Typical Chemiluminescent Reactions

77 shows the reaction catalyzed by the enzyme luciferase that produces the characteristic light of fireflies, while Eq. 16.78, a chemical analogue, shows the exposure of the common substance luminol to oxygen under basic conditions. 

The third example, Eq. 16.79, is a simple prototype, the thermolysis of tetramethyldiox-etane to produce two equivalents of acetone with the emission of light. The high ef ficiency of this last reaction and the fact that it is induced simply by heating have made it a favorite of mechanistic investigations, as we will see below. 

---

Thus a typical chemiluminescent reaction of luminol can be represented by Fig. 

If the reactants in a type I chemiluminescence reaction are rapidly mixed they will result in an emission whose intensity Ia, can be measured as a function of time. A typical time intensity curve for a CL reaction is shown in Figure 2. 

Typically, intense chemiluminescence in the UV/Vis spectral region requires highly exothermic reactions such as atomic or radical recombinations (e.g., S + S + M - S2 + M) or reactions of reduced species such as hydrogen atoms, olefins, and certain sulfur and phosphorus compounds with strong oxidants such as ozone, fluorine, and chlorine dioxide. Here we review the chemistry and applications of some of the most intense chemiluminescent reactions having either demonstrated or anticipated analytical utility. 

While luminol and isoluminol require an oxidant plus a catalyst for initiation of the chemiluminescent reaction, esters derived from A -methyl acridinium carboxylic acid require only alkaline hydrogen peroxide (W4). Acridinium esters were first introduced by McCapra s group (M23, M25, S32), based on earlier work on the bioluminescence of the lucigenin/luciferase system (G18), and reviewed in McCapra and Beheshti (M21). From Fig. 19, one can see the structural similarity between lucigenin and a typical acridinium ester. 

Emission spectra induced by oxidative reaction of typical chemiluminescent compounds... 

Chemiluminescence reaction of a typical peroxyoxalate reagent (bis (2,4,6-trichlorophenyl) oxalate TCPO) with hydrogen peroxide to form reactive intermediates, (b) Energy transfer from the reactive intermediates to another molecule that emits light. The overall process is an example of an indirect chemiluminescence reaction... 

Figure 7 shows the channel design and typical electropherograms for a microchip device used to determine taurine and amino acids in individual fibrosarcoma cells from mice. The device enabled cell loading and lysis, electrophoretic separation, and detection based on the enhancing effect of these analytes on the chemiluminescent reaction of luminol with hydrogen peroxide and Cu ". The limits of detection ranged from 0.068 fmol (0.26 pM) for Glu to 0.16 fmol (0.61 pM) for Tau. 

A typical chemiluminescence detector consists of a series-coupled thermal decomposition and ozone reaction chambers. The selective detection of nitrosamines is based on their facile low-temperature (275-300°C) catalytic pyrolysis to release nitric oxide. Thermal decomposition in the presence of oxygen at about 1000°C affords a mechanism for conversion of nitrogen-containing compounds to nitric oxide (catalytic oxidation at lower temperatures is also possible). Decomposition in a hydrogen-diffusion flame or thermal oxidation in a ceramic furnace is used to produce sulfur monoxide from sulfur-containing compounds. 

Antioxidants shift the autoaccelerating increase of chemiluminescence intensity to higher time. This is due to reactions 12 and 13 of the Bolland-Gee mechanism (Section 1, Scheme 2) in which peroxyl radicals and hydroperoxides are scavenged until antioxidants InFl and D are consumed. A typical example of such a behavior occurs for samples of PP containing 0.1 %wt. of Irganox 1010 (a sterically hindered phenol) (Figure 18 and Table 4). The presence of antioxidants usually reduces the maximum chemiluminescence intensity [61,62]. This may be explained by the quenching effect of the antioxidant on excited carbonyls, but it may be also related to the mechanism of oxidation of stabilized PP. Stabilizers in... 

Figure 6 CL emission profile with the time (a) after mixing of reagents, initiation of reaction, entrance and exit from the flow cell (FC) of the chemiluminescent solution (b) and typical peaks recorded after successive injections of the same analyte into the manifold (c).

As shown schematically in Figure 1, a gas-phase chemiluminescence detector consists of a reaction chamber, inlets for the analyte and reagent gas streams, a vacuum pump to lower the pressure in the reaction chamber (typically to a few torr), and a transducer such as a photomultiplier tube (PMT) to monitor the light produced in the reaction. The reagent gas, usually present in large excess, reacts with a trace concentration of analyte to produce an excited product that subse-... 

---