Hydrogel for rapidly detecting nitrite as well as preparation method and application of hydrogel

Abstract

The invention provides hydrogel for rapidly detecting nitrite as well as a preparation method and application of the hydrogel, and relates to the field of nitrite detection. The hydrogel comprises a sodium alginate-acrylic acid gel carrier, sulfanilamide and an N-(1-naphthyl) ethylenediamine color developing agent. The preparation method comprises the following steps: preparing a hydrophilic sodium alginate-acrylic acid gel precursor solution: dissolving sodium alginate in water to obtain a sodium alginate solution, and purging with nitrogen; adding ammonium persulfate, reacting, cooling, adding acrylic acid, and keeping at the temperature; then, N, N-methylene bisacrylamide is added and stirred, and a hydrophilic sodium alginate-acrylic acid gel precursor solution is obtained; loading a color developing agent: adding sulfanilamide and N-(1-naphthyl) ethylenediamine hydrochloride into the hydrophilic sodium alginate-acrylic acid gel precursor solution, stirring and dissolving, then transferring into a mold, and curing. The hydrogel prepared by the method is long in preservation time, uniform in color development, biodegradable and environment-friendly.

Description

Technical Field

[0001] The present invention relates to the field of nitrite detection, and in particular to a hydrogel for rapid nitrite detection, and a preparation method and application thereof. Background Art

[0002] In daily life, nitrite is widely used in food preservation and industrial coloring. However, excessive intake of nitrite can be harmful to human health. Colorimetry is one of the most common methods for nitrite detection. It converts nitrite into a colored compound through a diazotization reaction between nitrite and a colorimetric reagent. Quantitative analysis is then performed using an ultraviolet spectrophotometer to detect nitrite.

[0003] However, for the specific application scenario of food production, the traditional colorimetric method still has certain problems:

[0004] 1. The detection process is cumbersome and cannot achieve real-time monitoring. Traditional colorimetric methods require the addition of multiple reagents, and after color development, absorbance measurement is required. The absorbance is then fitted with a standard curve to obtain the final nitrite content. In the processing production line of fruits, vegetables and other foods, low detection efficiency will affect production progress and the actual nitrite detection results in food;

[0005] 2. In traditional colorimetric methods, the color developer is easily deactivated, and the waste liquid generated by the test is organic waste liquid, which needs to be treated separately before discharge. Otherwise, it will harm the environment and human health, and also increase the cost of testing.

[0006] 3. Existing gel color development technology suffers from uneven color development within the gel, which can cause errors. The color developer must be evenly loaded into the gel, and the color distribution must be ensured before absorbance measurement. Otherwise, the final nitrite detection results will be affected. Summary of the Invention

[0007] The purpose of the present invention is to provide a hydrogel for rapid detection of nitrite, which has a long storage time, uniform color development, biodegradability and environmental friendliness.

[0008] Another object of the present invention is to provide a method for preparing a hydrogel for rapid detection of nitrite. The hydrogel prepared by this method can encapsulate a color developer in the hydrogel to extend the shelf life of the color developer.

[0009] The third object of the present invention is to provide an application of a hydrogel for detecting the nitrite content in food, with a fast detection speed, no need to test absorbance, no waste liquid generated, and environmentally friendly.

[0010] The present invention solves the technical problem by adopting the following technical solutions.

[0011] On the one hand, an embodiment of the present invention provides a hydrogel for rapid detection of nitrite, comprising: a sodium alginate-acrylic acid gel carrier, and sulfonamide and N-(1-naphthyl)ethylenediamine loaded on the sodium alginate-acrylic acid gel carrier.

[0012] In some embodiments of the present invention, the mass ratio of the sodium alginate-acrylic acid gel carrier, sulfonamide and N-(1-naphthyl)ethylenediamine is 100:(0.5-0.8):(0.05-0.08).

[0013] In some embodiments of the present invention, the mass ratio of the sodium alginate-acrylic acid gel carrier, sulfonamide and N-(1-naphthyl)ethylenediamine is 100:0.5:0.05.

