JP6881018B2 - pH sensor - Google Patents

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 controlling 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 carried out. Patent Document 1 discloses a method for producing a fermented product, which comprises a step of once taking out the fermented product in the fermentation process and analyzing it using a sensor provided outside the fermentation tank. This manufacturing method is characterized by preventing foreign substances derived from the sensor from being mixed into the fermented product. Patent Document 2 discloses a glass electrode in which a glass response film is bonded to the tip of a glass support tube for the purpose of making it lead-free.

On the other hand, sensors that detect the concentration of specific ions in the liquid to be measured are disclosed in Patent Documents 3 to 5. The sensor of Patent Document 3 is a differential pH meter having a standard pH meter and a pNa glass electrode (comparative electrode), and makes it possible to 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 working poles and one FET for reference poles, and is characterized in that it is an all-solid-state type having no internal liquid. ..

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

Japanese Unexamined Patent Publication No. 2011-024530 Japanese Unexamined Patent Publication No. 2005-49190 Japanese Unexamined Patent Publication No. 2012-233818 Japanese Unexamined Patent Publication No. 06-288971 Japanese Unexamined Patent Publication No. 2012-168120 JP-A-2007-089511

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

In the sensor disclosed in Patent Document 3, both the working electrode and the reference electrode are glass electrodes, and the internal liquid is contained in a glass container (liquid-containing type). In such a glass electrode and the glass electrode disclosed in Patent Document 2, when the glass container is damaged, glass fragments and internal liquid will diffuse into the liquid to be measured. Therefore, for example, the risk of contamination is emphasized. It is difficult to use it as it is for measuring raw materials, intermediate products, products, etc. in the food manufacturing process.

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

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

The ion sensor of the present invention includes a working electrode made of a conductive solid material, a reference electrode, and a voltmeter for measuring a potential difference between the working electrode and the reference electrode, and the working electrode is electrically provided. It is characterized by being grounded.
Further, in the ion sensor of the present invention, the solid material may be a material containing carbon.
Further, in the ion sensor of the present invention, the solid material may be boron-doped diamond.
Further, in the ion sensor of the present invention, the solid material may be an ion-selective electrode material.
Further, in the ion sensor of the present invention, a resistor may be connected to the working electrode via a voltage source.
Further, in the ion sensor of the present invention, a field effect transistor element may be connected to the working electrode via a voltage source.
Further, in the ion sensor of the present invention, the solid material may constitute a container for accommodating an object to be measured.

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 on the surface thereof is subject to measurement. It is possible to avoid the problem of fluctuating due to the influence of the measurement liquid. 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 composed of only the electrode material. By grounding and suppressing fluctuations in the surface potential of the electrode material, the 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. 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 by the constituent material of the working electrode of the conventional method, that is, the problem of broken glass and the internal liquid diffusing into the liquid to be measured. Therefore, the pH sensor of the present invention can be used as it is for measuring the pH in the liquid to be measured in an environment where a glass material cannot be used or in an environment where diffusion contamination of the internal liquid is severe, for example, in a food manufacturing process. It is possible.

Further, the pH sensor of the present invention has a specific shape and a laminated structure because the working electrode is composed of only a solid material having conductivity and the electrode potential thereof can be easily controlled. You don't have to be. Therefore, the pH sensor of the present invention has a significantly simplified configuration as compared with the case where a field effect transistor controlled by three factors functions as a working electrode as in a conventional ion sensor.

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

Hereinafter, the pH sensor according to the 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, the featured parts may be enlarged for convenience, and the dimensional ratios of each component may not be the same as the actual ones. Absent. Further, the materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

<First Embodiment>
FIG. 1 is a diagram showing a schematic configuration and a usage pattern of the pH sensor (pH meter) 100 according to the first embodiment. The pH sensor 100 includes a working pole 111 made of a conductive solid material, a reference pole 120, and a voltmeter 130 for measuring the potential difference between the working pole 111 and the reference pole 120. FIG. 1 shows a mode in which the working electrode 111 and the reference electrode 120 of the pH sensor are immersed in the liquid to be measured L contained in the container V as a usage pattern of the pH sensor 100.

