Method for detecting sodium formaldehyde sulfoxylate based on nitrogen-doped graphene quantum dots ratio fluorescence

Abstract

The application discloses a method for detecting sodium formaldehyde sulfoxylate based on nitrogen-doped graphene quantum dots ratio fluorescence, and belongs to the technical field of harmful compound detection in food. The method is characterized in that: a to-be-detected sample solution, a nitrogen-doped graphene quantum dots solution and a 1,4-naphthoquinone solution are mixed to react, after the reaction, ratio fluorescence response (I 420 / I 440 ) under an excitation wavelength of 360 nm is measured by a fluorescence spectrophotometer, the measured fluorescence intensity signal is introduced into a standard curve, and the concentration of sodium formaldehyde sulfoxylate in the to-be-detected sample is calculated and obtained. The application has the advantages of low cost, simple operation, visible detection result, no need of using large instruments and professional operators, and accurate and reliable detection result, and can be used for qualitative and quantitative detection of ivory white.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of detection of harmful compounds in food, and particularly relates to a method for detecting sodium formaldehyde sulfoxylate based on nitrogen-doped graphene quantum dots ratio fluorescence. BACKGROUND

[0002] Sodium formaldehyde sulfoxylate, commonly known as ivory white block, is usually white powder or crystalline powder, is soluble in water, is relatively stable at room temperature, and can be decomposed into formaldehyde and sulfur dioxide when encountering acid or heating, and has strong reducing property, and thus is an industrial bleaching agent.

[0003] At present, the common detection method is mainly to detect the decomposition products formaldehyde or sulfur dioxide to determine whether the ivory white block exists, and these methods include gas chromatography (GC), liquid chromatography (LC), ion chromatography (IC) and colorimetry. The above methods are indirect detection through the decomposition products of the ivory white block, and the sensitivity and reliability need to be further improved, and the pretreatment operation is complex, and the required instrument is expensive. Therefore, it is imperative to establish a direct, specific, sensitive and simple method for detecting sodium formaldehyde sulfoxylate in food. SUMMARY

[0004] In view of the problems in the prior art, the purpose of the present application is to provide a method for detecting sodium formaldehyde sulfoxylate based on nitrogen-doped graphene quantum dots ratio fluorescence.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] A method for detecting sodium formaldehyde sulfoxylate based on nitrogen-doped graphene quantum dots ratio fluorescence, the steps are as follows:

[0007] The sample solution to be measured, the nitrogen-doped graphene quantum dot solution and the 1,4-naphthoquinone solution are mixed for reaction, and after the reaction, the fluorescence intensity at 420 nm and 440 nm under the excitation wavelength of 360 nm is measured by a fluorescence spectrophotometer, and the fluorescence intensity ratio I 420 / I 440 , I 420 / I 440 The standard curve is imported, and the concentration of sodium formaldehyde sulfoxylate in the sample to be measured is calculated.

[0008] In one specific embodiment, the nitrogen-doped graphene quantum dots are prepared by the following method:

[0009] Citric acid and urea are dissolved in water, stirred until the solution is clear, then heated to 180 DEG C within 20 minutes, and kept for 8 hours, after the reaction is completed, cooled to room temperature, and the nitrogen-doped graphene quantum dots are obtained.

[0010] In the method for detecting sodium formaldehyde sulfoxylate based on the ratio fluorescence of nitrogen-doped graphene quantum dots, the concentration of the nitrogen-doped graphene quantum dot solution is 0.1 mg / mL to 6 mg / mL, and in a specific embodiment, the preferred concentration is 1 mg / mL.

[0011] In a specific embodiment, the 1,4-naphthoquinone solution is prepared by dissolving 1,4-naphthoquinone powder in an acetonitrile / water (V:V=7:3) solvent.

