JP2007263970A - Carbon dioxide concentration measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring instrument for simply and rapidly measuring a carbon dioxide gas concentration in a solution.
[Solution]
Carbon dioxide gas concentration in a solution having a sealed resin container with a lid, a weighing device, a gas phase carbon dioxide gas measuring means, and a means for converting the carbon dioxide gas concentration in the solution from the carbon dioxide gas concentration in the gas phase Use a measuring instrument.
In particular, preferably, a measuring cylinder is used as the weighing instrument, and the container portion to be joined to the lid is circular with a diameter larger than that of the detection tube and smaller than 30 mm, and is made of resin. Moreover, it is preferable to use a sealed container having a volume of 200 to 1000 ml.
[Selection figure] None

Description

  The present invention relates to a measuring instrument for measuring the concentration of carbon dioxide in a solution. For example, carbon dioxide in a carbonated spring that is useful for hydrotherapy for the purpose of improving physiological functions can be measured easily and quickly on the spot. And a simple measuring instrument that is light and compact.

Since carbonated springs have an excellent heat retention effect, they have long been used in bathhouses that use hot springs. The warming action of carbonated spring is considered to be basically because the body environment is improved by the peripheral vasodilatory action of the contained carbon dioxide gas. In addition, the percutaneous approach of carbon dioxide gas increases and dilates the capillary bed, improving the blood circulation of the skin. For this reason, it is said that it is effective in the treatment of degenerative lesions and peripheral circulation disorders.
According to Article 2 of the Onsen Law, the carbon dioxide concentration of carbonated springs is defined and refers to those of 250 mg / l or more. Moreover, as a definition of the medical treatment spring of Article 13, the thing of 1000 mg / l or more is pointed out. Although there is no upper limit for these, in fact, the naturally occurring carbonated spring is about 1500 mg / l even at high concentrations.
On the other hand, in order to artificially obtain a carbonated spring, there are a chemical method for reacting carbonate and acid, a method using a combustion gas of a boiler, a device for directly blowing carbon dioxide into a pipe having a throttle, and the like. Recently, many methods for producing carbonated springs using membranes have been proposed, and among these, the method using a non-porous hollow fiber membrane has the best carbon dioxide dissolution efficiency.

The methods for measuring the concentration of carbon dioxide in water containing carbon dioxide such as carbonate spring include the Orsat method, gas absorption method, conductivity method, thermal conductivity method, infrared absorption method, gas chromatograph method, mass spectrometry method, ion An electrode method, a gas phase pressure / liquid phase temperature measurement method, a method of converting from pH and alkalinity, and the like are known.
For example, Patent Document 1 discloses a test water obtained by separating a flow path of a gas separation device with a gas permeable membrane and adding an acidic solution to one flow path of the gas separation device to separate carbon dioxide in the test water as carbon dioxide gas. Circulate, cause the alkali solution to circulate through the other channel, react with the carbon dioxide gas that has permeated through the gas permeable membrane of the gas separator, and measure the conductivity of the alkali solution reacted with the carbon dioxide gas downstream of the other channel. Thus, a method for measuring the carbonic acid concentration in the test water has been proposed.
Further, Patent Document 2 discloses a sample water introduction pipe provided with a hydrogen ion type strongly acidic cation exchange resin tower and a sample water flow rate detection unit, and a dilution water injection pipe provided with a dilution water flow rate detection unit joined thereto. A conductivity detector for measuring the conductivity of the diluted sample water, the two flow rate detectors, an arithmetic unit for calculating the carbonate concentration in the sample water from the signals of the conductivity detector, and the calculated carbonate concentration. A carbonic acid concentration measuring device having a display unit for displaying has been proposed.

In addition, the Japanese Industrial Standard (JIS) employs the Orsat method in which a sample is taken in a gaseous form, absorbed in a potassium hydroxide solution, and the percentage is calculated from the change in volume (JIS K1106).
On the other hand, in the mineral spring analysis method, a sample is taken in a sodium hydroxide standard solution to which citric acid-tartrate has been added in advance, and after gently stirring, titration is carried out with hydrochloric acid standard solution until the faint red color of phenolphthalein disappears. It is stipulated that free carbon dioxide is quantified from the consumption of sodium standard solution.

