bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phosphorescence Measurements, Applications of
Authors: Díaz García Marta E. , Badía Rosana 
Published: September 2006

Abstract
Luminescence is a term used for both fluorescence and phosphorescence. These are emission processes following the absorption of light, and the distinction between them is based upon the process of the deactivation mechanism. Phosphorescence has been identified as the light emitted from the triplet excited state to the ground state, a spin‐forbidden transition. Fluorescence is a radiational transition between electronic states of the same multiplicity.
The first analytical uses of phosphorescence were published in the 1950s, but the technique was not widely accepted due to the practical aspect of measuring the signal at cryogenic temperatures (77 K).
Developments in room temperature phosphorescence (RTP) have given rise to fundamental and practical advances which have stimulated interest in phosphorimetry. Solid‐surface room temperature phosphorescence (SSRTP) has been generally observed by immobilizing the lumiphor on a solid support such as filter paper or polymeric resins. SSRTP has been shown to be a sensitive and selective approach for the analysis of trace components in biological, pharmaceutical, and environmental samples. Techniques such as SSRTP combined with flow injection analysis provide new avenues for optical sensing transduction and improvement of SSRTP techniques. Applications of SSRTP in flowing systems include the sensing of cations, anions, oxygen, glucose, ethanol, antibiotics, and moisture.

A number of developments in RTP have focused on sensitized phosphorescence (SP) and on the use of ordered media (micelles and cyclodextrins (CDs)), allowing the observation of RTP in fluid solution. In SP the triplet energy of a donor (analyte) is transferred to an acceptor that phosphoresces in fluid solution and the emission of the acceptor is measured. Therefore, SP can only provide quantitative information. In ordered media, a micelle (or a CD) protects the long‐lived triplet state from the quenching processes that normally take place in solution, allowing both quantitative and qualitative measurements. SP and ordered media RTP provide the limits of detection for many lumiphors in the nmol
−1
range and calibration graphs have a wide linear range.

As new instrumental and basic insights emerge in SSRTP, Micelle Stabilized Room Temperature Phosphorescence (MSRTP), and solution‐sensitized RTP, these techniques will find much greater use in the trace and ultratrace analysis of dissolved, volatile, and gaseous substances in areas such as pharmaceutical analysis, environmental science, and clinical chemistry.
Column Technology in Gas Chromatography
Authors: Larson Paul 
Published: September 2006

Abstract
Column technology has fostered the development of gas chromatography (GC). As the manufacture of columns, especially capillary columns, has become more reproducible, the instruments have also improved. Chromatographic theory helps to guide the development of both the column and instrument in GC. Aspects of the theory directly related to the construction of columns are summarized. While packed columns can still be made in the local laboratory, the construction of capillary columns has moved to commercial vendors with the introduction of thin‐walled fused‐silica capillary columns. The technology required for the construction of columns is described.
Cavity Ringdown Laser Absorption Spectroscopy
Authors: Miller George P. , Winstead Christopher B. 
Published: September 2006

AbstractCavity ringdown laser absorption spectroscopy (CRDS), a distinctly new variant of classical absorption spectroscopy, is based upon the time required for the intensity of a light pulse in an optical cavity to decay. The sensitivity of the technique stems from the large number of passes that the light pulse makes within the cavity. For example, mirrors of 99.99% reflectivity in a 1‐m long cavity yield a ringdown time of approximately 33.4‐µs for an empty cavity. This is equivalent to a 10‐km pathlength traveled during the first time constant! The presence of a sample having an absorbance of 1 × 10−6inside the cavity will yield a readily measurable change in ringdown time of approximately 1%. When compared with traditional single‐pass absorption spectroscopy, which typically detects absorbances of the order of 1 × 10−3, the potential of CRDS becomesclear. As for any absorption technique, the conditions for Beer's law behavior must be fulfilled. One primary advantage of the cavity ringdown method is to allow the use of the extensive wavelength operating range of pulsed lasers for absorption spectroscopy. Because CRDS depends solely on the decay time, it is unaffected by the inherent shot‐to‐shot power fluctuations of pulsed lasers. Although still in the early stages of development, CRDS has been used to study chemical species in environments ranging from molecular beams and gas cells to atmospheric pressure flames and plasmas, in spectral regions ranging from the ultraviolet (UV) to the infrared (IR). It has only been very recently, with first couplings of CRDS and atomization sources (inductively coupled plasma (ICP), graphite furnace), that the technique has broadened to include analytical atomic spectroscopy. The potential of cavity ringdown for atomic spectroscopy has been demonstrated with the determination of mercury detection limits (DLs), in air, of less than 1 part per trillion.At the time of writing (1999), CRDS is very much still in its infancy, especially with regard to analytical applications. For a possible glimpse of the future, it should be noted that as the wavelength coverage of diode lasers continues to grow, the possibilities for constructing small, ultrasensitive CRDS spectrometers for analytical atomic and molecular spectrometry continue to increase. However, any inherent advantage of CRDS over other analytical techniques will be determined by the quality of mirrors used for cavity construction, the stability of the baseline ringdown time measurement, the atomization source, and the fluorescence characteristics of the element under consideration. Although the technology associated with the ringdown technique continues to advance rapidly, CRDS is as yet a novel approach for many analytical measurements, and is sure to continue to find new areas of application. The next few years should prove very exciting as new instrumentation becomes available and the technique's full potential is explored.
Interpretation of Infrared Spectra, A Practical Approach
Authors: Coates John 
Published: September 2006

