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    • 专利摘要:
    A potentiometric sensor comprises an electrochemical half cell with: an inner electrolyte (15), a discharge electrode contacting the inner electrolyte (15), and a sensor element (14) which can be brought into contact with a measuring medium, in particular into the measuring medium, to acquire measured values immersible, is, characterized in that the sensor element (14) is designed as a composite body which comprises an ion-selective component, which is in contact with the inner electrolyte (15).
    公开号:CH711880A2
    申请号:CH01550/16
    申请日:2016-11-23
    公开日:2017-06-15
    发明作者:Pechstein Torsten；Jagiella Manfred
    申请人:Endress+Hauser Conducta Gmbh+Co Kg；
    IPC主号:
    专利说明:

    Description: The invention relates to a potentiometric sensor. The sensor can be used, for example, for the measurement for measuring a quantity dependent on the activity of an analyte in a measuring medium. For example, this measure may be an activity or a concentration of the analyte, e.g. a particular ionic species, or a pH. The measuring medium may be a measuring liquid, for example a water-containing solution, emulsion or suspension.
    Potentiometric sensors are used in laboratory and process measurement technology in many areas of chemistry, biochemistry, pharmacy, biotechnology, food technology, water management and environmental metrology for the analysis of measuring media, in particular of measuring liquids. By means of potentiometric sensors, it is possible to record the activities of chemical substances, for example ionic activities, and thus correlated measured quantities in liquids. The substance whose concentration or activity is to be measured is also called analyte.
    Potentiometric sensors usually comprise a measuring half-cell and a reference half-cell as well as a measuring circuit. The measuring half-cell forms in contact with the measuring medium, e.g. a measuring liquid, a dependent of the activity of the analyte in the measuring medium potential, while the reference half cell provides a stable, independent of the concentration of the analyte reference potential. The measuring circuit generates an analog or digital measuring signal which represents the potential difference between the measuring half cell and the reference half cell. If necessary, the measuring signal is output by the measuring circuit to a higher-order unit connected to the sensor, which further processes the measuring signal. This may be a transmitter or a process controller, e.g. a PLC, act.
    The reference half cell potentiometric sensors comprises a reference element which is in contact with a reference electrolyte. The reference electrolyte is accommodated in a chamber formed in a housing of the reference half-cell. To carry out a potentiometric measurement, the reference electrolyte must be in electrolytic contact with the measurement medium. This contact is made by a transfer, which may for example consist of a through hole in the housing wall, a porous diaphragm or a gap. The potential of the reference half cell is defined by the reference electrolyte and the reference element. For example, if the reference half cell is configured as a silver / silver chloride reference electrode, the reference electrolyte is a high chloride aqueous solution, typically a 3 molar potassium chloride solution, and the reference element is a silver chloride coated silver wire. The reference element is connected to detect the potential difference between reference and measuring half-cell electrically conductive with the already mentioned measuring circuit.
    The measuring half-cell comprises a potential-forming sensor element which, depending on the type of potentiometric sensor, may comprise, for example, an ion-selective membrane. Examples of measuring half cells with ion-selective membrane are ion-selective electrodes (ISE). An ion-selective electrode has a housing closed by the ion-selective membrane, in which an inner electrolyte in contact with the membrane is accommodated. Furthermore, the ion-selective electrode comprises a discharge element, which is in contact with the inner electrolyte. The diverting element is electrically conductively connected to the measuring circuit. If the measuring medium is in contact with the ion-selective membrane for measurement, the membrane interacts selectively with a specific ionic species contained in the measuring medium, namely the ion to be detected selectively by means of the ISE. A change in the activity or concentration of the ion to be detected by the ion-selective electrode in the measuring medium causes a relative change in the equilibrium galvanic voltage between the measuring medium and the diverting element in contact with the ion-selective membrane via the inner electrolyte. A special case of such an ion-selective electrode, namely an electrode which selectively detects the H + or hydronium ion activity in a measuring liquid, is the known pH glass electrode comprising a glass membrane as a sensor element. Ion-selective electrodes are described, for example, in "Working with Ion-Selective Electrodes". , K. Cammann, H. Galster, Springer, 1996.
    The potential difference which can be detected by the measuring circuit between the diverting element of the measuring half cell and the reference element of the reference half cell is a measure of the measured variable dependent on the activity of the analyte. The measuring circuit is designed to detect the potential difference existing between the diverting element and the reference element, to amplify it if necessary and to convert it into a digital signal, and to output it as a measuring signal.
