Method for measuring total amount of molecular carbon dioxide in water body of carbon dioxide ultra-fine bubbles

Abstract

The application discloses a method for measuring total amount of molecular carbon dioxide in water containing carbon dioxide ultra-fine bubbles, and belongs to the technical field of analytical chemistry. The application directly measures water samples containing carbon dioxide ultra-fine bubbles by using a gas chromatography method, reduces carbon dioxide into methane through a methane catalytic converter after separation by a capillary column, detects by using a flame ionization detector, and uses a six-way valve to switch to blow water out of the chromatography system to prevent water from damaging the methane catalytic converter. The application quantifies by using an external standard method, converts the amount of substance of carbon dioxide in the water sample by using a standard curve, divides the sampling volume to obtain the concentration of the molecular carbon dioxide in the water sample. The application can simultaneously measure dissolved carbon dioxide molecules and carbon dioxide molecules in the form of ultra-fine bubbles in water, has no requirement for the existence of other gases and carbon-containing organic matters in the sample, and has the advantages of simple operation, high sensitivity, accurate results and the like.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry technology, specifically relating to a method for determining the total amount of molecular carbon dioxide in water containing ultrafine carbon dioxide bubbles. Background Technology

[0002] Carbon dioxide (CO2), as a core component of the Earth's carbon cycle and one of the most important basic raw materials in the industrial sector, has attracted much attention due to its multiple properties in the environmental, energy, and chemical industries. In nature, CO2 is the carbon source for plant photosynthesis and a key greenhouse gas regulating the Earth's temperature. In industrial applications, it is widely used in beverage carbonation, food preservation, welding shielding gas, fire extinguishing, and as a medium for supercritical fluid extraction. Therefore, its accurate detection is of vital importance in the fields of food and beverage, environmental monitoring, bio-fermentation, and water treatment, especially in carbonated beverage production, beer brewing, and greenhouse gas emission monitoring, where CO2 concentration directly affects product quality, biological health, and environmental safety.

[0003] In recent years, with the development of gas-liquid mixing technology, CO2 ultra-fine bubble (UBBs) water has been widely used in agricultural production, medical adjuvant therapy, industrial cleaning, and battery manufacturing due to its extremely high mass transfer efficiency, long residence time, and special interfacial reactivity. However, the unique physicochemical properties of ultra-fine bubbles, such as interfacial charge and internal high pressure, have brought new challenges to the accurate determination of CO2 content.

[0004] The determination of CO2 in water is inherently complex. Dissolved CO2 in water exists in various forms, including dissolved free CO2, carbonic acid, bicarbonate, and carbonate, and its distribution is closely related to the pH of the system. Furthermore, in ultrafine bubble water, CO2 exists in the form of ultrafine bubbles, which are easily dissolved or released due to various factors such as temperature, sampling, and transfer. Chemical titration was once the standard method for determining dissolved CO2 in water, but its operation is cumbersome, and when dealing with systems containing ultrafine bubbles, the slow dissolution and release characteristics of the bubbles can easily lead to sampling errors and underestimating results. In the field of online monitoring, methods based on various sensors are widely used. These methods can directly measure the partial pressure of dissolved CO2 in water, but when dealing with ultrafine bubble systems, localized flow and gas-liquid exchange at the sensing interface can affect accuracy. Moreover, distinguishing between the content of "free dissolved gas" and "gas encapsulated within bubbles" remains a challenge for current detection technologies.

[0005] In summary, although existing technologies can basically meet the detection requirements of CO2 under normal conditions, for the special system of CO2 ultrafine bubble water, due to the complex dynamic changes of its gas-liquid interface, traditional sampling and analysis methods often cannot truly reflect the total carbon content in the system.

[0006] Therefore, developing a CO2 content determination method that can take into account both free dissolved state and ultrafine bubble state, and has high precision and good stability, is a key prerequisite for promoting its large-scale application in high-end manufacturing and biomedical fields. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a method for determining the total amount of molecular carbon dioxide in water containing carbon dioxide microbubbles. This method can simultaneously determine dissolved carbon dioxide molecules and carbon dioxide molecules existing in the form of microbubbles in water, and has the advantages of simple operation, high sensitivity, and accurate results.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for determining the total amount of molecular carbon dioxide in water containing ultrafine carbon dioxide bubbles, comprising the following steps: (1) Establish a standard curve between the amount of carbon dioxide in gas chromatography and the peak area of ​​carbon dioxide; (2) A water sample containing carbon dioxide microbubbles is directly injected into a gas chromatograph. After separation by a capillary column, the carbon dioxide is reduced to methane in a methane catalytic converter under a sufficient hydrogen atmosphere. The methane is then detected by a flame ionization detector to obtain the chromatographic peak area of ​​carbon dioxide in the water sample. During the analysis, a six-way valve is used to purge water from the gas chromatograph to prevent water from entering the methane catalytic converter. (3) Substitute the chromatographic peak area obtained in step (2) into the standard curve in step (1) to calculate the amount of carbon dioxide in the injected water sample. Divide the amount of carbon dioxide in the injected water sample by the volume of the water sample to obtain the concentration of carbon dioxide in the water sample in the form of dissolved molecules and ultrafine bubbles.