[0012] In a specific embodiment, the standard curve is prepared by the following method:

[0013] The sodium formaldehyde sulfoxylate is prepared into standard solutions with concentrations of 20 μmol / L, 30 μmol / L, 40 μmol / L, 50 μmol / L, 60 μmol / L, 70 μmol / L, 80 μmol / L, 100 μmol / L, 120 μmol / L, 150 μmol / L, and 180 μmol / L by using an acetonitrile / water (V:V=7:3) solution, different concentrations of the sodium formaldehyde sulfoxylate standard solution and the 1,4-naphthoquinone solution are added into the acetonitrile / water (V:V=7:3) solution, the nitrogen-doped graphene quantum dot solution is added after uniform mixing, and the fluorescence intensity at 420 nm and 440 nm is measured under an excitation wavelength of 360 nm after 2 h of reaction, and the fluorescence intensity ratio I 420 / I 440 , the ratio fluorescence response I 420 / I 440 is calculated.

[0014] In the method for detecting sodium formaldehyde sulfoxylate based on the ratio fluorescence of nitrogen-doped graphene quantum dots, the concentration of the 1,4-naphthoquinone solution is 10 μmol / L to 60 μmol / L, and in a specific embodiment, the preferred concentration is 20 μmol / L.

[0015] The method for detecting sodium formaldehyde sulfoxylate based on the ratio fluorescence of nitrogen-doped graphene quantum dots is applied to the detection of sodium formaldehyde sulfoxylate in food, and the food is solid or powdered food, and specifically, the food is at least one of vermicelli, rice noodles, dried beancurd sticks, flour, canned food, and white sugar.

[0016] In a specific embodiment, the sample to be detected is first crushed and mixed uniformly before detection, an HCl-NaCl solution is added for sample pretreatment, and the sample is extracted by oscillation, the extraction liquid is centrifuged, and the supernatant is used for detection.

[0017] The method has the following beneficial effects:

[0018] The nitrogen-doped graphene quantum dots are prepared by using citrate and urea as carbon and nitrogen precursors through a hydrothermal synthesis method, and have high stability and sensitivity, and show yellow fluorescence in a reducing environment, and excellent redispersibility and biocompatibility in water.

[0019] The present application utilizes the strong reducing property of sodium formaldehyde sulfoxylate to occur redox reaction with oxidizing substances, electron transfer transition occurs in the solution, the fluorescence of the nitrogen-doped graphene quantum dots is quenched and weakened, and the color changes under the ultraviolet lamp, thereby playing a signal amplification effect. Since the emission wavelength of the nitrogen-doped graphene quantum dots is different from that of the reaction product 1,4-naphthalenediol, there are different fluorescence intensities and ultraviolet absorption peaks in the characteristic region; and as the reaction occurs, the fluorescence of the quantum dots at 440 nm is quenched and weakened, while the fluorescence of the product 1,4-naphthalenediol at 420 nm is enhanced, thereby producing ratio fluorescence, and the color change can be observed by the naked eye and under the ultraviolet lamp, thereby playing a qualitative and quantitative effect on the rapid detection of sodium formaldehyde sulfoxylate.

[0020] The detection method of the present application does not depend on large-scale instruments and equipment, has the advantages of rapidness, sensitivity, high efficiency and low cost, and improves the problems of inaccurate detection results, high cost, high requirement for instruments and equipment, and complicated method of the existing detection of ivory white block technology. Moreover, the method of the present application for detecting ivory white block does not need to use the method of distilling and absorbing the distillation liquid, and does not need to indirectly calculate the content of sodium formaldehyde sulfoxylate by measuring the content of formaldehyde and sulfur dioxide, thereby realizing qualitative and quantitative analysis of the ivory white block. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a schematic diagram of the detection principle of the present application;

[0022] Figure 2 It is a sodium formaldehyde sulfoxylate concentration-ratio fluorescence response value (I 420 / I 440 ) standard curve diagram;

[0023] Figure 3 It is the fluorescence intensity of NGQDs solution with different concentrations;

[0024] Figure 4 It is the ratio fluorescence intensity of the reaction system of 1,4-naphthalenediol with different concentrations;

[0025] Figure 5 It is a specificity test diagram. DETAILED DESCRIPTION

[0026] The raw materials or solvents used in the present application are as follows:

[0027] NaOH solution, HCl solution (for adjusting the pH of PBS buffer), acetonitrile, formaldehyde sodium sulfite, 1,4-naphthoquinone are all analytical pure or chemical pure.

