Combination electrode comprising a diaphragm having a cross-linked hydrogel, and method for producing the combination electrode

Abstract

The invention relates to a combination electrode (1) for measuring a working fluid, having a working electrode (2), a reference electrode (3), a diaphragm (10), and a first electrically conductive fluid (6), which is in contact with the reference electrode (3) and the diaphragm (10) such that the diaphragm (10) is connected to the reference electrode (3) in an electrically conductive manner via the first electrically conductive fluid (6), the diaphragm (10) having a cross-linked hydrogel and is stabilised by at least one support element. The invention also relates to a method for producing the combination electrode (1).

Description

[0001] Combination electrode with cross-linked hydrogel diaphragm and method for producing the combination electrode

[0002] The invention relates to a combination electrode with a diaphragm comprising a cross-linked hydrogel and mechanically stabilized by a first support element, and to a method for producing the combination electrode.

[0003] A combination electrode is a combination of a working electrode and a reference electrode housed in a single rod. The term "working electrode" is also used synonymously with the term "measuring electrode," and the term "reference electrode" is also used synonymously with the term "reference electrode." A combination electrode can be, for example, a redox sensor or a pH combination electrode used to determine a pH value. A pH combination electrode can be, for example, a pH glass electrode.

[0004] The reference electrode is often a metal wire immersed in a salt solution. The reference electrode is frequently a silver-silver chloride electrode comprising a silver wire coated with an AgCl layer, with the silver wire and AgCl layer immersed in a KCl solution. The KCl solution is enclosed within a diaphragm. During operation of the combination electrode, the diaphragm is in contact with the measuring fluid to be analyzed. The term "measuring fluid" is also used synonymously with the term "working fluid." The diaphragm is characterized by the fact that it prevents mixing of the KCl solution and the measuring fluid, yet allows charge transfer between the KCl solution and the measuring fluid.Diaphragms with a porous structure are often used for this purpose. However, the resulting large surface area of ​​the diaphragm is susceptible to contamination, which can impede charge transfer and thus lead to inaccurate measurements. Furthermore, KCl can flow out of the combination electrode, and changes in the KCl concentration and thus the electrochemical potential of the reference electrode can also cause inaccurate measurements.

[0005] Using a hydrogel diaphragm, KCl leakage and the degree of contamination can be significantly reduced (DE 10 2018 132 108 A1). Corresponding combination electrodes offer higher measurement accuracy and a longer service life.

[0006] For reuse, the combination electrodes must be frequently sterilized, e.g., by autoclaving. Under autoclave conditions (high temperatures of approximately 120°C and high pressure of approximately 2 bar), the hydrogel tends to swell, which impairs the service life of a corresponding combination electrode. A plug used in the above-cited publication DE 10 2018 132 108 A1 proved insufficient to provide a mechanical barrier for the hydrogel.

[0007] The task is to increase the stability of a hydrogel diaphragm.

[0008] This object is achieved by a combination electrode having the features of claim 1 and a method having the features of claim 12. Further embodiments and refinements of the invention emerge from the subclaims, the figures, and the exemplary embodiments. The embodiments of the invention can be advantageously combined with one another.

[0009] A first aspect of the invention relates to a combination measuring chain for measuring a working fluid, comprising a reference electrode arranged in a first volume containing a first electrically conductive fluid and a working electrode arranged in a second volume containing a second electrically conductive fluid, wherein the first volume is delimited by at least one diaphragm comprising a cross-linked hydrogel, and wherein at least one first support element permeable to the working fluid is arranged on the side of the diaphragm facing away from the first volume. It has surprisingly been found that a cross-linked hydrogel has significantly higher structural stability at elevated temperatures than a conventional, non-cross-linked hydrogel. It is advantageously stable at temperatures up to 140°C. In other words, the cross-linked hydrogel is melt-resistant at the temperatures prevailing during autoclaving.A corresponding diaphragm is therefore better suited for sterilization by autoclaving than a conventional hydrogel and thus gives a corresponding combination electrode a longer service life.

[0010] It has further been found that a first support element gives the diaphragm additional stability against the pressure prevailing during autoclaving. The first support element, which can also be referred to as the first holding element, is permeable to the working fluid. The permeability of the support element is prevented when pressure is applied to the support element. In other words, the support element then closes the fluid connection and prevents the cross-linked hydrogel of the diaphragm from being pushed outwards. The first support element acts as a mechanical barrier for the hydrogel. The first support element itself is mechanically stabilized by an internal projection in the material of the combination electrode, or by a step in the material of the combination electrode, or by tension, e.g. when the first support element is designed as a spring ring. The spring ring can be tensioned inwards or outwards.Particularly advantageously, the first support element is arranged directly on the diaphragm. The permeability of the first support element to the working fluid ensures charge transport from the working fluid to the hydrogel and further to the first electrically conductive fluid. The permeability can be controlled by material properties of the first support element itself, e.g., porosity, or by the arrangement of through-holes or grooves, for example. The cross-linking of the hydrogel and the mechanical barrier provided by the first support element thus act synergistically by counteracting the oozing of the hydrogel and thus the destruction of the diaphragm due to temperature and pressure, thus increasing the stability of the diaphragm and thus the service life of the combination electrode.