[0009] As a preferred method, the standard curve in step (1) is established by using carbon dioxide gas with a volume fraction of 10.01% or 99.999%, injecting different known amounts of carbon dioxide through the gas injection valve, injecting them into the gas chromatograph for detection, recording the peak area corresponding to each injection amount, and establishing a standard curve with the amount of carbon dioxide as the abscissa and the peak area as the ordinate.

[0010] Preferably, the operating conditions for gas chromatography in step (2) are as follows: Nitrogen was used as the carrier gas, and a constant flow mode was adopted. The column outlet flow rate was 10–15 mL / min, and the purge flow rate was 2–5 mL / min. The injection port temperature was 200–300℃. The chromatographic column is a molecular sieve capillary column; the column temperature is 50–80℃; the flame ionization detector temperature is 200–300℃; the hydrogen flow rate of the flame ionization detector is 30–50 mL / min, and the air flow rate is 300–500 mL / min.

[0011] Preferably, the carrier gas column outlet flow rate is 12 mL / min, and the purge flow rate is 3 mL / min; The injection port temperature is 250℃; The chromatographic column is a Msieve 5A molecular sieve column, 30.0 m long, with an outer diameter of 0.53 mm and an inner diameter of 50 μm; the column temperature is 60℃. The temperature of the flame ionization detector is 250°C; The hydrogen flow rate of the flame ionization detector is 40 mL / min, and the air flow rate is 400 mL / min.

[0012] Preferably, the amount of water sample injected in step (2) is 1 to 5 μL.

[0013] Preferably, the switching mode of the six-way valve in step (2) is as follows: 0-3.5 min and 9-10 min are forward flow modes, allowing gas to enter the methane catalytic converter and the flame ionization detector; 3.5-9 min is reverse flow mode, under the action of carrier gas, water is purged from the chromatograph.

[0014] It contains at least the following beneficial technical effects: (1) The method of the present invention does not require the presence or absence of other dissolved gases or carbon-containing organic matter in the sample. Each component is separated in the chromatographic column without interfering with each other.

[0015] (2) The method of the present invention does not require a specific concentration range of carbon dioxide in the sample, and the measurement results are accurate and suitable for single-point measurement.

[0016] (3) The method of the present invention can simultaneously measure carbon dioxide molecules dissolved in water and carbon dioxide molecules existing in the form of ultrafine bubbles, overcoming the technical difficulty of traditional methods in distinguishing between "free dissolved gas" and "gas encapsulated in bubbles".

[0017] (4) The present invention effectively removes the water introduced by the sample through the six-way valve backflushing technology, prevents water from entering the methane catalytic conversion furnace and damaging the catalyst, and ensures the long-term stable operation of the instrument and the reliability of the measurement results. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the working principle of the gas chromatograph in the determination method of the present invention.

[0019] Figure 2 This is a calibration curve of carbon dioxide gas chromatography in the determination method of this invention.

[0020] Figure 3 This is the gas chromatographic spectrum of carbon dioxide detection in the determination method of the present invention.

[0021] Figure 4 This is a carbon dioxide gas chromatography calibration curve used in an accurate method for determining the total carbon dioxide content in water containing ultrafine carbon dioxide bubbles.

[0022] Figure 5 This is a schematic diagram of the device connection for a thermal conductivity detector (TCD). Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] Unless otherwise specified, "room temperature" and "normal temperature" in this invention refer to 25±2℃.

[0029] Unless otherwise specified, all raw materials or instruments used in the following embodiments of the present invention are commercially available.

[0030] Example 1 Determination of total molecular carbon dioxide in water by gas chromatography using CO2 ultrafine bubble method This embodiment provides a specific method for determining the total amount of molecular carbon dioxide in water containing ultrafine carbon dioxide bubbles using a gas chromatograph.

