JP2018194467A - pH sensor - Google Patents

Abstract

To provide a pH sensor that can avoid risks of breakage of glass of an action electrode without making the entire structure more complicated and can measure the pH of a solution electrically stably.SOLUTION: A pH sensor 100 includes: an action electrode 111 made of a conductive solid material; a reference electrode 120; and a voltage meter 130 for measuring the difference in the voltage between the action electrode 111 and the reference electrode 120, the action electrode 111 being electrically connected to the ground.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pH sensor, and more particularly to a non-glass pH meter (glassless pH meter).

  In recent years, as a means for managing the fermentation state of a fermented product, research and development of an ion sensor that enables detection of the concentration of specific ions contained in the raw material of the fermented product has been actively conducted. Patent Document 1 discloses a method for producing a fermented product, which includes a step of taking out a fermented product in a fermentation process and analyzing it using a sensor provided outside the fermentation tank. This production method is characterized in that foreign substances derived from the sensor are prevented from being mixed into the fermented product. Patent Document 2 discloses a glass electrode in which a glass responsive film is bonded to the tip of a glass support tube for the purpose of lead-free.

On the other hand, Patent Documents 3 to 5 disclose sensors that detect the concentration of specific ions in a liquid to be measured. The sensor of Patent Document 3 is a differential pH meter having a standard pH meter and a pNa glass electrode (comparative electrode), and can calculate the Na ⁺ concentration from the amount of change in pH.

  The sensor (ion sensor) of Patent Document 4 is composed of two MOS-type FETs for a working electrode and one reference-electrode FET, and is characterized by an all-solid type having no internal liquid. .

  The sensor (ion sensor) of Patent Document 5 is configured such that a detection target is sandwiched between two p-channel field effect transistors, one field effect transistor functions as a working electrode, and the other field effect transistor. Functions as a reference electrode. A diamond thin film is provided on each channel surface for the purpose of stabilizing the potential.

JP 2011-024530 A JP 2005-49190 A JP2012-233818A Japanese Patent Laid-Open No. 06-288971 JP 2012-168120 A JP 2007-089511 A

  In the method for producing a fermented product disclosed in Patent Document 1, it is necessary to provide a sensing container outside the fermentation tank, which complicates the structure of the production apparatus and its control. Moreover, the measured pH value is outside the fermentation tank and may be deviated from the actual pH value of the fermented material in the fermentation tank.

  In the sensor disclosed in Patent Document 3, both the working electrode and the reference electrode are glass electrodes, and have a configuration (liquid-containing type) in which an internal liquid is contained in a glass container. Such a glass electrode and the glass electrode disclosed in Patent Document 2 emphasize the contamination risk, for example, because glass fragments and internal liquid diffuse into the liquid to be measured when the glass container is damaged. It is difficult to use as it is for measurement of raw materials, intermediate products, products, etc. in the production process of food.

  The ion sensor disclosed in Patent Documents 4 and 5 has a structure of a field effect transistor in both the working electrode and the reference electrode, and each has three factors (gate voltage, drain source voltage, drain source current). Control is required, and the configuration and driving method of the control circuit are complicated. In particular, in the ion sensor of Patent Document 4, since alkali-free glass is used as the material of the ion sensitive film, it is difficult to use it as it is for measurement of a liquid to be measured such as a food production process.

  The present invention has been made in view of the above circumstances, without complicating the overall configuration, avoiding the risk of glass breakage of the working electrode, it is possible to stably measure the pH of the solution, An object is to provide a pH sensor.

An ion sensor of the present invention includes a working electrode made of a solid material having conductivity, a reference electrode, and a voltmeter that measures a potential difference between the working electrode and the reference electrode, wherein the working electrode is electrically It is characterized by being grounded.
In the ion sensor of the present invention, the solid material may be a material containing carbon.
In the ion sensor of the present invention, the solid material may be boron-doped diamond.
In the ion sensor of the present invention, the solid material may be an ion selective electrode material.
In the ion sensor of the present invention, a resistor may be connected to the working electrode via a voltage source.
In the ion sensor of the present invention, a field effect transistor element may be connected to the working electrode via a voltage source.
Moreover, the ion sensor of this invention WHEREIN: The said solid material may comprise the container which accommodates to-be-measured object.

