Luminescence, analytical method

Wolfbeis O. S. (1988) Fiber Optical Fluorosensors in Analytical and Clinical Chemistry, in Schulman S. G. (Ed.), Molecular Luminescence Spectroscopy. Methods and Applications Part 2, John Wiley Sons, New York, pp. 129-281. 

The use of europium chelates, with their unusually long fluorescence decay times, as labels for proteins and antibodies has provided techniques that are referred to as time-resolved fluoroimmunoassays (TRFIA). Fluorophores as labels for biomolecules will be the topic of Sect. 3. Nevertheless, TRFIAs always have to compete with ELISA (enzyme-linked immunosorbent assays) techniques, which are characterized by their great versatility and sensitivity through an enzyme-driven signal amplification. Numerous studies have been published over the past two decades which compare both analytical methods, e.g., with respect to the detection of influenza viruses or HIV-1 specific IgA antibodies [117,118]. Lanthanide luminescence detection is another new development, and Tb(III) complexes have been applied, for instance, as indicators for peroxidase-catalyzed dimerization products in ELISAs [119]. 

An additional screening test for TCDD-like (aryl hydrocarbon receptor, AhR, active) chemicals has been developed (Garrison et al. 1996) and is available commercially (Anonymous 1997). Dubbed the CALUX (for chemically activated luciferase gene expression) system, the assay is based on recombinant cell lines into which researchers have inserted a firefly luciferase gene. When exposed to dioxin-like compounds, the recombinant cells luminesce. The method is sensitive to ppt levels of 2,3,7,8-TCDD equivalents in blood, serum, and milk (Anonymous 1997). Samples testing positive can be subjected to more definitive and specific analytical testing. 

Time-resolved lanthanide luminescence was used for the first time for immunoassays. This type of analytical method most effectively removes the background fluorescence, because serum contains many undesired co-existing materials, which raises significantly the background level when the sample is irradiated. 

Determination of lanthanide ions with a fairly low detection limit of 10-5-10-6 wt% is achieved with Ln111 /i-diketonates. Relying on this fact new, rapid, selective, and highly sensitive analytical methods essentially based on the luminescence properties of these complexes have been developed. After a preliminary work on Smm and Eum chelates (Topilova et al.,... 

Finally, in a novel application, some uniquely structured hexapyrrolidine derivatives of C60 with Th and D3 molecular symmetries have been synthesized and characterized by analytical methods and x-ray crystallography [260]. This work revealed strong luminescence, indicative of photophysical properties that are unusual in comparison with other fullerene derivatives. Therefore, the hexapyrrolidine adduct was utilized as a chromophore in the fabrication of a white light organic LED [261]. 

Luminescence has proven a useful probe of structure and dynamics in a broad range of heterogeneous media, from zeolites to micelles to biomaterials. The sensitivity of this process to its environment, and its ease of detection, make it a highly versatile analytical tool. To date, luminescence as a probe of solid-liquid interfacial processes in SAMs is still relatively limited. However, with the development of fluorescence-based analytical methods of increasing spatial and temporal resolution, it is likely to be used increasingly in answering fundamental questions regarding monolayer behavior. 

Many alternative techniques, both qualitative and quantitative, have been investigated either for screening purposes or as primary methods. Such techniques include atomic absorption spectrophotometry, molecular luminescence, electron spin resonance spectrometry, X-ray analysis methods, and electro analytical methods. Flameless atomic absorption spectrophotometry (FAAS) is the technique that has almost completely replaced NAA. 

Metallo-1,2-enedithiolates did not again come to the attention of those developing new analytical methods until the late 1990s. It was the chemical and photophysical properties of luminescent heterocyclic-substituted platinum-... 

Molecular fluorescence spectroscopy is a commonly employed analytical method that is sensitive to certain chemical properties of FA (9-13). Fulvic acid s molecular fluorescence is principally due to conjugated unsaturated segments and aromatic moieties present in the macromolecule (14). Several types of fluorescence spectra can be measured, including an excitation emission matrix or total luminescence spectrum, constant offset synchronous fluorescence, excitation spectra, and emission spectra, furnishing the researcher with useful data. The ability to resolve and select multiple fluorescent species makes these approaches extremely useful for studying FA relative to its chemical reactivity. 

In this section, we will present the most significant and recent literature data concerning the UV-visible absorption and luminescence spectroscopies of a variety of phenothiazine derivatives and BPHTs (Figs. 1-5). We will also describe the photophysical and photochemical properties as well as the characteristics of organized media or molecular complexes formed between a number of phenothiazine derivatives or BPHTs and either micelles or CDs. Finally, we will examine several analytical methods which have been developed to determine phenothiazines in biological samples and pharmaceutical formulations, due to biomedical interest, and other recent applications of phenothiazines and BPHTs in various fields. 

Luminescence spectroscopy is an analytical method derived from the emission of light by molecules which have become electronically excited subsequent to the absorption of visible or ultraviolet radiation. Due to its high analytical sensitivity (concentrations of luminescing analytes 1 X 10 9 moles/L are routinely determined), this technique is widely employed in the analysis of drugs and metabolites. These applications are derived from the relationships between analyte concentrations and luminescence intensities and are therefore similar in concept to most other physicochemical methods of analysis. Other features of luminescence spectral bands, such as position in the electromagnetic spectrum (wavelength or frequency), band form, emission lifetime, and excitation spectrum, are related to molecular structure and environment and therefore also have analytical value. 

Various techniques have been used depending on the polymer and the nature of the chemical transformations infrared, ultraviolet and electron spin resonance spectroscopy, vapour phase chromatography, mass spectrometry, molecular weight and gel fraction determination, luminescence measurements, etc. These techniques have recently been discussed in a well-documented review on analytical methods applied to the study of the photodegradation of polymers [19]. 

Section. 1 treats molecular s K ctroscopy in nine chapters that describe absorption, emission, luminescence. infrared, Raman, nuclear magnetic resonance. mass spectrometry, and surface analytical methods. 

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