JP2004132915A - Microbial electrode, oxygen electrode for microbial electrode, and measuring instrument using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To thin a thickness of an oxygen permeable membrane to enhance a response speed. <P>SOLUTION: This oxygen electrode is provided with the oxygen permeable membrane 5 in its tip to separate its inside from an outside, and a cathode 1 and an anode 3 are provided in the inside of the electrode. The cathode 1 contacts with the oxygen permeable membrane 5, and an internal liquid 9 is interposed between the cathode 1 and the anode 3. A cathode protecting body 12 is provided in the inside of the electrode to surround sides of the cathode, and a tip position of the cathode protecting body 12 is arranged to be substantially coplanar with a tip position of the cathode 1. A tip of the cathode protecting body 12 also contacts with the oxygen permeable membrane 5. A microbial membrane is provided by bonding porous membrane 13, 14 with an adhesive or pressure sensitive adhesive double coated tape 15 and by immobilizing microorganisms 16. The cathode 1 is brought into pressure contact with a microorganism immobilized membrane via the oxygen permeable membrane 5 of the oxygen electrode, when used. <P>COPYRIGHT: (C)2004,JPO

Description

【００５２】
（実施例２）
実施例１記載の電極及び装置を用い、３５℃で連続的に運転を行った。１ヶ月毎に電極を取り出し、２５℃における空気飽和水と窒素ガスにより酸素を除いた水に交互に電極を浸漬し、その応答速度を評価した。その結果を表２に示す。
６ヶ月まで応答速度に変化がないことが分かった。この結果から本発明の電極は応答速度及び安定性の点で優れることが分かった。
【００５３】
（比較例２）
比較例１記載の電極及び装置を用い、３５℃で連続的に運転を行った。１ヶ月毎に電極を取り出し、２５℃における空気飽和水と窒素ガスにより酸素を除いた水に交互に電極を浸漬し、その応答速度を評価した。その結果も表２に示す。
応答時間自体が実施例２に比べて遅いが、３ヶ月目までは大きな変化はなかった。しかし４ヶ月目で著しく遅くなり、６ヶ月目では出力自体が小さくなって測定不能となった。この状態で分解すると内部液自体が酸化鉛の沈殿で濁っており、その結果、正常な動作ができなくなったものと考えられる。
【００５４】
【表２】

【００５５】
【発明の効果】
本発明の酸素電極は、電極内部にカソードの側方を包囲するカソード保護体を設け、このカソード保護体の先端位置をカソードの先端位置とほぼ同一面になるように配置し、このカソード保護体の先端も酸素透過膜に接触させたので、酸素透過膜は保護体及びカソードでほぼ水平に保たれることになり、酸素透過膜に無理な力がかからず、酸素透過膜の膜厚を薄くして応答速度を速くすることができる。
アノードとしてアルミニウムを用い、内部液として少なくとも二塩基酸又はその塩を含む溶液を用いる場合には、沈殿が生成せず、長期間安定な測定が可能になり、またノイズも小さい。
本発明の酸素電極を備えた微生物電極、さらにその微生物電極を備えた測定装置は、応答速度を速くすることができる。
【図面の簡単な説明】
【図１】一実施例の微生物電極を示す概略断面図である。
【図２】一実施例の測定装置を示す流路図である。
【図３】従来の酸素電極を示す概略断面図である。
【符号の説明】
１　　　カソード
３　　　アノード
５　　　酸素透過膜
９　　　内部液
１０　　　カソード絶縁体
１２　　　保護体
１３，１４　　　多孔膜
１６　　　微生物
１７　　　試料水
１８　　　洗浄液
１９　　　標準液
２０　　　緩衝液
２１，２２，２３　　　バルブ
２５　　　ポンプ
２７　　　エアポンプ
２９　　　微生物電極
３０　　　酸素電極
３５　　　恒温槽[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an immobilized microorganism electrode suitable for environmental analysis and the like, a galvanic oxygen electrode used for the electrode, and a measuring device using the microorganism electrode.
[0002]
[Prior art]
For the purpose of environmental pollution prevention, it is very important to carry out high-precision quantification of various chemical substances in sampled water such as industrial wastewater and river water. In a sewage system that performs intensive water treatment, accurate grasp of the chemical substance concentration is economically significant for efficient facility operation. In these analyses, it is necessary to continuously monitor the status of contamination, and automatic analysis is desired as much as possible.
