A safe and stable oxygen indicator and a method for preparing the same

Abstract

The application relates to the technical field of oxygen indicators, in particular to a safe and stable oxygen indicator, which is prepared from raw materials including at least iron and ferrous salt, ethylenediaminetetraacetic acid and its salt, ascorbic acid and its salt, an alkaline buffer solution and water; the mass ratio of the iron and ferrous salt, the ethylenediaminetetraacetic acid and its salt and the ascorbic acid and its salt is 1:(5-25):(15-50); the oxygen indicator can obviously change color under a lower oxygen concentration, the monitoring precision is improved, the oxygen indicator can repeatedly change color when the oxygen concentration changes, and the service life is prolonged.

Description

A safe and stable oxygen indicator and its preparation method Technical Field

[0001] This invention relates to the field of oxygen indicator technology, specifically to a safe and stable oxygen indicator and its preparation method. Background Technology

[0002] With the widespread use of oxygen absorbers in the food industry, the demand for oxygen indicators in related scenarios is increasingly strong. On the one hand, oxygen absorbers rapidly reduce the oxygen concentration inside packaging, creating a low-oxygen environment for oxygen indicators, allowing them to more accurately reflect the amount of residual oxygen. On the other hand, the color change of the oxygen indicator provides direct feedback on the oxygen absorption effect. If the oxygen indicator does not change color as expected during the oxygen absorption process, it indicates a possible abnormality in the oxygen absorption function, helping to promptly identify problems in the preservation process. For example, when the oxygen absorber is working normally and the oxygen concentration inside the packaging decreases, the oxygen indicator should change color accordingly. The two mutually confirm each other, ensuring the reliability of the preservation effect. Therefore, the color change of the oxygen indicator can show the usage status of the oxygen absorber, i.e., the level or presence of oxygen, and can quickly identify whether the packaging is leaking, ensuring the safety of food during transportation and storage.

[0003] The main component of commonly used oxygen indicators in the food industry is methylene blue, a substance that changes color with redox reactions. In its oxidized state, methylene blue is blue; in its reduced state, it becomes colorless. In an oxygen-deficient environment, methylene blue remains in its colorless reduced state due to the action of reducing sugars; however, upon contact with oxygen in the air, it is oxidized and turns blue. Sometimes, to achieve a clearer color contrast, a non-reactive red pigment is added, causing the indicator to initially appear pink in an anaerobic environment and purple in an aerobic environment. However, this type of indicator requires strongly alkaline conditions to react, making it incompatible with carbon dioxide environments. Using it in conjunction with a constant-pressure deoxygenating agent results in poor performance. Another type is resaazine oxygen indicator, which, while compatible with carbon dioxide environments, is less commonly used in the food industry due to its higher cost. In its oxidized state, resaazine is deep blue or purple; in its reduced state, it becomes colorless or light blue. The reduction reaction of rezathoic acid involves two stages. First, it irreversibly forms halogen, changing its color from blue and purple to pink. Then, it reversibly transforms from halogen to colorless dihydrorezathoic acid. In biological culture, it is used to test anaerobic environments; when the color of the rezathoic acid oxygen indicator changes from pink to white, it indicates that anaerobic conditions have been met.

[0004] Existing oxygen indicators, whether methylene blue or resazurite, possess a certain degree of toxicity and exhibit poor stability, making them susceptible to environmental factors (such as temperature, humidity, pH, light, carbon dioxide, and oils). Strict control over storage and usage conditions is required, significantly limiting the use and promotion of oxygen indicator products. Some oxygen indicators (such as traditional methylene blue) have long reaction times (ranging from minutes to hours), failing to meet the demands for rapid detection. Chinese patent application (publication number CN 109588479 A) discloses an organically modified polyvanadate derivative. This substance, upon interaction with oxygen within a suitable oxygen concentration range, causes a color change in the derivative, thereby indicating changes in oxygen concentration. Chinese patent application (publication number CN 109856125 A) discloses a nanoscale polytungstate cluster oxygen indicator. This cluster is prepared by electrochemical reduction of a polytungstate cluster, achieving a nanoscale molecular size that effectively prevents the migration of the chromogenic agent into food, thus preventing unintended staining. However, both of these types of indicators exhibit a gradual color change as the oxygen concentration changes, resulting in low color contrast and low sensitivity. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a safe and stable oxygen indicator that exhibits a significant color change at lower oxygen concentrations, thereby improving monitoring accuracy. Furthermore, the indicator can repeatedly change color when oxygen concentration changes, extending its service life.

