration of linkages, the ring size (furanose or pyranose), the absolute configuration (DorL) and identify any other substituents present. There is no one method that can be used to determine their fine structure; instead we must use a combination of analytical methods to gain as much information as we can. For analysis of disaccharide and oligosaccharide mixtures, separation and quantification techniques such as colorimetric and enzymatic assays, thin‐layer chromatography (TLC) or high‐performance anion‐exchange chromatography may be applied. For polysaccharide analysis separation and extraction techniques, component analysis, methylation analysis, glycosidic hydrolysis, mass spectrometry (MS) methods, and nuclear magnetic resonance (NMR) spectroscopy are required to determine the fine structure and size exclusion chromatography (SEC) coupled with light scattering (LS) detectors to determine the molecular size distribution.
Verification of Chemicals Related to the Chemical Weapons Convention
Authors: Mesilaakso Markku , Rautio Marjatta
Published: September 2006

This article gives a short historical review of the Chemical Weapons Convention (CWC), discusses the tasks of the Organisation for the Prohibition of Chemical Weapons (OPCW) related to chemical analysis, and lists the chemicals scheduled in the CWC. The Recommended Operating Procedures (ROPs) proposed originally by Finland and, subsequently, developed further in international cooperation, as well as the Standard Operating Procedures (SOPs) of the OPCW are briefly discussed. Strategy for analysis of CWC‐related chemicals in an off‐site laboratory is presented. The international interlaboratory comparison (round‐robin) and proficiency tests are discussed.
Detection and Screening of Chemicals Related to the Chemical Weapons Convention
Authors: Nieuwenhuizen Maarten S.
Published: September 2006

The Organization for the Prohibition of Chemical Weapons (OPCW), which was established to achieve the object and purpose of the Chemical Weapons Convention (CWC), conducts verification activities and as a result numerous inspections take place. Detection plays a major role during many of the possible inspection scenarios and is a most important component of the health and safety policy of the Organization. This article deals with detection equipment for vapors, liquids, contaminated solids and industrial chemicals as well as explosive or flammable vapor mixtures or lack of oxygen.
Fourier Transform Infrared in On‐Site and Off‐Site Analysis of Chemicals Related to the Chemical Weapons Convention
Authors: Söderström Martin T.
Published: September 2006

Fourier transform infrared spectroscopy (FTIR) is an analytical technique, which gives characteristic spectra. The spectra can be used like fingerprints in the identification of chemicals. The chemicals can be identified by comparison with reference data or, in some cases, by interpretation, which can be followed by synthesis for confirmation.

When FTIR is connected to a gas chromatograph (GC) and the results are used together with those from mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy, very complex environmental samples containing unknown chemicals can be analyzed reliably.
Gas Chromatography/Mass Spectrometry in On‐Site Analysis of Chemicals Related to the Chemical Weapons Convention
Authors: Häkkinen Vesa M.A.
Published: September 2006

This article describes the current procedures for on‐site gas chromatographic/mass spectrometric analysis of samples collected during inspections related to the Chemical Weapons Convention (CWC). Such inspections are made by an inspection team compiled by the Organization for the Prohibition of Chemical Weapons (OPCW). The analytical procedures are described in a standard operating procedure covering gas chromatographic analysis, mass spectrometric analysis, data analysis, and quality control. The approved analytical instrumentation for on‐site inspections is also described.
Liquid Chromatography/Mass Spectrometry in Analysis of Chemicals Related to the Chemical Weapons Convention
Authors: Black Robin M. , Read Robert W.
Published: September 2006

Liquid chromatography/mass spectrometry (LC/MS) is the direct coupling of a chromatographic separation of analytes dissolved in a liquid phase with mass spectrometric detection/identification. Analytes are separated by one or more mechanisms, usually involving hydrophobic, polar or ionic interactions. The components eluting from the LC are introduced directly into the mass spectrometer via an interface, which removes the solvent and ionizes the analyte molecules to produce positive or negative ions. These ions are separated by the mass spectrometer on the basis of their mass‐to‐charge (m/z) ratios. The recent introduction of versatile and robust interfaces, which use atmospheric pressure ionization (API) (atmospheric pressure chemical ionization (APCI) and electrospray (ES) ionization), has lead to increasing application of LC/MS to the analysis of chemical warfare (CW)‐related analytes.