Examples of the solid material constituting the working electrode 111 include metals such as platinum, silver, iron, stainless steel, and gold, carbon-based materials such as graphite, graphene, carbon nanotubes, and boron-doped diamonds (materials containing carbon), and ion selection. A sex electrode material can be used.
In the present embodiment, the shape of this solid material is not particularly limited.

The reference electrode 120 is formed of a tubular member, contains a predetermined electrode material as an internal electrode 121, and contains KCl as an internal liquid 122 (liquid-containing type). The electrode material used as the reference electrode 120 is required to have low reactivity to the components contained in the liquid to be measured L, that is, to be chemically stable, and to be stable under high temperature, low temperature, high pressure, and low pressure, that is, Environmental resistance is required, and further, physical adsorption and chemical adsorption on the surface are required to be less likely to occur.

The ion-selective electrode that can be used as the working electrode 111 includes a solid film type ion- selective electrode , a liquid film type ion- selective electrode , and a diaphragm-type ion- selective electrode . The solid film-type ion-selective electrode, e.g., chloride ion Cl ^-, bromide ion Br ^-, iodide ion I ^-, cyanide ion CN ^-, cadmium ions Cd ^2+, copper ions Cu ^2+, silver ions Ag ⁺ , Sulfuric acid ion S ^2- , fluoride ion F-, ^{and the} like, and examples thereof include electrodes made of a material having selectivity. Examples of the liquid film type ion- selective electrode include an electrode formed of a material having selectivity for calcium ion Ca ²⁺ , potassium ion K ⁺ , and nitrate ion NO ^3- . Examples of the diaphragm type ion- selective electrode include an electrode formed of a material having selectivity for ammonium ion NH ^{4+ and the} like.

The working electrode 111 is electrically grounded and its potential is fixed. Therefore, it is possible to prevent the surface potential of the electrode member constituting the working electrode 111 from irregularly fluctuating due to a change in the state of 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, the surface potential of the electrode member is irregularly changed due to a change in the state of the electrode and the liquid due to impurities or the like. There is no effect, and only the 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 irregularly fluctuating components due to changes in the state of the electrode and the liquid, and accurately determines the pH of the liquid to be measured L. It will be reflected.

In the pH sensor according to the present 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 potential on the surface thereof is high. , The problem that fluctuates 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 composed of only the electrode material. By grounding and suppressing fluctuations in the surface potential of the electrode material, the 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. 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 by the constituent material of the working electrode of the conventional method, that is, the problem of broken glass and the internal liquid diffusing into the liquid to be measured. .. Therefore, the pH sensor of the present embodiment is used as it is for measuring the pH in the liquid to be measured in an environment where a glass material cannot be used or an environment where diffusion contamination of the internal liquid is severe, for example, in a food manufacturing process. Is possible.

Further, the pH sensor of the present embodiment has a specific shape and a laminated structure because the working electrode is composed of only a solid material having conductivity and the electrode potential thereof can be easily controlled. It doesn't have to be. Therefore, the pH sensor of the present embodiment has a significantly simplified configuration as compared with the case where the field effect transistor controlled by the three factors functions as the working electrode as in the conventional ion sensor.

<Second embodiment>
FIG. 2 is a diagram showing a schematic configuration and a usage pattern of the pH sensor 200 according to the second embodiment. In the pH sensor 200, the voltage source 240 and the resistor 250 are connected (connected) to the working electrode 211 in this order. The configuration of other parts of the pH sensor 200 is the same as the configuration of the pH sensor 100 according to the first embodiment, and the same effect as that of the pH sensor 100 can be obtained in the pH sensor 200.

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

<Third Embodiment>
FIG. 3 is a diagram showing 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 the working electrode 311. Specifically, the source electrode 343 and the drain electrode 344 constituting the field effect transistor element 340 are connected between the working electrode 311 and the drive circuit 330 via voltage sources 350 and 360, respectively. The configuration of other parts of the pH sensor 300 is the same as the configuration of the pH sensor 100 according to the first embodiment, and the same effect as that of the pH sensor 100 can be obtained in the pH sensor 300.