Abstract
The vibrational spectrum of a molecule is considered to be a unique physical property and is characteristic of the molecule. As such, the infrared spectrum can be used as a fingerprint for identification by the comparison of the spectrum from an “unknown” with previously recorded reference spectra. This is the basis of computer‐based spectral searching. In the absence of a suitable reference database, it is possible to effect a basic interpretation of the spectrum from first principles, leading to characterization, and possibly even identification of an unknown sample. This first principles approach is based on the fact that structural features of the molecule, whether they are the backbone of the molecule or the functional groups attached to the molecule, produce characteristic and reproducible absorptions in the spectrum. This information can indicate whether there is backbone to the structure and, if so, whether the backbone consists of linear or branched chains. Next it is possible to determine if there is unsaturation and/or aromatic rings in the structure. Finally, it is possible to deduce whether specific functional groups are present. If detected, one is also able to determine local orientation of the group and its local environment and/or location in the structure. The origins of the sample, its prehistory, and the manner in which the sample is handled all have impact on the final result. Basic rules of interpretation exist and, if followed, a simple, first‐pass interpretation leading to material characterization is possible. This article addresses these issues in a simple, logical fashion. Practical examples are included to help guide the reader through the basic concepts of infrared spectral interpretation.
Liquid Chromatography/Infrared Spectroscopy
Authors: Somsen Govert W. , Visser Tom 
Published: September 2006

AbstractAnalytical techniques that combine liquid chromatography (LC) and infrared (IR) spectroscopy have been developed primarily to permit specific detection and/or identification of sample constituents. LC is an important and extensively used method for the separation of mixtures into their individual components. IR spectroscopy is very useful for the characterization of functional groups and has strong compound‐identification capabilities which are especially suited for the differentiation of structural isomers. Over the past years the coupling of LC and IR spectroscopy (LC/IR) has been accomplished by two different approaches. The first and simplest approach is to use a flow cell through which the effluent from the LC column is passed while the IR spectra are continuously measured. The merits of flow‐cell IR detection include ease of operation, real‐time detection and low maintenance, but its main disadvantage lies in the significant IR‐absorption of the solvents commonly used in LC. These absorptions seriously limit both the detection sensitivity and the obtainable spectral information. The second approach involves elimination of the LC solvent prior to IR detection. In this approach an interface is used to evaporate the eluent and deposit the separated compounds onto a substrate suitable for IR detection. The primary advantages of solvent‐elimination LC/IR are the possibility to obtain full spectra of the analytes and the considerably enhanced sensitivity when compared to flow‐cell detection. Unfortunately, common LC solvents, and particularly aqueous eluents, are not easily removed and therefore the evaporation interfaces are often rather complex. This article reviews the developments, practical aspects, applications and current status of LC/IR, covering both coupling approaches. It follows that despite the unfavorable detection limits, flow‐cell LC/IR can be useful for the specific and quantitative detection of major components of mixtures. However, solvent‐elimination‐based IR‐detection should be used when small amounts of sample constituents have to be characterized with a high level of confidence. In general, the practical use of IR detection in LC is still limited, but the advent of various (commercial) flow‐cell and interface designs shows that LC/IR is more and more being recognized as a feasible and rewarding technique.
Electrocatalysis‐Based Kinetics Determinations
Authors: Bǎnicǎ Florinel Gabriel , Ion Ana 
Published: September 2006