Although LC/MS can be used for the direct analysis of CW agents in aqueous samples, its major application in this field is for the analysis of hydrolysis products of CW agents and other polar degradation products. Reversed phase LC/MS provides a rapid screening procedure for hydrolysis products such as phosphonic acids and thiodiglycol, avoiding the tedious isolation and derivatization required for gas chromatography/mass spectrometry (GC/MS). Increased structural information for unequivocal identification, or improved limits of detection in trace analysis, can be obtained using liquid chromatography/tandem mass spectrometry (LC/MS/MS). LC/MS/MS is also useful for detecting biological markers of poisoning by CW agents in cases where GC/MS is unsuitable.
Automation in the Clinical Laboratory
Authors: McPherson Richard A.
Published: September 2006

Total laboratory automation (TLA) is an approach to laboratory instrumentation that replaces human operators with robotic devices for the performance of highly repetitive tasks in the preparation and transport of specimens. TLA will consolidate the control and oversight for multiple different analytical instruments to a smaller number of operators, thus reducing the costs of labor in laboratory testing. Benefits of TLA include reduction of human errors in specimen handling and improvements in overall process control, including faster turn‐around‐times (TAT) from specimen collection to test result reporting. Possible detriments include very high costs for equipment installation and disruption of workforces trained in existing technologies. Most clinical laboratories will soon face a decision about implementing TLA (or portions of it) to reduce operating costs in order to offset falling reimbursements for medical services.
Biosensor Design and Fabrication
Authors: Urban G.A.
Published: September 2006

This paper presents the use of biosensor devices for bioanalytical purposes. In contrast to common analytical tools using sophisticated and bulky devices, biosensors should be able to perform measurements in untreated samples in a simple and inexpensive manner. As a model creating biosensors serves nature which produces a variety of selective molecules during evolution that can be used in technical sensor devices. Combining such natural molecules with methods from microelectronics, mass fabrication of laboratories on chip seems feasible. Emerging markets for such tools can be seen in medicine, drug screening and biotechnology.

After explaining the principles of biosensors different transducing methods are explained showing advantages and disadvantages for creating biosensors. The greatest emphasis is laid on electrochemical and optical principles which exhibit an overwhelming experience and the largest impact on future developments. Despite such developments, acoustic and calorimetric transducers are also explained. As biological sensing agents enzymes, antibodies and DNA are described with appropriate immobilizing procedures.

Additionally, new aspects for creating a laboratory‐on‐chip using microanalytical systems (μTAS) including microfluidics and actuator modules are given for creating sensing systems for metabolic parameters and also cell‐based and affinity‐based systems for screening purposes. The purpose of this section is to give an overview and to explain the present possibilities for creating biosensor systems and ends up with an outlook in the near analytical future for new sophisticated and miniaturized analytical systems.
Capillary Electrophoresis in Clinical Chemistry
Authors: Xu Yan
Published: September 2006

Capillary electrophoresis (CE) is electrophoresis in capillary format. It is the most efficient and versatile separation technique nowadays for analysis of small and large molecules. Clinical chemistry is a science that applies the knowledge of chemistry to the understanding of the human in health and disease. Implementation of CE technique in clinical laboratories will enhance the capability of the current clinical diagnostic system, and improve the quality of clinical testing. Owing to the nature of clinical diagnostics, the adoption of CE methods in clinical laboratories has been slow. However, CE has begun to replace some older and antiquated methods in some pioneering clinical laboratories.

This review includes a brief introduction to the CE technique (i.e. the separation principle, modes of operation, instrumentation, and practical considerations), and a summary of CE's applications in clinical chemistry (i.e. protein analysis, drug monitoring, DNA and RNA analyses, diagnosis of metabolic disorders, and single‐cell analysis), as well as the future prospects for the CE technique.
DNA
Arrays: Preparation and Application
Authors: Whitaker Tom J. , Jacobson K. Bruce , Doktycz Mitchel J.
Published: September 2006

DNA arrays, which may also be called DNA chips, biochips, genosensors, GeneChips
®
, microarrays, or other names, are considered by many researchers and entrepreneurs to be the most promising technology for economically determining whether a specific sequence of bases exists in an unknown DNA sample. The sequence of bases in DNA is the source of genetic information; consequently, DNA arrays can be used for a number of applications, including diagnosis of genetic diseases or mutations, detection of polymorphisms, and identification of microorganisms. In addition, DNA arrays can also establish the amount of one or more particular messenger RNA (mRNA) in a cell or tissue to reveal gene activity.

DNA arrays take on many forms and there are exceptions to almost any statement describing them. However, a typical array will have multiple segments of single‐stranded DNA (ssDNA) attached to the surface of a substrate. These probes have a known sequence and, under the right conditions, an unknown DNA sequence will bind or “hybridize” to one or more of them only if the unknown DNA has sequence that is related to the probe's sequence. This selective hybridization allows DNA arrays to provide sequence information about the unknown DNA.

