Luminescence Chemiluminescence

The third type of luminescence, chemiluminescence, is based on the emission of radiation by an excited species formed during a chemical reaction. In sonic instances. the excited species is the product ol a reaction belw-een the analyte and a suitable reagent (usually a strong oxidant such as ozone or hydrogen peroxide). The result is an emission spectrum characteristic of the oxidation product of the analyte or the reagent rather than the analyte itself. In other instances, the analyte is not directly involved in the chemiluminescence reaction. Instead, the analyte inhibits or has a cuialyiic effect on a chemiluminescence reaction. 

Chemiluminescent Immunoassay. Chemiluminescence is the emission of visible light resulting from a chemical reaction. The majority of such reactions are oxidations, using oxygen or peroxides, and among the first chemicals studied for chemiluminescence were luminol (5-amino-2,3-dihydro-l,4-phthalazinedione [521-31-3]) and its derivatives (see Luminescent materials, chemiluminescence). Luminol or isoluminol can be directly linked to antibodies and used in a system with peroxidase to detect specific antigens. One of the first appHcations of this approach was for the detection of biotin (31). 

Chemical off—on switching of the chemiluminescence of a 1,2-dioxetane (9-benzyhdene-10-methylacridan-l,2-dioxetane [66762-83-2] (9)) was first described in 1980 (33). No chemiluminescence was observed when excess acetic acid was added to (9) but chemiluminescence was recovered when triethylamine was added. The off—on switching was attributed to reversible protonation of the nitrogen lone pair and modulation of chemically induced electron-exchange luminescence (CIEEL). Base-induced decomposition of a 1,2-dioxetane of 2-phen5l-3-(4 -hydroxyphenyl)-l,4-dioxetane (10) by deprotonation of the phenoHc hydroxy group has also been described (34). 

Subsequent studies (63,64) suggested that the nature of the chemical activation process was a one-electron oxidation of the fluorescer by (27) followed by decomposition of the dioxetanedione radical anion to a carbon dioxide radical anion. Back electron transfer to the radical cation of the fluorescer produced the excited state which emitted the luminescence characteristic of the fluorescent state of the emitter. The chemical activation mechanism was patterned after the CIEEL mechanism proposed for dioxetanones and dioxetanes discussed earher (65). Additional support for the CIEEL mechanism, was furnished by demonstration (66) that a linear correlation existed between the singlet excitation energy of the fluorescer and the chemiluminescence intensity which had been shown earher with dimethyl dioxetanone (67). 

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

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. 

Chemiluminescent analyzers are based on the light (chemiluminescence) emitted in the gas-phase reaction of ozone with ethylene, which is measured with a photomultipHer tube. The resulting current is proportional to the ozone concentration (see Luminescent materials, chemiluminescence). 

Chemiluminescent labels, in which the luminescence is generated by a chemical oxidation step, and bioluminescent labels, where the energy for light emission is produced by an enzyme-substrate reaction, are additional labeling types (39,42). Luminol [521 -31 -3] CgHyN202, and acridine [260-94-6] C H N, derivatives are often used as chemiluminescent labels. 

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. 

In this work the development of mathematical model is done assuming simplifications of physico-chemical model of peroxide oxidation of the model system with the chemiluminesce intensity as the analytical signal. The mathematical model allows to describe basic stages of chemiluminescence process in vitro, namely spontaneous luminescence, slow and fast flashes due to initiating by chemical substances e.g. Fe +ions, chemiluminescent reaction at different stages of chain reactions evolution. 

OXIDATIVE LUMINESCENCE OF UV ABSORBING CHEMICALS. APPLICATION TO THEIR DETERMINATION IN SUNSCREEN PRODUCTS BY REVERSED PHASE LIQUID CHROMATOGRAPHY WITH CHEMILUMINESCENCE... 

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