    The sensor element conventional potentiometric sensors is usually in the form of a stable, self-supporting structure, for example in the case of a pH glass electrode as a self-supporting glass membrane or in the case of an ion-selective electrode as an ionophore and conductive salts comprehensive polymer membrane. The sensor element must fulfill a number of functions and properties. For its sensory functionality, it must have sufficient sensitivity and selectivity for the analyte. In addition, a sufficiently low impedance of the sensor element is desirable in order to keep the measurement error low. In order to enable an efficient production of the sensor, the sensor element should also be suitable to connect it with the simplest possible means with a sensor housing or to attach it liquid-tight in a formed in the wall of the sensor housing socket. If the sensor element is a pH-sensitive glass membrane which has been fused to a tubular glass shaft, its thermal expansion coefficient should be matched to that of the glass shaft, for example. The melting temperatures should be coordinated in this case. Furthermore, security-relevant aspects can play a role. Thus, the sensor element must not release any toxic substances in certain applications and / or it must be biocompatible. Other aspects such as sterilizability, availability of materials or manufacturing costs can play a role.
    The selection and composition of a sensor element often represents a compromise of these required properties and functions. Although pH glass membranes are highly selective on the one hand, they are usually designed with a wall thickness of a few tenths of a millimeter to an acceptable sensor impedance of <1 GOhm. Thus, the membranes are very fragile.
    Alternatives to the pH glass electrode for the potentiometric pH measurement are enamel electrodes, ISFET half cells or metal oxide pH half cells.
    Enamel electrodes have a pH-sensitive element of enamel, the potential of which is derived by means of a solid dissipation, i. the electrically conductive diverter is directly in contact with the enamel without internal electrolyte. However, such enamel electrodes have worse sensory properties than pH glass electrodes. Another disadvantage is their high sensitivity to polarization and the higher manufacturing costs compared to pH glass electrodes.
    ISFET half-cells are mechanically robust. In particular, for the pH measurement ISFET half-cells are available in the prior art, which have a higher selectivity than pH glass membranes. On the other hand, ISFET half cells are more expensive and chemically less resistant than pH glass electrodes.
    Metal oxide pH half-cells usually have significant leakage currents during measurement operation, so that their sensory properties, in particular their selectivity, are significantly worse than those of a pH glass electrode or an ISFET half cell.
    It is therefore an object of the present invention to provide a potentiometric sensor which overcomes the disadvantages described herein.
    This object is achieved by the potentiometric sensor according to claim 1 and a method for producing a potentiometric sensor according to claim 16. Advantageous embodiments are specified in the dependent claims.
    The potentiometric sensor according to the invention comprises an electrochemical half cell with: an inner electrolyte, a discharge electrode contacting the inner electrolyte, and a sensor element which can be brought into contact with a measuring medium, in particular immersible into the measuring medium, in order to acquire measured values Sensor element is designed as a composite body which comprises an ion-selective component which is in contact with the inner electrolyte.
    By means of the potentiometric sensor measured values of a measured variable can be detected, which depend on the activity of those ionic species in the measuring medium, which may in particular be a measuring liquid, with which the ion-selective component interacts selectively in contact with the medium. In addition to the ion activity itself, such measured quantities may be the ion concentration or measurement quantities which depend on the ion concentration or activity. An example of such a measure is the pH, which corresponds to the negative decadic logarithm of the activity of hydronium ions, also referred to as oxonium ions, in an aqueous solution. By indirect determination, non-ionic species can also be detected by allowing them to participate in a suitable chemical reaction in which ions are generated or consumed.
    The composite serves as a sensor element of the potentiometric sensor. It can be formed from the ion-selective component and at least one further component.
    By designing the sensor element of the potentiometric sensor as a composite body, which may comprise one or more further components in addition to the ion-selective component, the sensor element may be optimized with respect to several different desirable properties. This can be done by suitable combination of the further component or the further components of the composite body with the ion-selective component. Thus, for example, an ion-selective component that has high selectivity but inherently has unfavorable mechanical properties, e.g. low break strength or poor machinability, may be combined with other components which impart higher strength or improved machinability to the entire composite body. The composite is preferably heterogeneous in that the ion-selective component and the other components are designed as volume elements of the composite which are in contact with each other via common interfaces, e.g. in the form of a layer stack, each layer forming a component of the composite body.
    The ion-selective component can be formed from an ion-selective material, for example, from pH membrane glass, from an ion-conducting metal salt (eg, LaF3 as a fluoride-selective component), from a water-immiscible, an ionophore as a selectivity-giving component comprising liquid or from a matrix material, eg a polymer material containing an ionophore as a selectivity-giving component, if necessary, together with a conducting salt.
    In an advantageous embodiment, the ion-selective component is an ion-selective glass, in particular a pH membrane glass, wherein the thermal expansion coefficients of the ion-selective component and all other components of the composite are coordinated and preferably differ by less than 10% from each other. This ensures that the composite remains stable even in the event that it is exposed to temperature fluctuations during measurement operation.