[0011] Ring-shaped designs of the first support element are particularly suitable because they can advantageously close tightly around the usually round component of a combination electrode, around which the diaphragm is also arranged. The first support element is therefore preferably a ring-shaped element. For example, the first support element can be designed as a spring ring or a snap ring. The first support element is preferably a spring ring. Also suitable is a ring that is only attached on one side (for example by gluing or clamping) and has sufficient space on the other side for liquid to pass around it. In this respect, the term “ring-shaped” as used here refers not only to closed rings, but also three-quarter rings and similar designs.

[0012] Shapes other than ring-shaped are also possible.

[0013] In terms of material, the first support element can comprise spring steel, stainless steel, or polymers such as polyetheretherketone (PEEK), polysulfone (PSU), polyphenylenesulfone (PPSU), or glass fiber-reinforced polymers, e.g., glass fiber-reinforced polyamides. The first support element can also comprise sintered material.

[0014] Furthermore, the first support element can have through-openings, such as through holes or grooves. These through-openings advantageously allow the passage of fluid and close under high pressure.

[0015] The first support element preferably has a meandering structure. Meandering here means that at least part of the material is formed as a strand and is arranged with constant and uniform changes of direction, but overall closed and annular, so that individual sections of the strand are arranged parallel to one another. The meandering structure is particularly suitable for spring rings and advantageously enables an increase in the surface area and thus better pressure distribution in the spring ring compared to rings made of the same material without a meandering structure. Depending on their size, the gaps between the parallel strands can be referred to as microslots or macroslots. The width of the gaps can be between 40 and 500 pm. The gaps between the parallel strands can also be referred to as slits.

[0016] Alternatively or in addition to the meandering structure, the first support element preferably has recesses in the material. For example, the recesses can be arranged in the region of the inner edge of the first support element. Alternatively or additionally, the first support element can also have depressions in the surface. The recesses and depressions also advantageously enable an increase in the surface area and thus a better pressure distribution in the first support element, for example, the spring ring, compared to support elements made of the same material.

[0017] In particular, the first support element is formed in one piece. Furthermore, the first support element consists in particular of one material. In particular, it comprises only one material from which it is provided in one piece.

[0018] Preferably, at least one second support element permeable to the working fluid is arranged on the side of the first support element facing away from the diaphragm. The second support element, which can also be referred to as the second holding element, additionally stabilizes the first support element, so that the stability of the diaphragm is advantageously ensured even at high pressures. The second support element preferably has the function of a valve that closes under pressure. Preferably, the second support element is an annular element, more preferably an O-ring. The O-ring in particular comprises an elastic material so that the O-ring can be stretched, for example like rubber, around or against the material of the combination electrode. The elastic material is preferably a low-reaction polymer. Examples of suitable elastic materials are natural or synthetic elastomers, rubbers such as ethylene propylene diene rubber (EPDM) or fluororubber (FKM).or silicone. The second support element is permeable to the working fluid. As with the first support element, the permeability can be controlled by material properties of the second support element itself, e.g., porosity, or by the arrangement of, for example, through-holes or recesses. Furthermore, the second support element can be designed such that fluid passes along the sides of the second support element. Under pressure, the diaphragm and the first support element press against the second support element, whose permeability is then prevented, as with the first support element.

[0019] The hydrogel is preferably cross-linked by exposure to radiation. The hydrogel is particularly preferably cross-linked by exposure to beta radiation. Beta radiation, or ß-radiation, is ionizing radiation that occurs during radioactive decay, known as beta decay or beta transition. The atomic nucleus of a beta emitter is converted into the atomic nucleus of another chemical element. Upon such irradiation, polymer strands in the hydrogel are cross-linked (cross-linked) by the effect of the radiation energy. This results in direct cross-linking of the polymer strands as well as polymer strand breaks and the attachment of the corresponding bridges to one another, resulting in cross-linking of the polymer strands.

[0020] The hydrogel preferably has a degree of crosslinking in the range of 20 to 100%, more preferably from 35 to 90%, and particularly preferably from 50 to 80%. With a degree of crosslinking of less than 20%, the desired melt resistance of the hydrogel may be too low at the temperatures prevailing during autoclaving. With an excessively high degree of crosslinking, the hydrogel may become brittle, which may result in the desired sealing of the first volume by the diaphragm being lost. The degree of crosslinking can be controlled by the amount of energy applied. The hydrogel particularly preferably has a degree of crosslinking of 60 to 70%. The degree of crosslinking of the hydrogel can be determined by gel content measurements. The hydrogel is particularly preferably crosslinked by exposure to beta radiation with an energy dose of 100 kGy to 200 kGy, for example with an energy dose of 100 kGy, 150 kGy, or 200 kGy.With these energy doses, a degree of cross-linking of the hydrogel in the range of 50 to 80% can be achieved when the hydrogel is irradiated in a dry state.

[0021] Beta radiation is particularly suitable for crosslinking hydrogels because sufficient energy for crosslinking can be introduced into the hydrogel within a comparatively short period of time (a few seconds for up to 50 kGy compared to several hours with gamma radiation). Furthermore, reactions are more likely to be initiated with the electrically charged particles (e.g., electrons in the case of beta-minus radiation), whereas gamma radiation is more likely to lead to oxidative degradation of the hydrogel due to the long irradiation time required. Furthermore, the hydrogel to be crosslinked heats up significantly less with beta radiation than with gamma radiation. Typically, several irradiations are performed to deliver a specific energy dose to prevent the hydrogel from overheating (e.g., five irradiation units of 20 kGy each for 100 kGy).

