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  Electrochemical sensorsUSPTO Application #: 20080035481Title: Electrochemical sensors Abstract: wherein the area of the working electrode is from 500 μm2 to 0.1 m2. The uses of these electrodes and sensors are also described. An electrode for use in a electrochemical sensor comprises carbon modified with a chemically sensitive redox-active compound, excluding an electrode based on carbon having derivatised thereon two redox-active species wherein at least one of said species is selected from anthraquinone, phenanthrenequinone and N,N′-diphenyl-p-phenylenediamine (DPPD). The invention further provides a pH sensor comprising: a working electrode comprising carbon modified with a chemically sensitive redox active material; and a counter electrode, wherein the ratio of the surface area of the working electrode to the surface area of the counter electrode is from 1:10 to 10:1. Also provided is a pH sensor comprising: a working electrode comprising carbon modified with a chemically sensitive redox active material, and a counter electrode, (end of abstract) Agent: Renner Kenner Greive Bobak Taylor & Weber - Akron, OH, US Inventors: Sean P. McCormack, Richard G. Compton, Gregory George Wildgoose, Nathan Scott Lawrence USPTO Applicaton #: 20080035481 - Class: 204433000 (USPTO) Related Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Analysis And Testing, Measuring Carbon Or Ph The Patent Description & Claims data below is from USPTO Patent Application 20080035481. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The invention relates to electrochemical sensors for use in various environments, including non-downhole environments. For example, the sensors may be used for the determination of pH of substances in "dirty" environments, such as effluent and other waste streams the invention also relates to various materials, which may be used, for instance, in electrodes forming part of electrochemical sensors. BACKGROUND OF THE INVENTION [0002] U.S. Pat. No. 5,223,117 relates to self-assembly microelectrodes used in electrochemical sensors. The microelectrodes (which are the working electrode in the sensors) are modified with monolayer coverages of reference and indicator molecules, with both chemically sensitive redox materials and chemically insensitive redox materials being present on the same electrode. It is necessary for the microelectrodes to be significantly smaller than the counterelectrodes, for example the counter electrode area must be at least 10.sup.2 to 10.sup.3 times the working electrode area. An advantage of such a small working electrode with an internal reference is that the sensor is minimally invasive, and can therefore be used in biomedical sensing. [0003] UK Patent Application No. 2 391 314 describes electrochemical sensors for measuring the amount of hydrogen sulphide or thiols in a fluid. The sensor comprises a precursor and reaction solution which, together with the hydrogen sulphide or thiols, create a redox reaction. The current produced by this redox reaction is dependent upon the concentration of hydrogen sulphide or thiols. The sensors described in this document are for use in downhole applications, i.e. to extend down boreholes during a drilling operation. Given the size restrictions on apparatus which must extend into a borehole, the sensors must be relatively small. [0004] Carbon-based electrode materials have been in use for many decades. The main forms of carbon in common use are glassy carbon, carbon fibres, carbon black, graphite, carbon paste and carbon epoxy electrode. Carbon is an attractive electrode material as it is relatively chemically inert yet it has a high surface activity and a wide operational potential window (ca. -1.0 V to +1.0 V vs. the saturated calomel electrode in aqueous solution). [0005] However, there remains a need for more robust, reagentless sensors that can provide accurate results in hostile environments or "dirty" media such as effluents or sewage. Furthermore, there is a requirement for sensors to be used under various conditions, such as at temperatures above room temperature. There is renewed interest in developing sensors capable of measuring pH accurately at elevated temperatures. The present invention aims to address these issues. SUMMARY OF THE