  In the pH sensor of the present invention, since the working electrode is electrically grounded, even if the solid electrode material (solid material) constituting the working electrode is directly immersed in the liquid to be measured, the potential of the surface is not affected. Problems that fluctuate due to the influence of the measurement liquid can be avoided. Therefore, the working electrode of the present invention does not need to cover the electrode material with a glass container as in the conventional method (liquid-containing type), and can be constituted only by the electrode material. Since the fluctuation of the surface potential of the electrode material is suppressed by grounding, the potential difference between the reference electrode and the working electrode according to the pH value of the liquid to be measured can be accurately obtained, and the pH value of the liquid to be measured corresponding to this potential difference Can be obtained with high accuracy.

  According to the pH sensor of the present invention, it is possible to avoid the problem of contamination of the liquid to be measured due to the constituent material of the working electrode of the conventional system, that is, the problem that broken glass or internal liquid diffuses into the liquid to be measured. Therefore, the pH sensor of the present invention can be used as it is for the measurement of pH in a liquid to be measured in an environment where a glass material cannot be used or an environment severe to diffusion contamination of an internal liquid, for example, a food production process. Is possible.

  In addition, the pH sensor of the present invention has a specific shape and laminated structure because the working electrode is composed only of a conductive solid material and the electrode potential can be easily controlled. There is no need to be. Therefore, the configuration of the pH sensor of the present invention is greatly simplified as compared to the case where a field effect transistor controlled by three factors is made to function as a working electrode, as in a conventional ion sensor.

It is a figure which shows the schematic structure and usage pattern about the pH sensor which concerns on 1st embodiment of this invention. It is a figure which shows the schematic structure and usage pattern about the pH sensor which concerns on 2nd embodiment of this invention. It is a figure which shows the schematic structure and usage pattern about the pH sensor which concerns on 3rd embodiment of this invention. It is a figure which shows the schematic structure and usage pattern about the pH sensor which concerns on 4th embodiment of this invention. It is the schematic of the structure of the washing | cleaning liquid collection | recovery system which concerns on the example of application of this invention. It is a graph which shows the measurement result of pH of a to-be-measured liquid by the pH sensor of the Example of this invention. It is a figure which shows the schematic structure and usage pattern about the pH sensor of a prior art. It is a graph which shows the measurement result of pH of a to-be-measured liquid by the pH sensor of the comparative example of this invention.

  Hereinafter, a pH sensor according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent. In addition, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately changed and implemented without changing the gist thereof.

<First embodiment>
FIG. 1 is a diagram illustrating a schematic configuration and a usage pattern of a pH sensor (pH meter) 100 according to the first embodiment. The pH sensor 100 includes a working electrode 111 made of a solid material having conductivity, a reference electrode 120, and a voltmeter 130 that measures a potential difference between the working electrode 111 and the reference electrode 120. In FIG. 1, as a usage form of the pH sensor 100, a form in which the working electrode 111 and the reference electrode 120 of the pH sensor are immersed in the liquid L to be measured contained in the container V is shown.

Examples of the solid material constituting the working electrode 110 include metals such as platinum, silver, iron, stainless steel, and gold, carbon-based materials (materials including carbon) such as graphite, graphene, carbon nanotubes, and boron-doped diamond, and ion selection. Electrode material can be used.
In the present embodiment, the shape of the solid material is not particularly limited.

  The reference electrode 120 is made of a cylindrical member and includes a predetermined electrode material as the internal electrode 121 and includes KCl as the internal liquid 122 (liquid-containing type). The electrode material used as the reference electrode 120 is required to have low reactivity with respect to the components contained in the liquid L to be measured, that is, chemical stability, and is stable at high temperature, low temperature, high pressure, and low pressure. Environmental resistance is required, and further, physical adsorption and chemical adsorption on the surface are difficult to occur.

Electrode materials that can be used as the working electrode 111 include solid film type ions, liquid film type ions, and diaphragm type ions. Examples of solid membrane ions include chloride ion Cl ⁻ , bromine ion Br ⁻ , iodine ion I ⁻ , cyanide ion CN ⁻ , cadmium ion Cd ²⁺ , copper ion Cu ²⁺ , silver ion Ag ⁺ , and sulfide ion S. ²⁻ , fluoride ion F ^{− and the} like. Examples of liquid film type ions include calcium ion Ca ²⁺ , potassium ion K ⁺ , and nitrate ion NO ³⁻ . Examples of the diaphragm type ion include ammonium ion NH ^{4+ and the} like.