[0003]
Typical analysis items for these water samples include dissolved oxygen, pH, chemical oxygen demand (COD), total organic carbon (TOC), and biochemical oxygen demand (BOD). Numerous methods are known for these analysis methods.
[0004]
In recent years, attempts have been made to apply so-called biosensors, which use substances derived from living organisms such as enzymes, antibodies, genes, and microorganisms, or living organisms as elements, to environmental analysis. The advantages of the biosensor are as follows.
[0005]
(1) Biodegradable organic substances can be detected and biotoxicity can be detected by utilizing the selectivity of living organisms or biological substances compared to other analysis methods;
(2) the configuration is relatively simple and automation is easy;
(3) The analysis wastewater has a low possibility of containing harmful metals and organic substances, and clean analysis can be realized.
[0006]
The Japanese Industrial Standard K3602 has already defined a biochemical oxygen demand (BOD) sensor using a specific microorganism, and is widely used practically. In the device specified in this standard, an oxygen electrode is pressed against an immobilized microorganism membrane on which microorganisms are immobilized, and the amount of oxygen consumed when the sample is brought into contact with the sample is detected by the oxygen electrode.
[0007]
A device for detecting a toxic substance in a test water by incorporating an immobilized microbial membrane in which iron-sulfur bacteria or nitrifying bacteria are immobilized in a device having a similar configuration has also been put into practical use (for example, see Patent Documents 1 and 2). .).
[0008]
Various oxygen electrodes are used in these devices. The oxygen electrode is composed of at least a cathode for electrochemically reducing dissolved oxygen, a corresponding anode, and an oxygen-permeable membrane for selectively transmitting oxygen. From the configuration of the electric circuit, it is roughly classified into a polaro-type oxygen electrode using an electrochemical reaction driven by a constant external voltage and a galvanic-type oxygen electrode using a kind of battery reaction (for example, see Non-Patent Document 1). .).
[0009]
The former polaro-type oxygen electrode is composed of a platinum cathode and a silver anode, and a voltage of about 0.6 volt to the anode is applied to the platinum cathode to detect a reduction current of oxygen. If an electrolyte such as potassium chloride is present between the oxygen permeable membrane and the cathode and anode, the device operates and can be made relatively small. However, when an external voltage is applied, a reduction reaction of platinum oxide occurs on the surface of platinum used as a cathode, and it takes time until a stable output is obtained, and the base current (residual current) at a low oxygen concentration is reduced. It is a big problem that it is large and the measurement range is limited.
[0010]
On the other hand, the galvanic oxygen electrode has a slightly complicated structure, but is excellent in stability and small in residual current, and is suitable for a biosensor.
FIG. 3 shows an outline of a conventional galvanic oxygen electrode. A cathode 1 made of platinum or gold and an anode 3 made of lead are provided inside the electrode, which is isolated from the outside by an oxygen permeable film 5. The cathode 1 has its tip in contact with the oxygen permeable membrane 5 and its periphery is sealed in an insulator 10 such as glass. A resin film such as a fluororesin or polyethylene is used for the oxygen permeable film 5. Oxygen passes through the oxygen permeable membrane 5. Sealing materials 8 and 11 are inserted between the oxygen permeable membrane 5, the outer cylinder 7 and the tip member 6 to prevent leakage of the internal liquid 9 and intrusion of liquid from outside. Oxygen reduction occurs on the surface of the cathode 1 and lead oxidation proceeds on the surface of the anode 3. As a result, a current proportional to the oxygen concentration flows between the lead wire 2 of the cathode 1 and the lead wire 4 of the anode 3.
[0011]
In order to immobilize microorganisms and detect oxygen consumption by the microorganisms with an oxygen electrode, it is necessary to bring the cathode 1 as close as possible to the microorganisms through an oxygen permeable membrane. For that purpose, it is necessary that the portion of the oxygen permeable film 5 in contact with the cathode 1 protrudes from the tip member 6 and that the oxygen permeable film 5 be made as thin as possible.
However, when the protrusion amount is increased, the oxygen permeable membrane 5 is stretched and easily broken. Also, it becomes difficult to make the oxygen permeable film 5 thin. When the oxygen permeable membrane 5 is broken, the external liquid and the internal liquid 9 naturally mix, and accurate measurement becomes impossible. At the same time, the internal liquid 9 has an adverse effect on microorganisms.