[0028] HCl-NaCl solution: weigh 20g NaCl in a 1000mL volumetric flask, dissolve with water, add 60mL 37% hydrochloric acid, and add water to the mark.

[0029] The principle of the detection method of the present application is as follows:

[0030] Carve white block (formaldehyde sodium sulfite) has strong reducing property, and 1,4-naphthoquinone has oxidizing property. When 1,4-naphthoquinone and formaldehyde sodium sulfite undergo redox reaction, electron transfer occurs in the system, and in the redox process, the number of delocalized electrons and the nitrogen atoms doped in the carbon nucleus will undergo molecular configuration transformation, so that the fluorescence color and intensity of the quantum dots change, and the fluorescence of the product 1,4-naphthalenediol is enhanced, thereby producing ratio fluorescence. The nitrogen-doped graphene quantum dots prepared by the present application present yellow in the reducing environment, and with the progress of the reaction, the fluorescence of the quantum dots becomes blue, and the fluorescence intensity also changes (decreases). Although the product 1,4-naphthalenediol has strong fluorescence, the wavelength regions corresponding to the maximum fluorescence emission intensities of the two do not overlap. After the reaction of 1,4-naphthoquinone and formaldehyde sodium sulfite is completed, under 360nm excitation, fluorescence quenching at 440nm and fluorescence enhancement at 420nm will be detected, as shown in Figure 1 .

[0031] Unless otherwise specified, the other terms used in the present application generally have the meanings commonly understood by those of ordinary skill in the art. The present application will be described in further detail below in conjunction with specific examples and by reference to the data. The following examples are only intended to illustrate the present application, and in no way limit the scope of the present application.

[0032] Example 1

[0033] A method for detecting formaldehyde sodium sulfite based on nitrogen-doped graphene quantum dots ratio fluorescence, the steps are as follows:

[0034] (1) Accurately weigh about 5g of the sample to be tested, crush uniformly, add 100mL of HCl-NaCl solution for sample pretreatment, transfer into a triangular flask and shake for 40 minutes, pour the extraction liquid into a 20mL centrifuge tube, centrifuge at 10000rpm for 15 minutes, and reserve the supernatant for use.

[0035] (2) In a 15 mL cuvette, add 6 mL of the sample to be tested, 600 μL of nitrogen-doped graphene quantum dot (NGQD) solution (1 mg / mL), and 5 mL of 1,4-naphthoquinone (20 μmol / L) solution, then add acetonitrile / water (V:V = 7:3) solution to a constant volume of 15 mL. Shake well, incubate at room temperature for 10 min, then measure the fluorescence intensity of the sample to be tested at 420 nm and 440 nm under excitation at 360 nm, and calculate the ratio fluorescence response value (I 420 / I 440 ). In this step, acetonitrile / water is used as an organic solvent for organic reactions, and only when the water content of the system is 30% (i.e. V:V = 7:3), the fluorescence intensity of the system is maximally enhanced. Therefore, in this embodiment, acetonitrile / water (V:V = 7:3) is used to dilute the sample to be tested when detecting sodium formaldehyde sulfoxylate in the sample.

[0036] The NGQDs used in the above steps can be prepared by existing methods or by the following method:

[0037] Dissolve 1.68 g (8 μM) of citric acid and 1.44 g (24 μM) of urea in 40 mL of water, and stir for 5 minutes until the solution is clear. Then transfer the solution to a 50 mL stainless steel autoclave with good airtightness, heat to 180°C within 20 minutes, and maintain for 8 hours. After the reaction is completed, cool to room temperature to obtain a golden yellow product, i.e. NGQDs (nitrogen-doped graphene quantum dots).

[0038] When used, a certain amount of prepared NGQD powder is accurately weighed, and a 1 mg·mL -1 NGQD working solution is prepared with 0.01 mol / L PBS buffer (pH 8.0).