[0022] The hydrogel preferably comprises a thermoplastic polyurethane. In particular, the hydrogel consists essentially of the thermoplastic polyurethane. The thermoplastic polyurethane is in particular a block copolymer comprising a monomer A and a monomer B:

[0023] B

[0024] The monomer is in each case formed by the region extending from the left bracket to the right bracket. In the block copolymer, an oxygen atom can be attached to the left side of monomer A, or a hydroxyl group can be attached there to terminate the block copolymer. A carbon atom can be attached to the right side of monomer A, or a hydrogen atom can be attached there to terminate the block copolymer. An oxygen atom can be attached to the left side of monomer B, or a hydroxyl group can be attached there to terminate the block copolymer. A carbon atom can be attached to the right side of monomer B, or a hydrogen atom can be attached there to terminate the block copolymer. The block copolymer can essentially consist of blocks of monomer A and blocks of monomer B, and end groups to terminate the block copolymer.The end groups can be the aforementioned hydroxyl groups and / or the aforementioned hydrogen atoms.

[0025] In particular, the mass ratio of monomer B to monomer A is from 20 to 100, in particular from 30 to 90.

[0026] In particular, the number average molar mass M of the block copolymer is 50*10 3 g / mol to 180*10 3 g / mol, especially 80*10 3 g / mol up to 150*10 3 g / mol. The number-average molar mass M is:

[0027] —

[0028] M = where n is the number of polymer chains in the block copolymer and Mi is the molar mass of the polymer chain / . The block copolymer is commercially available under the brand name Tecophilic® from Lubrizol. Examples include Tecophilic® TG-500 and / or Tecophilic® TG-2000. The mass ratio of monomer B to monomer A is approximately 40 for Tecophilic® TG-500 and approximately 82 for Tecophilic® TG-2000. The number-average molar mass M of the block copolymer is approximately 1.4*10 5 g / mol and for Tecophilic® TG-2000 approximately 8*10 4 g / mol.

[0029] To produce a hydrogel, the block copolymer, which is provided, for example, as granules, is dissolved in a solvent, poured into a mold, and the solvent is evaporated. The solvent is preferably chloroform.

[0030] The hydrogel is irradiated after its production. The hydrogel is preferably irradiated in a swollen (wet) state. Irradiation of the hydrogel in a dry state is also possible, but is less effective than in a swollen state, resulting in a lower degree of crosslinking. Irradiation of the hydrogel in a dry state is easier to handle.

[0031] The hydrogel is preferably prepared from Tecophilic® TG-500 using chloroform as the solvent and is approximately 0.5 mm thick. The hydrogel is then irradiated, preferably in a dry state, with beta radiation at an energy dose of 150 kGy to crosslink.

[0032] The hydrogel can alternatively or additionally contain another thermoplastic polymer. The polymer must swell well in water to form a hydrogel upon swelling.

[0033] The hydrogel can, for example, also comprise a polymer used in soft contact lenses. Examples include hydroxyethyl methacrylate, methyl methacrylate, vinylpyrrolidone, and / or silicone hydrogels. The hydrogel can be a thermoplastic elastomer. The hydrogel can be a smart hydrogel. In particular, the smart hydrogel can be ion-responsive and / or thermoresponsive. An example of a smart hydrogel that is both ion-responsive and thermoresponsive is the aforementioned Tecophilic®. Another example of a smart hydrogel that is thermoresponsive is a polymer based on N-isopropylacrylamide copolymers.

[0034] Specifically, the hydrogel is a thermoplastic elastomer. Unlike other elastomers, this thermoplastic elastomer can be extruded into a film, and the diaphragm can then be punched out of the film. Unlike conventional thermoplastics, this thermoplastic elastomer retains its elastic properties at room temperature. An example of a thermoplastic elastomer is a block copolymer.

[0035] In particular, the hydrogel is a smart hydrogel, i.e., a stimuli-responsive hydrogel. Smart hydrogels are characterized by the fact that they react to specific environmental conditions with pronounced volume changes. It is particularly advantageous for the smart hydrogel to be ion-strength-responsive and / or thermoresponsive. If the smart hydrogel is ion-strength-responsive, the lower the salt concentration or conductivity of the working fluid, the more the smart hydrogel swells. An example of such an ion-strength-responsive smart hydrogel is the aforementioned block copolymer. The low salt concentration in the working fluid results in more ions being able to diffuse from the first electrically conductive fluid into the working fluid via the now more swollen diaphragm, resulting in a decreasing diffusion potential between the first electrically conductive fluid and the working fluid and thus higher measurement accuracy.The combination electrode with the ionic strength-responsive smart hydrogel is therefore suitable for measuring ultrapure water. If the smart hydrogel is thermoresponsive, it can be designed to shrink with increasing temperature. An example of such a thermoresponsive smart hydrogel is the aforementioned block copolymer. The shrinkage of the smart hydrogel makes it less prone to contamination and reduces the outflow of ions from the first electrically conductive fluid, thus extending the lifetime of the combination electrode even at elevated temperatures. Another example of a thermoresponsive smart hydrogel is a polymer based on N-isopropylacrylamide copolymers.