    The composite body may comprise as a further component a substrate comprising a solid on which the ion-selective component is arranged as a coating. Alternatively or additionally, the ion-selective component may have penetrated into pores of the substrate. This embodiment is advantageous, for example, if the ion-selective component is an ion-selective glass, for example pH glass. The substrate can stabilize the ion-selective glass mechanically, so that the risk of breakage is much lower than with a conventional pH glass membrane.
    The coating may cover at least one outer side of the substrate facing the measuring medium in the measuring mode and / or have penetrated into outwardly facing pores of the substrate, and be intended for contact with the measuring medium. In this case, the coating may cover both the outer side and an inner side of the substrate opposite this, which is remote from the measuring medium during measurement operation, and / or may have penetrated into both outwardly facing and inwardly facing pores of the substrate, so that the coating both the inner electrolyte can be contacted and brought into contact with the measuring medium. Advantageously, in this embodiment, an electrically conductive connection by means of electron and / or ion conduction between the coating covering the outer side of the substrate and the coating covering the inner side of the substrate in contact with the inner electrolyte. Such a conductive connection can be produced by the substrate having an electrical conductivity. This electrical conductivity can be ensured, for example, by an electron conductivity and / or an ion conductivity of the substrate. Another possibility is that the substrate has pores or larger cavities and / or channels, which are at least partially filled with the ion-selective component, so that the coating on the outer side and the coating on the inner side of the substrate by means of a continuous connection through the ion-selective component via the pores, cavities and / or channels in contact with each other.
    The substrate may comprise a liquid-permeable, in particular porous, solid. Advantageously, the pores may be at least partially filled with the liquid inner electrolyte. A ion-selective component arranged as a coating on at least the outer side of the substrate facing the measuring medium in the measuring operation of the sensor can thus be in contact with the inner electrolyte via the electrolyte-filled pores.
    The substrate may comprise a porous ceramic, in particular a porous, glass, a, in particular porous, metal, a metal mesh and / or a metal mesh.
    The substrate may alternatively comprise a glass, in particular a nuclear membrane glass, which has a specific impedance of 1 Gßmm2mm "1 to 104 1 Gßmm2mm" 1 at 25 ° C. The core membrane glass advantageously has a higher conductivity than a pH-sensitive glass membrane or as a typical ion-selective membrane. pH glass membranes typically have a specific impedance of 1 GQmm2mm "1 to 105 GQmm2mm" 1 at 25 ° C. The use of a composite of the ion-selective component and the substrate comprising a glass as a sensor element can thus serve to provide a lower impedance of the sensor element with improved mechanical stability.
    The ion-selective component can be configured in both aforementioned embodiments as a coating of the substrate or as a membrane applied to the substrate. For example, the ion-selective component may be a pH glass coating applied to the substrate on its outer side facing the measurement medium or a pH glass membrane resting on the outer side of the substrate. Alternatively, the ion-selective component can be an ion-selective membrane covering the substrate on its outer side, for example a polymer membrane comprising an ionophore and at least one conducting salt.
    The composite body may have a rod or disc shape. This is on the one hand favorable to integrate the composite body in the wall of a sensor housing in such a way that an outer side of the composite body can be acted upon with a measuring medium, while an opposite, the interior of the housing facing side can be in contact with the inner electrolyte. On the other hand, it is ensured in this way that the surface which can be acted upon by the measuring medium is flat, i. flat is designed. This leads in comparison to conventional glass electrodes with production-related dome-shaped glass membrane to a higher mechanical stability of the sensitive surface and allows to perform measurements with the sensor in a small measuring liquid Volu-mina.
    The composite body may be configured in an advantageous embodiment as a composite membrane.
    In one embodiment of the potentiometric sensor, the half-cell comprises a half-cell housing, in which a half-cell space is formed, wherein the inner electrolyte is accommodated in the half-cell space, wherein at least a portion of the Ableitelektrode is arranged in the half-cell space, and wherein the composite body to the half-cell space one side closes.
    The composite may be cohesively bonded to the half cell housing, e.g. by gluing or fusion.
    Advantageously, in this embodiment, the composite body may comprise a ceramic substrate integrally connected to a housing wall of the same ceramic, the ion-selective component being a coating applied on an outer side of the substrate, e.g. from pH-sensitive glass or other ion-selective substance is configured. It is also possible that the composite body is connected by means of a liquid-tight socket with the half-cell housing.
