JP3522512B2 - Biosensor-based water quality meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention monitors the chemical components of water in environmental treatment water, river water, lake water, and the like in water treatment and sewage treatment processes. The present invention relates to a biosensor applied water quality measuring instrument. 2. Description of the Related Art A biosensor utilizes a biomolecule such as an enzyme or an antibody, or a living body such as a microorganism or a cell as a molecular identification element for recognizing a substance to be measured in a test water. This sensor measures a chemical component in a sample by combining a film in which a material is immobilized by entrapping or covalently bonding a porous polymer film with a transducer such as an electrochemical detector. [0003] In a biosensor, a sample is brought into contact with an immobilized membrane of the above-mentioned biomaterial, and a change in the concentration of a substance produced or consumed by a chemical reaction caused by the change is detected as a change in the electrical output (voltage, current, etc.) of the detector. The concentration of the target substance in the test water is calculated from the sensor output for the test water using a calibration curve obtained from a standard solution of the substance to be measured having a known concentration. In the measurement, it is necessary to keep the temperature and pH conditions constant so that the immobilized biomaterial functions stably. Therefore, the biosensor-based measuring instrument is equipped with a heat exchanger that heats the test water to a constant temperature in order to keep the temperature constant, and a thermostat that keeps the sensor temperature constant. A buffer solution is used. [0004] Recently, the present inventors have disclosed Japanese Patent Publication No. 7-8507.
The biosensor for detecting toxic substances (harmful substances) in water described in No. 2 has been developed and put into practical use. This is a sensor that uses a microbial nitrifying bacterium that is extremely sensitive to toxic substances as a biomaterial, in other words, has high sensitivity as a sensor, and combines a membrane on which the nitrifying bacterium is immobilized and a dissolved oxygen electrode. And detects toxic substances in water. FIG. 1 is a flowchart showing a configuration of a water toxic substance detection apparatus to which a biosensor is applied, and FIG. 2 is a schematic diagram showing a configuration of a biosensor (microbial sensor). As shown in FIG. 2, a stainless steel wire mesh 26 is put in the flow cell 18 and Nitrosomonas europaea AT, a kind of nitrifying bacteria, is used.
CC25997), immobilized microbial membrane 25 immobilized thereon, and a dissolved oxygen electrode 19 mounted thereon and fixed with a nut.
The microorganism sensor 1 for detecting harmful substances is formed in close contact with the microorganism film 25. This is attached to a thermostat 2 set at 30 ° C. as shown in FIG. [0006] In FIG. 1, flow of a buffer solution A ₁ 6a and pure water 4 for the early zero-point calibration, and stores the current value stabilizes microbial sensor 1. Then, as the sensor output of the absence of toxic substances, closed valve 7d, and a valve 7e is opened, buffer B ₁ 6b and flow of pure water 4, the sensor output stabilizing after current including ammonium nitrogen Store the value. Next, the valve 7b is closed, the valve 7a is opened, and the measurement of the test water 3 is started. This device continuously monitors the water sample about once a day while performing the automatic calibration of the sensor as described above. A biosensor using nitrifying bacteria has a pH of 8 to 9.
In order to function stably at
A phosphate buffer solution with a buffer capacity around 8 was initially used. However, when the sample is environmental water such as river water or groundwater, purified water, sewage, etc., if the concentration of the hardness component (calcium ion) in the water is 20 mg / L or more, calcium ion and phosphate ion in the buffer solution will be Reacts to form calcium phosphate that is insoluble in water. The sediment adheres to the channel and the immobilized membrane, which causes a decrease in responsiveness and measurement sensitivity. Therefore, after that, a chelating agent (EDTA-4Na) that forms a complex with calcium ions in the test sample was added to the phosphate buffer solution to prevent calcium phosphate precipitation. However, it is necessary to change the amount of EDTA-4Na to be added depending on the calcium concentration in the test water, which complicates the operation at the time of preparing the reagent.
When DTA-4Na is added in excess, there is a problem that the nitrifying bacteria are adversely affected and the life is shortened. In addition, since the regulation of the drainage of nitrogen and phosphorus into the environment is strengthened by the revision of the drainage water quality standards, the buffer solution of the biosensor needs to have a buffer solution composition in which reagents containing nitrogen and phosphorus components are reduced. Therefore, the present inventors have developed a sodium tetraborate aqueous solution (pH 9) containing both chelated iron and magnesium ions as a buffer solution instead of the phosphate buffer solution, and disclosed in Japanese Patent Application No. 9-104126. Filed. [0010] As described above, a 10 mM aqueous sodium tetraborate solution (pH 9) containing both chelated iron and magnesium ions is used as a buffer solution for a water quality measuring instrument. I have. When a microbial membrane that has been refrigerated and stored in the experiment is newly attached to the flow cell and pure water is measured, the sensor output shows a constant value. However, when measuring environmental water such as river water or groundwater, purified water, sewage, etc., the sensor output is not affected by the dissolved ions such as carbonate ions even if the test sample contains no toxic substances. Was found to occur. This is because, for example, when it is desired to quickly start measurement within 24 hours, immediately after attaching the refrigerated microbial membrane to the microbial sensor, even if the biosensor applied measuring instrument has no abnormality in the water sample, There has been such a problem that the decrease in output is judged to be an