[0012]
Therefore, as the oxygen permeable membrane 5 for detecting oxygen consumption by microorganisms, one having a thickness of 50 μm to 1000 μm is mainly used.
In addition, since the thickness of the oxygen permeable membrane 5 is limited as described above, the response speed of the electrode is reduced, which is a factor that hinders the improvement of the analysis speed.
[0013]
[Patent Document 1]
JP 2002-90360 A [Patent Document 2]
JP-A-2-190763 [Non-Patent Document 1]
"Electrochemical Measurement Method", published by Gihodo, 1984
[Problems to be solved by the invention]
Although the present invention is directed to a galvanic oxygen electrode, an oxygen electrode suitable for an analyzer using immobilized microorganisms has not been obtained by conventional techniques.
A first object of the present invention is to provide an oxygen electrode having a structure which can easily increase the response speed of an electrode by thinning an oxygen permeable film.
A second object of the present invention is to provide a microbial electrode provided with such an oxygen electrode.
A third object of the present invention is to provide a measuring device provided with such a microbial electrode.
[0015]
[Means for Solving the Problems]
The oxygen electrode of the present invention includes an oxygen permeable membrane at the tip for isolating the inside and the outside, a cathode and an anode inside, and the cathode is brought into contact with the oxygen permeable membrane, and an internal liquid is interposed between the cathode and the anode. The present invention relates to a galvanic oxygen electrode which is provided with a cathode protection body surrounding the side of the cathode provided inside the electrode, and the tip position of the cathode protection body is arranged so as to be substantially flush with the tip position of the cathode. The tip of the cathode protector is also brought into contact with the oxygen permeable membrane.
[0016]
Since the oxygen permeable membrane is kept substantially horizontal by the protective body and the cathode, no excessive force is applied to the oxygen permeable membrane, and the oxygen permeable membrane is hardly damaged even when pressed against the microorganism membrane. Therefore, the thickness of the oxygen permeable film can be reduced.
[0017]
As the oxygen permeable film, for example, a resin film having a thickness in the range of 8 μm to 1000 μm can be used. From the viewpoint of increasing the response speed, the thickness of the oxygen permeable film is preferably thinner, for example, 50 μm or less.
[0018]
As the cathode, the anode and the internal solution, those conventionally used can be used, but the cathode is made of platinum or gold, the anode is aluminum, and the internal solution contains at least a dibasic acid or a salt thereof. It is preferred that it be composed of a solution.
[0019]
When lead is used for the anode, the lead in the anode becomes lead oxide due to the reaction inside the oxygen electrode and precipitates. When this precipitate is formed, the response speed of the electrode is adversely affected, and the precipitate enters between the cathode and the oxygen permeable membrane, so that a normal response value cannot be obtained. Therefore, in the oxygen electrode of this type, maintenance such as replacement of the internal liquid is required once every one to three months, which imposes a great burden on the analyst.
[0020]
Electrodes that use acetates in the internal solution have been developed, partly because they eliminate the adverse effects of leakage of the alkaline aqueous solution.However, precipitation of lead oxide and lead acetate cannot be prevented, and this is an essential solution. Was not. There is also a major problem in that the precipitation of lead oxide and lead acetate is a heavy metal salt, so that attention must be paid to its treatment.
Compared to the case where lead is used as the anode, aluminum is a light metal having relatively low toxicity, and is excellent in that no harmful waste is generated due to replacement of the internal solution.
[0021]
When aluminum is used as the anode and a solution containing at least a dibasic acid or a salt thereof is used as the internal solution, no precipitate is generated, and stable measurement can be performed for a long period of time.
A dibasic acid or a salt thereof is inexpensive, and has advantages such as being less odorous and stable for a long time as compared with an acid such as acetic acid due to low volatility.
[0022]
Electrodes that use platinum for the cathode, aluminum for the anode, and potassium chloride for the internal solution have also been developed, but the electrodes tend to carry noise on the signal, making them difficult to use for high-precision measurements. However, when aluminum is used as the anode and a dibasic acid or its salt is used as the internal solution, there is also an advantage that noise is reduced.
[0023]
The microorganism electrode of the present invention includes a microorganism-immobilized membrane in which microorganisms are immobilized on a porous membrane, and an oxygen electrode in which an oxygen-permeable membrane is brought into contact with the microorganism-immobilized membrane and electrochemically detects oxygen concentration. The sample is brought into contact with the surface of the immobilized membrane opposite to the surface in contact with the oxygen electrode to allow the chemical substance in the sample to pass through the porous membrane, and oxygen consumed when microorganisms bioconvert the chemical substance in the sample. This is to measure the concentration of a chemical substance by detecting the absorption of oxygen by the oxygen electrode. The oxygen electrode of the present invention described above is used as the oxygen electrode.