[0014] In a second aspect, an embodiment of the present invention provides a method for preparing a hydrogel for rapid detection of nitrite, comprising the following steps:

[0015] S1, preparing a hydrophilic sodium alginate-acrylic acid gel precursor solution: dissolving sodium alginate in water at 60-70°C to obtain a sodium alginate solution, and purging the solution with nitrogen for 30 minutes; adding ammonium persulfate, reacting at 60-70°C for 10-20 minutes, cooling to 25-30°C, adding acrylic acid, and maintaining at this temperature for 5-8 minutes; then adding N,N-methylenebisacrylamide and stirring for 20-30 minutes to obtain a hydrophilic sodium alginate-acrylic acid gel precursor solution;

[0016] S2, loading a color developer: adding sulfonamide and naphthylethylenediamine hydrochloride to a hydrophilic sodium alginate-acrylic acid gel precursor solution, stirring and dissolving, then transferring the solution to a mold and solidifying the solution to obtain the hydrogel.

[0017] In some embodiments of the present invention, in step S1, the concentration of the sodium alginate solution is 2-5 wt%.

[0018] In some embodiments of the present invention, in step S1, the concentration of the sodium alginate solution is 2 wt %.

[0019] In a third aspect, an embodiment of the present invention provides an application of a hydrogel for rapid detection of nitrite, including establishing a standard linear equation and a colorimetric chart: adding different concentrations of nitrite standard solutions to multiple groups of hydrogels, reacting for 5-8 minutes, extracting RGD from each group of hydrogels to obtain multiple R / G values; data processing, preparing a standard linear equation and a standard colorimetric chart;

[0020] Nitrite detection: drop the water sample to be tested into the hydrogel, react for 5-8 minutes, take a picture, read the RGB value of the color-developed hydrogel, obtain the R / B value, substitute the R / B value into the standard linear equation, and calculate the nitrite content in the water sample to be tested.

[0021] In some embodiments of the present invention, the hydrogel can be used for qualitative detection and quantitative calculation of nitrite in food.

[0022] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0023] The hydrogel provided by the present invention uses hydrophilic sodium alginate-acrylic acid as raw materials to form a three-dimensional skeleton network structure. The molecular chains constructing the network contain a large number of polar hydrophilic groups, and have the characteristics of high water content, high porosity, good tensile properties and formability. In addition, a color developer is loaded on the hydrogel, and the color developer can be evenly distributed in the hydrogel. The color development on the hydrogel is uniform. Moreover, by loading the color developer before the hydrogel is solidified, the loaded color developer can be stored for a long time and does not need to be prepared for immediate use.

[0024] Secondly, the hydrogel is biodegradable and produces no waste during the testing process, preventing secondary environmental pollution. Compared to traditional colorimetric methods, there is no need to consider how to dispose of wastewater generated during testing, reducing costs and avoiding the need for debugging and maintenance of testing equipment.

[0025] This hydrogel is used to detect nitrite levels in food. By directly reading the RGB values ​​of the discolored hydrogel with a smartphone and comparing them to a standard color chart, the nitrite content in food can be quickly and accurately determined, eliminating the need for cumbersome UV spectrophotometric testing required by traditional colorimetry. This approach transcends the traditional reliance on expensive and unportable equipment like spectrophotometers and ion chromatographs, enabling real-time nitrite detection in production processes and diverse applications in daily life, ensuring food safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 is the standard linear equation of the embodiment of the present invention;

[0028] Figure 2 A standard colorimetric card according to an embodiment of the present invention;

[0029] Figure 3 The colors after nitrite development at different concentrations in the embodiments of the present invention;

[0030] Figure 4 This is a diagram showing the selective detection of different ions by the hydrogel of the present invention. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0032] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0033] On the one hand, an embodiment of the present invention provides a hydrogel for rapid detection of nitrite, comprising: a sodium alginate-acrylic acid gel carrier, and sulfonamide and N-(1-naphthyl)ethylenediamine loaded on the sodium alginate-acrylic acid gel carrier. The mass ratio of the sodium alginate-acrylic acid gel carrier, sulfonamide, and N-(1-naphthyl)ethylenediamine is 100:(0.5-0.8):(0.05-0.08), and preferably, the mass ratio of the sodium alginate-acrylic acid gel carrier, sulfonamide, and N-(1-naphthyl)ethylenediamine is 100:0.5:0.05.

