MXPA97005676A - Metal electrochemical electrode / oxide from me - Google Patents

Abstract

An improved active electrode for use in flat sensors has been discovered, the electrode prepared by a process comprising combining a base component with a metal paste and heating the paste in the presence of air for a sufficient time to oxidize a portion of the electrode to produce the metal / metal oxide electrode. The electrodes can be incorporated in several flat sensor formats, particularly pH and C sensors

Description

METAL ELECTROCHEMICAL ELECTRODE / METAL OXIDE This invention relates to a flat metal / metal oxide active electrode that can be used in sensors that measure pH and / or C02. BACKGROUND Electrochemical means for measuring pH and C02 levels of liquid systems are well known. Glass sensors that have an electrode membrane type are commonly used as normal for pH and C02 measurements since the glass sensors are predictable and provide good measuring capability. Glass sensors are manufactured as three-dimensional items with many serviceable parts. Therefore, while demonstrating good measurement capability, these three-dimensional items are more expensive and complex to manufacture as they operate compared to flat-format sensors. Flat-format sensors have been described in the literature (such as those taught by Foos et al., EP-A0625704, incorporated herein by reference) and provide alternative means for measuring pH and C02 levels. Flat sensors are usually smaller than glass sensors and much cheaper to manufacture as well as operate. The flat format of the sensors typically comprises relatively thin layers of materials that are applied to substrates bases using thick film or thin film techniques, including, for example, silk screen printing. Flat sensors for pH and C02 measurement are more economically convenient than glass sensors, but flat sensors have been associated with performance problems. The limitations of flat pH sensors include, for example, input potential that requires frequent recalibrations; oxygen interference (02) (which may give incorrect answers due to the variation levels of 02); agents of sensitivity to reduction or oxidation (redox); and short sensor lifetime, particularly due to contamination by sample components or impurities present in other sensor components. The improvement in the performance of flat sensors is necessary in order to make the sensors more commercially convenient and well accepted as an alternative means to measure pH and C02. SUMMARY OF THE INVENTION The problem noted above has been solved with the discovery of an improved metal / metal oxide active electrode, the metal / metal oxide active electrode prepared by a process comprising combining a base component with a mixture of metal paste in the presence of air for a sufficient time to oxidize a portion of the mixture to form said metal / metal oxide electrode.

Also provided is a flat sensor for pH measurement, the sensor comprising an electrically non-conductive substrate applied thereto in a flat format; an electrically conductive material in at least one region adjacent to said substrate; a dielectric coating covering, at least a forward portion of said region of such electrically conductive material but leaving exposed, at least, an electrode area and a contact area on said region of said electrically conductive material; and a metal / metal oxide electrode in said exposed area of the electrode, wherein said metal / metal oxide electrode is prepared by a process comprising combining an ase component with a metal paste to form a metal paste mixture. , heating the metal paste mixture in the presence of air for a sufficient time to oxidize a portion of the mixture to form said metal / metal oxide electrode. A method for preparing a pH sensor is also provided, the method comprising: (1) selecting an electrically non-conductive substrate; (2) adhering to it in a flat format: an electrically conductive material in at least one region adjacent to said substrate; a dielectric coating covering at least one advancing portion of said electrically conductive region but leaving exposed at least one electrode area and a contact area of said electrically conductive region; and a metal / metal oxide electrode present in said exposed electrode area, wherein said metal / metal oxide electrode is prepared by a process comprising combining a base component with a metal paste in order to form a mixture of metal paste, heating the metal paste mixture in the presence of air for a sufficient time to oxidize a portion of the mixture in order to form said metal / metal oxide electrode. A method for measuring pH in a sample has also been discovered, the method comprising contacting a liquid sample with the flat pH sensor described above and a