阅读说明：本技术 用于清洁、调节、校准和/或调整电流传感器的方法 (Method for cleaning, adjusting, calibrating and/or adjusting a current sensor ) 是由 K·科伯特 H·舍普夫 T·温克勒 于 2019-05-31 设计创作，主要内容包括：为了提供一种用于清洁、调节、校准和/或调整包含电解质的测量设备的电流传感器以供确定电解质中的内容物质的方法(该电流传感器具有由选择性可渗透膜密封的测量腔室,其中布置有工作电极和与该工作电极电连接的参考电极,其中该膜对待确定的内容物质而言是可渗透的,其中在测量区间期间对内容物质的确定通过以下操作而发生：在工作电极和参考电极之间施加电压,测量流经工作电极和参考电极之间的电连接的电流并从测得的电流中推导出该内容物质),描述了一种方法,其特征在于,调节剂在测量设备中生成,其中在工作电极处还原的氧化剂或在工作电极处氧化的还原剂被用作调节剂。(In order to provide a method for cleaning, regulating, calibrating and/or adjusting a current sensor of a measuring device containing an electrolyte for determining a content substance in the electrolyte, the current sensor having a measuring chamber sealed by a selectively permeable membrane, in which a working electrode and a reference electrode electrically connected to the working electrode are arranged, wherein the membrane is permeable to the content substance to be determined, wherein the determination of the content substance takes place during a measuring interval by applying a voltage between the working electrode and the reference electrode, measuring a current flowing through the electrical connection between the working electrode and the reference electrode and deriving the content substance from the measured current, a method is described, characterized in that a conditioning agent is generated in the measuring device, wherein an oxidizing agent reduced at the working electrode or a reducing agent oxidized at the working electrode is used as conditioning agent.)

1. A method for cleaning, conditioning, calibrating and/or adjusting a current sensor of a measuring device for determining a content substance in a sample, wherein the measuring device comprises an electrolyte and the current sensor, the current sensor having a measuring chamber sealed by a selectively permeable membrane, wherein a working electrode and a working reference electrode electrically connected to the working electrode are arranged, and wherein the determination of the content substance during a measurement interval takes place by: applying a voltage between the working electrode and the working reference electrode, measuring a current flowing through the electrical connection between the working electrode and the working reference electrode and deriving the content substance from the measured current, characterized in that the method comprises the steps of:

■ generating a modulating agent at the working electrode and/or generator electrode disposed in the measurement device, wherein the modulating agent is an oxidizing agent or a reducing agent,

■ oxidizing the mediator at the working electrode if the mediator is a reducing agent or reducing the mediator at the working electrode if the mediator is an oxidizing agent.

2. The method of claim 1, wherein the generator electrode is disposed in the measurement chamber, the modulating agent being generated at the generator electrode.

3. the method of claim 1 or 2, wherein the generator electrode generates the modulating agent during the measurement interval.

4. Method according to claim 1 or 2, wherein the conditioning agent is generated during a conditioning interval, wherein the conditioning agent is preferably fed or generated during a plurality of conditioning intervals, wherein the conditioning interval is shorter than the interval between two consecutive conditioning intervals.

5. The method of claims 1 to 4, wherein the modulator is generated continuously.

6. Method according to one of claims 1 to 5, characterized in that a predetermined amount of regulator is generated.

7. Method according to one of claims 1 to 5, characterized in that the content substance to be determined is used as a conditioning agent.

8. Method according to one of the preceding claims 1 to 7, characterized in that a detection electrolyte is used as electrolyte, which electrolyte contains a component that is reduced or oxidized to a detection component by the content substance to be determined, wherein the detection component is preferably used as a conditioning agent.

9. Method according to one of claims 1 to 8, characterized in that the content substance to be determined is an oxidizing agent, such as oxidizing halogen compounds of chlorine, bromine and iodine, chloramines and bromamines, Cl₂、Br₂、O₃、ClO₂Peracetic acid, H₂O₂Chlorite or hypochlorite or the corresponding acid, preferably hypochlorous acid (HOCl).

10. Method according to one of claims 1 to 9, characterized in that an iodide solution is used as electrolyte, wherein iodine is preferably used as regulator.

