Determination of Melamine in Dairy Products and Melamine Tableware by Inhibition Electrochemiluminescent Method
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Abstract An electrochemiluminescent (ECL) method has been developed for the determination of melamine based on the inhibition of luminol ECL. A significant luminol ECL can be found at 1.47 V in the phosphate buffer solution at high pHs and low potential scan rates, this ECL signal can be inhibited obviously by melamine. The decrease of ECL intensity was linearly proportional to the logarithm of melamine concentration in the range of 1–100 ng/mL ( R 2 =0.9911) and with the detection limit of 0.1 ng/mL. The method has been applied successfully to determine melamine in dairy products and melamine tableware, the recoveries were in the range of 98.5%–103.7% and 95.5%–106.0%, respectively. The mechanism of the inhibition effect was also proposed, the active oxygen (O 2 · − ) generated from the electrooxidation of OH − reacted with luminol anion (L · − ) to generate light emission, and the present of melamine can eliminate the active oxygen, which cause the decrease of the ECL intensity.Keywords:
Luminol
Electrochemiluminescence
Phosphate buffered saline
Melamine is able to significantly enhance the chemiluminescence reaction of luminal and K3Fe(CN)6 in alkaline medium.This makes it feasible to establish a new flow injection chemiluminescence method for determining melamine in milk powder.The optimal condition for the determination was examined,and as-established method was adopted to determine melamine in commercial milk powder.It was found that under the optimal experimental condition,melamine concentration in the range of 1.0×10-6-4.0×10-5 g · L-1 was linearly proportional to enhancing chemiluminescence signals.The detection limit for melamine was determined to be 2.6×10-7 g · L-1,and the relative standard deviation for 11 consecutive measurements of melamine with a concentration of 4.0×10-6 g · L-1 was 3.42%.In the meantime,as-established method was successfully applied to determine melamine in commercial milk powder.
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Chemiluminescence, a low-temperarure light emission due to a chemical reaction, is demonstrated on the reaction of luminol (5-amino-2,3-dihydrophthalazine-1,4-dione), hydrogen peroxide, potassium hexacyanoferrate(III) and alkaline hydroxide. The synthesis of luminol from common chemicals and its impressive chemiluminescence are described.
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Potassium hydroxide
Peroxide
Potassium periodate
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Development of novel high-sensitivity chemiluminescence assay for luminol using thiourea derivatives
We have screened about 100 thiourea derivatives in order to develop a sensitive chemiluminescence detection for luminol derivatives. Among these derivatives, we found a new compound, 2-(3-methylthioureido) thiazole, that could be used to measure luminol in the presence of hydrogen peroxide (H2O2). The detection limits of luminol and N-(4-aminobutyl)-N-ethylisoluminol (ABEI) were 10 fmol and 100 fmol, respectively. The mechanism of proposed chemiluminescence reaction was studied by electron spin resonance (ESR) with and without superoxide dismutase (SOD) and the addition of ethanol. The results showed that 2-(3-methylthioureido) thiazole has the ability to generate hydroxyl radical from H2O2, and produces intense chemiluminescence in the presence of luminol. The proposed novel chemiluminescence reaction for luminol and luminol derivatives was applied to a high performance liquid chromatography (HPLC) assay for amino compounds. Copyright © 1999 John Wiley & Sons, Ltd.
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Luminol
Hydroxyl radical
Peroxide
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Abstract— The chemiluminescence reaction of luminol has been investigated using conditions of methylene blue photosensitized oxidation. The quantum yields of chemiluminescence obtained were dependent upon temperature and the concentrations of luminol and base; and under the optimum conditions of high temperature and low luminol concentration, the value of the quantum yield approached that for the chemical reaction where the oxidant is hydrogen peroxide and catalyst. An analysis of the results suggests that it is not the primary species produced on photosensitization which is responsible for the chemiluminescent reaction, but a species produced by reaction of the primary species with base.
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Methylene blue
Quantum yield
Base (topology)
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We explored the behaviour of a series of phenolic acids used as enhancers or inhibitors of luminol chemiluminescence by three different methods to determine if behaviour was associated with phenolic acid structure and redox character. All the phenolic acids inhibited chemiluminescence when hexacyanoferrate (III) was reacted with the phenolic acids before adding luminol. The redox character of these compounds was clearly related to structure. When hexacyanoferrate(III)-luminol-O2 chemiluminescence was initiated by phenolic acid-luminol mixtures some phenolic acids behaved as enhancers of chemiluminescence, and others as inhibitors. We propose a mechanism to explain these findings. We found direct relationships between the redox character of the phenolic acids and the enhancement or inhibition of the chemiluminescence of the luminol-H2O2-peroxidase system and we propose mechanism to explain these phenomena.
Luminol
Phenolic acid
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Chloramine derivatives of amino acids induce chemiluminescence of a luminol solution. The chemiluminescence is more prolonged than the emission of luminol produced by hypochlorite. Persistent chemiluminescence also appears under the action of hypochlorite on a mixture of luminol and amino acids. It is assumed that the chemiluminescence of luminol in suspensions of stimulated phagocytes may be associated with its oxidation by chloramines.
Luminol
Hypochlorite
Chloramine-T
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Luminol
Zymosan
Phagocyte
Antibody opsonization
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Luminol
Linear range
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