  In the method for measuring the concentration of carbon dioxide in water, carbon dioxide can be accurately quantified with methods using large analyzers, including the methods described above using conductivity, gas chromatographs, mass spectrometers, etc. However, since specialized techniques are required for the operation of the apparatus, it has to be carried out by a professional engineer at a place where there is an experimental facility such as a factory management room, and it is disadvantageous in that it is expensive. In addition, in order to use such a method, it is necessary to transport a sample from the field, but there is a drawback that the concentration of carbon dioxide gas in the water is lowered due to stimulation or change with time, and correct measurement cannot be performed.

On the other hand, the mineral spring analysis method is established for the purpose of local analysis and can be measured locally, but it requires several types of reagents and requires a technique for neutralization titration with a burette or the like. There was a drawback.
The ion electrode method can also be used in the field, but daily fluctuations are large and daily calibration is required. In addition, carbon dioxide bubbles are attached to the electrode when measuring at high concentrations of 500 mg / l or more, making accurate analysis unsuitable. Therefore, it was necessary to dilute the sample. In addition, there is a drawback that the response time is slow.
The method of converting from pH and alkalinity is a simple method that can convert the concentration of carbon dioxide gas by determining pH and alkalinity, and is also described in Patent Document 3, but is affected by different alkalinity depending on water. It was necessary to measure it every time, and it was necessary to measure the pH fairly accurately.

  The gas phase pressure / liquid phase temperature measurement method fills a sample in a sealed container, gasifies carbon dioxide dissolved in the sample by stimulation, and calculates the carbon dioxide concentration from the gas pressure and liquid phase temperature. It is a method to do. In this method, the carbon dioxide concentration is calculated according to Henry's law. Henry's law is that the amount of gas that dissolves in a certain liquid at a certain temperature is proportional to the pressure of that gas. Since carbon dioxide concentration can be measured only by pressure and temperature, it is simple and is often used for measuring water in which carbon dioxide is dissolved at a high concentration, such as carbonated beverages. However, even if the concentration of carbon dioxide gas in a carbonated spring, for example, in a carbonated spring, which is lower than that of a carbonated beverage, is measured using this method, the measurement is difficult because the gas pressure is small. In addition, the price was expensive, with several hundred thousand yen or more, and it was not easy to purchase.

JP-A-5-80009 JP 11-258191 A JP-A-10-277121

  The object of the present invention is to solve the above-mentioned problems. That is, an object of the present invention is to provide a method for measuring carbon dioxide concentration in a solution, particularly in water, simply and quickly on site, and a lightweight and compact simple measuring instrument used therefor.

The gist of the present invention that can solve such a problem is an instrument for measuring the concentration of carbon dioxide, a sealed resin container with a lid, a weighing instrument, a gas-phase carbon dioxide measuring means, and carbon dioxide in the gas phase. And a means for measuring the carbon dioxide concentration in the solution from the concentration.
Preferably, a graduated cylinder is used as a weighing instrument, and a container made of a resin having a circular shape with a diameter larger than the diameter of the detection tube and smaller than 30 mm is used. Moreover, it is preferable to use a sealed container having a volume of 200 to 1000 ml.

The carbon dioxide measuring instrument in the solution of the present invention is lightweight and compact, and by using this instrument, the carbon dioxide concentration in the solution can be measured easily and quickly on site.

Hereinafter, the present invention will be specifically described with respect to an example in which water is used as the solution, that is, the case where the carbon dioxide concentration in the carbonated spring is measured.
The measuring instrument of the present invention is preferably used for a solution whose carbon dioxide concentration is expected to be about 100 mg / l or more. This can be applied to carbonated beverages within the concentration range of carbonated springs adjusted with various natural and artificial carbonated spring devices.
The measuring instrument of the present invention is preferably used for a solution having a pH of about 6 or less. The ratio of carbon dioxide, bicarbonate ions, and carbonate ions varies depending on the pH of carbon dioxide in water. The higher the pH, the higher the latter ratio. When the pH is 6 or less, it is almost 100% carbon dioxide gas. However, when the pH is exceeded, it gradually becomes bicarbonate ions, and when the pH is 8, the carbon dioxide gas does not exist. Therefore, when trying to analyze a sample having a pH of 6 to 8, the pH is increased by shaking the sample, and the carbon dioxide gas in the water is changed to bicarbonate ions, so that accurate analysis cannot be performed. Further, since the carbon dioxide gas in water does not exist at pH 8 or higher, there is no point in analyzing itself.

