Carbon dioxide gas concentration measuring instrument and dissolved carbon dioxide gas concentration measuring method

Abstract

To provide an instrument for easily measuring an approximate concentration of carbon dioxide gas in a gas phase or a liquid phase without using a commercial power source and a method for easily measuring a concentration of dissolved carbon dioxide gas in an aquarium water tank or the like.SOLUTION: A carbon dioxide gas concentration measuring instrument storing a carbon dioxide gas measuring liquid containing bicarbonate ions and a pH indicator into a vessel partially or entirely composed of a gas permeable film is placed in an analyte, and pH of the carbon dioxide gas measuring liquid at the time when a carbon dioxide gas partial pressure of the analyte and a carbon dioxide gas partial pressure of the carbon dioxide gas measuring liquid reach equilibrium is measured by the pH indicator and is converted to a concentration of carbon dioxide gas. Further, water to be measured and a bicarbonate ion solution are mixed at a fixed ratio, and pH of this mixed solution is measured to measure a concentration of dissolved carbon dioxide gas.

Description

[Technical field]

[0001] The present invention relates to a carbon dioxide concentration measuring device and a method for measuring the concentration of dissolved carbon dioxide. [Background technology]

[0002] Carbon dioxide may be used as a gas, dissolved carbon dioxide, or may be removed as an emission, but it is often desirable to measure or approximately know the concentration.

[0003] In ornamental aquariums, carbon dioxide is often dissolved in the water to promote photosynthesis and grow and maintain the aquatic plants. Methods for dissolving carbon dioxide include using an aeration tube to disperse and dissolve the gas in the water, or confining carbon dioxide in a cylinder whose top end is sealed with a lid equipped with a carbon dioxide supply pipe and whose bottom end is open to the water, and dissolving and supplying the carbon dioxide from the surface that comes into contact with the water.

[0004] Since the appropriate carbon dioxide supply rate varies depending on the size of the aquarium, the amount of aquatic plants, the photosynthetic ability, the carbon dioxide dissolution efficiency, etc., it is desirable to measure the dissolved carbon dioxide concentration and maintain an appropriate concentration. Therefore, even if the accuracy is not sufficient, a simple carbon dioxide concentration measuring device or method is desired.

[0005] However, since it is not possible to obtain inexpensive dissolved carbon dioxide concentration measuring devices that are easy to maintain and use, general users at home and other places often do not measure the carbon dioxide concentration, but instead set the carbon dioxide supply amount based on experience.

[0006] As a practical dissolved carbon dioxide measuring device, a measuring device is known that has a gas permeable membrane at the tip, inserts a glass pH sensor into a cylinder that contains sodium bicarbonate liquid inside, measures the pH of the sodium bicarbonate liquid, and converts it into dissolved carbon dioxide concentration (Patent Document 1). However, although the measuring device is capable of continuous measurement, it takes time for the carbon dioxide gas concentration of the test liquid and the sodium bicarbonate liquid inside the sensor to reach equilibrium through the gas permeable membrane, and requires a pH sensor with a special shape with a flat tip that can contact the gas permeable membrane, a concentration measuring and display device, and a power source, and the maintenance and management of the gas permeable membrane of the sensor and the sodium bicarbonate liquid inside are complicated, calibration is necessary, and furthermore, measurement requires skill and is expensive. It is also complicated to carry and install, and although it is used for industrial purposes, it cannot be said to be a simple device that can be used at home.

[0007] Carbon dioxide is also sometimes supplied to plants grown on land in greenhouses, etc., and a carbon dioxide concentration measuring device that can be used easily without a power source is also desired. Infrared absorption gas concentration devices that measure and display the carbon dioxide concentration in the air are widely used. However, since a power source is required to operate the device, installation is limited to places where a power supply is available, and since it is an electronic device, the initial cost is high.