INVENTION [0006] According to the present invention, there is provided an electrode for use in a electrochemical sensor, said electrode comprising carbon modified with a chemically sensitive redox active compound which is not anthraquinone, phenanthrenequinone or N,N'-diphenyl-p-phenylenediamine (DPPD). [0007] The present invention also provides a pH sensor comprising: [0008] a working electrode comprising a chemically sensitive redox material; and [0009] a counter electrode, wherein the ratio of the surface area of the working electrode to the surface area of the counter electrode is from 1:10 to 10:1. [0010] The invention further provides a pH sensor comprising: [0011] a working electrode comprising a chemically sensitive redox material, and [0012] a counter electrode, wherein the area of the working electrode is from 500 .mu.m.sup.2 to 0.1 m.sup.2. [0013] These pH sensors have an advantage over those in the prior art in that they are less likely to be fouled or clogged by dirt in the fluid being measured, and accordingly they have a longer lifetime before they need to be replaced. [0014] The electrodes of the present invention may be used in an electrochemical sensor, and in particular in a pH sensor. The electrodes of the invention and the pH sensors of the invention are preferably suitable for use in a non-downhole environment. [0015] The invention also provides a method for preparing an electrode for use in an electrochemical sensor, said method comprising modifying carbon with a chemically sensitive redox active material with the proviso that the chemically sensitive redox active material is not anthraquinone, phenanthrenequinone or N,N.quadrature.-diphenyl-p-phenylenediamine (DPPD). [0016] Finally, the invention further provides a method for preparing an electrode in situ comprising applying carbon modified with a chemically sensitive redox active material to the surface of a substrate, wherein the chemically sensitive redox active material undergoes an irreversible chemical reaction when subjected to cyclic voltammetry. BRIEF DESCRIPTION OF THE FIGURES [0017] FIG. 1 is the voltammetric response of 6-nitro chrysene carbon immobilised on bppg after the development of the reversible system at pH 1.0 (0.1 M HCl+0.1 M KCl) varying the scan rate (25, 50, 100, 200, 300, 400, 500, 750, 1000 mV s.sup.-1) and the corresponding plot of oxidative peak potential vs. scan rate (insert). [0018] FIG. 2 shows the cyclic voltammograms of PAQ at each pH studied (pH 1, pH 4.6, pH 6.8, pH 9.2 and pH 12). Step potential 2 mV, scan rate 100 mV s.sup.-1. [0019] FIG. 3 is the base-line corrected oxidative and reductive square wave voltammograms of DPA at each pH studied (pH 1, pH 4.6, pH 6.8, pH 9.2 and pH 12). B) A corresponding plot of oxidative peak potential vs. pH. [0020] FIG. 4 shows cyclic voltammograms of diphenylamine derivatised carbon in pH 6.8 buffer showing the first, second and tenth scans. [0021] FIG. 5 shows cyclic voltammograms of thionin derivatised carbon particles immobilised on a bppg electrode in pH 12.0 (0.1 M NaOH+0.1 M KCl) buffer showing the first and fourth scans. [0022] FIG. 6 shows cyclic voltammograms of 6-nitrochrysene derivatised carbon powder immobilised on a bppg electrode in pH 9.2 buffer (0.05M sodium tetraborate+0.1 M KCl) showing the first and tenth scans. Inset: 10 CV scans 9-nitroanthracene derivatised carbon powder immobilised on a bppg electrode over the reversible systems (see text) at pH 6.8. [0023] FIG. 7 shows cyclic voltammograms of FBK derivatised carbon powder immobilised on a bppg electrode in pH 4.6 buffer (0.1 M acetic acid+0.1 M sodium acetate+0.1 M KCl) showing the first and second scans. [0024] FIG. 8 cyclic voltammograms of FBK derivatised carbon powder immobilised on a bppg electrode in pH 4.6 buffer (0.1 M acetic acid+0.1 M sodium acetate+0.1 M KCl) where the potential is cycled around system (II) only (see text) showing the first and tenth scans. Inset: CV scans of the same system with varying scan rate (25, 50, 75, 100, 200, 300, 400, 500, 600, 700, 800 and 900 mV s.sup.-1) Continue reading... Full patent description for Electrochemical sensors Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electrochemical sensors 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. 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