reference, connecting said exposed contact area of said sensor with a pH sensing instrument; connecting said reference with said pH sensor instrument; providing an electric current from said pH sensor instrument through said reference and right. contact area of such sensor and measuring a resulting electrical signal provided by said instrument pH sensors. A C02 flat sensor has also been discovered for the measurement of C02, the sensor comprising a non-electrically non-conductive substrate having adherently applied to it in a planar format: (a) an electrically conductive material in at least one first and second region adjacent said substrate; (b) a dielectric coating that covers at least one advancing portion of said first and second regions of such electrically conductive material but leaving exposed at least one area of electrodes and a contact area of said first and second electrodes. regions; (c) a silver / silver halide electrode in said exposed electrode area of said first electrically conductive region; (d) a metal / metal oxide electrode in said exposed electrode area of said second electrically conductive region, said metal / metal oxide electrode prepared by a process comprising combining a base component with a metal paste to form a metal paste mixture, heating the metal paste mixture in the presence of air for a sufficient time to oxidize a portion of the mixture to form said metal / metal oxide electrode; (e) an inner electrolyte layer applied adjacent to and superimposed on at least said metal / metal electrode and said silver / tin halide electrode; and (f) a membrane permeable to the adjacent gas and superposed on said internal electrolyte in, at least, the portion of said electrolyte layer covering said metal / metal oxide electrode and said silver / silver halide electrode. A method for preparing a C02 flat sensor is also provided, the method comprising: (1) selecting an electrically non-conductive substrate; (2) adhere to it in a flat format; (a) an electrically conductive contact material in at least first and second spaced regions; (b) a dielectric coating separating said first and second regions from said electrically conductive contact material, said dielectric coating covering at least one advancing portion of said first and second regions of said electrically conductive material but leaving exposed, so less, an electrode area and a contact area on said first and second regions; (c) a silver / silver halide electrode in said exposed electrode area of said first electrically conductive region; (d) a metal / metal oxide electrode in said exposed electrode area of said second electrically conductive region, said metal / metal oxide electrode prepared by a process comprising combining a base component with a metal paste to form a mixture of metal paste, heating the metal paste mixture in the presence of air for a sufficient time to oxidize a portion of the mixture to form said metal / metal oxide electrode; (e) an inner electrolyte layer applied adjacent to and superposed on at least said metal / metal formed electrode and said silver / silver halide electrode; and (f) a gas permeable membrane adjacent to and superimposed on said internal electrolyte in at least the portion of said electrolyte layer covering said metal / metal oxide electrode and said silver / silver halide material. A method for measuring C02 in a sample has also been discovered, the method comprising: contacting a liquid sample with the C02 sensor described above, connecting said exposed contact area of said first and second electrically conductive regions of said sensor with a C02 sensor instrument, providing an electrical current of said C02 sensor instrument through said contact areas, measuring an electrical signal provided by said C02 sensor instrument. The invention provides an economical method for manufacturing flat pH and C02 sensors capable of accurately measuring pH and C02 in sample fluids. The sensors that have been prepared using this electrode show a good response at pH or C02 while demonstrating minimum displacement and interference from 02. Description of the Drawings Figure 1 shows a flat metal / metal oxide sensor prepared according to the invention. Figure 2 shows a top view (2a) and a side view (2b) of a sample chamber. Figure 3 shows a sensor type C02 Sereringhaus. Figure 4 shows a flat sensor having a metal / metal oxide electrode and a reference electrode. Figure 5 shows a flat sensor having a metal / metal oxide electrode with a cover membrane and a reference electrode. Figure 6 shows a flat sensor with a metal / metal oxide electrode covered by an inner electrolyte layer and a neutral vehicle cover membrane placed on top of the electrolyte and a reference electrode. Figure 7 shows a Severinghaus type C02 sensor.