  The working electrode 111 is electrically grounded and its potential is fixed. Therefore, it is possible to suppress the surface potential of the electrode member constituting the working electrode 110 from irregularly changing due to a change in the state between the electrode and the liquid due to impurities or the like. On the other hand, since the electrode member constituting the reference electrode is covered with a container made of a solid material, irregular fluctuation components due to changes in the state of the electrode and the liquid due to impurities or the like with respect to the surface potential of the electrode member. There is no influence, and only a potential fluctuation according to the pH of the liquid to be measured is added as a volume component. Therefore, the potential difference between the working electrode 111 and the reference electrode 120 measured by the voltmeter 130 does not include the influence of irregular fluctuation components due to changes in the state of the electrode and the liquid, and the pH of the liquid L to be measured is accurately determined. It will be reflected.

  In the pH sensor according to this embodiment, since the working electrode is electrically grounded, even if the solid electrode material (solid material) constituting the working electrode is directly immersed in the liquid to be measured, the surface potential is The problem of fluctuating due to the influence of the liquid to be measured can be avoided. Therefore, the working electrode of the present embodiment does not need to cover the electrode material with a glass container as in the conventional method (liquid-containing type), and can be configured with only the electrode material. Since the fluctuation of the surface potential of the electrode material is suppressed by grounding, the potential difference between the reference electrode and the working electrode according to the pH value of the liquid to be measured can be accurately obtained, and the pH value of the liquid to be measured corresponding to this potential difference Can be obtained with high accuracy.

  According to the pH sensor of the present embodiment, it is possible to avoid the problem of contamination of the liquid to be measured due to the constituent material of the working electrode of the conventional method, that is, the problem of broken glass or internal liquid diffusing into the liquid to be measured. . For this reason, the pH sensor of the present embodiment is used as it is for the measurement of pH in a liquid to be measured in an environment where a glass material cannot be used or an environment severe to diffusion contamination of an internal liquid, for example, a food manufacturing process. Is possible.

  In addition, the pH sensor of the present embodiment has a specific shape and laminated structure because the working electrode is composed only of a conductive solid material and the electrode potential can be easily controlled. There is no need to be. Therefore, the configuration of the pH sensor of the present embodiment is greatly simplified as compared with a case where a field effect transistor controlled by three factors is made to function as a working electrode, as in a conventional ion sensor.

<Second embodiment>
FIG. 2 is a diagram illustrating a schematic configuration and a usage pattern of the pH sensor 200 according to the second embodiment. In the pH sensor 200, a voltage source 240 and a resistor 250 are sequentially connected (connected) to a working electrode 211. About the structure of the other part of the pH sensor 200, it is the same as that of the structure of the pH sensor 100 which concerns on 1st embodiment, The effect similar to the pH sensor 100 can be acquired also in the pH sensor 200.

  Further, in the pH sensor 200, the resistor 250 is connected to the grounded working electrode 211 via the voltage source 240, so that a portion not related to the liquid is included as a current path. Since the influence of the change can be suppressed small, the stability of the potential of the working electrode 211 is further improved.

<Third embodiment>
FIG. 3 is a diagram illustrating a schematic configuration and a usage pattern of the pH sensor 300 according to the third embodiment. In the pH sensor 300, a field effect transistor element (FET) 340 is connected (connected) to a working electrode 311. Specifically, a source electrode 343 and a drain electrode 344 constituting the field effect transistor element 340 are connected between the working electrode 311 and the drive circuit 330 through voltage sources 350 and 360, respectively. About the structure of the other part of pH sensor 300, it is the same as that of the structure of pH sensor 100 which concerns on 1st embodiment, The effect similar to pH sensor 100 can be acquired also in pH sensor 300.

  Furthermore, in the pH sensor 300, the field effect transistor element 340 is connected to the grounded working electrode 311 through a voltage source, so that the state can be stabilized by flowing Igs. Since it is possible to measure ions other than hydrogen ions by using the function as an FET, the stability of the potential of the working electrode 311 is further improved.

  As the field effect transistor element 340, for example, an ion sensitive field effect transistor (ISFET) can be used. Examples of the ion-sensitive field effect transistor include a silicon type (Si-ISFET) and a diamond type (diamond ISFET).

<Fourth embodiment>
FIG. 4 is a diagram illustrating a schematic configuration and a usage pattern of the pH sensor 400 according to the fourth embodiment. In the pH sensor 400, a solid material that functions as a grounded working electrode 410 constitutes a container (working electrode 410) that stores the liquid L to be measured. The device under test M and the reference electrode 420 are accommodated in this container. About the structure of the other part of the pH sensor 400, it is the same as that of the structure of the pH sensor 100 which concerns on 1st embodiment, and the effect similar to the pH sensor 100 can be acquired also in the pH sensor 400.