    In an advantageous embodiment, the inner electrolyte can touch the ion-selective component of the composite body on the side of the composite body facing the half-cell space. In this embodiment, the composite body may comprise a porous substrate, for example of a porous ceramic, the ion-selective component being a coating applied on an outer side of the substrate, e.g. from pH-sensitive glass or other ion-selective substance is configured. The pores of the substrate may be at least partially filled with an inner electrolyte contacting the coating on the back side. In this refinement, the discharge electrode can run at least in sections within the substrate, so that it is in contact with the inner electrolyte accommodated in the pores. In an extreme case, a region of the substrate facing away from the side of the substrate provided with the ion-selective coating can be free of inner electrolyte, so that the entire inner electrolyte of the half cell is present within the substrate. This is a very space-saving design that can be used for miniaturized potentiometric sensors.
    The composite body can be melted in a further embodiment in a wall of the half-cell housing or fixed mechanically via a sealing element by means of a with the wall, in particular again detachable, connectable fixing device in the wall.
    The potentiometric sensor may comprise, in addition to the already mentioned half-cell, which serves as a measuring half-cell, further a reference half-cell comprising: a reference half-cell space, a reference electrolyte containing in the reference half-cell space, a reference electrode at least in sections within the reference half-cell space, contacting the reference electrolyte, and an electrochemical transfer arranged in a wall surrounding the reference half-cell space, via which the reference electrolyte is in contact with a medium outside the wall, in particular the measuring medium. Furthermore, the potentiometric sensor may comprise a measuring circuit connected to the deflecting electrode and the reference electrode, which is designed to detect a potential difference between the deflecting electrode and the reference electrode and to output a measuring signal dependent thereon. The reference half-cell is designed to provide a stable reference potential independent of the composition of the measuring liquid, in particular of the ionic activity. The measuring signal of the measuring circuit thus represents the measured variable dependent on the activity of the ion species to be detected in a measuring medium in contact with the electrochemical transfer and the ion-selective component. The reference half cell may comprise a second type electrode, e.g. an Ag / AgCl reference electrode.
    According to the invention, a potentiometric sensor according to one or more of the embodiments described above can be produced by means of a method comprising the following steps: - producing a compound body comprising an ion-selective component; Bringing the ion-selective component into contact with an internal electrolyte; - Contacting the inner electrolyte with an electrically conductive Ableitelektrode.
    In order to bring the ion-selective component into contact with the inner electrolyte, the following steps can be carried out in a first process variant: connecting a wall of a measuring half-cell housing to the composite body such that a measuring half-cell housing is formed, which is closed by the composite body; - Filling the measuring half-cell space with the inner electrolyte, such that the ion-selective component of the composite body is brought into contact with the inner electrolyte.
    In a further step, at least a portion of the electrically conductive discharge electrode can be introduced into the measuring half cell space.
    Fabrication of the composite may comprise: applying an ion selective material, in particular an ion selective glass, e.g. a pH membrane glass, an ion-conducting metal salt or a liquid comprising an ionophore or an ionophore
    Polymer matrix, on a one, in particular porous or a nuclear membrane glass comprehensive, solid-containing substrate.
    In a further step, the composite body comprising the substrate and an ion-selective component formed from the ion-selective material can be connected to a shaft-shaped housing, in particular a hollow cylindrical housing, to form the measuring half-cell housing enclosing the measuring half-cell space. For this purpose, the composite body can be fused to the housing or by means of a socket, which, for example. a screw or clamp connection or the like may be connected to the housing, wherein the composite body is sealed against the shaft and / or against the socket via a seal.
    In a second variant of the method alternative to the first variant of the method, in a first step, a solid, in particular porous or a nuclear membrane glass, solid body with a hollow cylindrical shaft to form the measuring half-cell space enclosing measuring half-cell housing can be connected, and then in a second step to create the composite is an ion-selective material, in particular an ion-selective glass, eg a pH membrane glass, an ion-conducting metal salt, or an ionophore-containing liquid, or a polymer matrix comprising an ionophore, are applied to the outward-facing side of the solid-state bonded body. The solid body therefore serves as a substrate for the ion-selective component formed from the ion-selective material.
    The application of the ion-selective material can in both process variants, the immersion in a melt of an ion-selective glass or pH membrane glass, the melting of an ion-active or pH membrane glass, a thick film or a thin film process for applying a coating of the ion-selective material comprise the substrate.
    The, for example, formed from a ceramic substrate may initially have no pores in both embodiments and be provided with pores before or after the application of the ion-selective material.
    The invention will be explained in more detail below with reference to the embodiments illustrated in FIGS. Show it:
    1 shows a first embodiment of a potentiometric sensor for pH measurement.
    2 shows a measuring half cell of a potentiometric sensor according to a second embodiment;
    3 shows a measuring half-cell of a potentiometric sensor according to a third embodiment;
    4 shows a measuring half cell of a potentiometric sensor according to a fourth embodiment;
    5 shows a composite body with a pH-sensitive component.