[0008] Alternatively, when culturing animal cells, a technique is widely used in which a pH indicator such as phenol red is added to the culture solution, and the approximate pH is detected by the change in color of the culture solution. The pH of the culture solution is affected by the concentration of dissolved carbon dioxide, but it is also affected by various components in the culture solution in addition to carbon dioxide. In addition, since the indicator is added to the entire culture solution to be measured, a large amount of indicator is required for large-volume culture. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 1315306 Summary of the Invention [Problem to be solved by the invention]

[0010] In view of the above-mentioned drawbacks of the conventional techniques, the present invention provides a carbon dioxide concentration measuring device and a method for measuring dissolved carbon dioxide concentration, which do not require a power source and can easily measure dissolved or gas-phase carbon dioxide. [Means for solving the problem]

[0011] (1) The carbon dioxide concentration measuring device of the present invention is a container constituted in whole or in part by a gas permeable membrane; A carbon dioxide gas measuring solution containing bicarbonate ions and a pH indicator contained in the container; The device is configured to include:

[0012] According to this invention, since the carbon dioxide measurement liquid contains bicarbonate ions, the hydrogen ion concentration in the carbon dioxide measurement liquid is proportional to the carbon dioxide concentration. In addition, since the carbon dioxide measurement liquid contains a pH indicator, its pH can be detected. By using the detected pH and a previously prepared calibration curve for the carbon dioxide measurement liquid (a calibration curve showing the correlation between the pH of the carbon dioxide measurement liquid and the carbon dioxide concentration), it is possible to detect the carbon dioxide concentration of the test sample.

[0013] (2) This carbon dioxide concentration measuring device is The apparatus may further include a second gas-impermeable container that is connected to the container and is configured to be capable of transferring the refill carbon dioxide gas measuring solution stored therein to the container.

[0014] Carbon dioxide gas in the specimen that permeates the gas permeable membrane dissolves in the carbon dioxide gas measurement liquid, but the moisture in the carbon dioxide gas measurement liquid in the container also permeates as water vapor, causing a decrease in the carbon dioxide gas measurement liquid and an associated increase in the bicarbonate ion concentration inside the container, which could result in measurement errors or, if evaporation continues, make it impossible to measure. According to this invention, since the carbon dioxide gas measuring solution in the second container is connected to the container equipped with the gas permeable membrane, the carbon dioxide gas measuring solution can be replenished from the second container which does not have gas permeability, and the concentration can be kept stable for a long time, so that the performance deterioration and life of the device can be extended. To suppress evaporation, it is also effective to mix an evaporation prevention agent such as CMC or ethylene glycol into the carbon dioxide gas measuring solution.

[0015] (3) This carbon dioxide concentration measuring device is A plurality of the containers may be provided, each containing a plurality of the carbon dioxide gas measuring solutions having different compositions.

[0016] The carbon dioxide concentration measuring device of the present invention is not intended to accurately measure a wide range of carbon dioxide concentrations, but is effective for measuring carbon dioxide concentration by measuring the approximate pH of the color change range of a pH indicator and whether it is higher or lower than that color change range. Therefore, by using a carbon dioxide concentration measuring device that stores carbon dioxide measuring liquids with different target concentrations, i.e. different compositions, for measuring multiple target objects, it becomes possible to measure different carbon dioxide concentrations and a wider measurement range can be accommodated. Effective targets for changing the composition of the carbon dioxide measuring liquid are bicarbonate ion concentration, pH adjusters, and pH indicators, and differences in the type and concentration of these change the target concentration, so having multiple carbon dioxide concentration measuring devices makes it possible to measure concentrations over a wide range.

[0017] (4) The method for measuring the concentration of dissolved carbon dioxide of the present invention is providing a predetermined amount of test liquid; mixing a predetermined amount of bicarbonate ions into the test liquid according to the amount of the test liquid; Measuring the pH of the mixture; The device is configured to include:

[0018] According to the present invention, a predetermined amount of bicarbonate ion is mixed into a given amount of test liquid, so that the bicarbonate ion concentration of the test liquid can be set to a specified value. If a calibration curve of the pH and dissolved carbon dioxide concentration of the test liquid is prepared in advance, it becomes possible to measure the dissolved carbon dioxide concentration in the test liquid by measuring the pH of the test liquid. The pH can be measured using a normal glass membrane pH sensor.

[0019] (5) This method for measuring dissolved carbon dioxide concentration is mixing a pH indicator in a predetermined amount according to the amount of the test liquid; The concentration of carbon dioxide dissolved in the test liquid may be measured based on the color of the pH indicator.