Further, in the pH sensor 300, by connecting the field effect transistor element 340 to the grounded working electrode 311 via a voltage source, Igs can flow to stabilize the state, and the state can be stabilized. Since the function as a FET can be used to measure ions other than hydrogen ions, 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. The ion-sensitive field effect transistor includes a silicon type (Si-ISFET) and a diamond type (diamond ISFET).

<Fourth Embodiment>
FIG. 4 is a diagram showing 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 houses the liquid to be measured L. The object M to be measured and the reference electrode 420 are housed in this container. The configuration of other parts of the pH sensor 400 is the same as the configuration of the pH sensor 100 according to the first embodiment, and the same effect as that of the pH sensor 100 can be obtained in the pH sensor 400.

FIG. 4 shows a mode in which a container functioning as a working electrode 410 is used as a fermentation tank T for containing and fermenting a fermented product (measurement object M) as an application example of the present embodiment. .. A thermometer 440 is arranged at a desired position in the grounded container together with the fermented product to be the object M to be measured and the reference electrode 420. A source measure unit (SMU) is used here as a voltmeter 430 for measuring the potential difference between the working pole 410 and the reference pole 420.

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

The fermented food to be measured is not particularly limited, and examples thereof include yogurt, sake, soy sauce, and miso. As an example, a case where the pH sensor of the present invention is used in the yogurt manufacturing process will be described.

First, a yogurt production raw material liquid such as milk, skim milk (powder) milk, and fresh cream is housed in a fermentation tank T, and the pH sensor of the present invention is installed at one or a plurality of places in the tank T. Subsequently, a lactic acid bacterium starter for yogurt fermentation is added and fermented at a fermentation temperature suitable for the lactic acid bacterium used. As the lactic acid fermentation progresses, the pH value of the raw material liquid decreases to a predetermined value indicating acidity, and it can be determined that the fermentation step has been completed.

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 food / beverage / chemical production line, the tanks and pipes used in the production are cleaned and sterilized every time the production is completed. Chemicals used for cleaning and sterilization are recovered to reduce costs by reuse. In the CIP (Clean-in-Place) system (cleaning liquid recovery system) that recovers the cleaning liquid, a sensor is required for identification in the replacement of the cleaning agent and the cleaning water. Normally, a conductivity meter is used as this sensor, but the amount of change in conductivity differs for each cleaning solution (CIP cleaning solution), and the output of the conductivity meter can be used to identify the cleaning solution with a small amount of change in conductivity. It is difficult to do based on the value.

By using a grounded working electrode, the pH sensor according to the above embodiment suppresses fluctuations in the surface potential of the solid material constituting the working electrode, and measures the 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 the pH sensor according to the above embodiment is used will be described. FIG. 5 is a schematic diagram of the configuration of the CIP process using the pH sensor. The configuration of the CIP system shown in FIG. 5 is an example, and differs depending on each manufacturing process of products such as foods, beverages, and chemicals together with the cleaning agent (chemicals) used.

The cleaning sequence by the CIP system of FIG. 5 will be described. First, the inside of the tank and the pipe 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 pipe is washed with an alkaline solution (for example, 1.5% NaOH, 20 to 30% sodium hypochlorite, 10 to 30% caustic soda, 80 to 90 ° C., 1 MPa or less). Next, the inside of the tank and the pipe 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 the pipe is washed off 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 the addition of washing water, its concentration is monitored by the pH value. When the pH value reaches the standard value, the collection of the cleaning agent is stopped, and the rest is discharged to the drain line.

Similarly, the cycle of cleaning with different types of cleaning liquid, cleaning with fresh water, and recovery / release of the cleaning liquid is repeated. (The cycle may be only once.) In the final 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. The present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof.

(Example 1)
Using the pH sensor according to the first embodiment of the present invention, potential measurements were performed on samples of four carmody wide range buffers (pH buffers) prepared to have pH2, pH4, pH7, and pH10.