[0006] The present invention provides a safe and stable oxygen indicator, the raw materials for which include at least: iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, ascorbic acid and its salts, alkaline buffer solution, and water; wherein the mass ratio of iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, and ascorbic acid and its salts is 1:(5-25):(15-50).

[0007] In one embodiment, the concentration of the iron and ferrous salt is 0.02-0.1 mol / L.

[0008] In one embodiment, the concentration of the iron and ferrous salt is 0.05 mol / L.

[0009] In one embodiment, the mass ratio of the iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, and ascorbic acid and its salts is 1:(10-20):(20-40).

[0010] In one embodiment, the mass ratio of the iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, and ascorbic acid and its salts is 1:(15-18):(25-35).

[0011] In one embodiment, the mass ratio of the iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, and ascorbic acid and its salts is 1:18:30.

[0012] In one embodiment, the iron and ferrous salt are selected from at least one of ferric chloride, ferrous chloride, ferrous sulfate, ferrous sulfate, or sodium iron ethylenediaminetetraacetate.

[0013] In one embodiment, the ethylenediaminetetraacetic acid and its salts are selected from at least one of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, or tetrasodium ethylenediaminetetraacetic acid.

[0014] In one embodiment, the ascorbic acid and its salts are selected from at least one of ascorbic acid, sodium ascorbate, isoascorbic acid, or sodium isoascorbate.

[0015] In one embodiment, the concentration of the alkaline buffer solution is 0.2-0.4 mol / L.

[0016] In one embodiment, the concentration of the alkaline buffer solution is 0.3 mol / L.

[0017] In one embodiment, the alkaline buffer solution is selected from one of sodium dihydrogen phosphate-disodium hydrogen phosphate buffer solution, ammonia-ammonium chloride buffer solution, and sodium carbonate-sodium bicarbonate buffer solution.

[0018] In one embodiment, the alkaline buffer solution is a sodium carbonate-sodium bicarbonate buffer solution.

[0019] In one embodiment, the raw materials for preparing the safe and stable oxygen indicator include: ferrous salt, ethylenediaminetetraacetic acid salt, ascorbate, sodium carbonate-sodium bicarbonate buffer solution, and water.

[0020] In one embodiment, the ferrous salt is ferrous sulfate, the ethylenediaminetetraacetic acid salt is ethylenediaminetetraacetic acid tetrasodium, and the ascorbate is sodium ascorbate.

[0021] Currently, oxygen indicators developed based on methylene blue or resazurite have safety and stability issues. This invention addresses this problem by preparing a complex of (ferrous) salt, ethylenediaminetetraacetic acid (EDTA) salt, and ascorbic acid (AS) salt in a specific ratio. The complex indicates a bright yellow color under anaerobic reducing conditions and a reddish-brown color under aerobic oxidizing conditions, exhibiting high color contrast and sensitivity. Furthermore, this invention optimizes the synergistic working mode between the deoxygenating component and the oxygen indicator component by controlling the mass ratio of iron and ferrous salt, EDTA and its salt, and ascorbic acid and its salt to 1:(10-20):(20-40). This avoids inaccurate anaerobic environment monitoring caused by premature or delayed color change, ensures compatibility with carbon dioxide environments, and provides good performance when used in conjunction with constant-pressure deoxygenating agents.

[0022] The oxygen indicator provided by this invention can be used in various fields that require indication of changes in oxygen concentration, with a wide range of applications, especially in the food industry. All raw materials are approved food additives, ensuring high safety. The complex prepared using ferrous salt, ethylenediaminetetraacetic acid salt, and ascorbate is only sensitive to oxygen, has minimal photothermal influence, and high stability, effectively preventing moisture absorption, clumping, and the migration of dye molecules into food, thus avoiding unintended staining.

[0023] Another aspect of the present invention provides a method for preparing a safe and stable oxygen indicator, comprising at least the following steps: dissolving ascorbic acid and its salt in water, adding an alkaline buffer solution to pH = 9-11; adding iron and ferrous salt, stirring to dissolve; adding ethylenediaminetetraacetic acid and its salt, stirring to dissolve, thereby obtaining a safe and stable oxygen indicator.