  In FIG. 4, the form in the case of using the container which functions as the working electrode 410 as a fermentation tank T for accommodating and fermenting fermented material (measuring object M) is shown as one application example of this embodiment. . A thermometer 440 is disposed at a desired position in a grounded container together with a fermented product to be measured M and a reference electrode 420. As the voltmeter 430 that measures the potential difference between the working electrode 410 and the reference electrode 420, a source measure unit (SMU) is used here.

  For example, as disclosed in Patent Document 6, since there is a correlation between the pH of the fermented food and the progress of fermentation, the fermented product M is accommodated in the fermentation tank T, and the pH is adjusted using the pH sensor of the invention. By measuring, the progress of the fermentation process can be managed.

  Although it does not specifically limit as fermented food used as the object of a measurement, For example, yogurt, sake, soy sauce, miso, etc. are mentioned. As an example, the case where the pH sensor of the present invention is used in the yogurt manufacturing process will be described.

  First, yogurt production raw material liquids such as milk, skim (powdered) milk, and fresh cream are accommodated in the fermentation tank T, and the pH sensor of the present invention is installed at one or a plurality of locations in the tank T. Subsequently, a lactic acid bacteria starter for yogurt fermentation is added and fermented at a fermentation temperature suitable for the lactic acid bacteria used. As the lactic acid fermentation proceeds, the pH value of the raw material liquid decreases, and it can be determined that the fermentation process has been completed when it reaches a predetermined value indicating acidity.

  Note that, as in the second and third embodiments, a resistor and a field effect transistor may be connected to the working electrode 410, that is, the fermentation tank T.

(Application example: CIP cleaning system)
In the production line for foods, beverages and medicines, the tanks and piping used for the production are cleaned and sterilized every time the production is completed. The chemicals used for cleaning and sterilization are collected for cost reduction through reuse. In a CIP (Clean-in-Place) system (cleaning liquid recovery system) that performs recovery of such cleaning liquid, a sensor is required for identification in replacement of cleaning agent and cleaning water. Normally, a conductivity meter is used as this sensor, but the amount of change in conductivity differs for each cleaning liquid (CIP cleaning liquid), and the identification of the cleaning liquid with a small amount of change in conductivity can be made using Difficult to do based on value.

  The pH sensor according to the above embodiment uses a grounded working electrode to suppress fluctuations in the surface potential of the solid material constituting the working electrode, and measures pH corresponding to the potential difference between the working electrode and the reference electrode with high accuracy. can do. Therefore, the pH sensor according to the above embodiment is effective in identifying a cleaning liquid having a small change in conductivity, and can be used as a sensor suitable for the CIP system.

  The CIP system when using the pH sensor according to the above embodiment will be described. FIG. 5 is a schematic diagram of a configuration of a CIP process using a pH sensor. The configuration of the CIP system shown in FIG. 5 is an example, and differs depending on the manufacturing process of products such as foods, beverages, and medicines, as well as the cleaning agent (medicine) used.

A cleaning sequence by the CIP system of FIG. 5 will be described. First, the inside of the tank and the piping is washed with washing water such as fresh water (4 to 20 ° C., 1 MPa or less). Next, the inside of the tank and the piping is washed with an alkaline solution (for example, 1.5% NaOH, 20 to 30% sodium hypochlorite, 10 to 30% sodium hydroxide, 80 to 90 ° C., 1 MPa or less). Next, the inside of the tank and the piping is washed with an acid solution (for example, 1.5% HNO ₃ , 80 to 90 ° C., 1 MPa or less).

  Next, the cleaning agent remaining inside the tank and piping is washed away with cleaning water such as fresh water (4 to 20 ° C., 1 MPa or less). At this time, the cleaning agent is recovered, but since the recovered cleaning agent is gradually diluted by adding cleaning water, its concentration is monitored by the pH value. When the pH value reaches the reference value, recovery of the cleaning agent is stopped, and the rest is discharged to the drainage line.

  Similarly, a cycle of cleaning with different types of cleaning liquid, cleaning with fresh water, and recovery / release of the cleaning liquid is repeated. (There may be only one cycle.) In the last step, sterilization with steam (130 to 140 ° C., 1 MPa or less), washing with distilled water or deionized water may be performed. In this case, the inside of the tank and the pipe is further dried at 20 ° C. and 1 MPa, and washed with washing water such as fresh water (4 to 20 ° C., 1 MPa or less).

  Hereinafter, the effects of the present invention will be made clearer by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.

