Measurement method for oxygen concentration in ultra fine bubbles

Abstract

To calculate an oxygen amount in ultra fine bubbles in ultra fine bubble water.SOLUTION: A measurement method for oxygen concentration in ultra fine bubbles comprises: a Mn(II) oxidation step for adding to a water sample, an alkali solution, a polyphosphate solution and a manganese salt solution, for oxidizing Mn(II) to Mn(IV) while suppressing precipitation of Mn(II); a Mn(IV) reduction step for adding a strong acid solution to the water sample subjected to the Mn(II) oxidation step for stopping the oxidation reaction, and reducing the Mn(IV) formed in the Mn(II) oxidation step to the Mn(III); a first oxidation concentration measurement step for measuring absorbancy of a wavelength of light which is absorbed by the Mn(III) in the water sample subjected to the Mn(IV) reduction step, and calculating first oxygen concentration being oxygen concentration in the water sample; and a second oxygen concentration measurement step for measuring the same water sample as that subjected to the first measurement step by a fluorescent type DO meter for calculating second oxygen concentration, then the second oxygen concentration is subtracted from the first oxygen concentration for calculating the oxygen amount in the ultra fine bubbles in the water sample.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for measuring the concentration of oxygen contained in water, and more particularly to a method for measuring oxygen concentration using ultraviolet-visible spectroscopy. [Background technology]

[0002] Generally, there are three known methods for measuring the oxygen concentration in water: the diaphragm electrode method, the fluorescence method, and the Winkler method. Of these, the diaphragm electrode method and the fluorescence method are used because they are simple measurement methods, while the Winkler method is widely used because it allows for highly accurate measurement.

[0003] The Winkler method is shown in the following formulas (1) to (4). In the Winkler method, manganese sulfate and sodium hydroxide are added to the sample water to produce a brown precipitate of Mn(IV)O(OH)2, which is then converted into iodide ions I - and acid are added to 2+ and releases iodine ions (I3) depending on the amount of dissolved oxygen. - Sodium thiosulfate S203 2- The amount of dissolved oxygen is calculated from the amount of sodium thiosulfate required. 2Mn(II)+O2+4OH - →2Mn(IV)O(OH)2···(1) Mn(IV)O(OH)2↓+2I - +4H + →Mn(II)+I2+3H2O···(2) I2+I - →I3 - (3) I3 - +2S203 2- →S406 2- +3I - (4)

[0004] However, while the Winkler method has high measurement accuracy, it has problems such as the need for a large number of reagents, the time required for the titration process, and the fact that measurement accuracy is affected by interferences and changes in sample volume.

[0005] Therefore, in Non-Patent Document 1, the present inventors have disclosed a method for measuring dissolved oxygen concentration that has the same measurement accuracy as the Winkler method but overcomes these problems associated with the Winkler method.

[0006] The method for measuring dissolved oxygen concentration in Non-Patent Document 1 involves adding NaOH, (NaPO3)6, and MnSO4 to sample water, oxidizing Mn(II) to Mn(IV) without precipitating it through coacervation with (NaPO3)6, adding H2SO4 to the water, and reducing Mn(IV) to Mn(III). The absorbance at a wavelength of 517 nm due to the pink color of this Mn(III) is then measured using an ultraviolet-visible spectrophotometer. (NaPO3)6 Mn(II) → Mn(II)coacervation ···(5) (NaPO3)6 (1 / 2)02+2OH - +Mn(II)coacervation→ Mn(IV)O(OH)2[complexes form]~Mn(IV)complex (6) H + Mn(IV)complex+Mn(II)coacervation→2Mn(III)coacervation (7) [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Optimization of Procedure for Determining Dissolved Oxygen in Surface Water and Seawater Exploiting the UV-vis Absorption of Mn(III) Species;Tu Dang,Yasuaki Maeda,Yusuke Fujii,Norimichi Takenaka [Non-Patent Document 2] Concentration determination of oxygen nanobubbles in electrolyzed water Kenji Kikuchi, Aoi Iokaa, Takeo Okua, Yoshinori Tanaka, Yasuhiro Saihara, Zempachi Ogumi Summary of the Invention [Problem to be solved by the invention]

