Chemiluminescence analysis method

Chemiluminescence refers to the phenomenon of light radiation produced when molecules that have absorbed chemical reaction energy return from excited state to ground state. Chemiluminescence in a broad sense also includes electrochemiluminescence. A chemical reaction must meet the following conditions in order to produce chemiluminescence: first, the reaction must provide enough excitation energy and be provided by a certain step alone, because the energy released by the previous step will disappear due to vibration relaxation and cannot emit light in solution; The second is to have a favorable reaction process, so that the energy of chemical reaction can be accepted by at least one substance and generate excited state; the third is that the excited state molecule must have a certain chemiluminescence quantum yield to release photons, or it can transfer its energy to another molecule to make it enter the excited state and release photons. Chemiluminescence analysis is a highly sensitive micro and trace analysis method developed in recent 30 years, which has obvious advantages such as simple equipment, convenient operation, high sensitivity, wide linear response range and easy automation. Chemiluminescence reaction can be used for analysis and determination because the intensity of chemiluminescence is related to the reaction rate, so all factors affecting the reaction rate can be used as the basis for establishing the determination method.

Therefore, the concentration of a substance in the reaction system can be determined by measuring the chemiluminescence intensity. In principle, any chemiluminescence reaction can be quantitatively analyzed by Formula (7-9) as long as the reaction is first-order or pseudo-first-order. For example, in the above chemiluminescence reaction, if substance B remains constant, and the concentration change of substance A can be regarded as a first-order or pseudo-first-order reaction.
The substances determined by chemiluminescence analysis can be divided into three categories: the first category is the reactant in chemiluminescence reaction; the second category is the catalyst, sensitizer or inhibitor in chemiluminescence reaction; and the third category is the reactant, catalyst and sensitizer in coupling reaction. These three kinds of substances can also be used to determine other substances that people are interested in by labeling, which further expands the application scope of chemiluminescence analysis.
Luminol luminescence was discovered as early as 1928, and the quantum yield was between 0.01 and 0.05. Because of its good water solubility and high sensitivity, it is still the most studied and widely used chemiluminescence reagent. At present, the chemiluminescence system used in the analysis of environmental protection pigments mainly includes luminol-
H2O2 system. Luminol is oxidized to produce chemiluminescence in alkaline solution, and the content of components is determined according to the intensity of luminescence signal. Based on the enhancement or inhibition of compounds on the chemiluminescence reaction of luminol -HzOz system, the compounds with enhancement or quenching effects on chemiluminescence were determined. If catechin is used to strongly inhibit the chemiluminescence of luminol-hydrogen peroxide-copper (Ⅱ) system, the detection limit can reach 50×10-7 mol/L[5]. Shang Fanghong et al. [6] used genistein to enhance the sensitivity of potassium permanganate-luminol luminescence system, and the chemiluminescence intensity was directly proportional to its concentration in a certain concentration range. Combined with flow injection technology, a simple and rapid chemiluminescence analysis method for the determination of genistein could be established.

Chemiluminescence analysis can be used not only for the analysis and detection of environmental protection pigments, but also for the study of antioxidant activity of natural plant pigments, that is, anti-free radicals. Cu2X is reduced by ascorbic acid.
The reagent can react with HzO to generate OH, and hydroxyl radicals attack luminol to make it oxidize and emit light. Beet red pigment can scavenge free radicals and cause luminol's luminescence to weaken, and the ability of beet red pigment to scavenge free radicals can be expressed according to the degree of decrease of luminous intensity [7]. Sun Xiaodong also used this method to compare the antioxidant effects of flaxseed pigment and polysaccharide, pointing out that flaxseed pigment and polysaccharide can capture free radicals and resist the oxidative damage of free radicals to life macromolecules. Pigment is much stronger than polysaccharide, and also has stronger antioxidant ability than vitamin C [8]. In addition, 1,10- o-phenanthroline -H2O:-FeC. The system can also be used to study the antioxidant activity of natural plant pigments. For example, the study of monascus pigment shows that red pigment has the strongest antioxidant activity, followed by yellow pigment, and orange pigment has the worst antioxidant activity. Further research shows that the red pigment with a relative molecular weight of 365 has the strongest oxidation resistance, followed by the red pigment with a relative molecular weight of 391, and the red pigments with relative molecular weights of 380 and 900 have the worst oxidation resistance [9].
In recent years, while improving and perfecting the original luminescent reagents and systems, the synthesis of new luminescent reagents, the development of new systems and the combination with other technologies, especially the combination of flow injection technology, sensor technology, HPLC technology and various immobilized reagent technologies, have shown the advantages of rapid, sensitive and simple chemiluminescence analysis, and further broadened the application scope of chemiluminescence. At present, the development of new luminescent reagents with simple, economical and high luminous rate is still the research direction. In addition, designing an analytical instrument with higher automation, portability and real-time field detection will show the advantages of this method.