[0024]
The measurement apparatus of the present invention includes a mechanism for switching a sample to be measured, a washing solution, and a standard solution, a mechanism for aspirating each solution, and a mechanism for separately sending a buffer solution. Mixing, sending air to the mixed liquid, measuring the chemical substance concentration by bringing the gas-liquid mixture into contact with the microbial electrode, and using the above-described microbial electrode of the present invention as the microbial electrode It is.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
The outline of the microorganism electrode of the present invention will be described with reference to FIG.
At the bottom of the figure is a microbial membrane on which microorganisms are immobilized, and at the top of the figure is an oxygen electrode, which is assembled so that the oxygen permeable membrane of the oxygen electrode contacts the microbial membrane. It becomes.
[0026]
The oxygen electrode is provided with an oxygen permeable membrane 5 for separating the inside and the outside at the tip, and a cathode 1 and an anode 3 are provided inside the electrode. Cathode 1 is in contact with oxygen permeable membrane 5, and internal liquid 9 is interposed between cathode 1 and anode 3. Further, a cathode protector 12 surrounding the side of the cathode 1 is provided inside the electrode, and the tip position of the cathode protector 12 is arranged to be substantially flush with the tip position of the cathode 1. The tip of the cathode protector 12 is also in contact with the oxygen permeable membrane 5.
[0027]
The cathode 1 uses platinum or gold. In the case of gold, the cathode insulator 10 is desirably made of a plastic such as an epoxy resin or a fluororesin. In the case of platinum, the cathode insulator 10 is made of glass, and platinum can be sealed and used. This is because platinum and glass have close thermal expansion coefficients and good adhesion, and platinum withstands the heat processing temperature at the time of encapsulation in glass.
[0028]
Aluminum is used for the anode 3. The shape of the aluminum may be a rod, but it is desirable to use a tube arranged around the cathode insulator 10 because the anode 3 can be formed in a relatively narrow space. Aluminum is a light metal with relatively low toxicity, and is excellent in that no harmful waste is produced by exchanging the internal liquid. When lead is used as the anode, it is necessary to pay attention to the working environment at the time of processing. However, in the case of aluminum, the generation of dust may be prevented.
[0029]
It is desirable to use a dibasic acid or a salt thereof for the internal liquid 9. Examples of the dibasic acid include organic acids such as citric acid, lactic acid, and malic acid. These organic acids are inexpensive, and because of their low volatility, they have advantages such as no odor and long-term stability compared to acids such as acetic acid. In particular, citric acid is preferred because it has high solubility and excellent stability when stored in a reagent. A bacteriostatic agent such as sodium azide can be added to the dibasic acid for the purpose of sterilization.
[0030]
The concentration of the dibasic acid is desirably about 10 mM to about 1 M. If the concentration is too low, acid is consumed in the reaction with aluminum, and long-term stability cannot be ensured. Conversely, if the concentration is too high, the salt tends to precipitate, which is not suitable.
[0031]
In the past, potassium chloride was often used as the internal solution of a galvanic oxygen electrode combining platinum and other base metals.However, when potassium chloride was used, noise tended to increase, and high precision measurement was required. Not suitable. The reason why stable measurement can be performed for a long period of time by using a dibasic acid is that no precipitate is formed. This is presumably because the dibasic acid acts as a chelating agent for aluminum.
[0032]
Further, in the alkaline internal liquid, the pH of the internal liquid may fluctuate due to the dissolution of carbon dioxide, which may lower the accuracy. On the other hand, when a dibasic acid is used, the pH of the solution becomes acidic, and carbon dioxide generated at the same time as the consumption of oxygen by the microorganism is not dissolved.
Further, a dibasic acid or a salt thereof may be used in combination with an electrolyte such as sodium chloride or potassium chloride. The coexistence of the electrolyte limits the solubility of gases other than oxygen, and can further improve the accuracy.
[0033]
As the oxygen permeable film 5, a resin film such as a fluororesin or polyethylene is used. The oxygen permeable membrane 5 is covered over a protective body 12 surrounding the periphery of the cathode 1, and a sealing member 8 formed of an O-ring is inserted and fixed between the oxygen permeable membrane 5 and a distal end member 6 of an outer cylinder 7.
