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Electrochemical method and sensor for the detection of traces of explosivesRelated Patent Categories: Electrolysis: Processes, Compositions Used Therein, And Methods Of Preparing The Compositions, Electrolytic Analysis Or Testing (process And Electrolyte Composition), For Nitrogen Or Nitrogen Containing CompoundElectrochemical method and sensor for the detection of traces of explosives description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070163893, Electrochemical method and sensor for the detection of traces of explosives. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] The present application is a continuation of U.S. application Ser. No. 10/715,489 filed Nov. 19, 2003 by the present inventor. FIELD OF THE INVENTION [0002] The present invention relates to the detection of trace amounts of explosive materials such as nitro-aromatic compounds in air, using an electrochemical measurement technique, and specifically to improving the sensitivity of the measurement of trace explosive materials, and decreasing measurement time More specifically, the present invention relates to a method of explosives detection of low cost that is suitable for portable field-testing. BACKGROUND OF THE INVENTION [0003] As a consequence of recent efforts to thwart the recent upsurge in international terrorism, there is an increased interest in the detection of explosive materials. These materials include nitro-aromatic compounds including 2,4,6-trinitrotoluene (TNT), dinitrotoluene (DNT) and similar derivatives. [0004] Many detection methods have been used to detect explosive materials. These methods include gas and HPLC chromatography, x-ray scattering, neutron analysis, nuclear quadrupole resonance, and mass spectrometry (U.S. Pat. No. 6,571,649). These methods generally require expensive and sophisticated equipment, (e g. high vacuum), equipment that is not portable (e.g. cylinders of compressed gases), and/or have a complicated sample preparation These techniques, are therefore, not appropriate for low cost portable field-testing for trace explosive materials. A recent review of some of these methods for explosives detection is "Explosives detection systems (EDS) for aviation security" (Singh, S., Signal Processing vol. 83, 2003, p. 31-55). [0005] Another known method for the detection of trace amounts of explosive materials utilizes immunochemical sensors. For example, U.S. Pat. No. 6,573,107 is directed towards the immunochemical detection of explosive substances in the gas phase using surface plasmon resonance spectroscopy. Immunochemical detection methods potentially offer high selectivity and high sensitivity. [0006] Electrochemical detection refers to the use of electrodes, immersed in an electrolyte, and connected to an instrument that varies the voltage applied to the electrodes. The instrument measures the current flow between the electrodes Typically, the electrode potential is varied; and an electric current flows between the electrodes that is characteristic of the presence of electrochemical active substances in the electrolyte. The magnitude of the current is proportional to the concentration of the electrochemical active substances. It is well known that TNT and other nitro-aromatic compounds are reduced electrochemically at the cathode and may be detected by electrochemical detection. Wang et al. (Analytica Chimica Acta, vol. 485 (2003) p. 139-144) reported the monitoring of TNT in natural waters using an electrochemical technique. They reported a measurement sensitivity of 0.003 .mu.A/ppb of TNT in natural seawater. This sensitivity level was achieved by Wang et al. by subtracting the background signal, in natural seawater not contaminated by TNT, caused by the reduction of dissolved oxygen. The applicant reported (Reviews Analytical Chemistry vol. 18 no. 5, 1999, p. 293) the use of carbon/Hg film electrode materials in an aqueous solvent. This electrode material was successful to minimize the background by separating the atmospheric O.sub.2 background current from the TNT current, however the sensitivity reported was only .about.0.7 .mu.A/.mu.M (.about.0.003 .mu.A/ppb) and was comparable to the sensitivity reported by Wang. Despite these positive developments in the prior art, the sensitivity is still insufficient, and the kinetics of the TNT reduction reaction are too slow to achieve a practical portable field test for trace explosive materials. A practical electrochemical sensor for trace explosive materials should have high sensitivity, a short measurement time and in addition a way of cleaning the electrodes rapidly to perform further testing, [0007] There is thus a widely recognized need for an electrochemical method and sensor for the