[0031] 1. Instrument Configuration and Working Principle The working principle of the gas chromatograph used in this embodiment is as follows: Figure 1 As shown.

[0032] (1) Sample injection unit The water sample containing CO2 microbubbles was extracted using a microsyringe and injected directly into the gas chromatograph. The injection volume was 2 μL, and the injection port temperature was set to 250℃. The water sample vaporized instantaneously at the high-temperature injection port, where dissolved CO2 molecules and CO2 within the microbubbles were converted into gaseous CO2, which was then carried into the chromatographic column by the carrier gas.

[0033] (2) Water purging and methane conversion unit This unit employs a six-way valve mode-switching technology combined with a methane catalytic converter. The six-way valve is used to switch the gas path during analysis, while the methane catalytic converter reduces CO2 to methane in a sufficient hydrogen atmosphere, enabling the flame ionization detector (FID) to detect it. The temperature of the methane catalytic converter is 350℃.

[0034] The six-way valve can be switched in the following modes: Phase 1 (Mode A, analysis time 0–3.5 min): Gas flows forward, is separated by a capillary column, and then enters the methane catalytic converter and FID detector. In this phase, CO2 and other target components elute from the column and enter the converter to be reduced to methane, which is then detected by the FID.

[0035] Phase 2 (Mode B, analysis time 3.5–9 min): The six-way valve is switched to reverse flow mode, and the carrier gas back purges the chromatographic column, purging excess water vapor remaining in the column from the split outlet to the phase chromatograph, preventing water from entering the methane catalytic converter and causing catalyst poisoning and failure.

[0036] Phase 3 (Recovery Mode A, Analysis Time 9-10 min): The six-way valve returns to the forward flow mode, stabilizing the instrument and preparing for the next analysis.

[0037] (3) Gas phase analysis unit The carrier gas (nitrogen) carries the sample components through a capillary column for separation, and the separated components sequentially enter the detection system. The chromatographic conditions in this embodiment are as follows: Carrier gas: nitrogen, constant flow mode, column outlet flow rate is 12 mL / min, purge flow rate is 3 mL / min; Chromatographic column: Msieve 5A molecular sieve column, 30.0 m long, 0.53 mm outer diameter, and 50 μm inner diameter; Column temperature: 60℃; Flame ionization detector temperature: 250℃; FID hydrogen flow rate: 40 mL / min; FID airflow rate: 400 mL / min.

[0038] 2. Establishment of the standard curve A standard curve for the molar amount-peak area of ​​carbon dioxide was established using 99.999% carbon dioxide gas, converted to pure carbon dioxide at 20 °C and 1 atm in amounts of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, and 50 μL (corresponding to 0.01663, 0.02079, 0.02494, 0.02910, 0.03326, 0.03741, 0.04157, 0.16629, 0.20786, 0.24943, 0.29100, 0.33257, 0.37414, 0.41571, 0.62357, 0.83143, 1.03929, and 2.07857 μmol, respectively).

[0039] Inject different amounts of CO2 standard gas as described above, and record the peak area corresponding to each injection volume. Perform linear fitting with the amount of CO2 (X, μmol) on the x-axis and the FID signal peak area (Y) on the y-axis to establish a standard curve (e.g., ...). Figure 2 (As shown). The equation of the obtained standard curve is: Y = 164202145.972 X Fitting constant R 2 = 0.99858, with parallel repetitions n = 10, indicating that the amount of CO2 and the FID peak area have a good linear relationship in the range of 0.01663 to 2.07857 μmol.

[0040] 3. Actual water sample measurement Take 2 μL of a water sample containing CO2 ultrafine bubbles, inject it into the gas chromatograph under the above conditions, and perform analysis. The resulting chromatogram is shown below. Figure 3 As shown. From Figure 3 It can be seen that the CO2 peak appears at a retention time of 2.425 min, with a peak area of ​​13,775,802. The peaks at 3.5 min and 9 min are disturbance peaks caused by the six-way valve mode switching.