Figure 8 shows the electrical circuitry used in the Examples section. Figure 9 is a pH response curve, as described in Example 2, where line a is from a glass sensor (Type "A", NORMAL), lines b-3 are from flat sensors (Type "B", INVENTION) and the C-2 lines are from flat sensors (Type "C", COMPARATIVE). Figure 10 is a pH response curve, as described in Example 3, where line a is from a glass sensor (Type "A", NORMAL), the lines > í-3 are from flat sensors (Type "B", INVENTION) and lines Ci and C2 are from flat sensors (Type "C", COMPARATIVE). Figure 11 is a pH response curve, as described in Example 4, where line a is from a sensor (Type "A", NORMAL) and lines d1-4 are from a flat sensor ( Type "D", INVENTION). Detailed Description The invention is suitable for use in order to determine the pH and / or C02 of liquid samples. The invention is particularly useful for measuring the pH and / or C02 of biological fluids. The non-liquid samples can be prepared as liquid samples and therefore were tested as known to those skilled in the art. The pH scale that can be measured by the invention can vary greatly, with the particular sensitivity realized for a pH measurement from a pH of 3 to a pH of 11. According to the invention, to prepare the metal / oxide electrode of metal, metal paste can be purchased or prepared by known techniques. Preferably the paste is of a toxitropic consistency (so that the paste will flow) but does not have a thin, shifting consistency. The proper consistency of the paste will be readily determined by those skilled in the art to prepare flat formatted sensors. The metals that can be used in the preparation of the active electrode are noble metals as described, for example, in "Metal-Metal Oxide and Metal Oxide Electrodes at pH Sensor" by S. Glab, et al., Crit. Rev. Anal. Chem. 1_, 29-47, 1989. Suitable metals include, but are not limited to, palladium, rhodium, ruthenium, osmium, iridium, platinum, tin, antimony, bismuth, alloys thereof, and mixtures thereof. Most preferably the metal is palladium or rhodium, more preferably, palladium. A base component was combined with the metal paste to form the metal paste mixture to form the metal / metal oxide electrode. The selected base must be capable of generating a metal / metal oxide when the paste and base combination is heated. Preferably, the base is a salt, such as, for example, salts of an alkali metal (lithium, sodium, rubidium potassium and so on) and salts of an alkaline earth metal (beryllium, magnesium, calcium, and so on). More preferably, the salt is non-hydroscopic, that is, a salt that remains in a particulate form at ambient conditions. Preferred non-hydroscopic salts are represented by "MHB" and "MB", wherein M is defined as an alkaline earth metal or alkali metal, H is hydrogen and B is an anion selected from the group consisting of -C03, -OH, and -HC03 (including, for example, Na2C03, NaHCO3, K2C03, KHC03, MgC03 and mixtures thereof). The most preferred base component is NaHCO 3. The base component is more preferably a fine particulate material so that when sieving printing is the technique used to make the flat sensor, the particulate material does not exceed the mesh size of the screen (typically less than a size of about 400 meshes). The base should be used in an amount sufficient to provide an oxidation effect when the mixture of the metal paste is heated in the presence of air, but not in such an excessive amount that compromises the consistency of the paste for flat format. Generally, the base is used in an amount ranging from about 0.1% by weight to about 50% by weight, more preferably, in an amount ranging from 5% by weight to 25% by weight and even more preferably around 16% by weight, with said percentages by weight based on the total weight of the metal paste and base before removal. The metal paste and base can be combined before or during the flat format process. Additionally, the metal paste mixture can be heated in the presence of air to produce a metal / metal oxide electrode before placement on an electrically non-conductive substrate. For ease of manufacture, preferably the metal paste and base are combined, mixed and then applied to an electrically conductive contact material on the non-conductive substrate and then heated. The manner in which the metal paste mixture is applied to the electrically conductive contact material in the substrate, can be any suitable technique resulting in a flat format, including stenciling and known thin or thick film processes (such as is described in JL Pedigo, et al., Hybrid Circuit Technology, Feb. 1992, pp. 28-31, incorporated herein by reference). Particularly from an easy manufacturing point, silk screen printing is a preferred means for applying the metal paste mixture to the substrate. The thickness of the metal paste mixture can vary. The substrate materials that form the base support on which the sensors are made can be selected from any electrically non-conductive material. These materials are well known and include, for example, ceramic, glass, refractory and polymeric materials and combinations thereof and so on. Particularly small aluminum-based substrate fragments are preferred. Currently, most of the preferred substrates are from a combination of alumina and glass binder. Slots can be formed in the non-conductive substrate so that the layers can be applied specifically to the sections in the substrate.