This article describes some of the primary considerations in the design, construction, and implementation of DNA arrays. Items discussed are probe selection and design, selection of a suitable substrate, probe immobilization, array construction, hybridization, hybrid detection, how the application affects each of these factors, and how decisions made at one point of the process may affect other decisions.
Electroanalysis and Biosensors in Clinical Chemistry
Authors: Killard Anthony J. , Sequeira Margaret , Diamond Dermot , Smyth Malcolm R.
Published: September 2006

Electroanalysis involves the measurement or determination of a chemical or biochemical species, using a wide range of electrochemical methods. The species being measured can either bring about a direct electrochemical response that can be detected and measured, or can be induced to bring about such a response, resulting in a process that can be detected electrochemically. In both cases an interface is required between the chemical or biochemical species being measured, and the electrochemical system performing the measurement. This interface is referred to as an “electrode”. It is the transfer of electrons or ions between the electrode and the environment being sampled which is of concern in electroanalysis.

The application of electrochemistry in clinical analysis is concerned with the measurement of chemical and biochemical species present in biological fluids (primarily blood but also urine and other body fluids and tissues). It is applied in several areas of critical care where its rapidity, sensitivity, precision, and accuracy at biologically relevant concentrations make it an ideal choice over other, typically slower, biochemical techniques. Indeed, it is the speed of electrochemical analysis that principally differentiates it from other methods. It is not universally applicable to clinical chemistry, however, and has only been applied in situations where such analyses are relevant. This has principally been in the analysis of blood gases and pH and blood electrolytes. Electrochemical methods are, however, gradually being extended to the analysis of small biochemical components such as sugars, amino acids and other metabolites, with the advent of enzyme‐based “biosensors”. There is also little doubt that the application of electrochemistry in clinical analysis will be further exploited by the use of such biosensor devices based on other forms of biorecognition, such as antibodies, cell ligands, membranes, tissues and whole cells. These biosensor devices are also amenable to other forms of detection such as acoustic wave and optical measurements. Together, these techniques offer a wide range of advantages over traditional analytical methodologies, and will undoubtedly have a rapidly increasing impact on many types of clinical analysis. This article focuses on the use of electrochemical techniques and electrochemical biosensors and their application in clinical chemistry.
Electrolytes, Blood Gases, and BloodpH
Authors: Elser Robert C.
Published: September 2006

The term electrolytes, in the clinical sense, refers to the principal ionic constituents of blood: sodium (Na+), potassium (K+), chloride (Cl−), and bicarbonate (HCO3−). Technology for the measurement of these ions has evolved from colorimetric and spectrophotometric methods to ion selective sensors. With the evolution of the technology has come an important reduction in the quantity of sample required to make the determination of concentrations of the ions in blood.

The assessment of respiratory function and the acid–base balance of the blood is accomplished by the measurement of pH, PCO2, and PO2. These measurements are usually not made singly, but rather as a combination of determinations made at the same time on the same blood sample.

In critically ill persons, these seven analytes are of major diagnostic importance.
Glucose Measurement
Authors: Cardosi Marco F.
Published: September 2006

Because of the pivotal role of glucose in physiological processes, much effort has been devoted to the development of methods for measuring glucose in food, microbiological and clinical matrices. The development of direct methods to measure glucose has been hindered by the lack of a suitable chromophore or indeed an electrophore. Consequently, more complex indirect methods have been developed based either on the chemical reactivity of the sugar, a particular enzymatic reaction or an indirect electrochemical measurement based upon the measurement of tensametric peaks or waves.

Although accurate and offering good sensitivity, chemical methods for the analysis of glucose such as the o‐toluidine approach are not specific for glucose. Other hexoses such as mannose and galactose, some of their derivatives, aldopentoses and some disaccharides may also react, thereby complicating the measurement.

Because of the lack of specificity associated with chemical methods of measuring glucose, enzymatic methods have gained in popularity. Enzymes are very selective biological catalysts which carry out the conversion of a particular substrate into a product under mild operating conditions, i.e. room temperature, low ionic strength and near neutral pH. An enzyme will usually catalyze a single chemical reaction or a set of closely related chemical reactions. Side reactions leading to wasteful formation of by‐products rarely occur. Thus, quantitative assays may be done on crude materials with little or no sample preparation. The enzymes which are currently used for the measurement of glucose include hexokinase (EC 2.7.1.1; adenosine triphosphate (ATP):
D
‐hexose‐6‐phosphotransferase), glucose oxidase (EC 1.1.3.4; β‐
D
‐glucose: oxygen 1‐oxidoreductase) and glucose dehydrogenase (EC 1.1.1.47; β‐
D
‐glucose: (nicotinamide adenine dinucleotide phosphate (oxidized form)) NAD(P)
+
1‐oxidoreductase). The mode of detection that is used to measure the activity and hence concentration of glucose, ultimately depends upon the nature of the enzymatic reaction itself and is usually colorimetric or electrochemical.

