Abstract:
A method and a device for developing an electrochemical measuring system, in particular a sensor, is provided. A plurality of different electrode materials are applied to at least one substrate and introduced into a medium together with at least one reference electrode. Subsequently, the electrochemical potentials of the individual electrode materials in relation to the reference electrode are determined.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method and a device for developing an electrochemical measuring system, e.g., a sensor.  
         BACKGROUND INFORMATION  
         [0002]    Electrochemical measuring systems, e.g., sensors, are used customarily, for example, to determine a pH value of a liquid medium or also to determine a carbon dioxide concentration of a medium. Measuring systems configured for such purposes include potentiometric electrodes that may be configured in a variety of manners. To determine a pH, for example, a pH-sensitive glass electrode and a reference electrode are used. To determine a carbon dioxide concentration, for example, a platinum electrode is used in combination with a silver reference electrode.  
           [0003]    Potentiometric electrodes are classified as ion electrodes or redox electrodes. Ion electrodes are in turn classified as type 1 ion electrodes or type 2 ion electrodes. In the case of a type 1 ion electrode, the metal making up the electrode is submerged into a solution of its own salt. An electrode of this type is, for example, an Ag/AgNO 3  electrode. In the case of an ion electrode of the second type, a metal coated with a poorly soluble metal salt is submerged into an aqueous solution containing a readily soluble, chemically inert salt including the same anion as the metal salt.  
           [0004]    A redox electrode is made up of a neutral working electrode, which is made, for example, of platinum, and a solution containing a corresponding redox pair.  
           [0005]    An electrode of the second type is used, for example, as a reference electrode, because it allows uncomplicated handling when the potential signal is constant.  
           [0006]    To develop an electrochemical measuring system including one electrode, various materials are tested individually and in succession in relation to a suitable reference electrode for the selection of the electrode material. This method for selecting an electrode material has the disadvantage of being very time-consuming.  
         SUMMARY OF THE INVENTION  
         [0007]    The method of the present invention provides for testing of a plurality of electrode materials for selecting an electrode for an electrochemical measuring system, without requiring a laborious change of the electrode materials or of the medium. In particular, the method of the present invention facilitates a highly time-efficient process for determining an electrode material suitable for an electrochemical measuring system. The fact that a plurality of electrode materials are applied to the substrate allows testing of numerous electrode combinations in one operation. The method of the present invention allows a fast and direct comparison of different electrode materials because the required measurements, i.e., the determination of the electrochemical potential, may be performed within a short period of time and in the same medium.  
           [0008]    It is also possible that in the implementation of the method, a plurality of substrates, to which one or a plurality of electrode materials are applied, are inserted into the medium and the individual electrode materials are then tested in relation to the at least one reference electrode.  
           [0009]    Electrochemical measuring systems that are intended for use under unusual measuring conditions may be optimized using the method of the present invention. It is thus possible, for example, using the method of the present invention, to optimize electrodes of potentiometric sensors that are intended for use in media such as oils, fuels or the like. In these media, the chemical processes occurring are occasionally complex or even unknown from time to time.  
           [0010]    The substrate may be an electrical insulator made, for example, from a material such as aluminum oxide, silicon or glass.  
           [0011]    The individual electrode materials may be coated with one electrolyte each for the development of a type 2 electrode. For example, silver, which is used as an electrode material, may be provided with a silver chloride coating. Individual arrays of the same electrode material may also be coated with different electrolytes. This may allow screening of electrode combinations, electrolyte materials and electrolyte-electrode combinations simultaneously.  
           [0012]    The electrode materials are applied to the substrate using a suitable method, for example, a sputtering method, chemical vapor deposition (CVD), a galvanic method, a dispensing method, or even a suitable printing method.  
           [0013]    In order to miniaturize the substrate and the electrode materials arranged on it, the latter are, for example, applied to the substrate using a lithographic method. The electrolytes may also be applied to the electrode materials by suitable methods. This may allow analysis of the individual electrode materials in a small measuring vessel and using small quantities of the medium.  