[0036] Particularly preferably, in the combination electrode according to the invention, the first volume is a reference space formed between an outer tube and an inner tube and the second volume is an inner tube space enclosed by the inner tube, and in which the inner tube has a first longitudinal end which is closed and has a glass membrane which is electrically conductively connected to the working electrode arranged at a second longitudinal end of the inner tube by means of the second electrically conductive fluid, and in which the outer tube has a first longitudinal end at which the diaphragm is arranged, which is electrically conductively connected to the reference electrode arranged at a second longitudinal end of the outer tube by means of the first electrically conductive fluid.

[0037] The outer tube is also referred to as the outer tube, and the inner tube is also referred to as the inner tube. This also applies to compound words.

[0038] The diaphragm thus seals an opening of the reference chamber towards the working fluid, which opening is formed as an annular gap between the outer and inner tubes. The opening can be sealed particularly tightly with the diaphragm by first introducing the hydrogel into the opening in its dry state. After contact with the first electrically conductive fluid, the hydrogel swells and thus seals the opening. The hydrogel can be easily formed into a ring, for example by cutting and / or punching. The first support element is preferably an element that at least partially encloses the inner tube. As a result, the first support element can particularly well stabilize the diaphragm, which seals the annular gap between the outer and inner tubes. Annular designs of the first support element are particularly suitable because they can advantageously close tightly around the inner tube.Preferably, the first support element is a ring that is clamped around the inner tube. Alternatively, the ring can be clamped outward, i.e., against the outer tube. The ring is preferably a spring ring.

[0039] The second support element is also preferably an element that at least partially encloses the inner tube. As a result, the second support element can additionally stabilize the diaphragm and the first support element particularly well. Ring-shaped designs of the second support element are particularly suitable because they can advantageously close tightly around the inner tube. Preferably, the second support element is a ring that is stretched around the inner tube. The ring can, for example, comprise an elastic material and be stretched around the inner tube like a rubber band. Alternatively, the ring can be stretched outwards, i.e., against the outer tube. The ring is preferably an O-ring.

[0040] The first longitudinal end of the outer tube is preferably substantially flush with the first or second support element.

[0041] The combination electrode is preferably a pH combination electrode and / or a redox sensor. The pH combination electrode is particularly preferably a pH glass electrode.

[0042] The first electrically conductive fluid can be an aqueous KCl solution, for example an aqueous 3 M KCl solution. Alternatively, the first electrically conductive fluid can be a highly viscous liquid. For example, the aqueous KCl solution, in particular the aqueous 3 M KCl solution, can be thickened with a thickener, in particular hydroxyethylcellulose. The hydroxyethylcellulose is commercially available, for example, under the trade name Natrosol. Alternatively, the first electrically conductive fluid can be highly solidified. For this purpose, a monomer mixture is introduced into the combination electrode and polymerized there to form a polymer. The polymer can, for example, be a polymer obtained by polymerizing N-acryloylaminoethoxyethanol or by copolymerizing N-acryloylaminoethoxyethanol with a hydroxyalkyl methacrylate, as described, for example, in WO 2005 / 073704 A1.

[0043] The thickness of the diaphragm is preferably from 0.1 mm to 1.0 mm, in particular from 0.35 mm to 0.7 mm. It has been found that with these thicknesses, the outflow of KCl is low, but the charge exchange between the first electrically conductive fluid and the working fluid is so high that error-free measurements can be performed with the combination electrode.

[0044] A second aspect of the invention relates to a method for producing a combination measuring chain, comprising the steps:

[0045] - Providing an outer tube and an inner tube which is arranged within the outer tube, wherein a first volume referred to as a reference space is formed between the outer tube and the inner tube and the outer tube and / or the inner tube define an opening,

[0046] - arranging a working electrode and a second electrically conductive fluid in a second volume defined by the inner tube and a reference electrode within the outer tube,

[0047] - introducing a cross-linked hydrogel in a dry state into the opening, whereby the reference space is delimited by the cross-linked hydrogel,

[0048] - introducing a first electrically conductive fluid into the reference space and thereby contacting the hydrogel with the first electrically conductive fluid, whereby the hydrogel swells, thus forming a diaphragm and sealing the opening, and contacting the reference electrode with the first electrically conductive fluid, so that the diaphragm is electrically conductively connected to the reference electrode via the first electrically conductive fluid,

[0049] - Arranging at least one first support element permeable to a working fluid on the side of the diaphragm facing away from the first volume on the inner tube.

[0050] The advantages of the method correspond to the advantages of the combination electrode according to the invention. Particularly advantageously, the opening can be sealed simply and particularly tightly using the method according to the invention. Compared to conventional combination electrodes whose diaphragms do not contain hydrogel, the combination electrode produced by the method has a long service life, during which the combination electrode can perform error-free measurements. Furthermore, unlike conventional combination electrodes whose diaphragms do not contain cross-linked hydrogel and which do not have a first support element, the combination electrode produced by the method is suitable for sterilization by autoclaving. This property gives the combination electrode an even longer service life.The arrangement of the working electrode within the inner tube and the reference electrode within the outer tube can be done both before and after the introduction of the hydrogel.