[0034]
Oxygen reduction occurs on the surface of the cathode 1 and oxidation of aluminum proceeds on the surface of the anode 3. As a result, a current proportional to the oxygen concentration flows between the lead wire 2 of the cathode 1 and the lead wire 4 of the anode 3.
[0035]
By adopting this structure, an excessive force is not applied to the oxygen permeable film 5 as compared with the conventional oxygen electrode of FIG. 3, so that the film thickness can be reduced. The thickness of the oxygen permeable film can be changed in the range of about 8 μm to about 1000 μm, but is preferably about 10 to 50 μm in consideration of ease of handling and response speed. When a fluororesin membrane having a thickness of 25 μm is used, the response time until the output value becomes zero when immersed in distilled water that has been stabilized in air-saturated distilled water and deoxygenated with nitrogen gas is about 25 ° C. 10 seconds.
[0036]
Similarly, the response time when using a 50 μm thick oxygen permeable membrane was about 40 seconds, about 2 minutes for a 100 μm thick oxygen permeable membrane, and about 5 minutes for a 200 μm thick oxygen permeable membrane. In order to accurately follow the oxygen absorption of the microorganism, the response time is desirably 1 minute or less.
[0037]
The microbial membrane fixes the microbes 16 by bonding the porous membranes 13 and 14 with an adhesive or a double-sided adhesive tape 15. When placing these microorganisms, a filler made of glass fiber or the like may be placed to prevent the movement of the microorganisms, or two sheets of adhesive or the double-sided adhesive tape 15 may be used to prevent the movement of the microorganisms by reducing the thickness thereof. May be brought close to each other.
[0038]
The porous membrane used has a pore size such that microorganisms placed inside do not leak out and other microorganisms do not enter from the sample side, but a pore size in the range of 0.1 to 1 μm is desirable. As the material of the porous membrane, various materials such as regenerated cellulose, acetylcellulose, fluororesin, polyvinylidene fluoride, and polysulfone can be used. Is desirable.
[0039]
In this microorganism electrode, the cathode 1 is pressed against the microorganism-immobilized membrane via the oxygen permeable membrane 5 of the oxygen electrode. In this configuration, the protective body 12 is pressed against the microbial membrane, and the oxygen permeable membrane 5 kept substantially horizontal by the protective body 12 and the cathode 1 comes into contact with the immobilized portion of the microorganism 16. In the conventional oxygen electrode, an excessive force was applied to the oxygen permeable membrane, so that the membrane was damaged by the pressure contact with the microbial membrane and the internal liquid might leak, but the oxygen electrode of the present invention has a low possibility. .
[0040]
A microbial electrode using this oxygen electrode and combined with an immobilized microbial membrane can be used in a measuring device. An example of such a measuring device includes a mechanism for switching between a sample to be measured, a washing solution, and a standard solution, a mechanism for aspirating each solution, and a mechanism for separately sending a buffer solution, and a buffer for any of the switched solutions. The liquid is mixed, air is sent to the mixed liquid, the gas-liquid mixture is brought into contact with the microbial electrode, and the oxygen electrode reading when the cleaning liquid is being sent and the standard solution or sample is being sent. It has a function of storing the difference between the oxygen electrode indicated values, and comparing and calculating the difference between the oxygen electrode indicated values for the standard solution and the sample.
[0041]
An outline of the measuring device will be described with reference to FIG. The entire device is incorporated in a housing 34. The buffer solution 20 is sucked at a constant speed using a pump 24. Another pump 25 also operates at a constant speed. The sample water 17, the washing solution 18, and the standard solution 19 are connected to the pump 25 by tubes, and the pump and each solution are separated by valves 21, 22, and 23. Basically, any one of the valves is opened, so that any one of the sample water, the washing solution, and the standard solution joins the buffer solution at the junction 26. After merging, it flows into the tube 28 arranged in the thermostat 35. Air is blown by the air pump 27, and the gas-liquid mixture flows into the microbial electrode 29. The output of the oxygen electrode 30 is digitized and analyzed by the electric circuit 32 and output to the printer 33. The wastewater after the analysis is discarded in a wastewater bottle 31.