[0024] In one embodiment, the safe and stable oxygen indicator is in liquid form, and oxygen indicator products in different forms are obtained by modifying the safe and stable oxygen indicator.

[0025] In one embodiment, the oxygen indicator product includes at least oxygen indicator powder, oxygen indicator line, or oxygen indicator paper.

[0026] In one embodiment, the oxygen indicator powder is prepared by adding silica to a safe and stable oxygen indicator and stirring to obtain the oxygen indicator powder. The amount of silica added is 30-50% of the weight of the safe and stable oxygen indicator.

[0027] In one embodiment, the amount of silica added is 45% of the weight of a safe and stable oxygen indicator.

[0028] In one embodiment, the oxygen indicator line is prepared by immersing a white cotton thread in a safe and stable oxygen indicator. After the thread is saturated, it is dried at 40-50°C until the moisture content is 10-25 wt%, thus obtaining the oxygen indicator line.

[0029] In one embodiment, the oxygen indicator line is prepared by immersing a white cotton thread in a safe and stable oxygen indicator. After the thread is saturated, it is dried at 40-50°C until the moisture content is 18 wt%, thus obtaining the oxygen indicator line.

[0030] In one embodiment, the oxygen indicator paper is prepared by immersing absorbent paper in a safe and stable oxygen indicator until it is saturated, and then drying it at 40-50°C until the moisture content is 10-25 wt%, thus obtaining the oxygen indicator paper.

[0031] In one embodiment, the oxygen indicator paper is prepared by immersing white cotton thread in a safe and stable oxygen indicator until it is saturated, and then drying it at 40-50°C until the moisture content is 15wt%, thus obtaining the oxygen indicator paper.

[0032] The safe and stable oxygen indicator provided by this invention can be applied in liquid form, or it can be molded into oxygen indicator powder, oxygen indicator line or oxygen indicator paper and other forms of oxygen indicator products for application, to meet the application needs of different fields and has extremely high market application and promotion value.

[0033] Beneficial effects

[0034] 1. This invention provides a safe and stable oxygen indicator that can undergo a significant color change at lower oxygen concentrations, improving monitoring accuracy and enabling the indicator to repeatedly change color when oxygen concentration changes, thus extending its service life.

[0035] 2. The present invention prepares a complex by mixing (ferrous) salt with ethylenediaminetetraacetic acid (salt) and ascorbic acid (salt) in a certain ratio. The complex indicates a bright yellow color in the "anaerobic reducing state" and a reddish-brown color in the "aerobic oxidizing state", with high color contrast and high sensitivity.

[0036] 3. This invention optimizes the synergistic working mode between deoxygenating components and oxygen indicator components by controlling the mass ratio of iron and ferrous salts, ethylenediaminetetraacetic acid and its salts, and ascorbic acid and its salts to 1:(10-20):(20-40), thereby avoiding inaccurate anaerobic environment monitoring caused by premature or delayed color change. It is compatible with carbon dioxide environments and works well when used in conjunction with constant pressure deoxygenating agents.

[0037] 4. The oxygen indicator provided by this invention can be used in various fields that require indication of changes in oxygen concentration, with a wide range of applications, especially in the food industry. All raw materials are approved food additives, ensuring high safety. The complex prepared using ferrous salt, ethylenediaminetetraacetic acid salt, and ascorbate is only sensitive to oxygen, has minimal photothermal influence, and high stability, effectively preventing moisture absorption, clumping, and the migration of dye molecules into food, which could lead to unintended staining.

[0038] 5. The safe and stable oxygen indicator provided by this invention can be applied in liquid form, or it can be molded into oxygen indicator powder, oxygen indicator line or oxygen indicator paper and other forms of oxygen indicator products for application, to meet the application needs of different fields and has extremely high market application and promotion value. Detailed Implementation

[0039] Example 1

[0040] Example 1 of the present invention provides a safe and stable oxygen indicator, the raw materials for which include: ferrous salt, ethylenediaminetetraacetic acid (EDTA), ascorbate, sodium carbonate-sodium bicarbonate buffer solution, and water; wherein the ferrous salt is ferrous sulfate, the EDTA is tetrasodium EDTA, and the ascorbate is sodium ascorbate; the concentration of the ferrous salt is 0.05 mol / L, and the mass ratio of the ferrous salt, EDTA, and ascorbate is 1:18:30. The concentration of the sodium carbonate-sodium bicarbonate buffer solution is 0.3 mol / L.