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

FIG. 6 is a graph showing the results of potential measurement. The horizontal axis of the graph shows the pH of the measured pH buffer solution, and the vertical axis of the graph shows 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 highly accurate linear response to the pH of the sample.

Therefore, by using the pH sensor of the present invention, the 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 accurately obtained. It turns out that it is required.

Highly accurate linear response is obtained because the solid material that constitutes the working electrode is grounded, which suppresses irregular fluctuations in the surface potential of the solid material due to the influence of the sample. Conceivable.

(Comparative Example 1)
FIG. 7 is a diagram showing a schematic configuration and a usage pattern of the pH sensor 500 of the prior art. In the pH sensor 500, the working electrode 510 is not electrically grounded. The working electrode 510 is a container made of a solid material having conductivity, contains Ag / AgCl as an internal electrode 511, and contains an 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 prior art pH sensor 500 pH sensor shown in FIG. 7, four carmody wide range buffer (pH buffer) samples prepared to have pH 2, pH 4, pH 7, and pH 10 in the same manner as in Example 1 were prepared. The potential was measured.

FIG. 8 is a graph showing the results of potential measurement. The horizontal axis and the vertical axis of the graph are the same as those 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 results of a plurality of measurements, it can be seen that each plot varies greatly with respect to the approximate straight line, and the linear responsiveness is not obtained with the same accuracy as in Example 1.

Therefore, when the pH sensor of the prior art 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 accurately obtained, and the pH value of the liquid to be measured corresponding to this potential difference cannot be obtained accurately. It can be seen that it cannot be obtained with high accuracy.

The reason why highly accurate linear response cannot be obtained is that the solid material constituting the working electrode is not grounded, so that the irregular fluctuation of the surface potential of the solid material due to the influence of the sample is not suppressed. it is conceivable that.

100, 200, 300, 400, 500 ... pH sensor 111, 211, 311, 410, 510 ... Working electrode 120, 220, 320, 420, 520 ... Reference electrode 121, 221, 321, 421, 521 ... Glass container 122, 222, 322, 522 ... Internal electrode 123, 223, 323, 523 ... Internal liquid 130, 230, 330, 430, 530 ... Voltmeter 240 ... Power supply 250 ... Resistor 340 ... Field effect transistor element 341 ... Board 341a ... One main surface of the board 341A ... Source area 341B ... Drain area 341C ... Channel area 342 ... Gate oxide film 343 ... Field oxide film 344 ... Source electrode 345 ... Drain electrode 347 ... Protective film 350, 360 ... Voltage source 440 ... Side warmer 511 ... Internal electrode 512・ ・ ・ Internal liquid L ・ ・ ・ Liquid to be measured M ・ ・ ・ Fermented product V ・ ・ ・ Container

Claims (6)

A working electrode made of a solid material with conductivity and
With the reference pole,
A voltmeter for measuring the potential difference between the working electrode and the reference electrode is provided.
The working electrode is electrically grounded and
A resistor is connected to the working electrode via a voltage source.
The resistor and the voltage source form a part that is not related to the liquid to be measured as a current path.
A pH sensor characterized by that. A working electrode made of a solid material with conductivity and
With the reference pole,
A voltmeter for measuring the potential difference between the working electrode and the reference electrode is provided.
The working electrode is electrically grounded and
A field effect transistor element is connected to the working electrode via a voltage source.
A pH sensor characterized by that. A working electrode made of a solid material with conductivity and
With the reference pole,
A voltmeter for measuring the potential difference between the working electrode and the reference electrode is provided.
The working electrode is electrically grounded and
The solid material constitutes a container for accommodating an object to be measured.
A pH sensor characterized by that. The pH sensor according to any one of claims 1 to 3, wherein the solid material is a material containing carbon. The pH sensor according to any one of claims 1 to 4, wherein the solid material is boron-doped diamond. The pH sensor according to any one of claims 1 to 4 , wherein the solid material is an ion-selective electrode material.

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