11. Method according to one of claims 1 to 10, characterized in that an adjustment value is derived from the current values measured during the measurement interval, wherein a zero value is determined in the following manner: during an adjustment interval in which the content substance to be determined is not present, a voltage is applied between the working electrode and the working reference electrode, and a current flowing through the electrical connection between the working electrode and the working reference electrode is measured.

12. Method for calibrating and/or adjusting a measuring device according to one of claims 1 to 11, characterized in that the conditioning agent corresponds to the content substance in the sample to be determined and a defined quantity of conditioning agent is generated in the measuring chamber by electrolysis or a defined quantity of conditioning agent is generated in a part of the measuring device by electrolysis and fed to the measuring chamber, a voltage is applied between the working electrode and the working reference electrode and the current flowing through the electrical connection of the working electrode and the working reference electrode is measured.

13. Method according to one of claims 1 to 12, characterized in that the conditioning agent is generated in the measurement chamber by a generator electrode, wherein the generator electrode is operated as anode in case the working electrode is used as cathode and as cathode in case the working electrode is used as anode.

14. A current sensor for carrying out the method as defined in the preceding claims, wherein the sensor comprises at least one working electrode arranged in a measurement chamber arranged to hold an electrolyte, a working reference electrode and a selectively permeable membrane bounding the measurement chamber, characterized in that a generator electrode and a generator reference electrode are arranged in the measurement chamber, wherein a control device is provided with which a measurement voltage can be applied between the working electrode and the working reference electrode and with which a generator voltage can be applied between the generator electrode and the generator reference electrode, the level of the generator voltage being different from or equal to the level of the measurement voltage.

15. The current sensor of claim 14, wherein the working electrode has at least one cylindrical portion and the generator electrode has a hollow cylindrical portion, wherein the working electrode is arranged in the following manner: the cylindrical portion of the working electrode is disposed within the hollow cylindrical portion of the generator electrode.

16. The current sensor of claim 14 or 15, wherein the selectively permeable membrane has an effective surface less than or equal to a surface of the working electrode facing the membrane.

17. A measuring device for carrying out the method as defined in the preceding claims, wherein the device has at least one current sensor and a control device, characterized in that the measuring device has at least one generator electrode arranged in the measuring device.

18. Measuring device according to claim 17, characterized in that the measuring device has a current sensor according to one of claims 14 to 16.

19. Use of a conditioning agent produced according to the method of claims 1 to 13 for cleaning, conditioning, calibrating and/or adjusting a current sensor of a measuring device for determining a content substance in a sample.

Technical Field

The invention relates to a method for cleaning, conditioning, calibrating and/or adjusting a current sensor of a measuring device containing an electrolyte for determining a content substance in a sample, the current sensor having a measuring chamber which is sealed by a selectively permeable membrane, wherein a working electrode and a working reference electrode which is electrically connected to the working electrode are arranged, wherein the membrane is permeable to the content substance to be determined. The determination of the content quality during the measurement interval takes place by: a voltage is applied between the working electrode and the working reference electrode, a current flowing through the electrical connection between the working electrode and the working reference electrode is measured and the content substance is derived from the measured current. The invention also relates to a current sensor, a measuring device, and the use of a conditioning agent for carrying out the method according to the invention.

background

The results of electrochemical measurement methods for determining the content substance in a sample often depend to a large extent on the active electrode surface of the sensor. However, operation leads to deposits and variations on the electrodes over time, which reduces the effective electrode surface and thus adversely affects the results of the measurement method. This results in practice in a great deal of effort being spent on cleaning and adjustment and the risk of uncertain and incorrect measured values.

For this reason, it is necessary to clean the electrodes at regular intervals. Different methods of doing so are known from the prior art.

firstly, there is the possibility of mechanical cleaning, for example by grinding with sand, corundum or similar hard materials. However, this method is laborious and costly and in most cases results in unreliable measured values in the measuring device for contaminated samples. The device also needs to be disassembled at least for replacing the abrasive material.

Another possibility involves electrolytic degreasing. In this case, an alkaline detergent is added to the electrolyte and the electrodes are alternately polarized. The cleaning effect of the alkaline solution is enhanced by the generation of gas on the electrode surface. However, this method has hitherto only been used to a very limited extent, because of the fear of negatively influencing the polarization capability of the electrodes during the measurement by adding a base.