[0039] (3) Preparation of sodium formaldehyde sulfoxylate standard curve:

[0040] First, prepare a sodium formaldehyde sulfoxylate stock solution (10 mg / mL), and when used, take 1.00 mL of the above standard stock solution into a 100 mL volumetric flask, add water to the mark, and mix well. At this time, the concentration of the sodium formaldehyde sulfoxylate standard solution is 0.1 mg / mL. Add the above sodium formaldehyde sulfoxylate standard solution to acetonitrile / water (V:V = 7:3) to prepare a working solution with different concentration gradients, and the concentrations are 20 μmol / L, 30 μmol / L, 40 μmol / L, 50 μmol / L, 60 μmol / L, 70 μmol / L, 80 μmol / L, 100 μmol / L, 120 μmol / L, 150 μmol / L, and 180 μmol / L.

[0041] A 15-mL volumetric flask was added with the same volume of formaldehyde sodium sulfite standard solution 6 mL, 5 mL of 1,4-naphthoquinone (20 μmol / L) and 600 μL of NGQDs solution (1 mg / mL), and was diluted to 15 mL with acetonitrile / water solution (V:V = 7:3), and was mixed uniformly. After 2 h of reaction, the fluorescence intensity of the reaction solution at 420 nm and 440 nm was measured under 360 nm excitation, and the ratio fluorescence response value (I 420 / I 440 ) was taken as the ordinate, and the concentration of formaldehyde sodium sulfite was taken as the abscissa, to draw a standard curve. As shown in Figure 2 , the concentration of formaldehyde sodium sulfite between 20 and 180 μmol / L had a good linear relationship with the ratio fluorescence response. The linear regression equation was y = 0.0149x + 1.053, R 2 = 0.996, and the detection limit LOD was 0.62 μmol / L.

[0042] Detection limit calculation formula:

[0043] Average fluorescence ratio x = (0.123 + 0.119 + 0.125) / 3 = 0.122

[0044] Standard deviation s = Sqrt[(0.123-0.122)^2+(0.119-0.122)^2+(0.125-0.122)^2] / 2 = 0.00308

[0045] LOD = 3*0.00308 / 0.0149 = 0.620 μmol / L

[0046] (4) Result determination

[0047] The ratio fluorescence response value (I 420 / I 440 ) calculated in step (2) was introduced into the regression equation in step (3), and the concentration of formaldehyde sodium sulfite in the sample to be tested was calculated.

[0048] Example 2

[0049] Effect of concentration of NGQDs on detection results:

[0050] The NGQDs powder prepared by the method described in Example 1 was configured into NGQDs solutions with concentrations of 0.1 mg / mL, 1 mg / mL, 2 mg / mL, 4 mg / mL and 6 mg / mL using PBS buffer (0.01 mol / L, pH = 7.4), and then the fluorescence intensity of the NGQDs solution was tested by a fluorescence spectrometer under 360 nm excitation wavelength.

[0051] The test results are shown in Figure 3The results are shown in the following table:

[0052] The fluorescence intensity of the NGQDs solution is the highest at 1 mg / mL, and therefore, in practical applications, 1 mg / mL can be selected as the optimal concentration of the NGQDs solution to achieve better detection results.

[0053] Example 3

[0054] Effect of 1,4-naphthoquinone concentration on the detection results:

[0055] Different concentrations of 1,4-naphthoquinone solutions were prepared, and the concentrations were 10 μmol / L, 20 μmol / L, 40 μmol / L and 60 μmol / L. The above 1,4-naphthoquinone solutions of different concentrations were mixed with formaldehyde sodium sulfite solution (150 μmol / L) and NGQDs solution (1 mg / mL) to react, and the fluorescence intensity of each reaction solution at 420 nm and 440 nm was measured under an excitation wavelength of 360 nm, and the ratio fluorescence response value (I 420 / I 440 ) was calculated. Figure 4 As shown in the following table, when the concentration of 1,4-naphthoquinone was 20 μmol / L and 40 μmol / L, the ratio fluorescence response value was significantly higher than that of 10 μmol / L and 60 μmol / L; among them, the ratio fluorescence response value was the highest when the concentration of 1,4-naphthoquinone was 40 μmol / L, but there was little difference between 20 μmol / L and 40 μmol / L; therefore, in practical applications, 20 μmol / L can be selected as the optimal concentration to achieve better detection results and in accordance with the principle of economic saving.