[0041] Another aspect of Embodiment 1 of the present invention provides a method for preparing a safe and stable oxygen indicator, comprising the following steps: dissolving ascorbate in water, adding sodium carbonate-sodium bicarbonate buffer solution to pH=10; adding ferrous salt and stirring to dissolve; adding ethylenediaminetetraacetic acid salt and stirring to dissolve, thereby obtaining a safe and stable oxygen indicator.

[0042] Oxygen indicator powder is prepared by exfoliating a safe and stable oxygen indicator. The preparation method of the oxygen indicator powder is as follows: add silica to the safe and stable oxygen indicator and stir to mix to obtain the oxygen indicator powder. The amount of silica added is 45% of the weight of the safe and stable oxygen indicator.

[0043] An oxygen indicator line is prepared by molding a safe and stable oxygen indicator. The preparation method of the oxygen indicator line is as follows: white cotton thread is immersed in a safe and stable oxygen indicator. After absorption saturation, it is dried at 40°C until the moisture content is 18wt%, thus obtaining the oxygen indicator line.

[0044] Oxygen indicator paper is prepared by molding a safe and stable oxygen indicator. The preparation method of the oxygen indicator paper is as follows: absorbent paper is immersed in a safe and stable oxygen indicator, and after absorption saturation, it is dried at 40°C until the moisture content is 15wt%, thus obtaining the oxygen indicator paper.

[0045] Example 2

[0046] Example 2 of the present invention provides a safe and stable oxygen indicator and its preparation method. The specific implementation method is the same as that of Example 1, except that the mass ratio of the ferrous salt, ethylenediaminetetraacetic acid salt and ascorbate is 1:25:15.

[0047] Example 3

[0048] Example 3 of the present invention provides a safe and stable oxygen indicator and its preparation method. The specific implementation method is the same as that of Example 1, except that the mass ratio of the ferrous salt, ethylenediaminetetraacetic acid salt and ascorbate is 1:5:50.

[0049] Comparative Example 1

[0050] Comparative Example 1 of the present invention is a methylene blue oxygen indicator powder (oxygenated blue → oxygen-free red). The raw materials for its preparation, by mass percentage, include 3% glucose, 0.3% methylene blue, 5% 30wt% sodium hydroxide solution, 0.2% rose red pigment, and water to make up the balance. After stirring and dissolving the raw materials according to the mass ratio, a liquid indicator is obtained. Silica is added to the liquid indicator to prepare the methylene blue oxygen indicator powder. The amount of silica added is 50% of the total mass of the liquid indicator.

[0051] Comparative Example 2

[0052] Comparative Example 2 of the present invention is azadirachtin oxygen indicator powder (oxygenated pink → oxygen-free colorless). The raw materials for its preparation, by mass percentage, include 5% glucose, 0.01% azadirachtin, 2.5% sodium chloride, and citrate buffer (0.1M, pH 6.0) to make up the balance. After stirring and dissolving the raw materials according to the mass ratio, a liquid indicator is obtained. Silica is added to the liquid indicator to prepare azadirachtin oxygen indicator powder. The amount of silica added is 50% of the total mass of the liquid indicator.

[0053] Performance testing

[0054] 1. The oxygen indicator powders prepared in Examples 1-3 were packaged in polyethylene bags and then attached to 500cc of iron-based deoxidizer. They were then placed together in KOP (coated biaxially oriented polypropylene) bags, and then placed in an oxygen concentration tester and a thermometer and hygrometer. After filling with 500mL of air, the bags were sealed. The KOP bags were placed in a 25℃ constant temperature chamber (actual temperature 24.7℃, 62% RH) to detect changes in oxygen concentration and color of the oxygen indicator. Two samples were tested in parallel for each example.

[0055] Example 1 Test Results:

[0056] (1) Color change point: After 12 hours, the oxygen concentration of both parallel samples was 0.5% (v / v), and the oxygen indicator was reddish-brown. After 24 hours, the oxygen concentration of both parallel samples was 0.0% (v / v), and the oxygen indicator turned bright yellow. The color change point fell within the oxygen concentration range of 0.0% to 0.5%, indicating normal function.