Another possibility for cleaning is disclosed in patent specifications CH 672845 a5 and EP 1452858B 1. In these patent specifications, a method is described in which, in a cleaning section separate from the measurement operation, a voltage of alternating polarity is applied to the working electrode and the return electrode so that both the reducing gas and the oxidizing gas are alternately formed at the working electrode and the return electrode. As a result, impurities are separated from the electrodes and the effective electrode surface is exposed. However, the use of this method in a film-covered sensor is precluded due to the gases released during the cleaning operation.

In addition, in all the above-mentioned methods, it is first necessary to adjust the active electrode surface after the cleaning operation, i.e. the surface that can be measured must be formed by establishing an equilibrium, so that an almost constant blank value and a consistent sensitivity of the measurement parameters necessary for a reliable measurement are established. The adjustment behavior depends on the concentration of the content substance to be determined in the sample. In the case of very low concentrations of the content substance, this conditioning phase can take hours to days.

Another problem arises which cannot be solved or only inadequately solved with the methods of the prior art if the concentration of the content substance to be measured is below the threshold characteristic of the sensor type and therefore a very low current flow or sometimes no current flow at all occurs between the working electrode and the respective reference electrode ("zero sensor"). Over time, this can result in changes in the effective electrode surface. In this case, the working electrode also needs to be readjusted until the active electrode surface is formed again and meaningful measurements can be obtained.

In a membrane-covered current sensor, the measurement chamber is partially bounded by a membrane that is selectively permeable to the content substance to be determined. The membrane is in direct contact with the sample to be measured. If the sensor is inactive for a longer period of time due to the absence of the content substance, deposits, especially organic deposits (such as biofilm), form on the membrane surface or within the pores of the membrane. This can affect the diffusion of analyte through the membrane to the working electrode and can subsequently affect the sensitivity of the sensor and the accuracy of the measurement. As a maintenance step that generates cost, it is necessary to periodically replace the membrane cover surrounding the membrane.

Commercially available measuring device W&T/Siemens Deox/Some of the above problems are solved by feeding the conditioning agent continuously from the outside into the measurement chamber, and subsequently switching the conditioning agent at the working electrode. This permanently holds the electrodes in a state that can be measured. Modulators I₂Generated by the redox reaction of KI with chloramine T in a reaction tube mounted before the measurement chamber. Aqueous I₂the solution is then introduced into the measurement chamber by means of a peristaltic pump. In order to determine the concentration of the content substance in the sample, a defined amount of the sample is mixed with I before it is fed into the measurement chamber₂The solutions were mixed. The concentration of iodine is increased or decreased by reaction of iodine with the oxidized or reduced content material in the sample. This also changes the measured value of the current sensor, from which the concentration of the content substance to be determined can be derived. However, this method not only requires the integration of the reaction tube in the measurement device, but also the storage of a corresponding amount of reactive and in some cases unstable chemicals (such as chloramine T) for continuous operation. These chemicals can decompose during storage into undesirable byproducts that contaminate the sensor. Furthermore, the regulators can only be changed in a complex manner, i.e. by replacing the stored chemical substances.

Disclosure of Invention

It is an object of the present invention to provide a method for cleaning, conditioning, calibrating and/or adjusting a film-covered current sensor of a measuring device for determining a content substance in a sample, which method exhibits comparable or even better cleaning and conditioning effects than methods known from the prior art, for which method a simpler equipment setup is sufficient, in particular in which no chemical substances need to be stored, and which method makes it possible to extend the service life of the film.

According to the invention, this object is achieved by a method of the above-mentioned type, characterized in that it comprises the following steps:

■, generating a modulating agent at a working electrode and/or a generator electrode disposed in the measurement device, wherein the modulating agent is an oxidizing agent or a reducing agent,

■ if the modulator is a reducing agent, the modulator is oxidized at the working electrode, or if the modulator is an oxidizing agent, the modulator is reduced at the working electrode.

By electrochemical switching of the conditioning agent, the working electrode is cleaned and kept in a measurable state with an effective electrode surface, so that an almost constant blank value and a consistent sensitivity of the measurement parameters necessary for reliable measurement are established. If the working electrode is already in a measurable state, it is maintained in that state by electrochemical conversion of the modulator.

without being bound by theory, the inventors hypothesize that modulation of the working electrode occurs by removing deposits and depolarization.

