Luminescence in Analytical Chemistry

Luminescence can be increased by increasing the incident radiant power. 

For quantitative analysis, the intensity of luminescence (/) is proportional to (1) the concentration of the emitting species (c) over some limited concentration range and (2) the incident radiant power (Pq)  

Derivatization is the chemical alteration of an analyte so that it can be detected conveniently or separated from other species easily. 

Selenium is a trace element essential to life. For example, the selenium-containing enzyme glutathione peroxidase catalyzes the destruction of peroxides (ROOH) that are harmful to cells. Conversely, at high concentration, selenium can be toxic. 

An important application of luminescence is in immunoassays, which employ antibodies to detect analyte. An antibody is a protein produced by the immune system of an animal in response to a foreign molecule, which is called an antigen. An antibody specifically recognizes and binds to the antigen that stimulated its synthesis. 

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AM Garcia-Campana, WRG Baeyens, NA Guzman. Chemiluminescence detection in capillary electrophoresis. In AM Garcia-Campana and WRG Baeyens, eds. Chemi-luminescence in Analytical Chemistry. New York Marcel Dekker, 2001, pp 427-472. 

Winefordner, J. D. Schulman, S. G. O Haver, T. G. Luminescence Spectroscopy in Analytical Chemistry. Wiley-lnterscience New York, 1969. 

Much of the study of ECL reactions has centered on two areas electron transfer reactions between certain transition metal complexes, and radical ion-annihilation reactions between polyaromatic hydrocarbons. ECL also encompasses the electrochemical generation of conventional chemiluminescence (CL) reactions, such as the electrochemical oxidation of luminol. Cathodic luminescence from oxide-covered valve metal electrodes is also termed ECL in the literature, and has found applications in analytical chemistry. Hence this type of ECL will also be covered here. 

Vol. 34. Neutron Activation Analysis. By D. De Soete, R. Gijbels, and J. Hoste Vol. 35 Laser Raman Spectroscopy. By Marvin C. Tobin Vol. 36 Emission Spectrochemical Analysis. By Morris Slavin Vol. 37 Analytical Chemistry of Phosphorus Compounds. Edited by M. Halmann Vol. 38 Luminescence Spectrometry in Analytical Chemistry. By J. D.Winefordner, S. G. Schulman, and T. C. O Haver... 

Polyoxometalates are important reagents in analytical chemistry and they also find applications in catalysis, molecular biology, materials sciences, and medicine. A recent study of nine Ndm polyoxometalates (POM) showed their aqueous 5 mM solutions to be weakly luminescent, whereas no luminescence at all is seen for the aquo ion. In particular, the bis(POM) complexes better protect the Ndm ion from nonradiative deactivations, for instance t(4F3/2) = 411 6nsfor[Nd(PWn039)2]11- and67 2 ns for [Nd(As4W4oOi4o)]25 (But et al., 2005). 

Luminescence of the metal complexes can also be a result of the excited state population in an alternative way to absorption, eg as seen in the outcome of the chemical reaction (chemiluminescence) or electrochemical processes (electrochemiluminescence), which are often applied in analytical chemistry [24,25, 37, 39—44],... 

Dean JA. Electronic Absorption and luminescence spectroscopy. In Analytical chemistry handbook. New York McGraw-Hill Inc, 1995 Section 5. 

There are various potential applications of photophysical phenomena in analytical chemistry. The relatively short lifetimes of most excited states, however, is a serious drawback to the construction of practical devices but studies which focus on finding ways to extend triplet lifetimes have now been described by Harriman et al. Kneas et al. have examined new types of luminescent sensor on polymer supports, and both Neurauter et al. and Marazuela et al. have designed sensors based on the ruthenium(II) polypyridine complex for the detection of carbon dioxide. A system, based on the formation of twisted intramolecular charge transfer states, has been devised for measuring the molecular weight of polymeric matrices (Al-Hassan et a/.), and the chemical reactivity at the interface of self-assembled monolayers has been assessed using fluorescence spectroscopy (Fox et al). 

Costa-Femandez, J.M., Pereiro, R., and Sanz-Medel, A. (2005) The use of luminescent quantum dots for optical sensing. Trends in Analytical Chemistry TRAC, 25 (3), 207-218. 

Analytical Chemistry of Phosphorus Compounds. Edited by M. Halmann Luminescence Spectrometry in Analytical Chemistry. By J. D. Winefordner, S. G. Schulman, and T. C. O Haver... 

Fluorescence (fl) takes place when transitions occur between states of the same multiplicity. It is a rapid process (kfl 106 — 109s-1). For the luminescent reagents used in analytical chemistry, fluorescence corresponds to the transition Si — S0. As a result of internal conversions and radiationless transitions, fluorescence occurs from the lowest vibrational level of S) to the vibrational levels of S0. 

Extensive use is made of characteristic luminophores in analytical chemistry. Examples of such luminophores are crystallophosphors, activated mercury-like ions, uranyl ions, and lanthanides. They exhibit a glow similar to molecular luminescence. Their absorption and emission of radiation are associated with the electronic transitions occurring within a luminescence centre - the activator (Fig. 2 V). 

Spectral and luminescence properties of organic molecules have been found to depend on the electronic structure, or the relative position of lower electronically excited states, whatever their orbital nature and multiplicity that change under the influence of various structural factors and intermolecular interactions86-89 In terms of the characteristics of electronic orbitals of organic molecules which are used in analytical chemistry the four most important types can be indicated (in the S0-state) ... 

JD Winefordner, SG Schulman, TC O Haver. Luminescence Spectroscopy in Analytical Chemistry. New York Wiley-Interscience, 1972. 

Richmond, MD and RJ Hurtubise (1989). Analytical characteristics of beta.-cyclodextrin/salt mixtures in room-temperature soUd-surface luminescence analysis. Analytical Chemistry, 61(23), 2643-2647. 

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