[0057] (2) Thermal stability: The above-mentioned oxygen-free color-changing sample was placed in a high-temperature environment of 45℃ for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The thermal stability was good and was marked as "√" (the same below).

[0058] (3) Photostability: The above-mentioned oxygen-free color-changing sample was placed in an ultraviolet lamp irradiation environment for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The photostability was good and was marked as "√" (the same below).

[0059] Example 2 Test Results:

[0060] (1) Color change point: After 12 hours, the oxygen concentration of both parallel samples was 0.5% (v / v), and the color of the oxygen indicator had changed from reddish-brown to bright yellow. The color change point was earlier, which affected the determination of the oxygen-free conditions.

[0061] (2) Thermal stability: The above-mentioned oxygen-free color-changing sample was placed in a high-temperature environment of 45℃ for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The thermal stability is good and is marked as "√".

[0062] (3) Photostability: The above-mentioned oxygen-free color-changing sample was placed in an ultraviolet lamp irradiation environment for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The photostability was good and was marked as "√".

[0063] Example 3 Test Results:

[0064] (1) Color change point: After 24 hours, the oxygen concentration of both parallel samples was 0.0%, and the oxygen indicator was still reddish-brown. It was not until 48 hours later that the color change point changed from reddish-brown to bright yellow. The color change point was delayed, which affected the determination of oxygen-free conditions.

[0065] (2) Thermal stability: The above-mentioned oxygen-free color-changing sample was placed in a high-temperature environment of 45℃ for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The thermal stability is good and is marked as "√".

[0066] (3) Photostability: The above-mentioned oxygen-free color-changing sample was placed in an ultraviolet lamp irradiation environment for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The thermal stability was good, and it was marked as "√".

[0067] 2. The oxygen indicator lines prepared in Examples 1-3 were respectively attached to 500cc constant pressure deoxidizer with transparent tape, and then placed together in a KOP bag. An oxygen concentration tester and a thermometer and hygrometer were then placed in the bag, and 500mL of air was added before sealing. The KOP bag was placed in a 25℃ constant temperature chamber (actual temperature 25.1℃, 65%RH) to detect changes in oxygen concentration and color change of oxygen indicator. Two samples were tested in parallel for each example.

[0068] Example 1 Test Results:

[0069] (1) Color change point: After 24 hours, the oxygen concentration of both parallel samples was 0.5% (v / v), and the oxygen indicator was reddish-brown. After 48 hours, the oxygen concentration of both parallel samples was 0.0% (v / v), and the oxygen indicator turned bright yellow. The color change point fell within the oxygen concentration range of 0.0% to 0.5%, indicating normal operation, and was marked as "√".

[0070] (2) Thermal stability: The above-mentioned oxygen-free color-changing sample was placed in a high-temperature environment of 45℃ for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The thermal stability is good and is marked as "√".

[0071] (3) Photostability: The above-mentioned oxygen-free color-changing sample was placed in an ultraviolet lamp irradiation environment for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The photostability was good and was marked as "√".

[0072] Example 2 Test Results:

[0073] (1) Color change point: After 24 hours, the oxygen concentration of both parallel samples was 0.5% (v / v), and the color of the oxygen indicator had changed from reddish-brown to bright yellow. The color change point was earlier, which affected the determination of the oxygen-free conditions.

[0074] (2) Thermal stability: After 48 hours, the oxygen concentration of both parallel samples was 0.0% (v / v). The above-mentioned oxygen-free discoloration sample was placed in a high-temperature environment of 45℃ for 7 days. The oxygen indicator color did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The thermal stability was good and was marked as "√".

[0075] (3) Photostability: The above-mentioned oxygen-free color-changing sample was placed in an ultraviolet lamp irradiation environment for 7 days. The color of the oxygen indicator did not change. It turned back to reddish-brown within 10 minutes after the bag was opened (response time). The photostability was good and was marked as "√".

[0076] Example 3 Test Results:

[0077] (1) Color change point: After 48 hours, the oxygen concentration of both parallel samples was 0.0% (v / v), and the oxygen indicator was still reddish-brown. The color change point was delayed, which affected the determination of oxygen-free conditions.

[0078] (2) Thermal stability: The above-mentioned oxygen-free color-changing sample was placed in a high-temperature environment of 45℃ for 7 days. The color of the oxygen indicator did not change, and it turned back to reddish-brown within 10 minutes after the bag was opened (response time).