[0008] On the other hand, when both dissolved oxygen in water and oxygen contained in ultrafine bubbles are present, it was unclear whether the three conventional dissolved oxygen concentration measurement methods mentioned above were measuring only the dissolved oxygen in the water, or whether they were also measuring the oxygen contained in the ultrafine bubbles. For example, Non-Patent Document 1 states that the UV-vis method has the same measurement accuracy as the Winkler method, but also states that the UV-vis method can measure the combined concentration of both dissolved oxygen in water and oxygen in ultrafine bubbles. This suggests that the Winkler method can also measure the combined concentration of both dissolved oxygen in water and oxygen in ultrafine bubbles, but Non-Patent Document 2 states that the Winkler method only measures dissolved oxygen in water. Therefore, the inventors investigated whether the oxygen concentrations measured by the Winkler method, a fluorescent DO meter, and the measurement method of Patent Document 1 (hereinafter referred to as the "UV-vis method") include the oxygen contained in the ultra-fine bubbles.They found that while the measurements using the Winkler method and the fluorescent DO meter do not include the oxygen inside the ultra-fine bubbles, the measurements using the UV-vis method do include the oxygen inside the ultra-fine bubbles, and that the amount of oxygen present in the ultra-fine bubbles can be calculated from the difference between the two measurement values. That is, an object of the present invention is to provide a method for calculating the oxygen concentration contained in ultra-fine bubbles in water. [Means for solving the problem]

[0009] The invention made to solve the above problems is a method for measuring the oxygen concentration in ultra-fine bubbles in a water sample, which comprises the steps of: a Mn(II) oxidation step in which three types of reagents, namely an alkaline solution, a polyphosphate solution, and a manganese salt solution, are added to the water sample to oxidize Mn(II) to Mn(IV) while suppressing precipitation of Mn(II); and a strong acid solution is added to the water sample that has been subjected to the Mn(II) oxidation step to stop the oxidation reaction, and the Mn(IV) formed in the Mn(II) oxidation step is then oxidized to Mn(IV). to Mn(III); a first oxygen concentration measurement step of measuring the absorbance of light at a wavelength absorbed by Mn(III) in the sample water that has undergone the Mn(IV) reduction step and calculating a first oxygen concentration, which is the oxygen concentration of the sample water, from the absorbance; a second oxygen concentration measurement step of measuring a second oxygen concentration consisting only of dissolved oxygen in the same sample water as the water sample subjected to the first measurement step; and calculating the amount of oxygen in the ultra-fine bubbles in the sample water by subtracting the second oxygen concentration from the first oxygen concentration. In this specification, "dissolved oxygen" refers only to oxygen dissolved in the sample water, and does not include oxygen contained in fine bubbles such as microbubbles and ultrafine bubbles.

[0010] The first oxygen concentration is an oxygen concentration measured by the UV-vis method, and includes both the dissolved oxygen dissolved in the sample water made of ultra-fine bubble (hereinafter also referred to as "UFBO2") water and the oxygen contained within the ultra-fine bubbles, as described above. In contrast, for example, the Winkler method and a fluorescent DO meter measure only the dissolved oxygen contained in the sample water, so that the oxygen concentration of only the dissolved oxygen is set as the second oxygen concentration, and the oxygen concentration contained within the ultra-fine bubbles of the sample water can be calculated by subtracting the second oxygen concentration from the first oxygen concentration.

[0011] The wavelength of light for measuring absorbance in the first oxygen concentration measurement step is preferably 512 nm to 522 nm, 513 nm to 521 nm, 514 nm to 520 nm, 515 nm to 519 nm, 516 nm to 518 nm, or 517 nm. By measuring the absorbance of light with a wavelength closer to 517 nm, preferably measuring the absorbance at 517 nm, the first oxygen concentration can be measured more accurately.

[0012] In the method for measuring the oxygen concentration in ultra-fine bubbles of the present invention, it is preferable to use a NaOH solution as the alkaline solution, a (NaPO3)6 solution as the polyphosphate, and a MnSO4 solution as the manganese salt solution, and these are preferably added to the sample water in this order. This allows the oxygen concentration in the sample water to be measured more accurately.