The amount of sample in the container is 1 to 50% of the container volume, preferably 2 to 30%, more preferably 5 to 20%. If it is too low, the analysis accuracy will be lowered, and if it is too high, it will be difficult for carbon dioxide to be driven out into the gas phase even if shaken.
It is preferable to select the sample amount within a range where the carbon dioxide concentration in the gas phase newly constituted by shaking does not exceed 10%. According to Henry's law, the higher the pressure, the greater the solubility of the gas in water, and the higher the temperature, the smaller the solubility, but compared to the gas phase pressure / liquid phase temperature measurement method where the gas phase becomes high pressure. Since the present invention is at a low pressure, the solubility of gas in water is reduced and it is difficult to be affected by temperature. In addition, it is important to accurately weigh the amount of sample put in the container, and the error directly affects the measurement error. However, although it is weighed, it does not mean that anything can be used, and thin pipettes such as graduated cylinders, which have a high possibility that carbon dioxide gas will escape from the sample during weighing and injection, are not acceptable. preferable.

  Shaking can be expelled sufficiently to the gas phase even with the arm, but in that case, the amplitude is 3 cm or more, the shaking speed is 120 times / minute or more, and the shaking time is 15 seconds or more. preferable. If it is less than that, it will be difficult to expel the carbon dioxide gas sufficiently into the gas phase.

As a method for measuring the carbon dioxide concentration in the gas phase, a method of measuring using a detector tube type gas measuring device is simple and preferable.
The detector tube type gas measuring device is defined by JIS K0804, and means a gas measuring device comprising a detector tube type gas sampling device and a detector tube. As a feature, it does not require chemical preparation equipment, liquid reagents, etc., so it does not require measurement preparation and is lightweight, so it is convenient to carry and suitable for on-site measurement. In addition, the measurement operation is very simple, the measurement error by the measurer is small, and the measurement result can be obtained in a few minutes.

  The gas sampler has a function to ventilate a certain amount of sample gas into the detection tube by pressurizing or depressurizing the inside, and the sample gas is detected by an orifice installed inside the detection tube attachment port. Adjust the rate at which air is vented to the tube. The type is a cylinder type vacuum system in which the inside of the cylinder of the gas sampling device connected to the detection tube is depressurized by a piston, and the sample gas is sucked through the detection tube. After that, the cylinder type feeding system that discharges the sample gas through the detection tube by the piston, compresses the bellows, decompresses the bellows by the stress of the internal spring, and sucks the sample gas through the detection tube There are three types such as bellows. In addition, a disposable syringe can be used instead.

The detection tube is filled with a certain amount of detection agent or pretreatment agent in a transparent tube such as a glass tube with a uniform inner diameter and the same overall length, and a stopper is applied to prevent this from loosening, and both ends of the tube are sealed. It is used at the time of use. By sucking a certain amount of gas into the detection tube by the gas suction device, the detection agent filled in the detection tube reacts with the reaction gas and changes its color. In the case of carbon dioxide, a method of reacting with hydrazine impregnated in the detection agent to produce carbamic acid, which further discolors the pH indicator impregnated in the detection agent is suitable.
The detection method of the detection tube is a direct reading method that directly reads the concentration scale printed on the surface of the detection tube to obtain the concentration of the target gas, and compares the attached concentration table with the color change length of the detection agent. There are two types of concentration formulas for determining the gas concentration.
There are several types of detector tubes depending on the concentration range, but the detector tube is selected within the range in which the newly constructed gas concentration can be measured.

  The amount of sample added to the container is preferably such that the difference between the volume of the container and the amount of sample added to the container is at least twice the amount of suction used in the detector tube type gas detector tube, more preferably more than five times. is there. If it is below this range, the atmosphere is likely to be mixed into the detector tube in addition to the sample gas.