[0079] (3) Photostability: The above-mentioned oxygen-free color-changing sample was placed in an ultraviolet lamp irradiation environment for 7 days. The color of the oxygen indicator did not change, and it turned back to reddish-brown within 10 minutes after the bag was removed (response time).

[0080] 3. The oxygen indicator papers prepared in Examples 1-3 were respectively attached to 500cc of iron-based deoxidizer with transparent double-sided tape, and then placed together in a KOP bag. An oxygen concentration tester, a thermometer and hygrometer and a silica gel desiccant were then placed in the bag. After filling with 500mL of air, the bag was sealed and placed in a 25℃ constant temperature chamber (actual temperature 24.9℃, 41%RH). The changes in oxygen concentration and color of the oxygen indicator were detected. Two samples were tested in parallel for each example.

[0081] Test results of Examples 1-3:

[0082] Example 1: Color change point: After 12 hours, the oxygen concentration of both parallel samples was 0.5% (v / v), and the oxygen indicator color was reddish-brown; after 24 hours, the oxygen concentration of both parallel samples was 0.0% (v / v), and the oxygen indicator color turned bright yellow.

[0083] Example 2: Color change point: After 12 hours, the oxygen concentration of both parallel samples was 0.5% (v / v), and the color of the oxygen indicator had changed from reddish-brown to bright yellow. The color change point was earlier than expected, which affected the determination of the oxygen-free conditions.

[0084] Example 3: Color change point: After 24 hours, the oxygen concentration of both parallel samples was 0.0% (v / v), and the oxygen indicator color was still reddish-brown. The color change point was delayed, which affected the determination of the oxygen-free conditions.

[0085] 4. The oxygen indicator papers prepared in Examples 1-3 were respectively attached to 500cc of iron-based deoxidizer with transparent double-sided tape, and then placed in a KOP bag. An oxygen concentration tester, a thermometer and hygrometer and a wet cotton ball were then placed in the bag. After filling with 500mL of air, the bag was sealed. The KOP bag was placed in a 25℃ constant temperature chamber (actual temperature 24.8℃, 87%RH) and the changes in oxygen concentration and color of oxygen indicator were detected. Two samples were tested in parallel for each example.

[0086] Test results of Examples 1-3:

[0087] Example 1: Color change point: After 12 hours, the oxygen concentration of both parallel samples was 0.5% (v / v), and the oxygen indicator color was reddish-brown; after 24 hours, the oxygen concentration of both parallel samples was 0.0% (v / v), and the oxygen indicator color turned bright yellow.

[0088] Example 2: Color change point: After 12 hours, the oxygen concentration of both parallel samples was 0.5% (v / v), and the color of the oxygen indicator had changed from reddish-brown to bright yellow. The color change point was earlier than expected, which affected the determination of the oxygen-free conditions.

[0089] Example 3: Color change point: After 24 hours, the oxygen concentration of both parallel samples was 0.0% (v / v), and the oxygen indicator color was still reddish-brown. The color change point was delayed, which affected the determination of the oxygen-free conditions.

[0090] 5.a: When the methylene blue oxygen indicator powder provided in Comparative Example 1 is used in conjunction with the constant pressure deoxidizer, it always displays blue and cannot properly indicate the color of oxygen-free conditions.

[0091] b: After sealing the methylene blue oxygen indicator powder provided in Comparative Example 1 in a polyethylene bag, it was attached to 500cc of iron-based deoxidizer and placed together in a KOP bag. Then, an oxygen concentration tester and a thermometer and hygrometer were placed inside, 500mL of air was added, and the bag was sealed. The KOP bag was placed in a 25℃ constant temperature chamber (actual temperature 24.7℃, 62%RH) to detect changes in oxygen concentration and color of the oxygen indicator inside the bag.

[0092] (1) Color change point: After 12 hours, the oxygen concentration is displayed as 0.5%, and the color of the oxygen indicator has changed from blue to red. The color change point is earlier, which affects the determination of oxygen-free conditions.

[0093] (2) Thermal stability: The above-mentioned oxygen-free color-changing sample was placed in a high-temperature environment of 45℃ for 7 days. The color of the oxygen indicator did not change. It turned back to blue 30 minutes after the bag was opened (response time), indicating poor thermal stability.