    FIG. 1 shows a schematic representation of a pH sensor configured as a potentiometric single-rod measuring chain 10, which comprises a measuring half-cell 12 and a reference half-cell 11. The measuring half-cell 12 is formed in a tubular half-cell casing 13 of an insulating material, e.g. Glass or plastic, which is closed at one end by a pH-sensitive sensor element 14. In the half-cell housing 13, as the pH-sensitive sensor element 14 contacting inner electrolyte 15 is added a pH buffer solution into which an electrically conductive diverter 16 dips. In the present example, the discharge element 16 is formed as a chlorided silver wire.
    The reference half cell 11 is arranged concentrically around the measuring half cell 12. It comprises a reference half-cell housing formed by an outer, tubular housing part 17 made of an insulating material and the outside of the measuring half-cell housing 13. At its end facing the sensor element 14, the housing part 17 is connected in a liquid-tight manner to the measuring half-cell housing 13 of the measuring electrode 12, e.g. by merger. In the annular reference half-cell space thus formed, a reference electrolyte 20 is accommodated, in which the reference element 19 dips. The reference element 19 may be formed as the diverter 16 by a chlorided silver wire. Reference electrolyte 20 in the present example is a saturated potassium chloride solution thickened by means of a polymer. In the outer tubular housing part 17, an electrochemical transfer 21 designed as a passage opening is arranged here. To carry out pH measurements, a front end region of the combination electrode comprising the electrochemical transfer 21 and the pH-sensitive sensor element 14 is brought into contact with a measuring liquid. About the transfer 21 of the reference electrolyte 20 is in contact with the measuring liquid, so that a mass transport between the reference electrolyte 20 and measuring liquid is possible.
    At its rear side opposite the pH-sensitive sensor element 14, the housing of the combination electrode is closed by a bond 22. The reference element 19 and the diverting element 16 are each connected to a measuring circuit 25 via a contact point 23, 24 arranged outside the housing. The measuring circuit 25 is designed to detect a potential difference between the measuring half cell 12 and the reference half cell 11 and to output a measuring signal representing the potential difference. The measuring circuit 25 may be connected to a higher-level unit, for example a measuring transducer, to which it outputs the measuring signal.
    The sensor element 14 is configured in the present example as a composite body. The composite is designed as a composite glass membrane, which is formed of three superposed glass layers. The layers 14.1, 14.2 and 14.3 have different specific impedances. A middle layer 14.1 is formed of a core membrane glass having a conductivity of 1 GOmm2mm "1 to 104 Gm2mm" "1 at 25 ° C. On an outer side of the middle layer 14.1 facing the measuring liquid, a first layer 14.2 of a pH-sensitive membrane glass is arranged. On a side of the middle layer 14.1 facing the measuring half-cell space, a second layer 14.3 of the same pH-sensitive membrane glass is arranged. The area and the layer thicknesses of the individual layers are chosen so that the composite body has an impedance in the range of 1 MOmm2mm "1 to 10Gnmm2mm'1 at 25 ° C.
    In measuring operation, a swelling layer is formed on the surface of the first layer 14.2 contacting the measuring medium. In this case, a dissociation takes place at the interface between the membrane glass and the water-containing measuring liquid, in which alkali ions of the glass are replaced by H + ions from the measuring liquid, so that a multiplicity of hydroxyl groups are formed in the swelling layer. At the inner electrolyte contacting surface of the second layer 14.3 also forms a corresponding source layer. Depending on the pH value of the measuring medium, H + ions diffuse out of the source layer or into the source layer. Since the inner electrolyte has a constant pH value, a potential difference dependent on the pH of the measuring liquid thus results between the side in contact with the measuring liquid and the side of the sensor element 14 in contact with the inner electrolyte. This potential difference determines the measuring half cell potential. Interfacial effects at the interfaces between the three layers 14.1, 14.2, 14.3 cancel each other out and thus do not affect the measurement signal.
    The composite body formed from the layers 14.1, 14.2, 14.3 has a thermal expansion coefficient which is adapted to the expansion coefficient of the half-cell housing 13, and which differs preferably by less than 10% from the expansion coefficient of the half-cell housing. It is merged with the half-cell housing 13 in the present example. The designed as a composite body pH-sensitive element 14 may be designed much thicker than a pH glass membrane of a conventional glass electrode, which consists solely of the less conductive pH membrane glass due to the high conductivity of the nuclear membrane glass. This would achieve an impedance of substantially more than 1 GOhm with the same thickness and generate significant measurement errors when using a conventional signal processing electronics.
    As an alternative to the example shown here, the potentiometric sensor can also be used as a measuring chain with two separable, ie. not firmly mechanically interconnected half-cells be configured. The exemplary embodiments of measuring half-cells described below can also be designed both as part of a potentiometric sensor designed as a single-rod measuring chain and as individual half-cells which can be interconnected with a separate reference half-cell to form a potentiometric sensor.