[0051] The cross-linked hydrogel is introduced into the opening, preferably in a dry state. In this way, the reference chamber of the fully assembled combination electrode can be filled in a vacuum from below, i.e., from the first longitudinal end of the outer tube. It is also possible to introduce the cross-linked hydrogel into the opening in a swollen or slightly swollen state. However, the reference chamber must then be filled from above, i.e., from the second longitudinal end of the outer tube, and only then can the combination electrode be fully assembled. In the process, the cross-linked hydrogel is preferably treated with beta radiation before insertion. Advantageously, a larger amount of the hydrogel can be irradiated in this way and then cut to size for insertion into individual diaphragms. According to the description of the hydrogel, the process preferably includes irradiating the hydrogel with beta radiation at a specific energy dose.

[0052] It is also preferable to add a crosslinking accelerator to the hydrogel prior to treatment with beta radiation. When using the crosslinking accelerator, a lower energy dose is sufficient to achieve the desired degree of crosslinking of the hydrogel. Due to the lower energy dose, fewer polymer strand breaks occur in the hydrogel, thus counteracting potential degradation of the hydrogel during exposure to beta radiation. The crosslinking accelerator can be, for example, triallyl isocyanurate (TAIC). The crosslinking accelerator can, for example, be dissolved in a solvent together with a suitable polymer before the solution is poured into a mold and the solvent evaporates.

[0053] Preferably, in the method according to the invention, an annular element, more preferably a spring ring, is provided as the first support element.

[0054] In the method according to the invention, at least one second support element permeable to the working fluid is preferably additionally arranged on the inner tube on the side of the diaphragm facing away from the first volume. Particularly preferably, an annular element, more preferably an O-ring, is provided as the second support element.

[0055] The invention is explained in more detail with reference to the figures.

[0056] Figure 1 is a schematic representation of a longitudinal section through a combination measuring chain according to an embodiment of the invention with a spring ring. Figure 2 is a detailed representation of a spring ring with

[0057] recesses.

[0058] Figure 3 shows a detailed representation of a spring ring with a partially meander-shaped structure.

[0059] Figure 4 shows a section of the combination measuring chain according to Fig. 1 according to a further embodiment of the invention with a spring ring and an O-ring.

[0060] Figure 5 is a flow diagram of an embodiment of the process according to the invention.

[0061] A combination electrode 1 as shown in Fig. 1 comprises a working electrode 2, a reference electrode 3, a diaphragm 10, and a first electrically conductive fluid 6 for measuring a working fluid. The first electrically conductive fluid 6 is in fluidic contact with the reference electrode 3 and the diaphragm 10, so that the diaphragm 10 is electrically conductively connected to the reference electrode 3 via the first electrically conductive fluid 6.

[0062] Combination electrode 1 can be a pH combination electrode and / or a redox sensor. The pH combination electrode can be a pH glass electrode.

[0063] The combination electrode 1 has an outer tube 4 and an inner tube 5 arranged within the outer tube 4. The outer tube 4 is referred to here as the outer tube, and the inner tube 5 is referred to here as the inner tube.

[0064] The volume between the two tubes is designed as a reference space 20, in which the first electrically conductive fluid 6 is arranged. The outer tube 4 has a first outer tube longitudinal end 15 and a second outer tube longitudinal end 16. A first inner tube longitudinal end 17 is arranged in the region of the first outer tube longitudinal end 15. A second inner tube longitudinal end 18 is arranged in the region of the second outer tube longitudinal end 16.

[0065] An inner tube space 19 is formed in the inner tube 5, in which a second electrically conductive fluid 7 is arranged. Furthermore, the inner tube 5 according to Fig. 1 has a storage vessel 8 at its first longitudinal end 17, the volume of which is fluidly connected to the inner tube space 19 and has a larger diameter than the inner tube 5, so that a larger quantity of the second electrically conductive fluid 7 can be provided.

[0066] The combination electrode 1 has an opening of the reference chamber 20 in the form of an annular gap in the region of the first outer tube longitudinal end 15 and the first inner tube longitudinal end 17. The diaphragm 10 is arranged in the opening and seals the opening. The thickness of the diaphragm 10 is specified in relation to the extent between the first inner tube longitudinal end 17 and the second inner tube longitudinal end 18. The thickness of the diaphragm 10 can be from 0.1 mm to 1.0 mm, in particular from 0.35 mm to 0.7 mm. A liquid channel 11 can be provided from the diaphragm, which leads to the first outer tube longitudinal end 15 (Fig. 4).

[0067] The diaphragm 10 is characterized in that it prevents mixing of the first electrically conductive fluid 6 and the working fluid, but enables charge transport between the first electrically conductive fluid 6 and the working fluid. In order to perform a measurement during operation of the combination electrode 1, the side of the diaphragm 10 facing away from the first electrically conductive fluid 6 must be contacted with the working fluid. Furthermore, the combination electrode 1 has a glass membrane 9 in the region of the first longitudinal end 17 of the inner tube. The glass membrane 9 is electrically connected to the working electrode 2 via the second electrically conductive fluid 7. The first electrically conductive fluid 6 and the second electrically conductive fluid 7 are electrically insulated from one another.To measure the working fluid, the working fluid is also contacted with the side of the glass membrane 9 facing away from the second electrically conductive fluid 7 and an electrical voltage is measured between the working electrode 2 and the reference electrode 3.

[0068] According to the invention, the diaphragm 10 comprises a cross-linked hydrogel. The diaphragm 10 can also consist essentially of the cross-linked hydrogel.