           [0014]    The individual electrode materials are provided with a lead, to which a measuring device is connected. The individual leads may be insulated from each other by insulation layers, bridgings and/or back bondings.  
           [0015]    Cross-over circuits or the like may allow for measurement of various electrode combinations using a bonding.  
           [0016]    The measuring device includes, for example, a multiplexer, which allows activation of the different electrode materials, thus allowing variation of the electrode materials in parallel or sequentially in relation to the at least one fixed reference electrode.  
           [0017]    Also, in accordance with the present invention, a device for developing at least one electrochemical measuring system includes a potentiometric electrode. This device includes: at least one substrate onto which a plurality of different electrode materials are applied; at least one reference electrode; a measuring vessel in which the substrate and the reference electrode are arranged; and a measuring device via which it is possible to measure the electrochemical potential of the individual electrode materials in relation to the at least one reference electrode.  
           [0018]    The substrate is configured, for example, in the shape of a plate or cylinder.  
           [0019]    In order to be able to test different electrode combinations, the device according to the present invention may also include a motion device, which is in the form of, for example, an electric motor, which makes it possible to move the electrode materials and the reference electrode in relation to each other.  
           [0020]    Furthermore, the device of the present invention may include a spacer, which determines the spacing between the reference electrode and the electrode material placed in a measuring position. The spacer ensures that the measuring conditions are identical when different electrode combinations are tested. The spacer is made, for example from a plastic film, which is arranged in the areas of the substrate that are free from electrode materials. Thus, when two substrates including different electrode materials are used, the electrode materials of one substrate are in contact with the film forming the other substrate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 shows a system of a plurality of electrode materials and one reference electrode on a substrate.  
         [0022]    [0022]FIG. 2 shows an alternative system of a plurality of electrode materials on a substrate.  
         [0023]    [0023]FIG. 3 shows a cross-section taken through the system shown in FIG. 2.  
         [0024]    [0024]FIGS. 4 a - 4   c  illustrate a measuring principle for evaluating electrode materials, in which two substrates each including a plurality of electrode materials are moved in relation to each other.  
         [0025]    [0025]FIG. 5 shows two cylindrical substrates on which a plurality of electrode materials are arranged. 
     
    
     DETAILED DESCRIPTION  
       [0026]    [0026]FIG. 1 shows a substrate  10 , using which it is possible to develop an electrode combination for a potentiometric sensor and which is made from an electrical insulator such as aluminum oxide.  
         [0027]    A reference electrode  11  is applied to substrate  10 , the reference electrode including eight comb-like areas  12  through  19 . Comb-like electrode areas  12  through  19  interact with similarly comb-like working electrodes and counter-electrodes  20 ,  21 ,  22 ,  23 ,  24 ,  25 ,  26  and  27 , respectively. The reference electrode is a silver/silver bromide electrode. Counter-electrode  20  is made from platinum, counter-electrode  21  is made from palladium, counter-electrode  22  is made from copper, counter-electrode  23  is made from cobalt, counter-electrode  24  is made from nickel, counter-electrode  25  is made from iridium, counter-electrode  26  is made from rhodium and counter-electrode  27  is made from gold. Each of individual counter-electrodes  20  through  27  includes a separate lead.  
         [0028]    In order to manufacture the measuring system shown in FIG. 1, silver is first sputtered onto substrate  10  to form reference electrode  11 . Platinum, palladium, copper, cobalt, nickel, iridium, rhodium and gold are then sputtered onto substrate  10  to produce counter-electrodes  20  through  27 . The silver applied to form reference electrode  11  is then bonded. Substrate  10  is then submerged together with an external platinum electrode into a bath of 5% potassium bromide solution. A current is applied to the surface of the silver in such a manner that the silver surface is converted into silver bromide. This results in the production of a silver/silver bromide reference electrode. This electrode is a type 2 electrode.  
