Chemiluminescence, peroxy radical measurement

Ketone oxidation chains terminate when two peroxy radicals react with each other. This is the main reaction of chain termination if the ketone contains no inhibitor and the oxygen pressure is sufficiently high for fast conversion of R- to R02-. The values of kt measured by the chemiluminescence technique [81] are shown in Table 10. 

Another relatively recent development in thermal technique for polymers is equipment for reliable measurement of chemiluminescence. The luminescence is thought to be from the drop of an excited carbonyl group back to the neutral state after excitation from the termination of two peroxy radicals. Its use is primarily in determination of oxidation stability of polymers to determine an oxidative induction time (OIT) (194,195). It has also been used to monitor oxidation of polymers subjected to stress (196) and simulated weathering (197). 

The chemiluminescent reaction was ascribed to free peroxy radicals formed in the lipids of cell membranes.It is likely, therefore, that this test simply measured the radical-trapping power of the drug, which is probably not its only mode of protection. 

This is important in food analysis and technology, as affecting also the stability of plastics under every-day conditions, i.e. in the presence of air and light. The chemiluminescence observed is extremely weak (yields of 10" einstein/mole" or less). Such light emission is very probably caused by peroxy radical recombinations (see p. 23). Measurements of the spectra of such ultraweak chemiluminescence have been achieved [53-55]. 

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