According to the invention, the conditioning agent may be generated at a generator electrode arranged in the measurement device (preferably in the measurement chamber) and/or at a working electrode arranged in the measurement chamber. If the modulator is generated from a reducing agent or oxidizing agent contained in an electrolyte at a generator electrode arranged in the measuring device, the modulator is transported by diffusion and/or by a pump to a working electrode arranged in the measuring chamber and can be converted at the working electrode by applying the voltage required for the conversion. As a result, a regulating effect is achieved. The generation of the modulator may take place during a measurement interval or in a separate modulation interval. Preferably, the conditioning agent is converted back to the oxidizing or reducing agent contained in the electrolyte. Alternatively or additionally, the modulating agent may also be generated at the working electrode. In this case, the generation of the regulator can only take place in a single regulation interval, i.e. the measurement of the content substance must be suspended, and the regulator is generated from the reducing or oxidizing agent contained in the electrolyte by applying a corresponding voltage between the working electrode and the working reference electrode. The electrochemical redox reaction can then be reversed by a change in voltage, i.e. the mediator is no longer generated at the working electrode, but is switched. As a result, the conditioning effect starts. Preferably, the conditioning agent is converted back to the oxidizing or reducing agent contained in the electrolyte.

The method according to the invention also allows the further components of the current sensor, in particular the membrane and the further electrodes, to be free of impurities which influence the electrochemical reaction at the diffusion and working electrodes or which delay the deposition of impurities. This can be attributed to the oxidizing or reducing effect of the mediator, which can be dispersed in the electrolyte by diffusion.

A "measuring device" is a space-limited container that includes at least one current sensor and a control device. It may also contain one or more spatially limited modules for throughflow regulation, for measuring the pH value and a module with at least one generator electrode and one or more pumps. The current sensor may be connected to the further module (if provided) via one or more connections comprising an electrolyte. The content substance and/or the conditioning agent in the sample may be delivered to the measurement chamber via a pump. Simultaneously or alternatively, the content substance and/or the conditioning agent may reach the measurement chamber by diffusion. In this case, they diffuse through the membrane and switch within the measurement chamber at the working electrode.

The current sensor includes a measurement chamber containing an electrolyte and having disposed therein a working electrode and a working reference electrode electrically connected to the working electrode. In the context of the present invention, a "working electrode" is an electrode for determining a measurement value of a current sensor. The content substance in the sample to be determined is electrochemically oxidized or reduced at the electrode. For this purpose, during the measuring operation, a voltage is applied between the working electrode and a reference electrode electrically connected thereto, wherein the process is controlled using a suitable arrangement (e.g. potentiostat).

The determination of the content substance during the measurement interval is effected by: the current flowing through the electrical connection between the working electrode and the working reference electrode is measured and the content material is derived from the measured current.

in one embodiment, the current sensor further comprises a working return electrode also electrically connected to the working reference electrode, and a redox reaction occurs at the working return electrode to charge balance. The corresponding embodiment of the working electrode system is referred to as a three-electrode arrangement. In a preferred embodiment, the working reference electrode may also be simultaneously the working return electrode. This embodiment is referred to as a two-electrode arrangement.

In the context of the present invention, the term "electrolyte" covers ionically conductive media, in particular ionically conductive fluids, such as saline solutions or saline gels.

The measurement of the current sensor is the current intensity measured between the working electrode and the working reference electrode.

The "sample" whose content substance is to be determined is a fluid, preferably an ionically conductive fluid, such as water.

In one embodiment, the working electrode is composed of a noble metal, preferably platinum or gold, particularly preferably platinum. In another embodiment, the working electrode is composed of glassy carbon or other electrode materials known in the literature.

The "modifier" generated in the measurement device and reduced at the working electrode of the current sensor may be an oxidizing agent. In this context, an oxidizing agent means that a redox couple consisting of an oxidizing agent and a corresponding reducing agent has a redox potential such that the oxidizing agent is reduced to the corresponding reducing agent by a voltage applied to the working electrode, i.e. the voltage between the working electrode and the electrically connected working reference electrode is less than the standard redox potential of a redox couple consisting of an oxidizing agent and a corresponding reducing agent.