[0013] The method for measuring the oxygen concentration in ultra-fine bubbles of the present invention preferably includes a nitrogen flow process for flowing nitrogen into a three-way pipe connected to a sample water syringe containing the sample water and a nitrogen flow pipe for flowing nitrogen through the three-way pipe, and a nitrogen flow process for introducing any one of the reagents into the sample water syringe by switching the three-way valve to connect the sample water syringe and the reagent syringe. This makes it possible to suppress interference of oxygen in the air with the reaction between the sample water and the reagent.

[0014] In the method for measuring an oxygen concentration inside ultra-fine bubbles of the present invention, the second oxygen concentration measuring step preferably uses a fluorescent DO meter to measure the second oxygen concentration. In this way, the second oxygen concentration can be measured more simply than the Winkler method, which requires a large number of reagents and steps such as titration. Effect of the Invention

[0015] As described above, according to the method for measuring the oxygen concentration in ultra-fine bubbles of the present invention, the oxygen concentration contained in ultra-fine oxygen bubbles can be calculated. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a measuring device used in a method for measuring the oxygen concentration in ultra-fine bubbles according to one embodiment of the present invention. [Diagram 2] This is a graph showing the results of measurement, using a fluorescent DO meter and a UV-vis method, for Example 1, in which UFBO2 was added to distilled water and then bubbled with nitrogen, and Comparative Example 1, in which distilled water was bubbled with nitrogen without adding UFBO2. [Diagram 3] This is a graph showing the results of measurement, using a fluorescent DO meter and a UV-vis method, for Example 2, in which UFBO2 was added to distilled water and then bubbled with air, and Comparative Example 2, in which distilled water was bubbled with air without adding UFBO2. [Figure 4] 4 is a graph showing the results of measurements performed in addition to the results shown in FIG. 3 for Example 2 and Comparative Example 2. [Diagram 5] 1 is a calibration curve showing the relationship between the UFBO2 concentration determined by measurement and the UFBO2 concentration determined by calculation in Example 3. [Figure 6] 1 is a graph showing a comparison of oxygen concentrations determined by the Winkler method in Test Example 1 and Test Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described, however, the present invention is not limited to the following embodiment.

[0018] <Method of measuring oxygen in ultra-fine bubbles> The method for measuring the oxygen concentration in ultra-fine bubbles (UV-Vis method) according to this embodiment is used to measure the oxygen concentration contained in ultra-fine bubbles in a solution containing the ultra-fine bubbles, and includes a Mn(II) oxidation step S1, a Mn(IV) reduction step S2, a first oxygen concentration measurement step S3, a second oxygen concentration measurement step S4, and a calculation step S5 of the oxygen concentration in ultra-fine bubbles. The reagents and the like will be explained for each step.

[0019] [Mn(II) oxidation step S1] The Mn(II) oxidation step S1 is a step in which three types of reagents, namely, an alkaline solution B, a polyphosphate solution C, and a Mn(II) salt solution D, are added to sample water A to oxidize Mn(II) to Mn(IV) while suppressing the precipitation of Mn(II). As shown in the above formulas (5) and (6), by adding these three types of reagents to sample water A, Mn(II) is oxidized to Mn(IV) by the oxygen in sample water A. At this time, the precipitation of Mn(II) and Mn(IV) is suppressed by coacervation with polyphosphate solution C.

[0020] (Sample water A) In this embodiment, the sample water A to be measured for the oxygen concentration in ultra-fine bubbles is not particularly limited as long as it is an aqueous sample containing ultra-fine bubbles, and may be any of natural waters such as seawater and river water, and artificial waters such as tap water and distilled water.

[0021] (3 types of reagents) (Alkaline solution B) As the alkaline solution B, an aqueous solution of KOH, NaOH, or the like can be appropriately used, with an aqueous NaOH solution being preferably used.

[0022] (Polyphosphate solution C) As the polyphosphate solution C, (NaPO3)6 (sodium hexametaphosphate), (NaPO3)n (sodium polyphosphate), etc. can be used, and in particular, (NaPO3)6 (sodium hexametaphosphate) can be preferably used. Polyphosphates other than the sodium salt may also be used.

[0023] (Mn(II) salt solution D) As the Mn(II) salt solution D, MnSO4, MnCl2, Mn(NO3)2, etc. can be used, with MnSO4 being particularly preferred.

