Chemiluminescence general applications

Table 1.27 lists some general applications of chemiluminescence. Early CL studies were limited by a low S/N ratio. Thus, oxidation eould only be observed at high temperatures where other techniques provide more direct results. With the development of fast pulse analysers low light levels ean now be measured with great sensitivity (a few photons/s). Consequently, it has been claimed that low temperature luminescence measurements are useful in lifetime prediction [570]. Some major applications of the CL technique are identified as isothermal measurements in oxygen to study progress of oxidation, and in nitrogen to estimate the amounts of peroxides present... 

Applications of the oxalate-hydrogen peroxide chemiluminescence-based and fluorescence-based assays with NDA/CN derivatives to the analysis of amino acids and peptides are included. The sensitivity of the chemiluminescence and fluorescence methods is compared for several analytes. In general, peroxyoxalate chemiluminescence-based methods are 10 to 100 times more sensitive than their fluorescence-based counterparts. The chief limitation of chemiluminescence is that chemical excitation of the fluorophore apparently depends on its structure and oxidation potential. 

General books [213-217], chapters [218], and reviews were published in the 1980s reporting the suitability of CL and BL in chemical analysis [219-222], the specific analytical applications of BL [223], the CL detection systems in the gas phase [224], in chromatography [225, 226], the use of different chemiluminescent tags in immunoassay, and applications in clinical chemistry [227-232] as well as the applications of CL reactions in biomedical analysis [233]. 

This review deals mainly with BL analytical applications in the last 10-15 past years, but some previous fundamental works are also listed. In Table 3 some fundamentals references of general interest and the findings of recent symposia on this topic are collected. In the journal Luminescence, the Journal of Biological and Chemical Luminescence (previously Journal of Bioluminescence and Chemiluminescence) are also reported surveys of the recent literature on selected topics (like ATP or GFP applications), instruments, and kits commercially available. 

Optimization strategies and a number of generalized limitations to the design of gas-phase chemiluminescence detectors have been described based on exact solutions of the governing equations for both exponential dilution and plug-flow models of the reaction chamber by Mehrabzadeh et al. [12, 13]. However, application of this approach requires a knowledge of the reaction mechanism and rate coefficients for the rate-determining steps of the chemiluminescent reaction considered. 

Fortunately, the factors which affect rules derived from photochemical studies of energy transfer reactions it is possible in most cases to convert the chemically generated excited state efficiently into a photon of light (Wilson and Schaap, 1971 Belyakov and Vassil ev, 1970). Thus one is able to focus attention on the much less understood factors which affect (pCE. These factors are the subject of our remaining discussion on general requirements for chemiluminescent reactions. 

Electrocapillary methods, described in Sections 13.2 and 13.3, are very useful in the determination of relative surface excesses of specifically adsorbed species on mercury. As discussed in Section 13.4, such methods are less straightforward with solid electrodes. For electroactive species and products of electrode reactions, the faradaic response can frequently be used to determine the amount of adsorbed species (Section 14.3). Nonelectro-chemical methods can also be applied to both electroactive and electroinactive species. For example, the change in concentration of an adsorbable solution species after immersion of a large-area electrode and application of different potentials can be monitored by a sensitive analytical technique (e.g., spectrophotometry, fluorimetry, chemiluminescence) that can provide a direct measurement of the amount of substance that has left the bulk solution upon adsorption (7, 44). Radioactive tracers can be employed to determine the change in adsorbate concentration in solution (45). Radioactivity measurements can also be applied to electrodes removed from the solution, with suitable corrections applied for bulk solution still wetting the electrode (45). A general problem with such direct methods is the sensitivity and precision required for accurate determinations, since the bulk concentration changes caused by adsorption are usually rather small (see Problem 13.7). 

Chemiluminescence. Chemiluminescence (262—265) is the emission of light during an exothermic chemical reaction, generally as fluorescence. It often occurs in oxidation processes, and enzyme-mediated bioluminescence has important analytical applications (241,262). Chemiluminescence analysis is highly specific and can reach ppb detection limits with relatively simple instrumentation. Nitric oxide has been so analyzed from reaction with ozone (266—268), and ozone can be detected by the emission at 585 nm from reaction with ethylene. 

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

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