AbstractThe term “electrocatalysis” denotes the catalysis of an electrochemical reaction. In accord with the general definition of catalysis1 the effect of an electrocatalyst is to increase the rate of an electrochemical reaction without modifying the overall standard Gibbs energy change in the reaction. Taking the view of Faraday's law, the rate of an electrochemical reaction is expressed by the electrolytic current. Consequently, an increase in the electrolytic current is the main result of electrocatalysis. The benefits of electrocatalysis include making possible the quantitation of the catalyst itself or of some substrate compounds that are not electrochemically active or are not generally amenable to direct electrochemical determination. An appreciable improvement in selectivity may be brought about by electrocatalysis. Additionally, appropriate engineering of catalytic layers on electrode surfaces has led to the preparation of a huge variety of chemical and biochemical sensors. However, close control of the experimental conditions (temperature, electrolyte composition) is often required when dealing with electrocatalytic processes. Usually, such requirements do not give rise to any particular difficulties.
Capillary Electrophoresis
Authors: Siles Barbara A. 
Published: September 2006

Abstract

Over the past two decades, capillary electrophoresis (CE) has emerged as a family of powerful and versatile separation techniques. The electrically driven flow profiles generated in CE provide, routinely, separation efficiencies of 10
5
theoretical plates. Although theory predicts that the achievable separation efficiencies will be greatest for macromolecules with small diffusion coefficients, CE has also been successful in the analysis of small molecules, such as inorganic ions. Strategies to increase separation efficiencies on‐line have involved sample stacking and isotachophoretic techniques. The former promotes higher separation efficiencies based on differences in conductivity between the background electrolyte (BGE) and the sample buffer; the latter utilizes a discontinuous buffer system to create discrete solute zones. The instrumentation employed in CE is simple in design and is compatible with a variety of detection modes, including ultraviolet/visible (UV/VIS) absorbance, fluorescence, electrochemistry, mass spectrometry (MS), and chemiluminescence (CL). CE methodologies can be miniaturized on to a silicon wafer and integrated with sample preparation and chemical reactions. In addition to free‐solution capillary electrophoresis (FSCE) utilizing a BGE and potentially a variety of BGE additives, several alternative separation modes have been developed and implemented. These include micellar electrokinetic chromatography (MEKC), capillary isoelectric focusing (cIEF), size‐sieving capillary electrophoresis (SSCE), and capillary electrochromatography (CEC). Some of these separation modes have been adapted from the slab gel electrophoresis (SGE) format, or are reminiscent of separation mechanisms in liquid chromatography (LC). Currently, one of the greatest challenges in CE involves the maintenance of the capillary surface to provide reproducible electro‐osmotic flow (EOF) and significantly reduce capillary wall interactions. According to the mode of separation employed and the characteristics of the solutes to be analyzed, both covalent and noncovalent (dynamic) capillary wall modifications have been demonstrated.
Microscale High‐Performance Liquid Chromatography and the Evolution of Capillary Electrochromatography
Authors: Vallano Patrick T. , Chirica Gabriela S. , Remcho Vincent T. 
Published: September 2006

Abstract
Miniaturization is a general trend in analytical chemistry. In the field of separation science, this trend has led to the development of microscale techniques based on high‐performance liquid chromatography (HPLC) and electrophoresis. Two such techniques, microscale high‐performance liquid chromatography (or micro LC) and capillary electrochromatography (CEC) are the subjects of this article. Micro LC is a general term that encompasses HPLC separations in which the column diameter is less than 1.0 mm. CEC is a hybrid of micro LC and capillary electrophoresis (CE). Relative to the conventional scale technique, micro LC possesses several advantages, namely higher efficiency, often shorter analysis times, reduced solvent consumption and higher mass sensitivity. Micro LC is uniquely suited for analysis of very small sample volumes (e.g. biological cells). It is this type of analysis, a formidable challenge, which has propelled the technique's continued development. CEC most commonly employs conventional HPLC particles packed into fused silica capillary columns. A potential gradient is applied along the capillary; the resulting electro‐osmotic flow (EOF) then propels the mobile phase (and analytes) through the column. In CEC, the electric field (generated by a power supply) takes the place of pressure (generated by a pump) in an HPLC separation. One of the most important advantages of CEC relative to micro LC or CE is enhanced resolution. High resolution in CEC arises from the combination of high separation efficiency and selectivity inherent in the technique. CEC, however, is a relatively new technique and its ability to become a “workhorse” in the laboratory has not yet been demonstrated.
Supercritical Fluid Chromatography
Authors: Yuan Huimin , Olesik Susan V. 
Published: September 2006