If the regulator is, for example, I₂The working electrode must pass against the working reference electrode under standard conditions<540mV because the standard redox potential of the redox couple is I₂/2I^-540 mV. If the voltage is below this limit, the iodine is reduced to iodide:

I₂+2e^-→2I^-

If not operating under standard conditions, the applied voltage must be adjusted accordingly, as known to those skilled in the art. In addition to this, known overvoltages for different electrode materials have to be taken into account. The regulator produced in the measuring device can also be a reducing agent. In this context, reducing agent means that a redox couple consisting of a reducing agent and a corresponding oxidizing agent has a redox potential such that the reducing agent is oxidized to the corresponding oxidizing agent by an applied voltage at the working electrode.

In a preferred embodiment of the invention, the modulator is generated at the generator electrode. In the context of the present invention, a "generator electrode" is an electrode for electrolytically generating one or more regulators in a measuring device. For this purpose, a voltage is applied between the generator electrode and a generator reference electrode connected thereto at such a level that the regulator is generated from the reducing or oxidizing agent contained in the electrolyte. For this purpose, the potential between the generator electrode and the generator reference electrode is controlled using a suitable arrangement (e.g. potentiostat). In one embodiment, the measurement device further comprises a generator return electrode also electrically connected to the generator reference electrode, and at which a redox reaction occurs for charge balancing. The corresponding embodiment of the generator electrode system is referred to as a three-electrode arrangement. In a preferred embodiment, the generator reference electrode may also be simultaneously the generator return electrode. This embodiment is referred to as a two-electrode arrangement. The working electrode arranged in the measurement chamber and the generator electrode arranged in the measurement device may have the same reference electrode. It is also preferred that the working electrode and the generator electrode have the same return electrode. The shared use of electrodes allows the number of electrodes in the measurement device to be reduced accordingly. For example, the total number of electrodes reaching 6 in the three-electrode arrangement of the working electrode system and the three-electrode arrangement of the generator electrode system may be reduced to 4 by sharing the use of the same reference and return electrodes.

In one embodiment, the generator electrode is composed of a noble metal, preferably platinum or gold, particularly preferably platinum. In another embodiment, the working electrode is comprised of glassy carbon.

In a further preferred embodiment, the generator electrode consists of titanium.

The generator electrode may for example generate I₂As a regulator. For this purpose, the electrolyte must contain the corresponding reducing agent (iodide) and the generator electrode must pass through the reference electrode with respect to the generator>540mV because the standard redox potential of the redox couple reaches I₂/2I^-540 mV. If this limit is exceeded, the iodide is oxidized to iodine:

2I^-→I₂+2e^-Generator electrode reaction

The generated modulator (iodine) then diffuses to the working electrode. If the working electrode is polarized by <540mV relative to the working reference electrode, the iodine is reduced again there to iodide, as a result of which a regulating effect occurs.

I₂+2e^-→2I^-Working electrode reaction

In order to be able to generate the modulator at the generator electrode or the working electrode, the electrolyte must contain a sufficient concentration of the reducing agent or oxidizing agent corresponding to the modulator from which the modulator is generated. This may be achieved, for example, by the electrolyte contained in the measuring device being a salt solution, for example a salt solution of a metal iodide salt.

The modulator may also be generated by: at the generator electrode, a reducing agent or oxidizing agent is generated, which can reduce or oxidize the oxidation/reduction agent contained in the electrolyte to the conditioning agent.

If the regulator is, for example, I₂The modifier can then also be generated in the measuring device by: the electrolyte contains iodide ions and an oxidant is generated in the measuring device at the generator electrode, which can oxidize the iodide to I₂。

If the oxidizing agent is, for example, Br₂Then it is taken from I under standard conditions^-In the presence of a reducing agent to obtain a regulator I₂：

As a result of the reaction, I is produced₂Which is reduced as described above by applying a corresponding voltage at the working electrode. The conditioning effect is achieved by a reaction at the working electrode.

Preferably, the modifier is an oxidant, especially preferably bromide, chloride, iodide, most preferably iodine.

The modifier or corresponding oxidation/reduction agent generated by the working electrode or by the generator electrode may pass through the pores or through the material of the membrane. The deposition of a species (especially organic deposits such as biofilm) on the surface or within the pores of a membrane can be retarded or reduced by oxidation or reduction of the species. In this way, the service life of the membrane can be significantly extended.

In one embodiment of the invention, the modulating agent is generated at the generator electrode during the measurement interval. In this case, the reference value produced at the working electrode by the fed or generated conditioning agent will be subtracted from the measured value of the current sensor.

this allows to ensure a continuous measuring operation, i.e. the electrode surface of the working electrode remains effective and no cleaning and/or conditioning phase is required.