[0042]
A resin tube made of silicon, fluororesin, polyethylene, or the like can be used as a tube for connecting the components. An inner diameter of about 0.5 to 5 mm can be used, but if it is too thin, insoluble matter in the sample may be clogged, and if it is too thick, it takes too much time for the sample to pass, so that about 1.0 to 3 mm. Things are desirable. The pumps 24 and 25 used need only be able to obtain a stable flow rate during the analysis, but a tube pump that is less likely to be clogged with the insoluble matter in the sample is preferable. In many cases, the flow rate is analyzed at about 0.1 to 10 mL / min. However, considering the analysis time and the consumption of the sample and the buffer, the flow rate is preferably about 0.5 to 4 mL / min.
[0043]
Similarly, the valves 21, 22, and 23 are also preferable in that a pinch valve closed by sandwiching a tube avoids a failure due to clogging with an insoluble matter.
As the buffer solution 20, phosphates, borates and the like are used in accordance with the microorganism to be used, and those having a general composition of various pH can be used. However, when measuring an organic substance in a sample, a buffer containing an organic substance used by a microorganism cannot be used.
[0044]
The temperature of the thermostat 35 is changed according to the microorganism. In particular, when the optimal growth temperature of the microorganism is used, the oxygen consumption is often maximized. In some cases, cooling may be required instead of heating.
[0045]
【Example】
Hereinafter, the content of the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
[0046]
(Example 1)
(1) Oxygen Electrode In the oxygen electrode of FIG. 1, the cathode 1 is made of a platinum rod having a diameter of 2 mm, and is sealed in a cathode insulator 10 made of soft glass having an outer diameter of 4 mm. The anode 3 is arranged around a cathode insulator 10 from an aluminum tube having an inner diameter of 4 mm and an outer diameter of 6 mm. As the internal solution 9, a 0.5 M citric acid solution was used. As the oxygen permeable film 5, a fluorine resin film having a thickness of 25 μm was used.
[0047]
(2) Method for preparing microorganism membrane Trichosporon cutaneum (IFO-10466 strain) was cultured and immobilized. The turbidity of the culture was measured at 660 nm, and 50 L of the culture having a turbidity of 2 was used for immobilization. As the porous membranes 13 and 14 used for immobilization, those obtained by punching a hydrophilic Durapore membrane (manufactured by Millipore) having a pore diameter of 0.45 μm into a diameter of 18 mm were used. A polyester-based double-sided adhesive tape (manufactured by Nitto Denko) was used as the double-sided adhesive tape 15 to bond the two porous films 13 and 14 together.
[0048]
(3) Measuring device The microorganism-immobilized membrane and the oxygen electrode were mounted on the device shown in FIG. The temperature of the thermostat 35 was set to 35 ° C., and a 100 mM sodium phosphate buffer (pH 7.0) was sent as the buffer 20 at a flow rate of 0.5 mL / min. A glucose / glutamic acid mixed solution was used as the standard solution 19. The concentration was 20 mg / L as a BOD value. Distilled water was used as the washing liquid 18. As a sample 17, a glucose / glutamic acid mixed solution was used as in the case of the standard solution, and the concentration was 10 mg / L as a BOD value. The flow rates of these standard solution, washing solution, and sample were 1.5 mL / min.
After flowing the standard solution for 5 minutes, washing is performed for 15 minutes, and the samples are sent for 1, 3, and 5 minutes, respectively. The concentration C of the sample was calculated by comparing the response value A to the standard solution and the response value B to the sample. That is, it was calculated as C = 20 × (B / A).
[0049]
(4) Measurement result If the response speed of the electrode is sufficiently fast, the sample concentration should be calculated correctly, but if it is slow, the value should be lower. Table 1 shows the results. It can be seen from Table 1 that a constant value was obtained after approximately 3 minutes of liquid transfer.
[0050]
(Comparative Example 1)
Example 2 except that the electrode had the structure of FIG. 2, the cathode was platinum, the anode was lead, 1% sodium hydroxide was used for the internal solution, and the oxygen-permeable membrane was 100 μm thick fluororesin. The measurement was performed under the same conditions with the same structure as in Example 1.
The results are also shown in Table 1. In Comparative Example 1, it was found that a correct value was not obtained even when the liquid was sent for 5 minutes, and there was a remarkable difference in response speed.
[0051]
[Table 1]

[0052]
(Example 2)
Using the electrode and the device described in Example 1, the operation was continuously performed at 35 ° C. The electrode was taken out every one month, and the electrode was alternately immersed in air-saturated water at 25 ° C. and water from which oxygen was removed with nitrogen gas, and the response speed was evaluated. Table 2 shows the results.