More recently, new analytical methodologies based upon the direct electrochemical detection of glucose using pulsed amperometric detection (PAD) have been developed. Coupled with liquid chromatography (LC), this technique is proving to be a highly selective and sensitive method for the measurement of glucose in a wide variety of sample matrices.
Immunochemistry
Authors: Price Christopher P.
Published: September 2006

Immunochemistry is a generic term to describe all analytical methods that employ the reaction between an antigen and its complementary antibody for the recognition and/or quantitation of an analyte. The analyte may be the antigen or antibody and in each case the complementary species (antibody or antigen, respectively) will be the primary reagent in the analytical system. The analyte may be present in free solution (e.g. in blood, urine, fermentation broth, effluent, etc.) or may be structurally incorporated in a cell (e.g. red cell, bacterium, virus particle) or solid tissue. Our knowledge of the chemical structure and reactivity of the combining sites of antigens and antibodies (epitopes and paratopes, respectively) has meant that antigen‐ and antibody‐like species can now be synthesized. In the former case this may be undertaken to provide an appropriate immunogen or calibration material whilst several antibody mimics have been demonstrated.

The immunoassay format will depend on the purpose for which the assay is to be used. In that the antigen–antibody reaction is unique to two complementary partners, in terms of cells and tissues, there is no other technique that will provide the same specificity – with the exception of DNA. Quantitative assays are usually required for the analysis of molecules in complex fluids. In the research phase, chromatographic techniques, e.g. high‐performance liquid chromatography (HPLC), gas chromatography (GC), or capillary zone electrophoresis (CZE) can provide the characterization and quantitation required; however, these techniques are not always applicable when the need for the assay is established and a large workload is envisaged. An immunoassay then provides the necessary specificity and workload capability. In addition, when assays are used outside the laboratory, e.g. at the bedside, then only immunoassays are applicable because they can be encapsulated in microfabricated devices.

This article describes the underlying principles of immunoassay, the design of reagents and assay formats, and illustrates their application to a wide range of analytes.
Infrared Spectroscopy in Clinical Chemistry
Authors: Ng Lily M. , Simmons Reiko
Published: September 2006

Infrared (IR) spectroscopy measures the absorption of IR radiation by chemical bonds in a material. Chemical structural fragments of molecules, known as functional groups, tend to absorb IR radiation in the same frequency range regardless of the structure of the rest of the molecule in which the functional group is located. This correlation between the structure of a molecule and the frequencies at which it absorbs IR radiation allows the structures of unknown molecules to be identified and structural or chemical changes of the molecule to be followed. Traditionally, IR spectroscopy has been one of the most important physical methods in the chemical laboratory as it plays an important role in the elucidation of structures and the identification of organic and inorganic compounds. The quantitative analysis of samples is straightforward and is not affected by the physical state of the sample. Gaseous, liquid, and homogeneous and inhomogeneous solid samples all can be conveniently studied.

Applications of IR spectroscopy in clinical chemistry have progressed rapidly in recent years. IR pathological analysis is becoming increasingly important in the detection of biochemical changes in body fluids and tissues. Information obtained from their IR spectra can be used to identify diseases. Advanced investigations are carried out using different data‐analysis techniques such as multivariate analysis. Using a pattern‐recognition approach, IR spectroscopic data provide a nonsubjective aid in the diagnosis of the disease state and the staging of the disease. Unlike most colorimetric or electrochemical/enzymatic clinical chemistry assays, IR spectroscopic analysis is applicable to a variety of body fluids and tissues: whole blood, plasma or serum, synovial fluid, saliva, urine, cells, and membranes. The methodology is fast and readily automated. Sample preparation is simple and no special reagents or other consumables such as electrodes are required, making IR spectroscopy a low‐cost operation. The most attractive advantage of the method is the potential for a rapid multicomponent analysis to be carried out from a single spectrum.
Micro Total Analytical Systems in Clinical Chemistry
Authors: Hendrikse J. , van den Berg A.
Published: September 2006

