Analytical Applications of Luminescence

A fluorometric analysis results in the collection of two spectra, the excitation spectrum and the emission spectrum. The excitation spectrum should be the same as the absorption spectrum obtained spectropho tome trie ally. Differences may be seen due to instrumental factors, but these are normally small, as seen in Fig. 5.45, which shows the absorption and excitation spectra for Alizarin garnet R, a fluorometric reagent for aluminum ion and fluoride ion. The longest wavelength absorption maximum in the excitation spectrum is chosen as the excitation wavelength this is where the first monochromator is set to excite the sample. It would seem reasonable to choose the wavelength that 

Fluorescence occurs in molecules that have low-energy transitions such molecules are 

Curve B, quinine excitation Curve C, anthracene fluorescence and Curve D, quinine fluorescence. (From Guiibauit, G.G., ed., Practical Fluorescence, 2nd edn., Marcel Dekker, Inc., New York, 1990. With permission.) 

Many materials benefit from analysis at cryogenic temperatures. At 77 K, enhanced fluorescence and phosphorescence are seen, and low-temperature studies are used for elucidation of the mechanisms of photochemical reactions, characterizing bandgap changes in semiconductors and other applications. 

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The year under review has shown continual progress in elucidating the detailed behaviour of excited singlet and triplet states. This has been largely due to the improvement of experimental equipment especially in the very short time domains. The need for a complete understanding of photophysical processes in any application of excited-state properties is now fully accepted, particularly in analytical applications of luminescence and biochemistry. 

The scientific interests of Anatoly K. Babko ranged widely, especially in regard to fundamental aspects of analytical chemistry, applications of organic reagents in inorganic analysis, chemistry of complex compounds (including heteropolyacids), analytical applications of complex compounds in photometry, luminescence and chemiluminescence, ion chromatography, and liquid-liquid extraction. 

This chapter focuses on analytical applications of surface-modified QDs and general approaches to develop novel QD methodologies for chemical and biochemical analysis, an area of growing interest in the last few years. A brief discussion of the attractive luminescent properties of QDs, as compared with the more conventional organic dyes, is mandatory to understand such developments in (bio(chemical analysis. 

A limitation of the application of luminescence spectroscopy to the analysis of real samples is its lack of specificity owing to similarities in spectral bandshapes and spectral positions of the luminescence spectra of many compounds. An obvious solution to this problem is the separation of the analytical sample s interfering constituents from each other before quantitation by fluorescence. High-performance liquid chromatography (HPLC) and related separation methods can be coupled to fluorescence spectroscopy to take advantage of the sensitivity of the spectroscopic method and the specificity of the separation method. 

However, in spite of the increasing photophysical and analytical interest as well as the more and more numerous works concerning the biomedical and therapeutic role of these various compounds, to the best of our knowledge so far only two recent review articles have been devoted to the analytical applications of phenothiazines [11] and to the luminescence properties of BPHTs [25]. 

Fletcher P, Andrew KN, Calokerinos AC, Forbes S, Worsfold PJ. Analytical applications of flow injection with chemiluminescence detection-a review. Luminescence. 2001 16(l) l-23. 

Analytical Applications of Bio luminescence and Chemiluminescence. Editors Kricka LJ, Stanley PE, Thorpe GHG, Whitehead TP. London Academic Press 1984. pp. 602. ISBN 0-12-426290-2. 

The analytical applications of chemiluminescence fall into three broad categories. First, there are some chemiluminescent reactions that are catalyzed by specific compounds and that can, therefore, be diagnostic for the presence or quantitation of those compounds. For example, the hydrogen peroxide oxidation of the cyclic luminescent hydrazide luminol is catalyzed by transition metal ions such as Co(II), which can thereby be detected at a 10 pM concentration in a flow injection system (B33) and even down to 1 pM when the chemiluminescence is induced ultrasonically (K19). Other transition metal ions that have been similarly detected (in the 1-10 nM range) are Cr(III) (C13), Cu(II), and Ni(II) (S26). Other... 

Finally, in analytical applications the luminescence is often used only to detect specific components of interest. The microemulsion is then employed to extract these components, e.g., polycyclic aromatic hydrocarbons [81], or to separate neutral metal ion complexes by electrophoresis with charged microemulsion droplets [82]. But it must not always be luminescence induced by external light chemiluminescence in microemulsions was also reported [83] to give an appreciable increase in the intensity compared to homogeneous solutions. 

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. 

Fletcher, P., K. N. Andrew, A. C. Calocerinos, S. Forbes, and P. J. Worsfold. 2001. Analytical applications of flow injection with chemiluminescence detection—A review. Luminescence 16 1—23. 

Jablonski E.G. and De Luca M. (1982) Analytical applications of bioluminescence marine bacterial system, in Clinical and biochemical luminescence, (ed. L.J. Kricka and T.J.N. Carter), Dekker, New York, 75-87. 

Analytical Applications. Chemiluminescence and bioluminescence are useful in analysis for several reasons. (/) Modem low noise phototubes when properly instmmented can detect light fluxes as weak as 100 photons/s (1.7 x 10 eins/s). Thus luminescent reactions in which intensity depends on the concentration of a reactant of analytical interest can be used to determine attomole—2eptomole amounts (10 to 10 mol). This is especially useful for biochemical, trace metal, and pollution control analyses (93,260—266) (see Trace and residue analysis). (2) Light measurement is easily automated for routine measurements as, for example, in clinical analysis. 

The active state of luminescence spectrometry today may be judged ly an examination of the 1988 issue of Fundamental Reviews of Analytical Chemistry (78), which divides its report titled Molecular Fluorescence, Phosphorescence, and Chemiluminescence Spectrometry into about 27 specialized topical areas, depending on how you choose to count all the subdivisions. This profusion of luminescence topics in Fundamental Reviews is just the tip of the iceberg, because it omits all publications not primarily concerned with analytical applications. Fundamental Reviews does, however, represent a good cross-section of the available techniques because nearly every method for using luminescence in scientific studies eventually finds a use in some form of chemical analysis. Since it would be impossible to mention here all of the current important applications and developments in the entire universe of luminescence, this report continues with a look at progress in a few current areas that seem significant to the author for their potential impact on future work. 

Many current multidimensional methods are based on instruments that combine measurements of several luminescence variables and present a multiparameter data set. The challenge of analyzing such complex data has stimulated the application of special mathematical methods (80-85) that are made practical only with the aid of computers. It is to be expected that future analytical strategies will rely heavily on computerized pattern recognition methods (79, 86) applied to libraries of standardized multidimensional spectra, a development that will require that published luminescence spectra be routinely corrected for instrumental artifacts. Warner et al, (84) have discussed the multiparameter nature of luminescence measurements in detail and list fourteen different parameters that can be combined in various combinations for simultaneous measurement, thereby maximizing luminescence selectivity with multidimensional measurements. Table II is adapted from their paper with the inclusion of a few additional parameters. 

The optode transduces the non-optical signal from the environment to the optical one, readable by the photodetector. Various indirect optical sensors and theirs applications are described in literature35. The optode can work as a chemical sensor that detects certain analytes in aqueous solutions or in air on chemical way. It means that changes in the environment cause the changes in the photosensitive material, which is immobilized in the optode matrix. These chemical changes influence the observed light intensity (for example, due to absorption) or one can analyze the intensity or time decay of luminescence. There are numbers of publications devoted to the family of optical chemical sensors36. 

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