[0024] (Preparation of three types of reagents) The three types of reagents B, C, and D used in the Mn(II) oxidation process S1 are adjusted to appropriate concentrations using ultrapure water, and after removing dissolved oxygen with N2 bubbling, are stored in a sealed bottle with a septum.

[0025] (How to add reagents) When reagents B, C, and D are added to sample water A, a measuring device 1 shown in Fig. 1 is used. The measuring device 1 mainly comprises a sample water syringe 2, a reagent syringe 3, a three-way valve 4, and a nitrogen introduction pipe 5. When adding reagents B, C, and D to sample water A using measuring device 1, the reagents are removed from the septum-equipped sealed bottle using reagent syringe 3 with a needle, and reagent syringe 3 with the needle removed is immediately connected to three-way valve 4. 1(a), the three-way valve 4 is connected by operating the valve body so that the nitrogen inlet pipe 5 communicates with the reagent syringe 3. In this state, nitrogen is allowed to flow from the nitrogen inlet pipe 5 into the three-way valve 4. 2(b), the three-way valve 4 is switched to connect the reagent syringe 3 and the sample water syringe 2, and the reagent is introduced from the reagent syringe 3 to the sample water syringe 2. After the first sample water is introduced, the piston of the sample water syringe 2 is pulled back so that no reagent remains in the piping. In the same manner, the remaining two types of reagent are added in turn to the sample water syringe 2.

[0026] (Order of adding three types of reagents) When the three reagents are an aqueous NaOH solution, an aqueous (NaPO3)6 solution, and an aqueous MnSO4 solution, it is preferable to add them in this order, so that Mn(II) can be oxidized to Mn(IV) by coacervation of (NaPO3)6 without precipitating.

[0027] (Waiting time after adding reagent) In the Mn(II) oxidation step S1, the time from the introduction of the three reagents B, C, and D until the start of the Mn(IV) reduction step S2 is preferably, for example, 6 to 10 minutes, more preferably 7 to 9 minutes, in order to sufficiently oxidize Mn(II) to Mn(IV). In this way, Mn(II) can be sufficiently oxidized to Mn(IV).

[0028] [Mn(IV) reduction step S2] The Mn(IV) reduction step S2 is a step in which an acidic solution E is added to the sample water A that has been subjected to the Mn(II) oxidation step S1 to stop the oxidation reaction, and the Mn(IV) formed in the Mn(II) oxidation step is reduced to Mn(III). The acid solution E is introduced using a reagent syringe 3 by switching the three-way valve 4 . As shown in equation (7), when placed under acidic conditions, Mn(II) coacervate and Mn(IV) compound (Mn(IV)O(OH)2) react to form Mn(III) coacervate.

[0029] (Acidic solution E) A strong acid aqueous solution such as HCl, HNO3, or H2SO4 can be used as the acid solution E, and an H2SO4 aqueous solution is particularly suitable. The acid solution E is prepared using ultrapure water and stored in a sealed bottle with a septum.

[0030] [First oxygen concentration measurement process S3] The first oxygen concentration measurement process S3 is a process of measuring the absorbance of light at a wavelength absorbed by M(III) in sample water A that has undergone the Mn(IV) reduction process S2, and measuring the first oxygen concentration DO1, which is the oxygen concentration of the sample water, from the absorbance. The sample water A that has undergone the Mn(IV) reduction step S2 has a pink color with a peak at a wavelength of 517 nm due to the generated Mn(III). The absorbance at a wavelength of 517 nm correlates with the concentration of Mn(III), and the concentration of Mn(III) correlates with the oxygen concentration of the sample water A. Therefore, the oxygen concentration (first oxygen concentration) of the sample water A can be measured by measuring the absorbance at a wavelength of 517 nm with a UV-Vis spectrophotometer. However, even in oxygen-free sample water, slight absorption (background value) is observed at 517 nm. Therefore, when measuring the absorbance at a wavelength of 517 nm with a UV-Vis spectrophotometer, this background value is subtracted from the measured absorbance to calculate the oxygen concentration. The UV-Vis absorbance can be measured, for example, with a UV-Vis spectrophotometer (UV-1800) manufactured by Shimadzu Corporation. In this embodiment, the wavelength of the light used to measure absorbance in the first oxygen concentration measurement step is not limited to 517 nm, but may be any wavelength between 512 nm and 522 nm, and is preferably closer to 517 nm, such as between 513 nm and 521 nm, between 514 nm and 520 nm, between 515 nm and 519 nm, or between 516 nm and 518 nm, with exactly 517 nm being most preferable.