Example 1
Using the pH sensor according to the first embodiment of the present invention, potential measurements were performed on four carbody wide-range buffer (pH buffer) samples prepared to have pH 2, pH 4, pH 7, and pH 10.

  The pH sensor used was a boron-doped diamond electrode (BDD electrode) with the working electrode grounded and a silver / silver chloride electrode (Ag / AgCl electrode) as the reference electrode. The potential measurement was performed by immersing the working electrode and the reference electrode in each of the four pH buffer solution samples (measuring solutions).

  FIG. 6 is a graph showing the results of potential measurement. The horizontal axis of the graph indicates the pH of the measured pH buffer solution, and the vertical axis of the graph indicates the potential [V] of the working electrode with respect to the reference electrode measured for each sample. From this graph, it can be seen that the measured potential has a linear response with high accuracy to the pH of the sample.

  Therefore, by using the pH sensor of the present invention, a potential difference between the reference electrode and the working electrode corresponding to the pH value of the liquid to be measured can be accurately obtained, and the pH value of the liquid to be measured corresponding to this potential difference can be obtained with high accuracy. I understand that it is required.

  The reason why high-accuracy linear response is obtained is that irregular fluctuations in the surface potential of the solid material due to the influence of the sample are suppressed because the solid material constituting the working electrode is grounded. Conceivable.

(Comparative Example 1)
FIG. 7 is a diagram showing a schematic configuration and a usage pattern of a conventional pH sensor 500. In the pH sensor 500, the working electrode 510 is not electrically grounded. The working electrode 510 is a container made of a conductive solid material, and includes Ag / AgCl as the internal electrode 511 and the internal liquid 512. The configuration of other parts of the pH sensor 500 is the same as the configuration of the pH sensor according to the first embodiment.

  Using the pH sensor 500 of the prior art shown in FIG. 7, four carbody wide-range buffer solutions (pH buffer solutions) prepared to have pH 2, pH 4, pH 7, and pH 10 as in Example 1, Potential measurement was performed.

  FIG. 8 is a graph showing the results of potential measurement. The horizontal and vertical axes of the graph are the same as in FIG. From this graph, it can be seen that the measured potential has a linear response to the pH of the sample. However, in the measurement results of a plurality of times, each plot varies greatly with respect to the approximate straight line, and it can be seen that the linear response is not obtained with the same accuracy as in the first embodiment.

  Therefore, when a conventional pH sensor is used, the potential difference between the reference electrode and the working electrode corresponding to the pH value of the liquid to be measured cannot be obtained accurately, and the pH value of the liquid to be measured corresponding to this potential difference is not obtained. It can be seen that it is not required with high accuracy.

  The reason why high-accuracy linear response cannot be obtained is that the solid material that constitutes the working electrode is not grounded, and therefore irregular fluctuations in the surface potential of the solid material due to the influence of the sample are not suppressed. it is conceivable that.

100, 200, 300, 400, 500 ... pH sensors 111, 211, 311, 410, 510 ... Working electrodes 120, 220, 320, 420, 520 ... Reference electrodes 121, 221, 321, 421, 521 ... Glass containers 122, 222, 322, 522 ... Internal electrodes 123, 223, 323, 523 ... Internal liquids 130, 230, 330, 430, 530 ... Voltmeter 240 ... Power supply 250 ... Resistor 340 ... Field effect transistor element 341 ... Substrate 341a ... One main surface 341A of the substrate ... Source region 341B ... Drain region 341C ... Channel region 342 ... Gate oxide film 343 ... Field oxide film 344 ... Source electrode 345 ... Drain electrode 347 ... Protective film 350, 360 · The voltage source 440 ... side temperature 511 ... internal electrode 512 ... internal liquid L ... test solution M ... fermented V ... container

Claims (7)

A working electrode made of a solid material having conductivity;
A reference pole;
A voltmeter for measuring a potential difference between the working electrode and the reference electrode,
The pH sensor, wherein the working electrode is electrically grounded.   The pH sensor according to claim 1, wherein the solid material is a material containing carbon.   The pH sensor according to claim 1, wherein the solid material is boron-doped diamond.   The pH sensor according to claim 1, wherein the solid material is an ion-selective electrode material.   The pH sensor according to any one of claims 1 to 4, wherein a resistor is connected to the working electrode via a voltage source.   The pH sensor according to claim 1, wherein a field effect transistor element is connected to the working electrode via a voltage source.   The pH sensor according to any one of claims 1 to 6, wherein the solid material constitutes a container for accommodating an object to be measured.

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