Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For nitrogen or nitrogen containing compound
Patent
1994-11-23
1997-02-25
Tung, T.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For nitrogen or nitrogen containing compound
204412, 204418, 2057805, G01N 27333
Patent
active
056056176
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electronically conductive polymer film doped by mixed heteropolyanions having a catalytic activity, more particularly for the reduction of nitrite ions to ammonium ions.
More specifically, it relates to the use of electrodes modified by such films for the amperometric detection of nitrite ions and nitrogen monoxide.
Under atmospheric conditions nitrogen monoxide or nitric oxide (of chemical formula NO) is a colourless gas. It differs from nitrous oxide or laughing gas (of chemical formula N.sub.2 O), which is used as an anasthetic, and from nitrogen dioxide NO.sub.2, a reddish gas formed by nitrogen monoxide in the presence of oxygen. The toxicity of nitrogen monoxide results from its free radical structure, one of its unpaired electrons reacting easily. It has been known for some time that bacteria contain nitrogen monoxide, but it was never imagined that said compound exerted essential functions in mammals.
However, roughly 7 years ago studies in various fields of biology converged to reveal the biological importance of nitrogen monoxide. Nowadays the latter appears as an essential biological carrier enabling the white corpuscles to destroy tumour cells and bacteria and enabling neurotransmitters to dilate blood vessels.
In addition, nitrogen monoxide is an interneuronal carrier in the brain and in other regions of the body. It could belong to a new family of neurotransmitters differing very significantly from all known neurotransmitters. The explanation of its action procedure, its distrbution in the organism and its interactions with other biomolecules is opening new windows in connection with the operation of the memory and with respect to the treatment of neurodegenerative diseases (S. Snyder and D. Bredt, Pour la Science, no.177, 1992, p.70). The detection of this molecule named "molecule of the year 1992" by the journal Science, vol.258, p.1862 consequently has a considerable interest.
Nitrite ions occur in our natural environment and are widely involved in the preservation of foods. It is also of interest to have methods for detecting these ions, which are not only sensitive and precise, but also simple and fast, because the reaction of nitrites with most aliphatic and aromatic amines leads to the formation of N-nitrosamines, whereof a large number are recognized as having a significant cancerigenic power.
The known processes for the detection of nitrite ions present in a solution call on spectrophotometric, fluorometric or chromatographic methods, as described by Nakamura et al in Analytical Letters, 16 (A11), 1983, pp.811-819; by Ohta et al in Anal. Chem., 1986, 58, pp.3122-3135; and by Verma in Anal. Letters 25 (11), 1992, pp.2083-2093.
Electrochemical detection processes of nitrite ions by polarography based on the reaction of NO.sub.2.sup.- with sulphanilic or orthanilic acid, or on the reduction of NO.sub.2.sup.- to NO and then its reaction with diphenylamine are also known and are described by Sulaiman in Anal. Chem., 1984, 56, pp.2405-2407 and by Holak et al in Anal. Chem., 1992, 64, pp.1313-1315.
Processes are also known for the detection of nitrite ions which use selective electrodes based on cobalt porphyrin or vitamin B12, as described by Li et al in Anal. Chem., 1991, 63, pp.2168-2174 and by Daunert et al in Anal. Chem., 1989, 61, pp.499-503.
Among these processes, great interest is attached to chromatographic processes because they have a good sensitivity. However they are difficult to carry out and the costs involved are high.
Spectrophotometric processes are very sensitive and very selective, but require a strict control of the pH and temperature. Moreover, the results can be disturbed by the presence of certain ions such as heavy metal ions and Cu.sup.2+, Fe.sup.3+ and I.sup.-.
Electrochemical processes using selective electrodes suffer from the disadvantage of a long response time and also give rise to interference with certain ions. such as NO.sub.3.sup.- and thiocyanate ions.
Recently research has been carried out on other processes for the d
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Toth, et al., "Electrocatalytic Reduction of Nitrite and Nitric Oxide to Ammonia With Iron-Substituted Polyoxotungstates", vol. 111, pp. 2444-2451, Journal of the American Chemical Society, (1989) month unavailable, Washington, D.C.
Kwok-Keung shiu, et al., "Attempts to Immobilize Catalytically Active Heteropolytungstates On the Surfaces of Electrodes", vol. 309. No. 1 & 2, pp. 115-129, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, Jul. (1991), Lausanne.
Bidan Gerard
Fabre Bruno
Lapkowski Mieczyslaw
Commissariat a l''Energie Atomique
Tung T.
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