[0069] The hydrogel may comprise a thermoplastic polyurethane. The thermoplastic polyurethane may be a block copolymer comprising a monomer A The monomer is in each case formed by the region extending from the left bracket to the right bracket. In the block copolymer, an oxygen atom can be attached to the left side of monomer A, or a hydroxyl group can be attached there to terminate the block copolymer. A carbon atom can be attached to the right side of monomer A, or a hydrogen atom can be attached there to terminate the block copolymer. An oxygen atom can be attached to the left side of monomer B, or a hydroxyl group can be attached there to terminate the block copolymer. A carbon atom can be attached to the right side of monomer B, or a hydrogen atom can be attached there to terminate the block copolymer. The block copolymer can essentially consist of blocks of monomer A and blocks of monomer B, and end groups to terminate the block copolymer.The end groups can be the aforementioned hydroxyl groups and / or the aforementioned hydrogen atoms.

[0070] The mass ratio of monomer B to monomer A can be from 20 to 100, in particular from 30 to 90.

[0071] The number average molar mass M of the block copolymer can be from 50*10 3 g / mol to 180*10 3 g / mol, especially 80*10 3 g / mol up to 150*10 3 g / mol. The number average molar mass M is: M = where n is the number of polymer chains of the block copolymer and Mi is the molar mass of the polymer chain / .

[0072] The block copolymer is commercially available under the brand name Tecophilic® from Lubrizol. Examples include Tecophilic® TG-500 and / or Tecophilic® TG-2000. The mass ratio of monomer B to monomer A is approximately 40 for Tecophilic® TG-500 and approximately 82 for Tecophilic® TG-2000. The number-average molar mass M of the block copolymer is approximately 1.4*10 for Tecophilic® TG-500. 5 g / mol and for Tecophilic® TG-2000 approximately 8*10 4 g / mol.

[0073] The hydrogel can, for example, also comprise a polymer used in soft contact lenses. Examples include hydroxyethyl methacrylate, vinylpyrrolidone, and / or silicone hydrogels. The hydrogel can be a thermoplastic elastomer. The hydrogel can be a smart hydrogel. In particular, the smart hydrogel can be ionically responsive and / or thermoresponsive. If the smart hydrogel is thermoresponsive, it can be designed to swell and / or shrink more at higher temperatures. There can be a transition temperature at which the hydrogel changes its behavior between swelling and shrinking. An example of a smart hydrogel that is both ionically responsive and thermoresponsive is the aforementioned Tecophilic®. Another example of a thermoresponsive smart hydrogel is a polymer based on N-isopropylacrylamide copolymers.

[0074] The polymers in the hydrogel are cross-linked by irradiation with beta rays. The degree of cross-linking of the hydrogel can be 20 to 100%, in particular 50 to 80%, and more preferably 60 to 70%. The cross-linked hydrogel exhibits increased temperature resistance compared to conventional, non-cross-linked hydrogels. In particular, the cross-linked hydrogel is stable at temperatures up to 140°C.

[0075] The hydrogel is made of Tecophilic® TG-500 and has a thickness of approximately 0.5 mm. The hydrogel was irradiated in a dry state with beta radiation at an energy dose of 150 kGy to crosslink.

[0076] As further shown in Fig. 1, a spring ring 30 is arranged as the first support element in the area on the side of the diaphragm 10 facing away from the reference space 20. As an alternative to the spring ring 30, a sintered ring can also be arranged. The spring ring 30 is mechanically held by a step in the corresponding area of ​​the first outer tube longitudinal end 15. The spring ring is made of spring steel, stainless steel or polymers such as polyetheretherketone (PEEK), polysulfone (PSU), polyphenylene sulfone (PPSU) or glass fiber reinforced polymers, e.g. glass fiber reinforced polyamides. The spring ring 30 has an outer edge (outer edge) 31 and an inner edge (inner edge) 32. In the embodiment shown in Fig. 2, recesses 34 in the form of bulges, also referred to as slots, are arranged in the spring ring 30, starting from the inner edge 32.The slots can be selected to be larger or smaller in terms of their size and spacing, and can then be referred to as macroslots (Fig. 2A) or microslots (Fig. 2B). Furthermore, the slots can be designed in various shapes, e.g., elongated (Fig. 2A) or rounded (Fig. 2B), but are not limited to these.

[0077] In one embodiment, the first outer tube longitudinal end 15 is arranged substantially flush with the spring ring 30.

[0078] In the embodiment shown in Fig. 3, the material of the spring ring 30 is formed in a meandering shape. The material is arranged in a strand form with constant changes in direction, so that a section of the material is arranged parallel to its adjacent, connected sections, and overall forms a ring shape. In the embodiment according to Fig. 3, the spring ring is completely formed with a meandering structure 33. In alternative embodiments, the spring ring can also be formed only partially in a meandering shape, e.g., in the region of the inner edge 32, and with a compact structure in the region of the outer edge 31.