    In the production of the sensor shown in FIG. 1, first of all the composite body formed from the layers 14. 1, 14. 2, 14. 3 can be produced and subsequently fused to the measuring half-cell housing 13. Alternatively, it is also possible first to blow only a membrane formed from the core membrane glass to the tubular housing 13 and to coat the membrane thus formed on both sides, for example by means of physical or chemical layer technologies, with the membrane glass after solidification.
    Fig. 2 shows a schematic representation of an embodiment of a measuring half-cell 112 of a potentiometric sensor, which may otherwise be constructed similar to the potentiometric sensor described with reference to FIG. 1. The measuring half cell 112 comprises a disk-shaped ion-selective sensor element 114, which is configured as a composite body of a porous ceramic substrate 114.1 and an ion-selective coating 114.2 applied to an outer side of the substrate 114.1 for contact with a measuring liquid. The coating 114.2 serves as an ion-selective component of the sensor element 114. The coating 114.2 may comprise an ion-selective polymer material or a pH membrane glass. The substrate 114.1 can be formed from a porous glass ceramic whose thermal expansion coefficient is matched to that of the coating 114.2. Suitable ceramic materials are for example zirconium dioxide, in particular magnesium- or yttrium-stabilized zirconia ceramics. The pH glass can be based on a conventional pH silicate glass.
    The ion-selective sensor element 114 is clamped via elastomer seals 128 in a measuring half-cell housing and fixed in the wall of the housing so that the ion-selective coating 114.2 is directed outwards and one of the ion-selective coating 114.2 opposite side of the ion-selective sensor element 114 to one of the housing enclosed half-cell space points. A liquid inner electrolyte 120, which contacts the side of the ion-selective sensor element 114 facing the half-cell space, is accommodated in the half-cell space. The liquid inner electrolyte 120 also fills out the pores of the substrate 114.1, so that the ion-selective coating 114.2 is in contact with the inner electrolyte 120 at the rear. Between the side of the coating 114.2 which is in contact with the measuring medium and the side of the coating 114.2 in contact with the inner electrolyte 120, a potential difference which depends on the ion concentration to be detected in the measuring liquid thus forms, which determines the measuring half-cell potential. An electrically conducting diverting element 119, which (as described with reference to FIG. 1) can be connected to a measuring circuit of the potentiometric sensor, which detects the potential difference between the measuring half-line and a reference half-cell, is immersed in the inner electrolyte 120.
    The measuring half-cell housing is formed in the present example from a first tubular housing part 126 and a second annular housing part 127. The annular housing part 127 is designed as a union nut and connectable via a threaded connection 128 with the first housing part 126. Above and below the ion-selective sensor element 114 arranged sealing rings 128 made of an elastomer are pressed together by screwing the housing part 127 with the housing part 126 and thus the ion-selective sensor element 114 is fixed liquid-tight in the housing. The skilled person many other ways are known to clamp a disk-shaped element in a housing wall via elastomer seals liquid-tight and / or fix. These can of course also be used for the purpose shown here.
    An advantage of this embodiment, the high mechanical stability, which has designed as a composite body ion-selective sensor element 114. This makes it possible to fix the ion-selective sensor element 114 under a certain mechanical load by clamping between two elastomer seals in a liquid-tight manner in a housing wall. The housing, since it is not materially connected to the ion-selective sensor element 114, may be made of any non-electrically conductive material, e.g. a plastic or a ceramic. This allows an optimization of the manufacturing process and the manufacturing costs, as well as an improvement of the mechanical properties of the sensor housing. At the same time, it is possible to design the coating 114.2 to be very thin, so that the impedance of the ion-selective sensor element 114 can desirably be kept low.
    In the manufacture of the sensor, the ceramic substrate 114.1 can be coated with the ion-selective membrane glass either before installation in the housing or after installation in the housing.
    Instead of the ion-selective sensor element 114 shown here in FIG. 2, which is composed of a porous ceramic substrate 114.1 and an ion-selective coating 114.2 of an ion-selective polymer material applied to an outer side of the substrate 114.1 for contact with a measuring liquid The measuring half cell 112 may also comprise a composite body of a porous ceramic substrate and an ion-selective component filling the pores of the ceramic substrate. To produce such a composite body, the porous ceramic substrate may be impregnated with a liquid ion-selective component comprising an ionophore which solidifies, for example by polymerization, in the pores of the substrate. In this case, it is not necessary for a closed coating to be formed on a surface of the substrate, as in the embodiment shown in FIG. 2. An ion-selective component of the composite present in the pores of the substrate is sufficient to provide sufficient ion selectivity of the sensor element 114. Incidentally, in this alternative embodiment, the measuring half cell 112 may be configured as shown in FIG. 2 and described above.