In another embodiment of the invention, the conditioning agent is generated at the working electrode or the generator electrode in a separate cleaning and/or conditioning operation. Advantageously, the conditioning behavior of the electrode is dependent on the concentration of the conditioning agent. The conditioning phase can be shortened by generating correspondingly high concentrations of conditioning agent.

In another embodiment, the modulator is generated discontinuously (preferably in a pulsed manner), wherein the time interval during which the modulator is generated is much shorter than the time interval during which the modulator is not generated. If the modulating agent is generated at the generator electrode during the measuring operation, the reference value produced at the working electrode by the modulating agent will be subtracted from the measurement value of the sensor. Alternatively, the measurement is also suspended for a short time interval during which the modulator is generated.

In one embodiment of the invention, the modulator is produced continuously. If this continuous generation occurs at the generator electrode during the measurement interval, a defined, almost constant reference value is obtained at the working electrode by the conditioning agent, which reference value is to be subtracted from the measurement value of the working electrode. As a result of the continuous production of conditioning agent, a consistent cleaning and conditioning effect is achieved. This prevents impurities from being able to accumulate on and alter the structure of the electrode surface of the working electrode in a manner that renders the surface of the working electrode ineffective. Thus, the total amount of regulating agent generated at the generator electrodes can be kept low.

In a preferred embodiment, the predetermined amount of conditioning agent is generated in the measuring device.

In one embodiment of the invention, the generated modulating agent is a content substance in the sample as determined by the current sensor. This can advantageously be used for determining content substances in a sample having a concentration below the detection limit of the sensor, wherein no conditioning agent is fed into or generated in the measurement chamber.

The detection limit of the sensor is the value of the measurement method up to which the measured variable can still be reliably measured.

The measured values at the detection limits have increased inaccuracy, however without exceeding a predetermined statistical confidence interval. The measured values with greater inaccuracy than the predetermined interval are below the detection limit and are described as being unmeasurable or undetectable in terms of measurement technology.

The criteria for "reliable detection" are generally related to the accuracy of the measurement method in null measurements that produce a blank value. This means a statistical error or fluctuation (e.g., standard deviation from a blank value) of the measurement signal in the absence of a sample.

In the context of the present invention, a measurement is considered to be proof (valid) if it lies at least three standard deviations above the blank value.

In order to determine the content substance of the sample at a concentration below the detection limit of the measuring device, in which no regulator is generated in the measuring device, the content substance to be determined is generated in the measuring device at the generator electrode during the measurement or at the working electrode before the measurement. During the transition at the working electrode, a measured value is obtained as the sum of the reference value generated at the working electrode by the modulating agent and the value generated at the working electrode by the content substance in the sample. In this way, the obtained measurement value can be raised to a value above the detection limit. The content substance in the electrolyte may be determined by subtracting the reference value from the measured value.

In another embodiment of the invention, the modulating agent generated at the working electrode or the generator electrode is not a content substance determined by the current sensor. In another embodiment, several different oxidizing and/or reducing agents may be generated at the generator electrode or the working electrode. Advantageously, in the process according to the invention, the regulator can be changed very rapidly. If the electrolyte already contains different respective oxidizing or reducing agents, the change can be made effective by adapting the voltage at the working electrode or the generator electrode. The modifier may also be altered by: a corresponding oxidizing or reducing agent, which has not been contained therein, is added to the electrolyte, and the voltage at the working electrode or generator electrode is adjusted such that the corresponding oxidizing or reducing agent is converted into a modulator.

In one embodiment, a detection electrolyte is used as the electrolyte. The detection electrolyte contains a component that is reduced or oxidized to a detection component by the content substance in the sample to be determined. The detection component is oxidized or reduced at the working electrode, and the content substance to be determined is derived based on the measured current intensity. If, for example, an iodide salt solution is used as a measuring instrument for determining Cl in a sample₂The detection electrolyte of (2), the content substance (Cl) to be determined in the sample₂) I to be contained in a detection electrolyte^-Oxidized to the detection component I₂。

Detection ofComponent I₂It is possible to subsequently reduce it at the working electrode and to deduce the content substance Cl via the current intensity obtained as a measurement value₂。

In a preferred embodiment, a detector component is used as a modulator.