[0034] Using hydrophilic sodium alginate-acrylic acid as raw materials, a three-dimensional skeleton network structure is formed. The molecular chains that construct the network contain a large number of polar hydrophilic groups, and have the characteristics of high water content, high porosity, good tensile properties and formability. A color developer is loaded on the hydrogel, and the color developer can be evenly distributed in the hydrogel. The color development on the hydrogel is uniform, and by loading the color developer on the hydrogel, the color developer can be stored for a long time and does not need to be prepared for immediate use.

[0035] A method for preparing a hydrogel for rapid detection of nitrite comprises the following steps:

[0036] S1. Preparing a hydrophilic sodium alginate-acrylic acid gel precursor solution: dissolving sodium alginate in water at 60-70° C. to obtain a sodium alginate solution, purging the solution with nitrogen for 30 minutes; adding ammonium persulfate, reacting at 60-70° C. for 10-20 minutes, cooling to 25-30° C., adding acrylic acid, and maintaining the temperature at that temperature for 5-8 minutes; then adding N,N-methylenebisacrylamide and stirring for 20-30 minutes to obtain a hydrophilic sodium alginate-acrylic acid gel precursor solution; the sodium alginate solution has a concentration of 2-5 wt %. Preferably, the concentration is 2 wt %.

[0037] S2, loading a color developer: adding sulfonamide and naphthylethylenediamine hydrochloride to a hydrophilic sodium alginate-acrylic acid gel precursor solution, stirring and dissolving, then transferring the solution to a mold and solidifying the solution to obtain the hydrogel.

[0038] A hydrogel for rapid nitrite detection can be used for quantitative calculation and qualitative detection of nitrite in food. The method includes establishing a standard linear equation and a colorimetric chart: adding different concentrations of nitrite standard solutions to multiple groups of hydrogels, reacting for 5-8 minutes, and then extracting the RGD of each group of hydrogels to obtain multiple R / G values; data processing, and the creation of a standard linear equation and a standard colorimetric chart;

[0039] Nitrite detection: drop the water sample to be tested into the hydrogel, react for 5-8 minutes, take a picture, read the RGB value of the color-developed hydrogel, obtain the R / B value, substitute the R / B value into the standard linear equation, and calculate the nitrite content in the water sample to be tested.

[0040] This hydrogel is used to detect nitrite levels in food. By directly reading the RGB values ​​of the discolored hydrogel with a smartphone and comparing them to a standard color chart, the nitrite content in food can be quickly and accurately determined, eliminating the need for cumbersome UV spectrophotometric testing like traditional colorimetry. This approach transcends the traditional reliance on expensive and unportable equipment like spectrophotometers and liquid chromatography, enabling real-time nitrite detection in production processes and diverse applications in daily life, ensuring food safety.

[0041] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0042] Example 1

[0043] 1. Prepare the hydrogel as follows:

[0044] S1, preparation of hydrophilic sodium alginate-acrylic acid gel precursor solution:

[0045] Dissolve 1g of sodium alginate (SA) in 50mL of water at 70°C to prepare a 2wt% SA solution, and purge the solution with nitrogen for 30min to remove dissolved oxygen. Add 0.024g of ammonium persulfate and react at 70°C for 10min to form free radicals on the hydroxyl groups of sodium alginate. After cooling to 30°C, quickly add 6g of acrylic acid (AA) and maintain for 5min. Subsequently, add 0.02g of N,N-methylenebisacrylamide and stir for 20-30min to obtain a hydrophilic sodium alginate-acrylic acid gel precursor solution;

[0046] S2, loading the developer: adding 0.4 g of sulfonamide and 0.04 g of naphthylethylenediamine hydrochloride to the hydrophilic sodium alginate-acrylic acid gel precursor solution, stirring to dissolve, then transferring to a mold and solidifying to obtain the hydrogel film.