[0031] (How to calculate background values) First, the absorbance of a plurality of samples not containing UFBO2 is measured using an ultraviolet-visible spectrophotometer and the DO concentration is measured using a fluorescent DO meter, and a calibration curve is created for the relationship between the absorbance and the DO concentration. When measuring the first oxygen concentration using light with a wavelength of 517 nm, the absorbance of light at 517 nm is then measured using an ultraviolet-visible spectrophotometer for distilled water into which nitrogen has been bubbled. Then, using the calibration curve, the DO concentration corresponding to this absorbance is read and used as the background value.

[0032] [Second oxygen concentration measurement step S4] The second oxygen concentration measurement step S4 is a step of measuring a second oxygen concentration consisting only of dissolved oxygen contained in the water for the same water sample A as that used in the measurement of the first oxygen concentration. The measurement of the second oxygen concentration is not particularly limited as long as it is possible to measure only the dissolved oxygen contained in the water, and any known method and device can be used, including a method using a fluorescent DO meter, a diaphragm electrode method, a Winkler method, etc. The present inventors have confirmed that only the dissolved oxygen in the water can be measured by a fluorescent DO meter, as described below. As the fluorescent DO meter, for example, an optical sensor (Hach HQ30D) manufactured by DKK-TOA Corporation can be used.

[0033] [Calculation process of oxygen concentration in ultra-fine bubbles S5] After measuring both the first oxygen concentration DO1 and the second oxygen concentration DO2, the second oxygen concentration DO2 is subtracted from the first oxygen concentration DO1 to calculate the oxygen concentration in the ultra-fine bubbles of sample water A, which consists only of oxygen in the ultra-fine bubbles. EXAMPLES

[0034] Next, examples of the present invention and comparative examples will be described, but the present invention is not limited to the following examples.

[0035] [Example 1] (Sample water A) Using a UFB generator (Lab-nano-2004-GN-JF-405) manufactured by the Institute for Nanoscience, 300 mL of distilled water was circulated for 30 minutes while oxygen of 99.5% purity was passed through the water to form UFBO2-containing water. The number concentration of UFBO2 was measured using a nanobubble measuring device (NBF-202 type) manufactured by the same company, and was found to be approximately 10 11 pieces / cm 3 It was. The UFBO2-containing water thus prepared was left in a thermostatic chamber at 298 K for at least one hour, after which the dissolved oxygen concentration measured by a fluorescent DO meter in the thermostatic chamber was stable (±0.2 mg / cm 3 Nitrogen gas was bubbled through the solution using an impinger for 30 minutes or more until the solution reached a concentration of 0.01%. This was used as sample water A.

[0036] (reagent) Three reagents used in the Mn(II) oxidation step S1, 5 mol dm -3 of NaOH solution (alkaline solution B), 0.2 kg dm -3 (NaPO3)6 aqueous solution (polyphosphate solution C), and 1.5 mol dm -3 MnSO4 aqueous solution (manganese(II) salt solution D) and 25 mol dm -3 The H2SO4 aqueous solution (acid solution E) was prepared using ultrapure water. Dissolved oxygen was removed from all solutions except the H2SO4 aqueous solution by bubbling with N2. All of the obtained reagents were stored in sealed bottles with septa.

[0037] (Mn(II) oxidation step S1) NaOH solution, (NaPO3)6 solution, and MnSO4 solution were added to 0.20 cm 3 One by one, in this order, the water was removed from the septum-equipped airtight container into the reagent syringe 3, and then introduced into the sample water syringe 2 while N2 gas was flowing through the three-way valve 4.

[0038] (Mn(IV) reduction step S2) In the Mn(II) oxidation step S1, 8 minutes after all three reagents were added, an aqueous H2SO4 solution was added to the sample water syringe 2.

[0039] (First oxygen concentration measurement process S3) The absorbance at 517 nm of the pink sample water A thus obtained was measured using a UV-1800 manufactured by Shimadzu Corporation. A background value, which will be described later, was subtracted from the obtained measurement value to obtain a first oxygen concentration DO1.