In a preferred embodiment, the content substance in the sample to be determined is an oxidant reduced at the working electrode, for example oxidizing halogen compounds (such as chlorine, bromine and iodine), chloramines and bromamines, Cl₂、Br₂、O₃、ClO₂Peracetic acid, H₂O₂Chlorite or hypochlorite or the corresponding acid, preferably hypochlorous acid (HOCl).

in a preferred embodiment, the electrolyte is an iodide salt solution and the conditioning agent is I₂。

In a preferred embodiment, the method according to the invention is used for monitoring the functionality of a sensor. For this purpose, a defined quantity of the content substance to be determined is generated at the generator electrode and a voltage is applied between the working electrode and the working reference electrode, and the current flowing through the electrical connection between the working electrode and the working reference electrode is measured and compared with a known value. In this way, any fault such as a sensor defect, a cable break or an error in the evaluation system can be detected.

In a preferred embodiment, an adjustment value is derived from the current values measured during the measurement interval, wherein the adjustment value is determined in the following manner: during an adjustment interval in which the content substance in the sample to be determined is not present in the electrolyte, a defined amount of the content substance to be determined is generated at the generator electrode and a voltage is applied between the working electrode and the working reference electrode and the current flowing through the electrical connection between the working electrode and the working reference electrode is measured.

In another preferred embodiment, the modulator in the measurement chamber is generated by a generator electrode. It is particularly advantageous to operate the generator electrode as an anode in the case of the working electrode being used as a cathode and as a cathode in the case of the working electrode being used as an anode.

The invention also comprises a current sensor for carrying out the method defined above, wherein the sensor comprises at least one working electrode arranged in a measurement chamber containing an electrolyte, a working reference electrode and a selectively permeable membrane bounding the measurement chamber, wherein a generator electrode and a generator reference electrode are arranged in the measurement chamber, and wherein a control device is provided with which a measurement voltage can be applied between the working electrode and the working reference electrode and with which a generator voltage can be applied between the generator electrode and the generator reference electrode.

In the method according to the invention, the direction of diffusion of the modulator derives from its concentration gradient. In one embodiment of the invention, the modulating agent is generated at a generator electrode arranged in the measuring device. The concentration of the modifier is higher at the generator electrode because the modifier is generated there from the corresponding oxidizing/reducing agent. Conversely, at the working electrode, the modulator is switched so that the concentration is generally lower there. In general, in the case of an arrangement of the generator electrodes outside the measurement chamber, the conditioning agent therefore flows into the measurement chamber and is converted there. However, if the generator electrodes are arranged within the measurement chamber, the concentration is typically lowest outside the measurement chamber. The modulating agent generated at the generator electrode flows out of the measurement chamber, where most passes through the permeable membrane and therefore cannot be used as a modulating agent. If the generator electrode is arranged in the measuring chamber, it is therefore advantageous to arrange the working electrode in the direction of diffusion of the conditioning agent in order to maximize the cleaning and conditioning effect of the conditioning agent. If the working electrode is arranged in this direction, the conditioning agent is oxidized or reduced there to the corresponding reducing or oxidizing agent before leaving the membrane and subsequently diffuses back to the generator electrode. Thus, a closed loop is formed, with the result that little oxidant or reductant can diffuse out of the membrane.

In one embodiment, to achieve such an arrangement of the working electrode and the generator electrode, the working electrode may have at least one cylindrical portion and the generator electrode may have a hollow cylindrical portion, wherein the working electrode is arranged in the following manner: the cylindrical portion of which is arranged within the hollow cylindrical portion of the generator electrode. Preferably, the working electrode is arranged within the hollow cylindrical part of the generator electrode in such a way that the two base surfaces of the working electrode and the generator electrode directed towards the selectively permeable membrane are flush with each other, or the base surface of the generator electrode is arranged at a greater distance from the selectively permeable membrane than the base surface of the working electrode. As a result, the regulator generated at the generator electrode is oxidized or reduced at the working electrode and diffuses to only a small extent through the membrane to the outside.

Preferably, the active surface (i.e., the permeable surface) of the selectively permeable membrane is less than or equal to the base surface of the working electrode facing the membrane. The result is that the flow direction of the conditioning agent generated at the generator electrode has a component directed radially inwards (i.e. towards the working electrode), so that the conditioning agent diffuses in this direction and is reduced or oxidized there.