[0047] 2. Establishment of standard linear equation and colorimetric card:

[0048] The hydrogel films were cut into 1*1.5 cm samples. 0.1 mL of nitrite standard solution of different concentrations (0, 5, 10, 20, 40, 45, and 50 μmol / L) was added to each of the hydrogels. After 5 min of reaction, photos were taken with a smartphone and the RGD of each hydrogel was extracted to obtain multiple R / G values. Data were processed to create a standard linear equation and a standard colorimetric chart. The linear equation was y = 0.01399x - 0.03886, and R 2 =0.99869, and the detection limit is 5μmol / L. Its standard linear equation is as follows Figure 1 As shown, the horizontal axis is the concentration of nitrite, in μmol / L, and the vertical axis is the R / G value of the color taken by the mobile phone. The standard color chart is as follows Figure 2 shown.

[0049] 3. Nitrite detection: 1 mL of the water sample to be tested is dropped into an unused hydrogel sample, and a photo is taken. The RGB values ​​of the colored hydrogels in four parallel experiments are read to obtain the R / B value. The R / B value is substituted into the standard linear equation to calculate the nitrite content in the water sample to be tested. Figure 3 shown.

[0050] 4. Selectivity and anti-interference test:

[0051] Prepare 4mmol / L SO4 2- , NO3 - , Cl - , K + , CO3 2- ,HPO4 2- , H2PO4 - , SO32- , CH3COO - ,HCO3 - , Ca 2+ , Al 3+ , Mg 2+ , K + , Fe 3+ , MoO4 2- , Zn 2+ , B4O7 2- ion solution, and 4μmol / L NO2 - The solution is tested for selectivity. The concentration of ions in the above other ion solutions is NO2 - The concentration is 100 times that of Figure 4 As shown. Only NO2 - The detection gel can be colored purple-red, and the ΔR / G is much larger than the ΔR / G of other ions. Other ions cannot change the color of the hydrogel, which shows that the detection method is effective for NO2 - Be selective.

[0052] 5. Actual sample testing and comparison with traditional methods

[0053] The nitrite content in some daily foods was determined using the above hydrogel as follows:

[0054] a. Sample pretreatment

[0055] Vegetables and Fruits: Wash fresh vegetable and fruit samples with tap water, rinse with water, and air-dry. Mince and mix the edible portion. Quarter the chopped sample, take an appropriate amount, and use a food grinder to create a homogenized slurry. Set aside. If water is added, record the amount.

[0056] Meat, eggs, aquatic products and their products: take an appropriate amount or all of them using the quartering method, use a food grinder to make a homogenate, and set aside.

[0057] Solid dairy products such as milk powder, soy milk powder, and infant formula powder (excluding cheese): Place the sample into a covered container that can hold twice the volume of the sample. Mix the sample thoroughly by repeatedly shaking and inverting the container until the sample is homogenized.

[0058] Fermented milk, milk, condensed milk and other liquid dairy products: Mix the sample thoroughly by stirring or repeatedly shaking and inverting the container.

[0059] Cheese: Grind an appropriate amount of the sample into a uniform slurry. To avoid water loss, avoid excessive heat during the grinding process.

[0060] b Extract

[0061] Vegetable, fruit, and other plant-derived samples: Weigh 5 g of sample (accurate to 0.001 g; the sample size may be adjusted appropriately; the same applies below) into a 150 mL stoppered conical flask. Add 80 mL of water and 1 mL of 1 mol / L potassium hydroxide solution. Ultrasonic extraction is performed for 30 minutes, shaking every 5 minutes to ensure complete dispersion of the solid phase. Place in a 75°C water bath for 5 minutes, remove and allow to cool to room temperature, quantitatively transfer to a 100 mL volumetric flask, dilute to the mark with water, and mix thoroughly. Filter the solution through filter paper, centrifuge a portion at 10,000 rpm for 15 minutes, and reserve the supernatant.

[0062] Meat, eggs, fish, and their products: Weigh 5 g of sample homogenate (accurate to 0.001 g) into a 150 mL stoppered conical flask. Add 80 mL of water and perform ultrasonic extraction for 30 minutes, shaking every 5 minutes to ensure complete dispersion of the solid phase. Place in a 75°C water bath for 5 minutes, remove and allow to cool to room temperature, quantitatively transfer to a 100 mL volumetric flask, dilute to the mark with water, and mix thoroughly. Filter the solution through filter paper, centrifuge a portion at 10,000 rpm for 15 minutes, and reserve the supernatant.