    In Fig. 3, a third embodiment of a measuring half-cell 212 of a potentiometric sensor is shown. Here, the measuring cell housing 213 and a substrate 214.1 of an ion-selective composite body are integrally formed from a ceramic. The measuring cell housing 213 is formed by a ceramic tube, which is closed at its front, intended for immersion in a measuring liquid end by a disc-shaped wall, which also forms the substrate 214.1 of the ion-selective composite body. As an ion-selective component, the composite body comprises an ion-selective coating 214.2. In the present example, the measuring half cell 212 is designed as a pH measuring half cell. The ion-selective coating 214.2 is correspondingly formed as a pH-selective coating of a pH membrane glass. The ceramic from which the measuring cell housing 213 and the substrate 214.1 are formed is selected such that their thermal expansion coefficient differs from that of the pH membrane glass by less than 10%. In the measuring half-cell space enclosed by the wall of the measuring cell housing 213 and the side of the substrate 214.1 opposite the coating 214.2, a liquid inner electrolyte 220, which can be, for example, a pH buffer solution, is accommodated. In the inner electrolyte 220, a diverter 219 is immersed, which serves to derive the half-cell potential.
    The ceramic material is provided in the region of the substrate 214.1 with pores, which are filled by the inner electrolyte 220, so that the coating 214.2 is back in contact with the inner electrolyte 220. The pores can be produced, for example, during the production of the housing 213, 214.1 by a sintering process. Alternatively, the pores can be introduced locally into this only by a subsequent treatment of the substrate 214.1. It is also possible that both the substrate 214.1 and the tubular housing wall 213 are made of a porous ceramic, wherein the tubular housing is configured at least on its outside with a liquid-impermeable coating or surrounded by a liquid-impermeable surrounding housing, so that when immersing the measuring half-cell 212th in a measuring liquid this does not penetrate through the housing 213 in the half-cell space.
    FIG. 4 schematically shows a further exemplary embodiment of a pH measuring half cell 312 which is particularly compact and therefore suitable for use in a miniaturized potentiometric sensor. The measuring half-cell 312 has a composite body 314, which has a substrate 314.1 made of a porous ceramic, on which on one side, which is intended for contact with a measuring liquid, a coating 314.2 made of a pH-sensitive membrane glass is applied. The substrate 314.1 may have a thickness in the range of a few mm, the coating 314.2 may have a thickness in the range of less than .mu.m. The pores of the substrate 314.1 are filled with a liquid or solidified inner electrolyte 320 in a region adjoining the coating 314.2 on the rear side.
    权利要求:
    Claims (19)
    [1]
    A section of a discharge element extends within the substrate 314.1 in such a way that it contacts the inner electrolyte 320 and can derive a measuring half-cell potential forming on the coating 314.2 in contact with a measuring liquid. The composite body 314 can either be fixed in a housing similar to the composite body of the measurement half cell shown in FIG. 2, so that the inner electrolyte is sealed off from the measurement liquid. Alternatively, those surface areas of the substrate 314.1 that are not covered by the coating 314.2 may be covered by a water-impermeable coating. In Fig. 5, an embodiment of a composite body 414 is shown schematically, which can be used as a sensor element in a potentiometric sensor, quite analogous to the sensor elements of the embodiments described above. The composite body 414 comprises an electrically conductive, in particular metallic, sieve 414.1, which may be formed, for example, from platinum or an Fe-Ni-Co alloy. This is surrounded by a layer 414.2 from a niederim-pedanten glass. On both sides of the layer 414.2 is in each case a layer 414.3, 414.4 of an ion-selective membrane glass, e.g. a Na-selective membrane glass, applied. The composite body 414 may be used in a measurement half-cell of a potentiometric sensor such that one of the layers 414.3, 414.4 is in contact with the measurement liquid, while the opposite layer 414.3, 414.4 is in contact with an inner electrolyte such that one of the Analyte activity in the measuring medium dependent Meßhalbzellenpotential sets. Particularly advantageous in this embodiment, on the one hand, the high mechanical stability of the composite body 414, on the other hand, the very low impedance of the composite body, since in the bulk phase electron conduction via the metal. To produce the composite body 414, first the screen of conductive material may be immersed in a melt of the low-impedance glass. After solidification of the glass, the substrate thus formed from two components can be coated on both sides with the ion-selective membrane glass. claims
    A potentiometric sensor, comprising an electrochemical half-cell comprising: an inner electrolyte, a lead electrode contacting the inner electrolyte, and a sensor element, which can be brought into contact with a measuring medium, in particular immersed in the measuring medium, in order to acquire measured values, characterized that the sensor element is designed as a composite body which comprises an ion-selective component which is in contact with the inner electrolyte.
    [2]
    2. A potentiometric sensor according to claim 1, wherein the composite body of the ion-selective component and at least one further component is formed.