The electrically conductive material used in the sensors is preferably a noble metal, with gold being preferred. The electrically conductive material can be applied to the substrate in various ways, although more preferably the material adheres to the substrate by heating normally, before applying the dielectric coating and metal paste mixture. Normally for pH sensors, at least one region of the electrically conductive material is applied to the substrate. For C02 sensors, at least two separate regions of the electrically conductive material are applied to the substrate. Preferably, a dielectric coating is present between the two regions in the C02 sensor thus isolating the conductive regions from one another. Normally the dielectric coating (widely available commercially) is also present in at least the advancing portions of the electrically conductive regions but is not present in an exposed electrode area and an exposed contact area in each region of the conductive material. The metal paste mixture is applied adjacent to the electrically conductive region in at least the exposed electrode area. The metal paste is heated at a temperature and for a period sufficient to oxidize a portion of the metal paste mixture thereby forming a metal / metal oxide electrode. Since oxygen may normally be present in the base component oxygen does not have to be present during heating. In addition, heating is preferably presented in the presence of oxygen (more conveniently air). The heating time and temperature can be adjusted according to the type of heating source used, the temperature used and the exposure time. Preferably, the metal paste mixture is heated for a period sufficient to provide an active electrode having a balance of metal to metal oxide content, such as that described, e? S. Glab, and others (referred to previously in this). More preferably, to transform the metal oxide paste to a metal / metal oxide electrode (preferably present in the substrate), the paste is heated for a period of about 1 minute to 30 minutes (more preferably 5 minutes to 15 minutes). minutes) at a temperature of about 450 ° C to about 600 ° C (more preferably 525 ° C to 575 ° C) to oxidize a portion (but not all) of the electrode. Additionally, the electrode may overheat during the manufacture of the entire sensor if desired. The metal / active metal oxide electrode can be used in different types of sensors, even more preferably flat pH and C02 sensors. The components described herein, as well as additional aspects, may be arranged in the flat format or in substrates on conductors in various configurations. As shown in Figure 1, a pH sensor 5 is present in an electrically non-conductive substrate 10 having therein present an electrically conductive material in a region 15, 20, 25 applied adherently adjacent the substrate 10. The dielectric coating 26 insulator, electrically conductive advancing portion 20 is applied on the substrate but not on an exposed electrode area 15 and an exposed contact area 25. In the exposed electrode area 15, the metal paste mixture is applied and becomes the active electrode made of metal / metal oxide 30 when heated in the presence of air. The exposed contact area 25 is where the electrical contact can be made between the sensor 5 and the pH sensor instrument. As shown in Figure 2a (top view) and 2b (side view), it can be superimposed on the exposed electrode area 15, 30 of the sensor 5 so that the fluid sample enters and exits through the sample tube 33 and is confined to a sample chamber contact region 32 so that contact is made between the sample and the active electrode 30 (and the reference electrode when present in the integrated circuit). Alternatively, the sensor 5 can be immersed directly in a fluid sample so that a sample chamber is not part of the sensor configuration. Figure 3 shows a Severinghaus type of sensor 35 that can be used in the measurement of C0. This sensor 35 differs from the pH sensor 5 by having an additional region of electrically conductive material 37, 38, 39 with an exposed, active electrode area 38 (without dielectric coating) having thereon present a silver / silver halide material. which is used as an internal reference electrode. The second region of the electrically conductive material also has an exposed contact area 37 and a dielectric coating 26 on an advancing portion of the electrically conductive material. The metal / metal oxide electrode area 15, 30; advances 20; and contact area 25, are isolated from the silver / silver halide electrode 39, feed 38, and contact area 37 that form the internal reference electrode by the dielectric coating. In the Severinghaus sensor 35, the mV output between the metal / metal oxide electrode 30 and the silver / silver halide electrode 39 are linearly related to the pC02 register. Preferably the halide of the internal reference electrode is chloride. The silver / silver halide electrode can be preformed and plated on, at least, the exposed electrode area of the substrate conductive material can be applied as a paste and therefore heated to form the silver / silver halide electrode. In Figure 4, a pH sensor is shown wherein the electrical contact between the active electrode 30, the reference electrode 50, and the sensor equipment (or instrument) 55 is made using the electrically conductive regions 15, 20, 25 of the sensor thus resulting in a pH measurement. As shown in Figure 5, the pH sensor may have a neutral vehicle cover membrane 36 present. When present in the pH sensor, the cover membrane functions to protect the active electrode from the outside environment and degrading materials. sensor performance, such as redox centers and biological materials. As defined herein, the neutral vehicle cover membrane by itself, is capable of capturing the pH concentration, where the protons do not pass through the pH measurement but establish a potential through the cover membrane . The cover membrane can be applied to the flat sensor in several ways, including dip coating, and so on. The materials that can be used to prepare the cover membrane are well known water-permeable, gas-permeable polymeric materials known to those skilled in the art. Particularly preferred polymeric or copolymer materials that can be used include polyvinyl halide monomers. More preferably, as the main component of the cover membrane is a polyvinyl chloride (more preferably a plasticized polyvinyl chloride). Other components that are normally included in the cover membrane are ionophores and known lipophilic salts. Figure 6 shows a sensor formatted so that an internal electrolyte 27 is superimposed on the active electrode region 15, 30 and neutral vehicle cover membrane 36 is superimposed on the inner electrolyte layer 27. The internal electrolyte normally functions for keep the pH constant in the vicinity of the electrode and its pH can be regulated if desired. The pH regulators that may be included are well known in the art.