[0040] (Method of measuring background value and measured value) For several samples taken from distilled water without UFBO2, the absorbance was measured using a UV-Vis spectrometer, and the DO concentration was measured using a fluorescent DO meter. A calibration curve was created for the relationship between the absorbance and DO concentration thus obtained. Separately, the absorbance of 517 nm light was measured using a UV-Vis spectrometer for distilled water into which nitrogen had been bubbled, and the DO concentration corresponding to this absorbance was read using the calibration curve, which was used as the background value.

[0041] (Second oxygen concentration measurement step S4) In parallel, the second oxygen concentration DO2 of sample water A was measured using a fluorescent DO meter (Hach HQ30D optical sensor) manufactured by DKK-TOA Corporation.

[0042] [Comparative Example 1] Except for using distilled water without adding UFBO2, sample water A was formed by bubbling with N2 gas in the same manner as in Example 1, and steps S1 to S4 were carried out to measure the first oxygen concentration DO1 and the second oxygen concentration DO2.

[0043] (Measurement results of DO concentration in Example 1 and Comparative Example 1 with nitrogen bubbling) The measurement results of the first oxygen concentration DO1 and the second oxygen concentration DO2 measured in Example 1 and Comparative Example 1 are shown in Fig. 2. The error bars in Fig. 2 indicate the standard deviation of 3 to 5 measurements. In Example 1, in which nitrogen was bubbled after UFBO2 was introduced, the first oxygen concentration DO1 measured by the UV-vis method was 1.7 mg cm- 3 The second oxygen concentration, DO2, measured by a fluorescent DO meter is 0 (zero) mg cm- 3 In contrast, in Comparative Example 1, in which nitrogen bubbling was performed without introducing UFBO2, the first oxygen concentration DO1 measured by the UV-vis method and the second oxygen concentration DO2 measured by the fluorescent DO meter were both 0 mg cm− 3 It was.

[0044] (Calculated UFBO2 concentration) Here, if the diameter of the UFBO2 is 100 nm, the internal pressure of the bubble is 29.7 atmospheres according to the Young-Laplace equation pi=pe+2σ / r (pi: internal pressure, pe: external pressure, σ: surface tension of water, r: internal diameter of the bubble). If the internal pressure is 29.7 atmospheres, the number concentration of UFBO2 in Example 1 is 1×10 11 Since the concentration is calculated as oxygen particles / mL, the UFB concentration is calculated to be 2.07 mg / L, which is very close to the measured value of 1.7 mg / L by the UV-vis method described above. The slight difference is considered to be due to errors in the diameter, internal air pressure, and number of particles of the UFBO2. From this, it is presumed that the measured value by the UV-vis method in Example 1 is the oxygen concentration inside the UFBO2.

[0045] [Example 2] As in Example 1, UFBO2 was introduced into distilled water, which was left for 30 minutes or more, and then air was bubbled in instead of N2 gas, and the mixture was left for 1 hour or more to allow the microbubbles to disappear. Except for this, steps S1 to S4 were carried out in the same manner as in Example 1, and the first oxygen concentration DO1 and the second oxygen concentration DO2 were measured. Air bubbling was continued until the oxygen concentration measured by the fluorescent DO meter became constant.

[0046] [Comparative Example 2] The same procedure as in Example 2 was used except that no UFBO2 was added to the distilled water. The water was then left for one hour or more to form sample water A. Steps S1 to S4 were carried out, and the first oxygen concentration DO1 and the second oxygen concentration DO2 were measured.

[0047] (Measurement results of DO concentration in Example 2 and Comparative Example 2 in which air was bubbled) In both Example 2 and Comparative Example 2, four sample water A were prepared, and the first oxygen concentration DO1 and second oxygen concentration DO2 measured for one of the sample waters (Actual 2-1) (Ratio 2-1) are shown in Figure 3, and the first oxygen concentration DO1 and second oxygen concentration DO2 measured for the other three sample waters (Actual 2-2 to Actual 2-4) (Ratio 2-2 to Actual 2-4) are shown in Figure 4 and Table 1. As shown in Figures 3 and 4 and Table 1, in Comparative Example 2 in which air was bubbled without introducing UFBO2, the first oxygen concentration DO1 measured by the UV-vis method and the second oxygen concentration DO2 measured by the fluorescent DO meter (FLDO) were consistent. This is similar to Comparative Example 1 in which nitrogen was bubbled without introducing UFBO2. In contrast, in Example 2, in which air was bubbled after UFBO2 was introduced, the first oxygen concentration DO1 measured by the UV-vis method was higher than the second oxygen concentration DO2 measured by the fluorescent DO meter. This is similar to Example 1, in which nitrogen was bubbled after the introduction of UFBO2.