AbstractSupercritical fluid chromatography (SFC) employs fluids that are raised above their critical pressure (Pc) and critical temperature (Tc) as mobile phases. Carbon dioxide, CO2, is the supercritical fluid most commonly used as a mobile phase for SFC. It is capable of solvating mostly nonpolar analytes. Cosolvents, such as methanol and acetonitrile, are added toincrease the polarity of the analytes that can be analyzed by SFC. SFC is most commonly practiced using a normal‐phase retention mechanism. In other words, the stationary phase is typically more polar than the mobile phase and the retention order is in increasing order of polarity. The advantages of SFC over liquid chromatography (LC) include higher efficiency separations and faster speed of analysis. The advantage that SFC has over gas chromatography (GC) is that SFC can efficiently separate thermally labile compounds. The disadvantage of SFC is that the polarity of the mobile phase is limited. Highly polar solutes are not soluble in supercritical fluids, even when modifiers are added. SFC is commonly used to separate petroleum distillates and by‐products, moderately polar pesticides and herbicides, and more recently for the separation of chiral compounds, such as pharmaceutical drugs.
Time‐of‐Flight Mass Spectrometry
Authors: Weinberger Scot R. , Davis Stephen , Makarov Alexander , Thompson Steve , Purves Randy , Whittal Randy M. 
Published: September 2006

AbstractThis article reviews the developmental history, fundamental technology, and general applications of time‐of‐flight mass spectrometry (TOFMS). The fundamentals of instrument operation and components are discussed. Applications in terms of gas chromatography (GC), liquid chromatography (LC), capillary electrophoresis (CE), laser desorption, multiphoton desorption, plasma desorption (PD), matrix‐assisted laser desorption, surface‐enhanced laser desorption, inductively coupled plasma (ICP), and secondary ion mass spectrometry (SIMS) are presented. A review of tandem time‐of‐flight (TOF) techniques with a focus on ion trap TOF instrumentation is provided.The purpose of this article is to provide the reader with a fundamental understanding of TOFMS principles and applications. Information is presented in a simple, straightforward, didactic fashion.
Carbon‐13 Nuclear Magnetic Resonance Spectroscopy
Authors: Neiss Thomas G. 
Published: September 2006

AbstractCarbon‐13 (13C) nuclear magnetic resonance spectroscopy (NMR) is the measurement of the precession or resonance frequencies of the net magnetization for13C nuclei whose individual magnetic moments have been oriented in a strong magnetic field. Nuclei differing in their electronic shielding precess about the magnetic field at different Larmor or resonance frequencies. A high‐power radiofrequency (rf) pulse is used to perturb the magnetization vectors from their equilibrium distribution, generating an observable transverse magnetization. Precession of this net magnetization vector about the static magnetic field induces a voltage into the NMR probe coil. Relaxation pathways promote the repartitioning of the individual magnetic moments to their equilibrium Boltzmann distributions and a dephasing of the individual magnetization vectors in the transverse plane. This signal is detected as a function of time through a phase‐sensitive receiver, digitized and Fourier transformed (FT) into a frequency domain spectrum. The NMRs, referenced relative to the resonance frequency of a standard are shifted in a manner characteristic of hybridization of the atom, electronegativity of the substituents attached and the steric environment of the nucleus. These shifts typically follow a standard set of rules and thus spectra can be simulated either empirically through measurement of the additive effects of substituents or through ab initio and semi‐empirical computational methods. Scalar couplings to directly attached hydrogen‐1 (1H) nuclei split resonance lines into (nH + 1) lines and require the use of broadband1H decoupling to remove this splitting for sensitivity enhancement. The presence of attached or nearest neighbor1H atoms also provides a means of enhancing the signal intensity of13C spectra and for selective observation of13C signals through polarization transfer. Multidimensional NMR experiments are available which permit the13C13C or13C1H correlations as well as a means of measuringnJCHcouplings.Analysis of samples can be done without the need for internal standards or calibration standards since NMR signals are directly proportional to the moles of analyte present and there are no response factors or absorptivities to be determined for quantitative analysis. Although13C NMR spectroscopy is widely used and is a very powerful structural technique in organic and polymer chemistry, the technique suffers from an inherent lack of sensitivity due to a natural abundance of only 1.1 percent and a small magnetogyric ratio (γC). Long relaxation times present in small molecules undermine the quantitative accuracy of this method or require lengthy amounts of instrument time to acquire an NMR spectrum. Quantitative results can be obtained with the selection of appropriate experimental parameters often combined with the use of relaxation agents.