Figure 7 shows a Severinghaus type sensor of C02 having a metal / metal oxide electrode area 15, 30 and an internal silver / silver halide reference electrode area 39, 40 present. As shown, the Permeable membrane of C02 28 is superimposed on the internal electrolyte 27. The permeable membrane of C02 is not permeable to acid and separates the sample from the sensor. The permeable membrane 28 can be applied to the sensor by various techniques including dip coating, and so on. Materials that can be used include polymeric and copolymeric materials, as is well known in the art. In the Severinghaus sensor, the silver / silver halide internal reference electrode provides a stable reference potential. A bicarbonate filler solution is normally used as the internal electrolyte 27 before use. Since the C02 of the sample diffuses through the membrane and reaches equilibrium, the pH of the bicarbonate filler solution changes and is detected by the sensor. The change in pH refers to the measurement log of the partial pressure of C02. In addition to using the metal / metal oxide component in the pH and C02 sensors described above, other sensor systems can incorporate the metal / metal oxide electrode, since it can be achieved by techniques well known to those skilled in the art. matter. The different components of the sensors are adherently applied to the substrate by well-known techniques. For example, the electrically conductive material is preferably heated in the substrate before being applied to the metal paste mixture (and silver / silver halide material). Additionally, preferably the silver / avocado halide is heated on a substrate after application to the conductive region. The dielectric coating can be heated and / or dried. The different membranes are dried normally and / or heated on the substrate. It should be understood that various modifications of the invention will be apparent and can easily be made by those skilled in the art, given the description herein, without departing from the scope and materials of this invention. It is noted that the following examples given herein are intended to illustrate and not limit the invention to them. EXAMPLES The electrical circuitry used for all the examples is shown in Figure 8. The further description of the circuitry can be found in Lon-Selective Electrode Methodology, Vol. 1, De. Arthur K. Covington, CRC Press, 1979 p. 32-33. (incorporated herein by reference). Three-dimensional, free-flowing glass ("Type A") pH sensors (available from Ciba Corning Diagnostics Corp., Medfield, MA, series 278), identified as Type "A" sensors, were used as normal. Three other types of sensors (all flat) were prepared and identified as Types "B", "C" and • D. A silk-screen printing technique was used in the manufacture of flat sensors in the format shown in Figure 3. As shown in Figure 3, a metal / metal oxide and an Ag / AgCl electrode were present on the internal circuit of the substrate, however, in the present group of examples, the Ag / AgCl electrode was not used, instead, an eternal AG / AgCl reference was used. The electrical circuits of the substrate on which each type of flat sensors were manufactured were wafers of 5.4 cm by 5.4 cm perforated to form a total of 40 sensors. The wafers were made of approximately 96% alumina and approximately 4% glass binder, sold by Coors Ceramic Company, Grand Junction, Colorado. As shown in the Figure 3, an electrically conductive gold region (Au) was applied at 15, 20, 25. Parallel to this strip, a gold strip was applied to the - region 37 and the upper portion of 38. The lower region of 38 continues and including 39 applied thereto a silver paste (obtained from Metech, Elverson PA). The gold was purchased in E.l. DuPont DeNemours &; Company of Wilmington, Delaware. By depositing the conductor regions on the integrated circuits of the substrate 10, the integrated circuits were heated at 850 ° C for 6 minutes. A dielectric insulating material 26 (Cat. No. 9615 of The DuPont DeNemours &Co.) was applied on the substrate and conductive regions except for a first exposed portion 15 and 25 on the first gold strip and a second exposed region. and 37 on the second strip. The integrated circuits were then reheated to 850 ° C for 6 minutes. Then, the different metal pastes, as described below, were applied to the other gold strip in the exposed electrode area. A preformed Ag / AgCl electrode plate was deposited on the exposed silver region 39 to form the internal reference region 40. In the Type B and D sensors (both