[0048] [Table 1]

[0049] [Examples 3 to 7] Distilled water containing UFBO2 and then bubbled with nitrogen in the same manner as in Example 1, and distilled water not containing UFBO2 and bubbled with nitrogen in the same manner as in Comparative Example 1 were mixed at different mixing ratios to prepare five samples (Examples 3 to 7) with different number concentrations of UFBO2. The number concentrations of these UFBO2 were also measured in the same manner as in Example 1. For Examples 3 to 7, the first oxygen concentration DO1 and the second oxygen concentration DO2 were measured, and the mass concentration of UFBO2 was calculated by taking the difference between them in the same manner as in Example 1. In addition, the UFBO2 mass concentration was calculated from the UFBO2 number concentration of each sample in the same manner as in Example 1. Figure 5 shows the relationship between the UFBO2 concentration determined by measurement and the UFBO2 concentration determined by calculation. The straight line in the figure is the calibration curve determined by the least squares method, and Y and R2 indicate the slope and coefficient of determination. The error bars in Figure 5 indicate the standard deviation of multiple measurements.

[0050] (detection limit) Among Examples 3 to 7, Example 3 had the lowest UFBO2 number concentration. The standard deviation of the UFBO2 mass concentration obtained by measuring five times was tripled to calculate the detection limit of the method for measuring the oxygen concentration in ultra-fine bubbles according to this example. The value obtained was 0.71 mg / L.

[0051] [Test Example 1] In the same manner as in Example 2, UFBO2 was added to distilled water, and then air was bubbled into the sample water A, and the oxygen concentration was measured by the Winkler method. The results are shown in Figure 6. The number of samples in Test Example 1 was 6, and the average oxygen concentration was 8.89 mg cm-. 3 , the standard deviation was 0.266.

[0052] [Test Example 2] The oxygen concentration of sample water A obtained by bubbling air into distilled water without adding UFBO2 in the same manner as in Comparative Example 1 was measured by the Winkler method. The results are shown in Figure 6. The number of samples in Test Example 1 was 12, and the average oxygen concentration was 8.95 mg cm- 3 , the standard deviation was 0.409.

[0053] (Consideration) -About the measured values ​​of the optical DO meter Since there was no difference in the second oxygen concentration measured by the fluorescent DO meter between Examples 1 and 2, in which ultrafine bubbles (UFBO2) were introduced, and Comparative Examples 1 and 2, in which UFBO2 was not introduced, it is believed that the fluorescent DO meter measures only the oxygen concentration dissolved in the sample water A.

[0054] About UV-vis measurement values In Examples 1 and 2, in which UFBO2 was introduced, the measured oxygen concentration by the UV-vis method was higher than in Comparative Examples 1 and 2, in which UFBO2 was not introduced. Moreover, in Comparative Examples 1 and 2, in which UFBO2 was not introduced, the oxygen concentration by the UV-vis method and the measurement results by the fluorescent DO method were not different. From the above, it was made clear that the UV-vis method according to this embodiment measures an oxygen concentration consisting of the sum of oxygen dissolved in a solution containing ultra-fine bubbles and oxygen inside the ultra-fine bubbles.

[0055] -Oxygen concentration in ultra-fine bubbles From the above, it became clear that the oxygen concentration of only the oxygen contained in the ultra-fine bubbles can be calculated by subtracting the second oxygen concentration DO2 measured using a fluorescent DO meter from the first oxygen concentration DO1 measured using the UV-vis method in the ultra-fine bubble solution.