What is prepared with the simple measuring instrument of the present invention is a closed container with a lid, a weighing instrument, a means for measuring carbon dioxide in the gas phase, and converts the carbon dioxide concentration in the solution from the carbon dioxide concentration in the gas phase. Means. As a means for converting the carbon dioxide gas concentration in the solution from the carbon dioxide gas concentration in the gas phase, a calibration curve of the carbon dioxide gas concentration in water and the carbon dioxide gas concentration in the gas phase measured using this method is used.
Use a sealed container with a lid. By using this, the time for a series of operations can be shortened, and the container can be used many times.
Moreover, it is good to use the airtight container whose container part joined to a lid | cover is a circle larger than the outer diameter of a detection tube and smaller than 30 mm. When the gas in the container is analyzed, the atmosphere is opened to the atmosphere. By setting this range, the gas in the container is hardly replaced with the atmosphere.

Furthermore, when a resin container is used, it is light and convenient to carry, and a commercially available empty container for soft drinks in a plastic bottle can also be used.
The capacity of the sealed container is preferably 200 to 1000 ml. If it is smaller than this range, the accuracy is lowered. Conversely, if it is larger than the range, the accuracy is not affected, but it is inconvenient in terms of carrying.

The present invention will be specifically described with reference to examples.
Example 1
As a sealed container, a 500 ml plastic bottle empty container for soft drinks, as a weighing instrument, as a 50 ml resin graduated cylinder, as a device for measuring carbon dioxide in the gas phase, as a gas sampler (manufactured by GASTECH, GV-100S), gas A detector tube (manufactured by Gastec, product name 2L, scale range 0.25 to 3.0%, 100 ml suction) was prepared.
The sample to be measured was accurately weighed 50 ml with a graduated cylinder and gently poured into a 500 ml plastic bottle. The plastic bottle was sealed with a cap and shaken by hand for 30 seconds. After that, the cap of the plastic bottle was removed, the detection tube attached to the collector was put into the plastic bottle, 50 ml was sucked, and the value was read.
First, carbonated water with different carbon dioxide concentrations having a water temperature of 40 ° C. was prepared, and a calibration curve with the concentration of carbon dioxide in the gas phase was prepared. In addition, the value converted from pH and alkalinity was used for the carbon dioxide gas concentration in water used for the calibration curve. Table 1 and FIG. 1 show the relationship between the value converted from pH and alkalinity and the indicated value by the detector tube.

  Using this FIG. 1 as a calibration curve, the indicator value of the detector tube of the present invention is calculated from the calibration curve of FIG. 1 for carbonated water whose carbon dioxide concentrations converted from pH and alkalinity are 200, 780 and 1270 mg / l. Comparison was made with the converted carbon dioxide concentration. The results are shown in Table 2.

(Example 2)
In the same manner as in Example 1, the same calibration curve was used to measure samples with different water temperatures. The results are shown in Table 2. The carbon dioxide concentration converted from the indicated value of the detector tube showed a value almost equal to the value converted from pH and alkalinity. Moreover, there is little influence of temperature.

(Comparative Example 1)
A sample having a measured value of carbon dioxide concentration converted from pH and alkalinity of 10 mg / l was measured. The results are shown in Table 2, and the detection tube did not change color and was not measurable.

  The carbon dioxide concentration measuring instrument, hot spring, carbonated spring and the like according to the present invention can be publicly used in the measurement of the carbon dioxide concentration in a carbon dioxide solution such as carbonated drinking water.

It is explanatory drawing which shows the relationship between the instruction | indication value of a detection tube, and a carbon dioxide gas density | concentration.

Claims (4)

An instrument for measuring carbon dioxide concentration,
Carbon dioxide gas concentration in a solution having a sealed resin container with a lid, a weighing device, a gas phase carbon dioxide gas measuring means, and a means for converting the carbon dioxide gas concentration in the solution from the carbon dioxide gas concentration in the gas phase measurement tool.   The instrument for measuring the concentration of carbon dioxide in a solution according to claim 1, wherein a measuring cylinder is used as the weighing instrument.   The instrument for measuring the concentration of carbon dioxide in a solution according to claim 1 or 2, wherein the container part to be joined to the lid is a closed container having a circular shape larger than the outer diameter of the detection tube and smaller than 30 mm. The instrument for measuring the concentration of carbon dioxide in a solution according to any one of claims 1 to 3, wherein a sealed container having a volume of 200 to 1000 ml is used.

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