[0020] According to the present invention, the pH of the mixture varies depending on the carbon dioxide concentration of the test liquid, and the concentration of dissolved carbon dioxide in the test liquid can be measured from the color tone of the pH indicator.

[0021] It is also possible to provide a device and a method for measuring the concentration of dissolved carbon dioxide that can easily measure the approximate concentration of carbon dioxide in a test specimen even without a power source. [Brief description of the drawings]

[0022] [Figure 1] 1 is a cross-sectional view of a carbon dioxide concentration measuring device according to a first embodiment of the present invention. [Diagram 2] Front view of the second embodiment of the present invention [Diagram 3] Cross section AA of Figure 2 [Figure 4] Rear view of the second embodiment of the present invention [Diagram 5] Cross section B-B of Figure 3 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, examples to which the present invention is applied will be described. However, the present invention is not limited to the following examples. In other words, all configurations described in the following examples are not necessarily essential to the present invention. In addition, the present invention includes any combination of the following contents.

[0024] When carbon dioxide dissolves in water, the equilibrium (1) is reached and equation (2) holds. TIFF2025000522000001.tif2358If the bicarbonate ion concentration is kept constant by adding bicarbonate ions, the hydrogen ion concentration and carbon dioxide concentration are proportional, so once a calibration curve of pH and dissolved carbon dioxide concentration is created and the pH is measured, the carbon dioxide concentration can be calculated.

[0025] The inventors bubbled carbon dioxide gas of various concentrations with a nitrogen balance of 0.2 to 100% from a cylinder into a 0.01N sodium bicarbonate and 0.1N salt mixture, measured the pH at equilibrium, and obtained the results in Table 1. Within the above concentration range, the logarithm of the carbon dioxide gas concentration had a linear relationship with the pH.

[0026] [Table 1]

[0027] From Table 1, the relationship between carbon dioxide concentration (C) and pH is The result is TIFF2025000522000003.tif1094, and the carbon dioxide concentration can be calculated from the pH. Since the gas phase and dissolved carbon dioxide have the same partial pressure at equilibrium, the concentrations are both expressed as %. For example, to measure a carbon dioxide concentration of approximately 1 to 10% from Table 1, a mixture of 0.01 N sodium bicarbonate and 0.1 N salt is adjusted to the same partial pressure as the carbon dioxide concentration of the test sample, and bromothymol blue, which changes color in the pH range of approximately pH 6.0 to 7.6, or phenol red, which changes color in the pH range of 6.8 to 8.4, is used as an indicator. From the color change, the approximate pH can be measured, and the carbon dioxide concentration of the test sample can be calculated using equation (3) based on this pH.

[0028] For measuring low concentrations, an indicator such as phenolphthalein, which has a color change range of 8.3 to 10.0 and shifts toward the alkaline side, can be used. For example, if phenolphthalein turns red, the pH is 8.4 or higher, and the dissolved carbon dioxide concentration is 0.2% or less. Wide-range pH test paper carrying an indicator on paper can also be used. In the experiment in Table 1 above, a 0.01N solution of sodium bicarbonate and 0.1N salt was used as the carbon dioxide concentration measurement liquid that dissolves carbon dioxide, but similar results can be obtained with a carbon dioxide concentration measurement liquid without salt.

[0029] As can be seen from equation (2), the pH of the carbon dioxide measuring solution that becomes equilibrium with the carbon dioxide concentration depends on the bicarbonate ion concentration and the pH of the carbon dioxide measuring solution before it absorbs carbon dioxide. The present invention is a carbon dioxide concentration measuring device that contains a carbon dioxide measuring solution containing bicarbonate ions and a pH indicator in a container that is partially or entirely made of a gas-permeable membrane. The pH of the carbon dioxide measuring solution that has reached partial pressure equilibrium with the specimen through the gas-permeable membrane can be measured by the color of the indicator, so the carbon dioxide concentration can be measured visually. Since the carbon dioxide measuring solution is stored in a container, it is easy to carry and can measure both gas-phase and dissolved carbon dioxide without using electricity.