[0056] -Relationship between measured UFBO2 concentration and calculated UFBO2 As shown in Fig. 5, the relationship between the measured UFBO2 concentration and the calculated UFBO2 concentration was determined by the coefficient R 2 A highly reliable calibration curve with a Y-axis of 0.986 was obtained. The calibration curve had an intercept of 0 and a slope of Y=0.9431, which indicates that the method for measuring the oxygen concentration in ultra-fine bubbles according to this embodiment can measure the concentration of only the oxygen in ultra-fine bubbles with high accuracy.

[0057] -Oxygen concentration obtained by Winkler method Since there was no significant difference in the oxygen concentration measured by the Winkler method between Test Example 1, which contained UFBO2, and Test Example 2, which did not contain UFBO2, it was found that the oxygen concentration obtained by the Winkler method does not include oxygen in the UFBO2, but only includes dissolved oxygen in the water.

[0058] As described above, the method for measuring the oxygen concentration in ultra-fine bubbles according to the present invention is not limited to the above-mentioned embodiment. For example, a reagent may be mixed with sample water without using a three-way valve or without flowing nitrogen gas through the three-way valve. [Explanation of symbols]

[0059] 1. Measuring equipment 2. Sample water syringe 3 Reagent Syringes 4 Three-way tube 5 Nitrogen transport pipe

Claims

1. A method for measuring an oxygen concentration in ultra-fine bubbles in a water sample, comprising the steps of: a Mn(II) oxidation step in which three kinds of reagents, namely an alkaline solution, a polyphosphate solution, and a manganese salt solution, are added to the sample water to oxidize Mn(II) to Mn(IV) while suppressing precipitation of Mn(II); a Mn(IV) reduction step in which a strong acid solution is added to the sample water that has been subjected to the Mn(II) oxidation step to stop the oxidation reaction, and the Mn(IV) formed in the Mn(II) oxidation step is reduced to Mn(III); a first oxygen concentration measurement step of measuring the absorbance of light at a wavelength absorbed by Mn(III) in the sample water that has been subjected to the Mn(IV) reduction step, and calculating a first oxygen concentration, which is the oxygen concentration of the sample water, from the absorbance; a second oxygen concentration measuring step of measuring a second oxygen concentration consisting only of dissolved oxygen in the same sample water as that used in the first measurement step; A method for measuring an oxygen concentration in ultra-fine bubbles in a water sample, comprising the steps of: subtracting the second oxygen concentration from the first oxygen concentration to calculate the amount of oxygen in the ultra-fine bubbles in the water sample.

2. 2. The method for measuring an oxygen concentration in ultra-fine bubbles according to claim 1, wherein the wavelength of light used to measure absorbance in the first oxygen concentration measurement step is 512 nm or more and 522 nm or less, 513 nm or more and 521 nm or less, 514 nm or more and 520 nm or less, 515 nm or more and 519 nm or less, 516 nm or more and 518 nm or less, or 517 nm.

3. The method for measuring an oxygen concentration in ultra-fine bubbles according to claim 1, wherein the alkaline solution is a NaOH solution.

4. The polyphosphate solution was prepared by adding (NaPO 3 ) 6 The method for measuring an oxygen concentration in ultra-fine bubbles according to claim 1, wherein a solution is used.

5. The manganese salt solution may be MnSO 4 The method for measuring an oxygen concentration in ultra-fine bubbles according to claim 1, wherein a solution is used.

6. The strong acid solution is H 2 SO 4 The method for measuring an oxygen concentration in ultra-fine bubbles according to claim 1, wherein a solution is used.

7. The alkaline solution, the polyphosphate solution, and the manganese salt solution were each a NaOH solution, (NaPO 3 ) 6 solution, MnSO 4 2. The method for measuring the oxygen concentration in ultra-fine bubbles according to claim 1, wherein solutions are used and are introduced into the sample water in the following order.

8. a nitrogen flowing step of flowing nitrogen into a three-way pipe in a state where the sample water syringe containing the sample water and a nitrogen flow pipe for flowing nitrogen are connected to the three-way pipe; 2. The method for measuring an oxygen concentration in ultra-fine bubbles according to claim 1, further comprising the steps of: switching the three-way valve to communicate the sample water syringe with the reagent syringe, and introducing one of the reagents into the sample water syringe.

9. 2. The method for measuring an oxygen concentration in ultra-fine bubbles according to claim 1, wherein the second oxygen concentration is measured using a fluorescent DO meter in the second oxygen concentration measuring step.

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