representing the INVENTION), the metal paste was a base and the metal paste mixture was prepared by mixing approximately 5 g of palladium paste (purchased as Catalog No. PC10141 from Metech Company of Elverson, PA). In the integrated circuits of the Type C sensor, (representing a COMPARATIVE), the metal paste applied to the gold strip was an already formed palladium oxide paste purchased from Metech under Catalog No. PC10119. The metal paste was applied to the exposed electrode area 15 of the gold strip on the substrate by silk screening and then the entire integrated circuit was heated to about 550 ° C for about 10 minutes in the presence of air, thus forming the electrode active of Pd / Pd oxide. Type D sensor integrated circuits differed from Type B sensors by Type D sensors by having an internal electrolyte layer adjacent to the electrodes, as well as a neutral vehicle cover membrane superimposed on the inner electrolyte layer, as is shown in Figure 6. The inner electrolyte layer was prepared as a coating using a solution formed by first dissolving about 2% w / v. of 100% hydrolysed polyvinyl alcohol in 100 ml of water and then adding 0.8 ml of a 0.1 M solution of NaHCO3 and KCI. This coating solution was then deposited on the active electrode and the silver electrode on the integrated circuit. A cover membrane was then applied to the upper part of the inner membrane of the electrolyte. The cover membrane was a polymer solution of 5% w / v tetrahydrofuran of 68.9% by weight of dioctyl phthalate (a plasticizer), 26.0% by weight of polyvinyl chloride (PVC), 3.1% by weight (TDDA, ionophore for pH), 2% by weight of tetra- (p-chlorophenyl) borate potassium (KTpCIPB). An aliquot of this solution was evenly dispersed over the entire integrated circuit and the solvent was allowed to evaporate to form the PVC-based cover membrane. When the electrical contact between the Type D sensors and the sensor instrument was formed, the cover membrane was scraped from the electrical contact area 25 before use. The acrylic sample chambers, as shown and described in Figure 2, were used for all the flat sensors used. Example 1 This example demonstrated a linear mV response of the normal glass sensors (Type A) and two types of the flat sensors (Types B and C) when tested in aqueous solution containing bicarbonate. Variations in the pH level were produced by varying the percentage of C02 in solution and the concentration of bicarbonate, with the solution maintained at approximately 37 ° C. Carbon dioxide was used to generate the pH values. The 02 levels also varied with the C02 levels to test the 02 interference. A total of three different pH conditions and C02 gas levels were tested in aqueous samples containing bicarbonate. The output of the pH sensors was measured as the potential (volts) between the active electrode and an external reference. The mV output of the sensors was measured, with the results summarized in Table 1 below and illustrated in Figure 9. As shown in the figure, line a is the mV output of the glass sensors (Type A) ), lines b 3 are from flat pH sensors Type B (INVENTION), and lines d.2 are from flat pH sensors Type C (COMPARATIVE). The results indicated that all sensors provided adequate inclination and linearity to give an acceptable pH measurement. TABLE < | Linearity of pH SENSOR TYPE A TYPE B TYPE B TYPE B TYPE C TYPE C TILES- -60.87 -74.03 -73.06 -73.62 -73.94 -72.94 CION Rsq. 0.9998 0.9995 0.9995 0.9995 0.9997 0.9998 Example 2 The amount of oxygen (02) varied to test the displacement induced by changes in oxygen levels (ie, 02 interference). The pH and C02 present were kept at a constant 3% during all the tests. As shown in Figure 10, a Type A glass sensor (line a) was tested as well as three flat Type B sensors (INVENTION, lines >; -3) and two Type C flat sensors (COMPARATIVES, lines cJ-2). The data show few or no change of response in the output of Type B sensors ranging from 0 to 26% of 02 (at 3% constant of C02). In contrast, Type C sensors show undesirable deviations in the V output induced by. the changes in levels of 02, that is, 02 interference. Example 3 Using flat Type D sensors (INVENTION), samples were tested at three different pH conditions. Type A glass sensors were also tested under the same conditions to provide a normal, with the data collection method described in Example 1 and 2. The results are summarized in Table II and illustrated in Figure 11. As shown, Type D flat sensors provided inclinations and linearity comparable to those provided by the normal.