    [3]
    3. Potentiometric sensor according to claim 1 or 2, wherein the ion-selective component of an ion-selective glass, in particular a pH membrane glass, an ion-conducting metal salt, a liquid comprising an ionophore or at least one ionophore comprising matrix material is formed.
    [4]
    4. A potentiometric sensor according to any one of claims 1 to 3, wherein the ion-selective component is an ion-selective glass, in particular a pH membrane glass, and wherein the thermal expansion coefficients of the ion-selective component and all other components of the composite body are coordinated, and preferably by less than 10% different from each other.
    [5]
    5. Potentiometric sensor according to one of claims 1 to 4, wherein the composite body as a further component comprising a solid substrate comprising, on which the ion-selective component is arranged as a coating and / or has penetrated into pores of the substrate.
    [6]
    6. The potentiometric sensor according to claim 5, wherein the coating covers at least one outer side of the substrate and / or has penetrated into the measuring medium facing pores of the substrate, and is intended for contact with the measuring medium.
    [7]
    7. Potentiometric sensor according to claim 6, wherein the coating covering both the outer side and one of these opposite, in contact with the inner electrolyte side of the substrate and / or in the inner electrolyte facing pores of the substrate has penetrated.
    [8]
    8. Potentiometric sensor according to one of claims 5 to 7, wherein the substrate comprises a liquid-permeable, in particular porous, solid.
    [9]
    9. Potentiometric sensor according to one of claims 5 to 8, wherein the substrate comprises a porous ceramic, a, in particular porous, glass, in particular a porous metal, a metal mesh and / or a metal fabric.
    [10]
    10. A potentiometric sensor according to any one of claims 5 to 9, wherein the substrate comprises a glass, in particular a nuclear membrane glass, which has a specific impedance of 1 GQmm2mm "1 to 104 Gßmm2mm" 1 at 25 ° C.
    [11]
    11. A potentiometric sensor according to any one of claims 1 to 10, wherein the composite body has a rod or disc shape.
    [12]
    12. A potentiometric sensor according to any one of claims 1 to 11, wherein the composite body is configured as a composite membrane.
    [13]
    13. A potentiometric sensor according to any one of claims 1 to 12, wherein the half-cell comprises a half-cell housing in which a half-cell space is formed, wherein the inner electrolyte is accommodated in the half-cell space, wherein at least a portion of the discharge electrode is arranged in the half-cell space, and wherein the Composite body closes the half-cell space on one side.
    [14]
    14. A potentiometric sensor according to claim 13, wherein the inner electrolyte contacts the ion-selective component of the composite body on the half-cell space facing side of the composite body.
    [15]
    15. A potentiometric sensor according to any one of claims 13 or 14, wherein the composite body is melted into a wall of the half-cell housing or mechanically fixed via a sealing element by means of a with the wall, in particular again detachable, connectable socket in the wall.
    [16]
    16. A method for producing a potentiometric sensor, in particular according to one of claims 1 to 15, comprising: - producing a composite body comprising an ion-selective component; Bringing the ion-selective component into contact with an internal electrolyte; - Contacting the inner electrolyte with an electrically conductive Ableitelektrode.
    [17]
    17. The method of claim 16, further comprising: - connecting a wall of a measuring half-cell housing with the composite body such that a measuring half-cell housing is formed, which is closed by the composite body; - Filling the measuring half-cell space with the inner electrolyte, such that the ion-selective component of the composite is brought into contact with the inner electrolyte; and - introducing at least a portion of the discharge electrode into the measuring half-cell space.
    [18]
    18. The method according to claim 16, comprising: bonding a, in particular porous or glass-comprising solid body with a hollow cylindrical shaft to form the measuring half-cell space enclosing measuring half-cell housing; and then, to make the composite, apply to an ion selective material, particularly an ion selective glass, e.g. a pH membrane glass, an ion-conducting metal salt or a liquid comprising an ionophore or a polymer matrix comprising an ionophore, on the outwardly facing side of the solid body connected to the shaft.
    [19]
    A method according to any one of claims 16 or 17, wherein preparing the composite body comprises: applying an ion selective material, in particular an ion selective glass, e.g. a pH membrane glass, an ion-conducting metal salt or a liquid comprising an ionophore or a polymer matrix comprising an ionophore, on a substrate comprising, in particular, a porous or a nuclear membrane glass, a solid body.
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    同族专利:
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    US20200300808A1|2020-09-24|
    US20170160228A1|2017-06-08|
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    法律状态:
    2019-11-29| AZW| Rejection (application)|
    优先权:
    申请号 | 申请日 | 专利标题
    DE102015121364.8A|DE102015121364A1|2015-12-08|2015-12-08|Potentiometric sensor|
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