It was found that there was no change in response speed until 6 months. From this result, it was found that the electrode of the present invention was excellent in response speed and stability.
[0053]
(Comparative Example 2)
The operation was continuously performed at 35 ° C. using the electrode and the device described in Comparative Example 1. The electrode was taken out every one month, and the electrode was alternately immersed in air-saturated water at 25 ° C. and water from which oxygen was removed with nitrogen gas, and the response speed was evaluated. Table 2 also shows the results.
Although the response time itself was slower than that of Example 2, there was no significant change until the third month. However, in the fourth month, it became extremely slow, and in the sixth month, the output itself became small and measurement became impossible. When decomposed in this state, it is considered that the internal liquid itself became cloudy due to the precipitation of lead oxide, and as a result, normal operation could not be performed.
[0054]
[Table 2]

[0055]
【The invention's effect】
In the oxygen electrode of the present invention, a cathode protector surrounding the side of the cathode is provided inside the electrode, and the tip position of the cathode protector is arranged so as to be substantially flush with the tip position of the cathode. Since the tip of the oxygen permeable membrane was also in contact with the oxygen permeable membrane, the oxygen permeable membrane was kept almost horizontal by the protective body and the cathode, and no excessive force was applied to the oxygen permeable membrane, and the thickness of the oxygen permeable membrane was reduced. The response speed can be increased by making it thinner.
When aluminum is used as the anode and a solution containing at least a dibasic acid or a salt thereof is used as the internal solution, no precipitation occurs, stable measurement can be performed for a long period of time, and noise is small.
The microbial electrode provided with the oxygen electrode of the present invention and the measuring device provided with the microbial electrode can increase the response speed.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a microbial electrode according to one embodiment.
FIG. 2 is a flow chart showing a measuring apparatus according to one embodiment.
FIG. 3 is a schematic sectional view showing a conventional oxygen electrode.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cathode 3 Anode 5 Oxygen permeable film 9 Internal solution 10 Cathode insulator 12 Protector 13, 14 Porous film 16 Microorganism 17 Sample water 18 Washing solution 19 Standard solution 20 Buffer solution 21, 22, 23 Valve 25 Pump 27 Air pump 29 Microbial electrode 30 Oxygen electrode 35

Claims (6)

A galvanic type in which an oxygen permeable membrane for isolating the inside and outside is provided at the tip, a cathode and an anode are provided inside, and the cathode is brought into contact with the oxygen permeable membrane, and an internal liquid is interposed between the cathode and the anode. At the oxygen electrode,
A cathode protector surrounding the side of the cathode is provided inside the electrode, and the tip position of the cathode protector is arranged so as to be substantially flush with the tip position of the cathode. An oxygen electrode contacted with an oxygen permeable membrane. The oxygen electrode according to claim 1, wherein the cathode is made of platinum or gold, and the anode is made of aluminum. The oxygen electrode according to claim 1, wherein the oxygen permeable film has a thickness in a range of 8 μm to 50 μm. 4. The oxygen electrode according to claim 1, wherein said internal liquid is a solution containing at least a dibasic acid or a salt thereof. A microorganism-immobilized membrane in which microorganisms are immobilized on a porous membrane, and an oxygen electrode, wherein an oxygen-permeable membrane is brought into contact with the microorganism-immobilized membrane to electrochemically detect an oxygen concentration, and the oxygen electrode of the microorganism-immobilized membrane is provided. The sample is brought into contact with the surface opposite to the surface in contact with the sample to allow the chemical substance in the sample to pass through the porous membrane, and the absorption of oxygen consumed when microorganisms bioconvert the chemical substance in the sample is measured using the oxygen electrode. In microbial electrodes that detect and measure the concentration of chemical substances,
A microbial electrode, wherein the oxygen electrode is the oxygen electrode according to any one of claims 1 to 4. A mechanism for switching between the sample to be measured, the washing solution, and the standard solution, a mechanism for aspirating each solution, and a mechanism for separately sending a buffer solution, and a buffer solution was mixed with any of the switched solutions and mixed. In a measuring device for sending air to the liquid and bringing the gas-liquid mixture into contact with the microbial electrode to measure the concentration of the chemical substance,
A measurement device, wherein the microorganism electrode is the microorganism electrode according to claim 5.

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