[0030] The gas-permeable membrane that can be used in the practice of the present invention is a membrane that is permeable to gas but not to water, and examples of such membranes include silicon, thin plastic membranes, porous water-repellent membranes, and membranes made of cloth that has been treated to be water-repellent. The liquid containing bicarbonate ions can be prepared by dissolving a bicarbonate salt such as baking soda, and this may be mixed with a salt such as sodium chloride or potassium chloride, or a pH adjuster such as hydrochloric acid or caustic soda.

[0031] It is preferable to select a pH indicator of the present invention that has an appropriate color change range depending on the concentration of carbon dioxide to be measured. When the pH is 5 to 9, bromothymol blue, phenol red, neutral red, naphtholphthalein, etc., or a mixture thereof can be used as the indicator. When the carbon dioxide concentration of the object to be measured is low, the carbon dioxide concentration measurement liquid will be on the alkaline side, so cresolphthalein or phenolphthalein, which have a color change range on the alkaline side, can be used.

[0032] Specific examples to which the present invention is applied will be described below. Fig. 1 shows a cross-sectional view of the first embodiment of the present invention. The carbon dioxide concentration measuring device 1 is configured by filling a mixture of sodium bicarbonate solution and a pH indicator as a carbon dioxide measuring liquid 3 in a semi-transparent tube 2 made of silicon, which is an example of a gas-permeable material, and sealing both ends of the tube with stoppers 4. When the carbon dioxide concentration measuring device 1 is placed in the atmosphere of the test specimen, carbon dioxide moves through the tube 2, the partial pressure of carbon dioxide in the test specimen and the partial pressure of carbon dioxide in the carbon dioxide measuring solution are equilibrated, and the indicator in the carbon dioxide measuring solution 3 changes color according to its pH. Various carbon dioxide measuring devices were prepared by filling the tube 2 with various carbon dioxide measuring solutions made by adding phenolphthalein or phenol red as a pH indicator to sodium bicarbonate solutions of various concentrations.

[0033] Table 2 shows the color change of the carbon dioxide concentration measuring solution 3 in the tube 2 when the various carbon dioxide measuring devices were placed in carbon dioxide of various concentrations, which were made by mixing air and carbon dioxide. The color change is reversible, and even if it changes color once, it will change color again depending on the carbon dioxide concentration of the environment. In other words, the carbon dioxide concentration can be measured from the color change. If the liquid in the tube is left in an air phase of 25°C and a humidity of about 50%, air bubbles will form in the tube after a few hours. This is due to the evaporation of the carbon dioxide measuring solution in the tube.

[0034] [Table 2]

[0035] When installing the carbon dioxide concentration measuring device of this embodiment in an ornamental aquarium, it can be easily installed by fixing the carbon dioxide concentration measuring device 1 to a suction cup attached to the inner wall of the aquarium.

[0036] Figures 2 to 5 show Example 2. Figure 2 shows a front view, Figure 3 shows a cross-sectional view taken along line AA in Figure 2, Figure 4 shows a rear view, and Figure 5 shows a cross-sectional view taken along line BB in Figure 3. The plastic housing 32 has a generally thin box shape and is provided with a transparent plate 22 in front of the detection section 31 and a gas permeable membrane 24 on the back. A part of the housing 32 is provided with a gas impermeable liquid storage section 33, and the detection section 31 and the liquid storage section 33 store a carbon dioxide gas measurement liquid 3, which liquid communicates with each other via a communication section 23. A part of the liquid storage section 33 is open to the atmosphere through a small hole 26, and the open section 26 is sealed with a gas permeable filter 27, so that the carbon dioxide gas measurement liquid 3 does not leak out even if the housing 32 is turned upside down.

[0037] When this carbon dioxide concentration measuring device is placed in a gas-phase measurement location such as the atmosphere, the carbon dioxide measuring liquid 3 evaporates through the gas permeable membrane 1, reducing the amount of liquid and concentrating the sodium bicarbonate, but the carbon dioxide measuring liquid is replenished from the liquid reservoir 33, extending the life of the carbon dioxide measuring liquid 3. This embodiment is effective when measuring the gas-phase carbon dioxide concentration, where the carbon dioxide measuring liquid evaporates.