[0079] In a further embodiment according to Fig. 4, the combination electrode has an O-ring 40 as a second support element, which is arranged in the area on the side of the spring ring 30 facing away from the diaphragm 10. The O-ring 40 has, in particular, an elastic material as its material. In particular, the O-ring consists essentially of the elastic material. Examples of suitable elastic materials are natural or synthetic elastomers, rubbers such as ethylene propylene diene rubber (EPDM) or fluororubber (FKM), or silicone. The O-ring 40 is designed as a static spring, which is arranged to stabilize the spring ring 30 and thus also to stabilize the hydrogel against increased pressure. As can be seen from Fig. 1, the combination electrode 1 can have a seal 21, which is introduced into the inner tube 5 and seals the inner tube space 19.The second electrically conductive fluid 7 is thus arranged between the first inner tube longitudinal end 17 and the seal 21. The seal 21 can be an adhesive, in particular a silicone adhesive.

[0080] In addition, the combination electrode 1 can have a seal 14 arranged in the annular gap between the outer tube 4 and the inner tube 5 in the region of a second outer tube longitudinal end 16, which is arranged remote from the first outer tube longitudinal end 15, and seals the reference chamber 20. Thus, the first electrically conductive fluid 6 is arranged between the diaphragm 10 and the seal 14.

[0081] As can be seen from Fig. 1, the combination electrode 1 can have a head part 12 that surrounds the outer tube 4 at its second longitudinal end 16. Furthermore, the head part 12 protrudes from the second outer tube longitudinal end 16. The head part 12 has a cavity inside it that is filled with a sealing compound 13. The sealing compound 13 can provide an additional seal in addition to the seal 14 and the seal 21. The sealing compound 13 can be a silicone adhesive.

[0082] In a method for producing a combination measuring chain 1 according to Fig. 5, an outer tube 4 and an inner tube 5 are provided in a first step S1, wherein the inner tube 5 is arranged in the outer tube 4. The first volume delimited by the tubes forms a reference space 20 having an opening.

[0083] In a second step S2, a second electrically conductive fluid 7 is arranged in the second volume delimited by the inner tube, also referred to as the inner tube space 19, and a working electrode 2 is arranged at the second inner tube longitudinal end 18. A reference electrode 3 is arranged in the reference space 20 within the outer tube 4 at the second outer tube longitudinal end 16. In a third step S3, a hydrogel treated with beta radiation and thus cross-linked is introduced into the opening in a dry state. The reference space 20 is thus delimited by the cross-linked hydrogel. The irradiation of the hydrogel is carried out in a separate device provided for this purpose in a manner clear to a person skilled in the art. The hydrogel is cross-linked by exposure to beta radiation with an energy dose of 100 kGy to 200 kGy. In one embodiment of the method, a cross-linking accelerator is added to the hydrogel before irradiation with beta radiation.Triallyl isocyanurate (TAIC) is used as a cross-linking accelerator. TAIC is used at a concentration of 1 to 3% and allows the desired degree of cross-linking of the hydrogel to be achieved at lower energy doses. The cross-linking accelerator is added to the hydrogel by dissolving it together with the hydrogel polymer in a solvent before the solution is poured into a mold and the solvent is allowed to evaporate. Alternatively, the cross-linking accelerator can be added to the hydrogel after casting.

[0084] Before being introduced into the opening, the hydrogel is cut into an appropriate shape adapted to the dimensions of the combination measuring chain 1. When the hydrogel is introduced into the opening in its dry state, the hydrogel can be smaller than the opening, and after the first electrically conductive fluid 6 is introduced into the reference chamber 20, the formed diaphragm 10 can be subject to compressive stress. To achieve the compressive stress, the person skilled in the art can, in a preliminary test, contact hydrogels of different sizes, which are in their dry state and smaller than the opening, with the first electrically conductive fluid 6 and allow them to swell. After swelling, the size of the hydrogels in their swollen state is determined, and only those of the different sized hydrogels that are larger than the opening in their swollen state are considered for the diaphragm 10.Hydrogels of various sizes can be selected that, in their swollen state, are from 10% to 100% larger than the opening, in particular from 30% to 50% larger than the opening. The degree of swelling Q of the hydrogel can be from 115% to 1000%, in particular from 150% to 800%, in particular from 180% to 350%. The degree of swelling Q is defined as Q = (VQ-VT)ZVT, where VT is the volume of the hydrogel in its dry state and VQ is the volume of the hydrogel in its state swollen with the first electrically conductive fluid 6.

[0085] In a fourth step S4, a first electrically conductive fluid 6 is introduced into the reference chamber 20. This brings the hydrogel into contact with the first electrically conductive fluid 6, causing it to swell and thus form a diaphragm 10 and seal the opening. In the process, the reference electrode 3 is also brought into contact with the first electrically conductive fluid 6, so that the diaphragm 10 is electrically conductively connected to the reference electrode 3 via the first electrically conductive fluid 6. To introduce the first electrically conductive fluid 6 into the reference chamber 20, the first outer tube longitudinal end 15 is immersed in the first electrically conductive fluid 6, the combination electrode 1 is placed into a vacuum container together with the first electrically conductive fluid 6, and the vacuum container is evacuated and then vented, so that the first electrically conductive fluid 6 enters the reference chamber 20 via the opening.The sealing of the second outer tube longitudinal end 16 can be achieved by means of the sealing ring 14 and / or by means of the head part 12 and the sealing compound 13. The vacuum container can be evacuated to a pressure of 50 mbar to 100 mbar, in particular 80 mbar.