In a particularly preferred variant of this embodiment, the working electrode is arranged in the direction of diffusion of the conditioning agent as follows:

The working electrode is cylindrical and the generator electrode is hollow-cylindrical, wherein the working electrode with the smaller diameter is arranged within the hollow cylinder of the generator electrode. On the side facing the membrane, the two cylindrical base surfaces are flush with one another. The selectively permeable portion of the membrane is smaller than the base surface of the cylinder of the working electrode and is arranged such that its projection on the base surface of the working electrode is at least 90% on the base surface of the working electrode. Preferably, the selectively permeable portion of the membrane is arranged concentrically with the base surface of the cylinder of the working electrode. Fig. 1 shows an apparatus suitable for performing such a preferred method.

The invention also comprises a measuring device for carrying out the method defined above, wherein the device has at least one current sensor and a control device, and at least one generator electrode arranged in the measuring device. With the control device, a measurement voltage can be applied between the working electrode and the working reference electrode, and a generator voltage can be applied between the generator electrode and the generator reference electrode, the level of which generator voltage can be different from or equal to the measurement voltage, but with their polarities reversed.

Drawings

The figures show a particular embodiment of the invention in which:

Fig. 1 shows a schematic representation of a particular embodiment of a measurement chamber according to the invention with a selectively permeable membrane and a generator electrode arranged therein.

Fig. 2 shows a schematic representation of a part of a special embodiment of a measurement chamber according to the invention with a selectively permeable membrane and a generator electrode arranged therein.

Fig. 3 shows a schematic representation of a particular embodiment of a measurement device according to the invention having a measurement chamber with a selectively permeable membrane and a generator electrode arranged physically close to the measurement chamber.

Fig. 4 shows a schematic representation of a particular embodiment of a measuring device according to the invention having a measuring chamber with a selectively permeable membrane and a separate module containing a generator electrode.

Detailed Description

Fig. 1 shows a schematic representation of a measurement chamber 6 of a current sensor according to the present invention having a selectively permeable membrane 1, a working electrode 2, a generator electrode 3 and associated reference or return electrodes 4 and 5. The working electrode 2 and the generator electrode 3 are cylindrical with different diameters, wherein the working electrode with the smaller diameter is formed within the hollow cylindrical generator electrode. The base surfaces of the working electrode and the generator electrode facing the selectively permeable membrane are flush with each other, wherein the projection of the effective surface of the membrane is located only on and smaller than the base surface of the working electrode.

Fig. 2 shows a cross-section of a representation of a particular embodiment of a current sensor according to the invention with a selectively permeable membrane 1, a working electrode 2 and generator electrodes 3, 3'. The working electrode is arranged at a closer distance to the active surface of the selectively permeable membrane than the generator electrode, and the active surface of the membrane is smaller than the surface of the working electrode directed towards the active surface. The two surfaces are also concentric. The cross section also shows the flow vector of the moderator formed at the generator electrodes. The working electrode is arranged in the diffusion direction of the modulating agent. This improves the cleaning and conditioning effect of the oxidizing or reducing agent.

Fig. 3 schematically shows a special embodiment of a measuring device according to the invention with a current sensor and an arrangement of generator electrodes 3, 3' outside the measuring chamber 6. The generator electrodes 3, 3' generating the modulator are arranged at a closer distance from the membrane. The modulator may diffuse through the selectively permeable membrane 1 and reach the working electrode where it is reduced to the corresponding reducing/oxidizing agent. The flow vector of the modulator formed at the generator electrode is also illustrated. For the sake of simplicity, the control device and the generator reference electrode are not included in the figure.

Fig. 4 schematically shows a special embodiment of a measuring device according to the invention with a current sensor and a module 8 in which the generator electrodes 3 are arranged. The conditioning agent generated at the generator electrode diffuses from the module 8 via the connection 7 towards the measurement chamber 6, passes through its selectively permeable membrane 1 and is reduced at the working electrode 2. The flow vector of the modulator formed at the generator electrode is also illustrated. For the sake of simplicity, the control device and the generator reference electrode are not included in the figure.

List of reference numerals

1 selectively permeable Membrane

2 working electrode

3, 3' generator electrode

4,5 reference or return electrode

6 measuring chamber

7 connection

8 Module with Generator electrodes