         [0029]    Subsequently, reference electrode  11  and counter-electrodes  20  through  27  are bonded and submerged into a measuring liquid, which is arranged in a measuring vessel. Using a measuring device, which includes a multiplexer and a high-resistivity measuring instrument, counter-electrodes  20  through  27  are now switched to oppose reference electrode  11 , the potential applied in each case being measured using the high-resitivity measuring device.  
         [0030]    Furthermore, the concentration of an analyte contained in the measuring liquid may be varied so that a correlation of the measured potential in relation to the concentration of the analyte may be used to determine the best electrode combination for the application in question.  
         [0031]    It is also conceivable that more than eight counter-electrodes, for example, 30 counter-electrodes, and a corresponding number of reference electrodes are arranged on substrate  10 , it being possible to switch or measure the reference electrodes potentiometrically in relation to the 30 counter-electrodes using a multiplexer.  
         [0032]    [0032]FIGS. 2 and 3 show a substrate  30  made from an electrical insulator used for the development of an electrochemical sensor, nine electrodes  31  through  39  made of different materials being applied in strips to substrate  30 . Electrode materials  31  through  39  may be connected to a measuring instrument, via a through hole leading to the back of substrate  30 .  
         [0033]    To determine an optimal electrode combination for the sensor, substrate  30  is arranged in a measuring vessel opposite a second substrate  40 , which is also provided with nine different electrode materials  41  through  49 , as is shown in FIGS. 4 a  through  4   c . Substrate  40  and electrode materials  41  through  49  are used to develop a reference electrode from an optimized material.  
         [0034]    To be able to test different electrode combinations in one medium, at least one of substrates  30  and  40  is provided with a motion device configured, for example, as a linear motor, via which substrates  30  and  40  may be displaced in relation to each other in such a manner that each of electrode materials  41  through  49  is arranged adjacent to each of electrode materials  31  through  39 . A measurement of electrode material  31  in relation to electrode materials  41  and  42 , and a measurement of electrode material  33  in relation to electrode materials  43  and  44 , are possible, for example, in the representation shown in FIG. 4 a . In the arrangement shown in FIG. 4 c , electrode material  31  is measurable in relation to electrode materials  43  and  44 , and electrode material  33  is measurable in relation to electrode materials  45  and  46 . In FIG. 4 b , the system is shown during the transfer of substrate  40  from one measuring arrangement to another.  
         [0035]    To define the distance of substrate  30  to substrate  40  in measuring position, an electrically insulating plastic film is arranged on substrates  30  and  40  between electrode materials  31  through  39  and  41  through  49 , respectively, the plastic film having a thickness of, for example, 150 mm. In measuring position, the electrode materials are in contact with the film areas of opposite substrate  30  and  40 , respectively.  
         [0036]    An exemplary embodiment of two substrates  50  and  60 , which are movable in relation to each other, is shown in FIG. 5, each of substrates  50  and  60  being in the form of a cylinder and rotatable in relation to each other along direction arrows X and Y using an electric motor. Distributed over the perimeter of substrate  50  are eight electrode materials  51  through  58 , each axially oriented and varying with respect to their chemical composition, electrode materials  51  through  58  being used for the development of a counter-electrode of an electrochemical sensor, and distributed over the perimeter of substrate  60  are eight electrode materials  61  through  68 , which vary with respect to their chemical composition and are used for the development of a reference electrode of the electrochemical sensor, each forming a reference electrode in this case.  
         [0037]    To determine the optimal electrode combination for a specific analyte, both substrates  50  and  60  are arranged in a measuring vessel containing the medium, which includes the analyte. The various electrode material combinations are then interconnected, cylindrical substrates being rotated into the corresponding measuring positions. In the position shown in FIG. 5, substrates  50  and  60  are arranged in such a manner that electrode material  43  arranged on the substrate  50  is measurable in relation to electrode materials  66  and  67  arranged on substrate  60 . Rotating substrate  50  and/or substrate  60  makes it possible for all permutations of electrode combinations to be analyzed with respect to the delivered electrochemical potential.