[0063] In order to test the accuracy of the test, a spike recovery test was performed, and standard nitrite solutions of different concentrations (0, 5, 10, 20 μM) were added to the above-mentioned food samples; the recovery rate of the samples detected by this method was between 84.84% and 114.60% (as shown in Table 1), indicating the accuracy of the method. The detection method was also compared with the national standard ultraviolet spectrophotometry method (national standard method) to determine the nitrite concentration. As shown in Table 1, the nitrite results detected by the hydrogel were close to the nitrite concentration determined by the ultraviolet spectrophotometry method, indicating that the test accuracy of this method is high and the test results are highly credible.

[0064] Table 1

[0065]

[0066]

[0067] In summary, embodiments of the present invention provide a hydrogel that can be used to detect nitrite content in food. By directly reading the RGB value of the discolored hydrogel via a smartphone and comparing it to a standard color chart, the nitrite content in food can be quickly and accurately detected, eliminating the need for cumbersome UV spectrophotometric testing as with traditional colorimetry. This approach transcends the traditional detection methods that rely on expensive and unportable equipment such as spectrophotometers and liquid chromatography, and can meet diverse needs for real-time nitrite detection during production processes and in daily life, ensuring food safety.

[0068] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. A hydrogel for rapid detection of nitrite, characterized in that: It includes: Sodium alginate-acrylic acid gel carrier, and sulfonamide and N-(1-naphthyl)ethylenediamine loaded on the sodium alginate-acrylic acid gel carrier.

2. The hydrogel for rapid detection of nitrite according to claim 1, characterized in that The mass ratio of the sodium alginate-acrylic acid gel carrier, sulfonamide and N-(1-naphthyl)ethylenediamine is 100:(0.5-0.8):(0.05-0.08).

3. The hydrogel for rapid detection of nitrite according to claim 1, characterized in that The mass ratio of the sodium alginate-acrylic acid gel carrier, sulfonamide and N-(1-naphthyl)ethylenediamine is 100:0.5:0.

05.

4. A method for preparing a hydrogel for rapid detection of nitrite according to any one of claims 1 to 3, characterized in that: The following steps are included: S1, preparing a hydrophilic sodium alginate-acrylic acid gel precursor solution: dissolving sodium alginate in water at 60-70°C to obtain a sodium alginate solution, and purging the solution with nitrogen for 30 minutes; adding ammonium persulfate, reacting at 60-70°C for 10-20 minutes, cooling to 25-30°C, adding acrylic acid, and maintaining at this temperature for 5-8 minutes; then adding N,N-methylenebisacrylamide and stirring for 20-30 minutes to obtain a hydrophilic sodium alginate-acrylic acid gel precursor solution; S2, loading a color developer: adding sulfonamide and naphthylethylenediamine hydrochloride to a hydrophilic sodium alginate-acrylic acid gel precursor solution, stirring and dissolving, then transferring the solution to a mold and solidifying the solution to obtain the hydrogel.

5. The method for preparing a hydrogel for rapid detection of nitrite according to claim 4, wherein In step S1, the concentration of the sodium alginate solution is 2-5 wt%.

6. The method for preparing a hydrogel for rapid detection of nitrite according to claim 4, wherein: In step S1, the concentration of the sodium alginate solution is 2 wt%.

7. A use of the hydrogel for rapid detection of nitrite according to any one of claims 1 to 3, characterized in that: include, Establishing a standard linear equation and a colorimetric card: adding different concentrations of nitrite standard solutions to multiple groups of the hydrogels, reacting for 5-8 minutes, extracting RGD from each group of hydrogels to obtain multiple R / G values; processing the data to prepare a standard linear equation and a standard colorimetric card; Nitrite detection: drop the water sample to be tested into the hydrogel, react for 5-8 minutes, take a picture, read the RGB value of the color-developed hydrogel, obtain the R / B value, substitute the R / B value into the standard linear equation, and calculate the nitrite content in the water sample to be tested.

8. The use of the hydrogel for rapid detection of nitrite according to claim 7, further characterized in that: Used for qualitative detection and quantitative calculation of nitrite in food.

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