detection of traces of explosives, and it would be highly advantageous to have an electrochemical method and sensor for the detection of traces of explosives, with high sensitivity, and fast reaction kinetics. SUMMARY OF THE INVENTION [0008] According to the present invention, there is provided a system for electrochemical assay of nitro-aromatic compounds, including: (a) a working electrode having a surface modified with a chemical that increases electron transfer kinetics of the nitro-aromatic compounds. [0009] Preferably, the chemical that increases the electron transfer kinetics is an aromatic compound, for example al amino-aromatic compound, an alkyl-aniline compound, a halide derivative of an alkyl aniline compound and/or an hydroxyl-aniline compound. Most preferably, the chemical modifier is phenylene-diamine, diphenylene-diamine, diphenylene-triamine, or aniline. [0010] Preferably, the working electrode contains elemental carbon or gold; the working electrode includes submicron particles and the elemental gold is a coating on the electrode surface. Preferably, the working electrode includes carbon paper. [0011] Preferably, the system includes in addition, (b) an electrolyte for dissolving the nitro-aromatic compounds, and the electrolyte is chosen to minimize background current resulting from oxygen reduction. [0012] Preferably, the electrolyte includes an aprotonic solvents, and/or dipolar solvents; such as dimethylformamide, acetonitrile, propylene carbonate and optionally also a solvent such as ethanol, propanol, ethylene-glycol, and/or propylene-glycol. [0013] Preferably, the system further includes (c) a mechanism for inputting air suspected to include the nitro-aromatic compounds, into the electrolyte in order to dissolve the nitro-aromatic compounds in the electrolyte. [0014] According to the present invention, there is provided an electrochemical method of assaying trace compounds in air, including the steps of (a) dissolving the trace compounds in an electrolyte that includes aprotonic solvents, and/or dipolar solvents; (b) immersing a working electrode in the electrolyte; (c) applying a varying potential to the working electrode; and (d) measuring an electrical current consequent to the varying potential, thereby providing measurement results indicative of a concentration of the trace compounds. [0015] Preferably, after measurement, the electrochemical method includes (e) regenerating the working electrode by applying a negative potential to the working electrode. [0016] Preferably, the dissolving of trace compounds is performed by bubbling air containing the trace compounds through the electrolyte. [0017] Preferably, the electrochemical method includes, prior to dissolving the trace compounds in the electrolyte, the steps of: (f) measuring a background electrical current, while applying a varying potential, thereby obtaining background current results; and (g) subtracting the background current results from the measurement results, thereby obtaining calibrated measurement results. [0018] Preferably, the electrolyte used in the electrochemical method includes dimethylformamide, acetonitrile, and/or propylene carbonate; optionally also ethanol, propanol, ethylene-glycol, and/or propylene-glycol and preferably the electrolyte has pH greater than 7. Preferably, the electrochemical method includes preconditioning the working electrode thereby increasing electron transfer kinetics of the trace compounds. The preconditioning modifies the working electrode with a chemical such as amino-aromatic compounds, alkyl-aniline compounds, halide derivatives of alkyl aniline compounds and/or hydroxyl-aniline compounds. According to the present invention, there is provided an electrochemical method of assaying nitro-aromatic compounds in air, including the steps of: (a) dissolving the nitro-aromatic compounds in an electrolyte that includes an aprotonic solvent, and/or a dipolar solvent; (b) immersing a working electrode in the electrolyte; (c) applying a varying potential to the working electrode; (d) measuring an electrical current consequent to the varying potential, thereby providing measurement results, indicative of a concentration of the nitro-aromatic compounds. BRIEF DESCRIPTION OF THE DRAWINGS [0019] The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein; Continue reading about Electrochemical method and sensor for the detection of traces of explosives... Full patent description for Electrochemical method and sensor for the detection of traces of explosives Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electrochemical method and sensor for the detection of traces of explosives patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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