abnormality in water quality and an alarm may be issued. The present invention has been made to solve this problem, and an object of the present invention is to provide a biosensor-based water quality meter that is stable and environmentally friendly. [0013] In order to solve the above-mentioned problems, the present invention provides a borane obtained by adding sodium bicarbonate to a conventional sodium tetraborate aqueous solution containing chelated iron and magnesium ions. An acid buffer solution will be used. By using this buffer solution, since it contains carbonate ions in advance, it is not affected by dissolved ions such as carbonate ions contained in river water, etc., and the sensor output does not decrease when starting the biosensor. Stable long-term monitoring has become possible. The present invention will be described below with reference to embodiments. Table 1 shows the composition of a buffer solution B ₂ of a conventional buffer solution B ₁ and the present invention used in Example. [Table 1] Using these two types of buffer solutions B ₁ and B ₂ , the stability of the sensor output when the biosensor was started was compared. FIG.
Course of the sensor output when the mineral water and pure water was passed in this order two different buffer as the test water solution B ₁ and B ₂
It is compared with. The sensor output here is expressed as a relative value of the sensor output at each measurement, with the current value at the zero point at the time of calibration being 0% and the current value at the time of flowing a buffer solution containing ammonia nitrogen being 100%. I have. In addition, since mineral water contains similar components to river water and contains no toxic substances, it is possible to reproduce the conditions actually used for river water measurement and whether sensor outputs can be obtained stably. Used to be appropriate to consider. As a result, when the mineral water was measured after the biosensor was set up, the conventional buffer B ₁
Whereas the sensor output decreases, the buffer B ₂ of the present invention with the addition of sodium hydrogen carbonate, the sensor is seen to be usable stably showed no decrease in output. FIG.
This is the result of performing the same measurement as in FIG. 3 on an actual river. [0017] In this measurement, the same as the result of the above, the buffer B ₂ of the present invention, after the biosensor startup, be measured river water, the sensor output is constant, not observed decrease,
It turns out that it can be used stably. From the above results, it was found that a borate buffer solution obtained by adding sodium bicarbonate to a conventional sodium tetraborate solution containing both chelated iron and magnesium ions is suitable for a biosensor-based water quality meter. . The reason why the buffer solution of the present invention to which sodium bicarbonate is added does not show a decrease in the output of the sensor even when the river water is measured after the start of the biosensor is as follows. It is estimated to be. When chemolithoautotrophic bacteria including nitrifying bacteria fix carbon dioxide, carbon dioxide (carbonate ion) is the only carbon source. When nitrifying bacteria fix nitrogen, ammonia ions are used as an energy source. Nitrifying bacteria do not require oxygen in the case of carbonate fixation using carbonate ions, but need oxygen in the case of nitrogen fixation using ammonia ions. This is the respiration of nitrifying bacteria. When the microbial membrane holding the nitrifying bacteria is mounted on the biosensor and calibration is performed, the nitrifying bacteria remain carbon deficient because the buffer solution does not contain carbonate ions. Here, when a sample containing carbonate ions flows in, the fixation of carbonic acid by nitrifying bacteria starts at once, and the amount of fixation becomes larger than the fixation of nitrogen, that is, the respiration rate. For this reason, it is considered that the sensor does not consume oxygen apparently, and the sensor output decreases. For this reason, if sodium bicarbonate, which is a source of carbonate ions, is added to the buffer solution, the carbonic acid is fixed even during calibration, and the balance with respiration is maintained. It is considered that a decrease in the sensor output can be prevented. By using the buffer of the present invention,
The biosensor can be started up stably, and the measurement accuracy of the biosensor applied measuring instrument can be improved and malfunction can be prevented. As a result, the water quality can be stably and continuously monitored, and a more practical biosensor applied water quality meter can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart showing the configuration of a biosensor-based water quality meter. FIG. 2 is a schematic diagram showing the configuration of a biosensor (microbial sensor). FIG. 3 is a diagram showing carbonic acid when measuring mineral water. Comparison diagram of effect of sodium hydrogen [Figure 4] Comparison diagram of effect of sodium hydrogen carbonate when measuring river water [Explanation of reference numerals] 1: Biosensor 2: Temperature chamber 3: Test water 4: Pure water 5: Acid Washing water 6a: Buffer solution A 6b: Buffer solution B 7a to 7g: Solenoid valves 8a to 8b: Solution pump 9: Heat exchanger 10: Air pump 11: Pressure sensor 12: Roller clamp 13: Two-way switching three-way valve 14: Display unit 15: Control unit 16: Recorder 17: Measurement unit 18: Flow cell 19: Dissolved oxygen electrode 20: Sample channel 21: Positive electrode 22: Negative electrode 23: Electrode solution 24: Diaphragm 25: Immobilization Microbial membrane 26: stainless steel wire mesh 27a-27c: O-ring 28a-28b: lead wire 29: washer

Continuation of the front page (56) References JP-A-58-56700 (JP, A) JP-A-1-242956 (JP, A) JP-A-6-222041 (JP, A) JP-A-64-63850 (JP) , A) JP-A-63-115048 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/416 G01N 27/327 G01N 33/18 JICST file (JOIS)

Claims (1)

(57) [Claims] [Claim 1] A buffer solution used in a water quality meter using a biosensor for measuring chemical substances in raw water of tap water such as river water and groundwater, and in the inflow water of a wastewater treatment process. But,
A biosensor-based water quality meter, which is an aqueous solution of sodium tetraborate to which sodium bicarbonate, chelated iron and magnesium ions are added.