TABLE 2 Linearity of pH SENSOR TYPE A TYPE B TYPE B TYPE B TYPE C TYPE C TILT- -61.9 -54.6 -56.9 -56.8 -58.4 -53.5 CION Rsq. 0.99995 0.99986 0.99984 0.99994 0.99992 0.9998 It is not intended that the scope of the following appended claims be limited to the description as set forth herein, but that the claims be construed as encompassing all aspects of patentable novelty which resides in the present invention, including all aspects that could be treated as equivalents thereof by those skilled in the art to which the invention pertains.

Claims (16)

1. CLAIMS 1. A metal / metal oxide active electrode prepared by a process comprising combining a base component with a metal paste to form a metal paste mixture, heating the metal paste mixture in the presence of air for a period of time. sufficient time to oxidize a portion of the mixture in order to form said metal / metal oxide electrode.
2. 2. An active electrode according to claim 1, said metal is a noble metal selected from the group consisting of palladium, rhodium, ruthenium, osmium, iridium, platinum, tin, antimony, bismuth, alloys thereof, and mixtures thereof and said base component is a salt selected from the group consisting of alkali metal salts and alkaline earth metal salts.
3. 3. An active electrode according to claim 2, wherein said salt is non-hydroscopic.
4. 4. An active electrode according to claim 3, wherein said metal is a palladium paste and said base component is NaHCO3.
5. 5. An active electrode according to claim 4, wherein said heating is presented at a temperature of about 450 ° C to 600 ° C for a period of about 1 minute to about 30 minutes. An active electrode according to claim 5, wherein said heating is at a temperature of 525 ° C to 575 ° C for a period of about 5 minutes to 15 minutes and said salt is present in a varying amount of about 0.1 % by weight to about 50% by weight, based on the total weight of the mixture before heating. 7. An active electrode according to claim 6, wherein said salt is present in an amount of about 16% by weight. 8. A flat pH sensor comprising an electrically non-conductive substrate having thereon applied in a flat format: (a) an electrically conductive material in at least one region adjacent to said substrate; (b) a dielectric coating covering at least one advancing portion of said region of such electrically conductive material but leaving exposed, at least, one electrode area and a contact area in said region of such electrically conductive material; and (c) a metal / metal oxide electrode in said exposed electrode area, wherein said metal / metal oxide electrode was prepared by a process comprising combining a base component with a metal paste to form a mixture of metal paste, heating the metal paste mixture in the presence of air for a sufficient time to oxidize a portion of the mixture to form said metal / metal oxide electrode. 9. A flat pH sensor according to claim 8, wherein in said process for preparing said active electrode, said metal is a noble metal selected from the group consisting of palladium, rhodium, ruthenium, osmium, iridium, platinum, tin, antimony, bismuth, alloys thereof and mixtures thereof and said base component is a salt selected from the group represented by MHB and MB wherein M is an alkaline earth metal or alkali metal, H is hydrogen, and B is a selected anion from the group consisting of -C03, -OH, and -HC03. A flat pH sensor according to claim 9, wherein in said process for preparing said active electrode, said base is a non-hydroscopic salt. 11. A flat pH sensor according to claim 8, wherein said process for preparing said active electrode, said metal is a palladium paste and said base component is NaHCO3. A flat pH sensor according to claim 8, wherein in said process for preparing said metal / metal oxide electrode, said metal paste and said al to combine to form a metal paste mixture which is applies to such an electrode area on said substrate before said heating. A pH sensor according to claim 8, further comprising a neutral vehicle cover membrane that is superimposed on at least the metal / metal oxide electrode portion of the sensor. 14. A pH sensor according to claim 13, further comprising an inner electrolyte layer at the top and adjacent said metal / metal oxide layer. 15. A method for preparing a pH sensor, said method comprising: (1) selecting an electrically non-conductive substrate; (2) adhering to it in a planar format: (a) an electrically conductive material in at least one region adjacent to said substrate; (b) a dielectric coating covering at least one advancing portion of said electrically conductive region, but leaving exposed at least one electrode area and a contact area of said electrically conductive region, and (c) a metal / metal oxide electrode present in said exposed electrode area, wherein said metal / metal oxide electrode is prepared by a process comprising combining a base component with a metal paste to form a paste mixture of metal. metals, heating the metal paste mixture in the presence of air for a sufficient time to oxidize a portion of the mixture to form said metal / metal oxide electrode. 