[0038] As another embodiment, a carbon dioxide concentration measuring device is provided for one measurement target, the carbon dioxide concentration measuring device including a plurality of carbon dioxide concentration measuring devices each containing a carbon dioxide measuring liquid having a different composition. When the present measuring device in which the carbon dioxide concentration measuring liquid in the silicon tube 2 shown in Example 1 is a 0.001 N sodium bicarbonate liquid containing phenol red and the present measuring device in which the 0.01 N sodium bicarbonate liquid containing phenolphthalein is placed in the same measurement target environment, if the former turns yellow, it is understood from Table 2 that the carbon dioxide concentration is 1 or more, and if the latter placed at the same time turns light pink, it is understood that it is 10 or less, and therefore the carbon dioxide concentration of the measurement target is found to be 1 to 10%. By using a color sample corresponding to the carbon dioxide concentration, it is possible to narrow down the concentration range even further.

[0039] As an example of a method for measuring dissolved carbon dioxide, equal amounts of a test liquid, such as water from an aquarium with aquatic plants, and a carbon dioxide measuring liquid made by mixing 0.02 N sodium bicarbonate and 0.2 N sodium chloride, are mixed together, the pH is measured with a glass pH sensor, and the carbon dioxide concentration calculated from equation (3) is doubled to obtain the carbon dioxide concentration in the test liquid. In the above-mentioned embodiment, the carbon dioxide gas measuring solution was mixed with the test liquid, but the carbon dioxide gas measuring solution can also be made by mixing sodium bicarbonate and table salt, forming them into tablets, and adding them to the test liquid to make the carbon dioxide gas measuring solution in the test liquid.

[0040] In the above example, the pH of the mixture of the test liquid and the carbon dioxide gas measuring liquid was measured with a glass pH sensor, but the approximate concentration of dissolved carbon dioxide gas can also be measured with a pH indicator. Bicarbonate ions may be added in the form of a solution, or a certain weight of a bicarbonate compound, such as a tablet or capsule containing sodium bicarbonate, may be dissolved in the test liquid to generate bicarbonate ions.

[0041] The conventional carbon dioxide sensor described in Patent Document 1 separates the carbon dioxide measurement solution and the test solution in a container with a gas-permeable membrane, but this measurement method is a batch measurement in which bicarbonate ions are directly dissolved in the test solution and the pH is measured, so a carbon dioxide sensor is not required and the operation is simple. Sodium bicarbonate solution, which is an example of bicarbonate ions, has a pH buffer effect, so it is not easily affected by the dissolved components and pH of the test solution, and in solutions with low ionic strength such as those in an aquarium with aquatic plants, measurements can be made with almost no effect from those components. [Explanation of symbols]

[0042] 1...carbon dioxide concentration measuring device, 2...silicon translucent tube, 3...carbon dioxide measuring liquid, 4...stopper, 22...transparent plate, 23...liquid junction, 24...gas permeable membrane, 26...small hole, 27...water repellent filter, 31...detection part, 32...plastic housing, 33...liquid storage part

Claims

1. a container constituted in whole or in part by a gas permeable membrane; A carbon dioxide gas measuring solution containing bicarbonate ions and a pH indicator contained in the container; A carbon dioxide concentration measuring device comprising:

2. 2. The carbon dioxide concentration measuring device according to claim 1, further comprising a second gas impermeable container that is connected to the container and is configured to be capable of transferring the refill carbon dioxide measuring liquid stored therein to the container.

3. 3. The carbon dioxide concentration measuring device according to claim 1, further comprising a plurality of containers each containing a plurality of carbon dioxide measuring solutions having different compositions.

4. providing a predetermined amount of test liquid; mixing a predetermined amount of bicarbonate ions into the test liquid according to the amount of the test liquid; measuring a concentration of dissolved carbon dioxide in the test liquid by measuring a pH of the test liquid; A method for measuring a dissolved carbon dioxide concentration, comprising:

5. The method further includes a step of mixing a pH indicator in a predetermined amount according to the amount of the test liquid, A method for measuring dissolved carbon dioxide concentration, characterized in that in the step of measuring the dissolved carbon dioxide concentration in the test liquid, the dissolved carbon dioxide concentration in the test liquid is measured based on the color of the pH indicator.

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