[0094] (3) Photostability: The above-mentioned samples that change color in the absence of oxygen are placed in an ultraviolet lamp irradiation environment for 7 days. After the lamp is turned on, they remain red and do not turn blue. This is marked as "×".

[0095] 6. After sealing the azurlan oxygen indicator powder provided in Comparative Example 2 in a polyethylene bag, attach it to 500cc of iron-based deoxidizer, put them together into a KOP bag, then put in an oxygen concentration tester and a thermometer and hygrometer, fill it with 500mL of air and seal it. Place the KOP bag in a 25℃ constant temperature chamber (actual temperature 24.7℃, 62%RH) and detect the change in oxygen concentration and the color change of the oxygen indicator inside the bag.

[0096] (1) Color change point: After 48 hours, the oxygen concentration is displayed as 0.0%, and the oxygen indicator is still pink. The color change point is delayed, which affects the determination of oxygen-free conditions.

[0097] (2) Thermal stability: The above-mentioned oxygen-free color-changing sample was placed in a high-temperature environment of 45℃ for 7 days. After opening, it remained colorless and did not turn red. It was marked as "×".

[0098] (3) Photostability: The above-mentioned samples that change color in the absence of oxygen are placed in an ultraviolet lamp irradiation environment for 7 days. After the lamp is turned off, they remain colorless and do not turn red. This is marked as "×".

[0099] 7. After sealing the azurlan oxygen indicator powder provided in Comparative Example 2 in a polyethylene bag, attach it to 500cc of constant pressure deoxidizer, put them together into a KOP bag, then put in an oxygen concentration tester and a thermometer and hygrometer, fill it with 500mL of air and seal it. Place the KOP bag in a 25℃ constant temperature chamber (actual temperature 24.7℃, 62%RH) and detect the change in oxygen concentration and the color change of the oxygen indicator inside the bag.

[0100] (1) Color change point: After 48 hours, the oxygen concentration is displayed as 0.0%, and the oxygen indicator is still pink. The color change point is delayed, which affects the determination of oxygen-free conditions.

[0101] (2) Thermal stability: The above-mentioned oxygen-free color-changing sample was placed in a high-temperature environment of 45℃ for 7 days. After opening, the color of the oxygen indicator did not change and remained colorless and did not turn red. This was recorded as "×".

[0102] (3) Photostability: The above-mentioned samples that change color in the absence of oxygen are placed in an ultraviolet lamp irradiation environment for 7 days. After the lamp is turned off, they remain colorless and do not turn red. This is marked as "×".

[0103] The results of performance tests 1-7 are summarized in Table 1 below.

[0104] Table 1

[0105]

[0106] In Table 1, “-” indicates that the measurement was not performed; “--” indicates that the relevant data could not be obtained.

Claims

1. A safe and stable oxygen indicator, characterized in that, The raw materials for its preparation include at least: ferrous sulfate, tetrasodium ethylenediaminetetraacetate, sodium ascorbate, alkaline buffer solution, and water; the mass ratio of ferrous sulfate, tetrasodium ethylenediaminetetraacetate, and sodium ascorbate is 1:(10-20):(20-40); the concentration of ferrous sulfate is 0.02-0.1 mol / L; the alkaline buffer solution is a sodium carbonate-sodium bicarbonate buffer solution, and the concentration of the alkaline buffer solution is 0.2-0.4 mol / L.

2. A method for preparing a safe and stable oxygen indicator according to claim 1, characterized in that, At least the following steps are included: Dissolve sodium ascorbate in water, add alkaline buffer solution to pH 9-11; add ferrous sulfate and stir to dissolve; add tetrasodium ethylenediaminetetraacetate and stir to dissolve, thus obtaining a safe and stable oxygen indicator.

3. The method for preparing the safe and stable oxygen indicator according to claim 2, characterized in that, The safe and stable oxygen indicator is in liquid form. Different forms of oxygen indicator products are obtained by shaping the safe and stable oxygen indicator. The oxygen indicator products include at least oxygen indicator powder, oxygen indicator line or oxygen indicator paper.

4. The method for preparing the safe and stable oxygen indicator according to claim 3, characterized in that, The oxygen indicator powder is prepared by adding silica to a safe and stable oxygen indicator and stirring to obtain the oxygen indicator powder. The amount of silica added is 30-50% of the weight of the safe and stable oxygen indicator.

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