16. A method for preparing a pH sensor according to claim 15, wherein in said process for preparing said active electrode, said metal is a palladium paste and said base component is a NaHCO3 and said electrically conductive material comprises gold. 16. A method for preparing a pH sensor according to claim 15, wherein said electrically conductive material is heated before the application of said metal / metal oxide electrode and said metal / metal oxide electrode is applied to said exposed electrode area as said metal paste mixture and then heating. 18. A method for measuring pH in a sample, the method comprising: (a) contacting said liquid sample with the flat pH sensor described in claim 8 and a reference, (b) contacting said exposed contact area. of said sensor with a pH sensor instrument; (c) contacting said reference with said pH sensor instrument; (d) providing an electric current of said pH sensing instrument through said reference and said contact area; and (e) measuring an electrical signal provided by said pH sensor instrument. 19. A C02 planar sensor comprising an electrically non-conductive substrate having adhered to it in a planar format: (a) an electrically conductive material in at least one first and second region adjacent to said substrate; (b) a dielectric coating covering at least one advancing portion of said first and second regions of said electrically conductive material but leaving it exposed in at least one electrode area and a contact area over said first and second regions; (c) a silver / silver halide electrode in said exposed area of electrodes of said first electrically conductive region; (d) a metal / metal oxide electrode in said exposed electrode area of said second electrically conductive region, said metal / metal oxide electrode, heating the metal paste mixture in the presence of air for a time "sufficient for oxidizing a portion of the mixture to form said metal / metal oxide electrode; (e) an inner electrolyte layer applied adjacent to and superimposed on said at least said metal / metal electrode and said silver / silver halide electrode and (f) a gas-permeable membrane adjacent to superimposed on said internal electrolyte in, at least, the portion of said electrolyte layer covering said metal / metal oxide electrode and said silver / silver halide material. 20. A C02 flat sensor according to claim 19, wherein said base is NaHCO 3 and said metal in said mixture • Metal paste is palladium. 21. A method for preparing a C0 flat sensor said method comprising: (1) selecting an electrically non-conductive substrate; (2) adhere to it in a flat format: (a) an electrically conductive contact material in at least the first and second separate regions; (b) a dielectric coating separating said first and second regions from said electrically conductive contact material, said dielectric coating covering at least one advancing portion of said first and second regions of said electrically conductive material but leaving exposed, so less, an electrode area and a contact area on said first and second regions; (c) a silver / silver halide electrode in said exposed area of electrodes of said first electrically conductive region; (d) a metal / metal oxide electrode in said exposed electrode area of said second electrically conductive region, said metal / metal oxide electrode prepared by a process comprising combining a base component with a metal paste to form a metal paste mixture, heating the metal paste mixture in the presence of air for a sufficient time to oxidize a portion of the mixture to form said metal / metal oxide electrode; (e) an inner electrolyte layer applied adjacent to and superimposed on at least said metal / metal electrode and said silver / silver halide electrode formed; and (f) a gas permeable membrane adjacent to and superimposed on said internal electrolyte in at least the portion of said electrolyte layer covering said metal / metal oxide electrode and said silver / silver halide electrode. 22. A method for preparing a C02 sensor according to claim 21, wherein said electrically conductive material is heated prior to the application of said metal / metal oxide electrode and said metal / metal oxide electrode is applied to such electrode area exposed as said metal paste mixture and then heated. 23. A method for measuring C02 in a sample, the method comprising: contacting a liquid sample with the C02 sensor described in claim 19, connecting said exposed contact area of said first and second electrically conductive regions of said sensor with a C02 sensor instrument, providing an electrical current of said C02 sensor instrument through such contact areas, by measuring an electrical signal provided by said C02 sensor instrument.