[0041] Substituting the peak area into the standard curve equation, the amount of CO2 in the injected water sample can be calculated: X = Y / 164202145.972 = 13775802 / 164202145.972 = 0.084 (μmol) Given that the molar mass of CO2 is 44.01 g / mol and the injection volume V is 2 μL, the concentration c of molecular CO2 in the water sample is: c = (X × M) / V = ​​(0.084 × 44.01) / 2 = 1.848 (g / L) 4. Thermal conductivity detector verification As one of the verification methods, this embodiment also uses a thermal conductivity detector (TCD) to monitor the generation process of CO2 ultrafine bubble water in real time. Figure 4 This is a schematic diagram of the thermal conductivity detector device used in the accurate determination method of total carbon dioxide content in water containing carbon dioxide ultrafine bubbles according to the present invention. In the diagram, 1 is the air inlet pipe (CO2) of the ultrafine bubble generator, 2 is the water outlet pipe of the ultrafine bubble generator, 3 is the water inlet pipe of the ultrafine bubble generator, 4 is the water inlet pipe of the thermal conductivity detector, 5 is the water outlet pipe of the thermal conductivity detector, and 6 is the air inlet pipe of the carrier gas (N2) for the thermal conductivity detector.

[0042] Figure 5 This is a carbon dioxide gas chromatography calibration curve used in the accurate determination of total carbon dioxide content in water containing ultrafine carbon dioxide bubbles. The horizontal axis represents the amount of CO2 in μmol, denoted as X; the vertical axis represents the peak area of ​​the gas chromatographic FID signal, denoted as Y. The standard curve equation is Y = 164202145.972X, with a fitting constant R² = 0.99858 and a parallel replication factor n = 10.

[0043] When a sample was taken after a purge time of 20 s for GC-FID detection, the carbon dioxide content in the sample was found to be 0.028 g / kg, while the TCD showed no response at this time. This example illustrates that the TCD method has lower sensitivity than the GC-FID method, indirectly demonstrating the reliability of the GC-FID method for single-point determination.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for determining the total amount of molecular carbon dioxide in water containing ultrafine carbon dioxide bubbles, characterized in that, Includes the following steps: (1) Establish a standard curve between the amount of carbon dioxide in gas chromatography and the peak area of ​​carbon dioxide; (2) A water sample containing carbon dioxide microbubbles is directly injected into a gas chromatograph. After separation by a capillary column, the carbon dioxide is reduced to methane in a methane catalytic converter under a sufficient hydrogen atmosphere. The methane is then detected by a flame ionization detector to obtain the chromatographic peak area of ​​carbon dioxide in the water sample. During the analysis, a six-way valve is used to purge water from the gas chromatograph to prevent water from entering the methane catalytic converter. (3) Substitute the chromatographic peak area obtained in step (2) into the standard curve in step (1) to calculate the amount of carbon dioxide in the injected water sample. Divide the amount of carbon dioxide in the injected water sample by the volume of the water sample to obtain the concentration of carbon dioxide in the water sample in the form of dissolved molecules and ultrafine bubbles.

2. The method according to claim 1, characterized in that, The method for establishing the standard curve in step (1) is as follows: using carbon dioxide gas with a volume fraction of 10.01% or 99.999%, different known amounts of carbon dioxide are injected through the gas injection valve and injected into the gas chromatograph for detection. The peak area corresponding to each injection amount is recorded, and the standard curve is established with the amount of carbon dioxide as the abscissa and the peak area as the ordinate.

3. The method according to claim 1, characterized in that, The operating conditions for gas chromatography described in step (2) are as follows: Nitrogen was used as the carrier gas, and a constant flow mode was adopted. The column outlet flow rate was 10–15 mL / min, and the purge flow rate was 2–5 mL / min. The injection port temperature was 200–300℃. The chromatographic column is a molecular sieve capillary column; the column temperature is 50–80℃; the flame ionization detector temperature is 200–300℃; the hydrogen flow rate of the flame ionization detector is 30–50 mL / min, and the air flow rate is 300–500 mL / min.

4. The method according to claim 3, characterized in that, The measured flow rate at the outlet of the carrier gas column is 12 mL / min, and the purging flow rate is 3 mL / min; The injection port temperature is 250℃; The chromatographic column is a Msieve 5A molecular sieve column, 30.0 m long, with an outer diameter of 0.53 mm and an inner diameter of 50 μm; the column temperature is 60℃. The temperature of the flame ionization detector is 250°C; The hydrogen flow rate of the flame ionization detector is 40 mL / min, and the air flow rate is 400 mL / min.

5. The method according to claim 1, characterized in that, The water sample injection volume in step (2) is 1 to 5 μL.

6. The method according to claim 1, characterized in that, The switching modes of the six-way valve in step (2) are as follows: 0-3.5 min and 9-10 min are forward flow modes, allowing gas to enter the methane catalytic converter and the flame ionization detector; 3.5-9 min is reverse flow mode, under the action of carrier gas, water is purged from the chromatograph.

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