[0086] In a fifth step, a spring ring 30 is arranged as the first support element on the side of the diaphragm 10 facing away from the reference chamber 20, on the outside of the inner tube 5. Optionally, in a further step, an O-ring 40 can be arranged as the second support element on the side of the spring ring 30 facing away from the diaphragm 10, on the outside of the inner tube 5. List of reference symbols

[0087] 1 combination electrode

[0088] 2 working electrode

[0089] 3 Reference electrode

[0090] 4 outer tube

[0091] 5 inner tube

[0092] 6 first electrically conductive fluid

[0093] 7 second electrically conductive fluid

[0094] 8 storage container

[0095] 9 Glass membrane

[0096] 10 Diaphragm

[0097] 11 Fluid channel

[0098] 12 headboard

[0099] 13 Casting compound

[0100] 14 Seal

[0101] 15 first outer pipe longitudinal end

[0102] 16 second outer tube longitudinal end

[0103] 17 first inner tube longitudinal end

[0104] 18 second inner tube longitudinal end

[0105] 19 Inner tube space

[0106] 20 Reference room

[0107] 21 Seal

[0108] 30 spring ring

[0109] 31 Outer edge of the spring ring

[0110] 32 Inner edge of the spring ring

[0111] 33 meandering structure

[0112] 34 recess

[0113] 40 O-ring

Claims

Patent claims 1. Single-rod measuring chain (1) for measuring a working fluid, comprising a reference electrode (3) arranged in a first volume comprising a first electrically conductive fluid (6) and a working electrode (2) arranged in a second volume comprising a second electrically conductive fluid (7), wherein the first volume is bounded at least by a diaphragm (10) comprising a cross-linked hydrogel, and wherein at least a first support element permeable to the working fluid is arranged on the side of the diaphragm (10) facing away from the first volume.

2. Single-rod measuring chain (1 ) according to claim 1, wherein the first support element is an annular element, preferably a spring ring (30).

3. Single-rod measuring chain (1) according to claim 1 or 2, wherein the first The support element has a meandering structure (33).

4. Single-rod measuring chain (1) according to one of the preceding claims, wherein the first support element consists of a material and has recesses (34) in the material.

5. Single-rod measuring chain (1 ) according to one of the preceding claims, in which at least a second support element permeable to the working fluid is arranged on the side of the first support element facing away from the diaphragm (10).

6. Single-rod measuring chain (1 ) according to claim 5, wherein the second support element is an annular element, preferably an O-ring (40).

7. Single-rod measuring chain (1) according to one of the preceding claims, wherein the Hydrogel is cross-linked by the action of radiation.

8. Single-rod measuring chain (1) according to claim 7, wherein the hydrogel is formed by The effects of beta radiation are interconnected.

9. Single-rod measuring chain (1) according to one of the preceding claims, wherein the hydrogel has a degree of cross-linking in the range of 20 - 100%.

10. Single-rod measuring chain (1) according to one of the preceding claims, wherein the Hydrogel is a thermoplastic polyurethane.

11. Single-rod measuring chain (1) according to one of the preceding claims, wherein the first volume is a reference space (20) formed between an outer tube (4) and an inner tube (5), and the second volume is an inner tube space (19) enclosed by the inner tube (5), and wherein the inner tube (5) has a first longitudinal end (17) which is closed and has a glass membrane (9) which is electrically conductively connected by means of the second electrically conductive fluid (7) to the working electrode (2) arranged at a second longitudinal end (18) of the inner tube (5), and wherein the outer tube (4) has a first longitudinal end (15) at which the diaphragm (10) is arranged, which is electrically conductively connected by means of the first electrically conductive fluid (6) to the reference electrode (3) arranged at a second longitudinal end (16) of the outer tube (4).

12. Method for manufacturing a single-rod measuring chain (1 ), comprising the steps: - Providing an outer tube (4) and an inner tube (5) arranged inside the outer tube (4), wherein a first volume referred to as a reference space (20) is formed between the outer tube (4) and the inner tube (5), and the outer tube (4) and / or the inner tube (5) define an opening, - Arranging a working electrode (2) and a second electrically conductive fluid (7) in a second volume bounded by the inner tube (5) and a reference electrode (3) inside the outer tube (4), - Introducing a cross-linked hydrogel into the opening, thereby limiting the reference space (20) to the cross-linked hydrogel, - Introducing a first electrically conductive fluid (6) into the reference chamber (20) and thereby contacting the hydrogel with the first electrically conductive fluid (6), causing the hydrogel to swell, thus forming a diaphragm (10) and sealing the opening, as well as contacting the reference electrode (3) with the first electrically conductive fluid (6), so that the diaphragm (10) is electrically connected to the reference electrode (3) via the first electrically conductive fluid (6), - Arranging at least one first support element permeable to a working fluid on the side of the diaphragm (10) facing away from the first volume on the inner tube (5).

13. The method of claim 12, wherein the hydrogel is treated with beta radiation before being introduced.

14. The method of claim 13, wherein a crosslinking accelerator is added to the hydrogel prior to treatment with beta radiation.

15. Method according to one of claims 12-14, wherein first A spring ring (30) is provided as a support element.

16. Method according to one of claims 12 - 15, wherein at least one additional support element permeable to the working fluid is arranged on the side of the diaphragm (10) facing away from the first volume on the inner tube (5).

17. Method according to claim 16, wherein the second support element is an O-ring. (40) is provided.

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