A micro total analytical system (μTAS) is a system that enhances the performance of a complete chemical analysis by minimizing the scale on which it is performed. The main advantages are automated analyses, higher speed and better separation performance as well as the ability to analyze extremely small (picoliter) sample volumes and reactions involving minute amounts of reagents. A complete analysis may involve taking a sample, its pretreatment and separation into its different components and their detection. In order to perform this sequence of functions, the sample is transported through microchannels that connect the various system parts performing these tasks, while the various (feedback) signals are transported through a separate microelectronic network. Examples of system parts in silicon, glass and polymers that perform tasks such as hydrodynamic and electroosmotic pumping, laminar and turbulent reagent mixing and (di)electrophoretic separations of DNA fragments and particles and cells are presented. Currently, μTAS are mainly being developed and used for remote environmental and process monitoring, patient monitoring and the analysis of nucleic acids. An integrated system in each of these areas is discussed.
Nucleic Acid Analysis in Clinical Chemistry
Authors: Thompson Michael , Deisingh Anil K.
Published: September 2006

This article examines the role of nucleic acid analysis in clinical chemistry. It is a broad‐based article and begins with the background knowledge which will be needed to appreciate the succeeding sections. In the Introduction, structure and function of nucleic acids, hybridization, probe labeling, hybridization protection, polymerase chain reaction (PCR) and sequencing are discussed. Major sections are devoted to microbiological analysis (with particular emphasis on bacteriology), genetic diseases and screening [discussions are provided for cystic fibrosis (CF), heriditary fructose intolerance (HFI) and hemochromatosis along with an introduction to the Human Genome Project and single nucleotide polymorphisms (SNP)], other areas of human medicine (oncology, colorectal cancer and Alzheimer's disease (AD) are considered) and the biosensor approach. A discussion of interesting current and future developments, not only in nucleic acid analysis, but also in gene therapy, concludes the article.
Pharmacogenetic Testing
Authors: Weber Wendell W. , Cronin Maureen T.
Published: September 2006

Drugs are administered to patients with the intention of achieving a planned therapeutic response. Yet drug prescription is a medical art because of the wide variation in individual responses to standard drug doses. In the 1960s, the field of pharmacogenetics emerged from the dedicated work of a small group of investigators who began to enrich the discipline of pharmacology by integrating it with human genetics. Pharmacogenetics provides the experimental framework to understand variability in human reactions to drugs and other exogenous substances as a function of intrinsic human genetic variability. The maturation of the human genome initiative has provided a wealth of primary genetic information and functional genomic data to fuel the understanding of genetic polymorphism and its functional consequences. Today, the field of pharmacogenetics is a well‐integrated, worldwide network engaging a vast community of academic and industrial scientists.

One hallmark of pharmacogenetics studies is the large amount of genetic data that must be accumulated and integrated for high‐resolution drug‐response genotyping and subsequent phenotype profiling. This need for highly parallel genetic analysis has, in turn, fueled a demand for technical innovation to provide the tools necessary for its execution. The response has been a flurry of inventions in microfluidics and nanotechnology, some of which are scaled down versions of existing technologies, such as capillary electrophoresis and mass spectrometry, and some are completely new inventions. Outstanding in this technical revolution are DNA microarrays. Array technology has emerged as the most versatile and widely applied tool to support pharmacogenetics, for several reasons: arrays have the largest and most scalable capacity for parallel analysis, their inherent flexibility permits them to be used as independent analysis tools or as integrated components of more complex microfluidic systems and, finally, a wide variety of methods can be used to design and fabricate them. Pharmacogenetics is experiencing a period of rapid growth and definition. Arrays have proven themselves to be a technology capable of responding to the growing and changing needs of the current research environment and are likely to be equally important as pharmacogenetics moves into the clinical arena.
Phosphorescence, Fluorescence, and Chemiluminescence in Clinical Chemistry
Authors: Schulman Joanna M. , Schulman Stephen G.
Published: September 2006

Molecular luminescence spectroscopy, including fluorescence, phosphorescence, and chemiluminescence (CL), is among the most sensitive of analytical methods. Its use in clinical chemistry has been extensive since the late 1950s and is constantly expanding. Modern separation and immunoassay methods coupled with luminescence detection have revolutionized the detection and determination of endogenous substances, xenobiotics, and their metabolites. Newer techniques such as time‐resolved fluorimetry and phosphorimetry, detection by fiber‐optic sensors, and derivatization with infrared (IR)‐emitting dyes are expanding the range of clinical analysis into new realms of analytical selectivity, sensitivity, and expediency on a scale unimagined until recently. This article considers some of the aspects of fluorescence, phosphorescence, and CL spectroscopy that have contributed to important recent advances in clinical analysis.