[0056] Example 4

[0057] Specificity of the method for detecting formaldehyde sodium sulfite based on nitrogen-doped graphene quantum dots ratio fluorescence

[0058] The detection method of the present application is based on an oxidation-reduction reaction, and certain ions (such as CO 3- , H2PO 4- , SO 3- , Cl - , Na + ) and reducing substances (such as ascorbic acid, glucose, sodium citrate, tartaric acid) in food may interfere with the detection; in order to verify the specificity of the detection method of the present application, the above ions, reducing substances and formaldehyde sodium sulfite were all prepared into 6 mL of a test solution with a concentration of 180 μmol / L for specificity testing.

[0059] The specific method is shown in the following table:

[0060] Add 5mL of 1,4-naphthoquinone solution (20μmol / L) and 600μL of NGQDs solution (1mg / mL) of the same volume and concentration into the above to-be-tested solution respectively, and react for 2h at room temperature in a 15mL centrifuge tube, and measure the ratio fluorescence response value (I 420 / I 440 ) of each to-be-tested solution under excitation at 360nm.

[0061] The test results are shown in Table 1. Figure 5

[0062] The formaldehyde sodium sulfite to-be-tested solution has a greater fluorescence weakening, and the color becomes blue. The quantum dot fluorescence of other ion and reducing substance to-be-tested solutions is almost not weakened, and the color change is not obvious. This shows that the detection method of the application has specificity for formaldehyde sodium sulfite.

[0063] Application Example 1

[0064] The detection method verification is shown as follows.

[0065] A method for detecting formaldehyde sodium sulfite (sodium sulfite) in a food sample comprises the following steps:

[0066] Add 5mL of 1,4-naphthoquinone solution (20μmol / L) and 600μL of NGQDs solution (1mg / mL) into 6mL of formaldehyde sodium sulfite standard solution with a concentration of 50μmol / L, 80μmol / L and 120μmol / L respectively, and measure the ratio fluorescence intensity (I 420 / I 440 ) of the system under excitation at 360nm after reacting for 2h, as the theoretical value.

[0067] Subsequently, take 6 wheat flour blank matrix samples, and divide them into 3 groups. Add 500μL of formaldehyde sodium sulfite standard solution with a concentration of 50μmol / L, 80μmol / L and 120μmol / L to one sample in each group respectively, as a spiked sample; and do not add formaldehyde sodium sulfite standard solution to another sample in each group, as a blank sample; then add 5mL of 1,4-naphthoquinone solution (20μmol / L) and 600μL of NGQDs solution (1mg / mL) into each sample, and measure the ratio fluorescence intensity (I 420 / I 440 ) of the system under excitation at 360nm after reacting for 2h, and detect each sample system for 3 times.

[0068] Calculate the ratio fluorescence intensity (I 420 / I 440 ) of the spiked sample and the ratio fluorescence intensity (I 420 / I 440 ​The difference between the measured value and the theoretical value is calculated, and then the ratio of the difference to the theoretical value is the recovery rate of the standard addition. The recovery rate of the standard addition is shown in Table 1. As shown in Table 1, the recovery rate of the standard addition ranges from 97.44% to 99.10%, indicating that the method has high accuracy.

[0069] Table 1

[0070]

[0071] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any person skilled in the art can modify or change the above disclosed technical content into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change and modification of the above embodiments made according to the technical essence of the present application without departing from the technical solution of the present application still falls within the protection scope of the present application.

Claims

1. A method for detecting sodium formaldehyde sulfoxylate based on nitrogen-doped graphene quantum dots ratio fluorescence, characterized in that, The steps are as follows: The sample solution to be measured, the nitrogen-doped graphene quantum dot solution and the 1,4-naphthoquinone solution are mixed for reaction, and after the reaction, the fluorescence intensities at 420 nm and 440 nm under an excitation wavelength of 360 nm are measured by a fluorescence spectrophotometer, and the fluorescence intensity ratio I 420 / I 440 , and I 420 / I 440 The standard curve is imported, and the concentration of sodium formaldehyde sulfoxylate in the sample to be measured is obtained. 2.The method according to claim 1, wherein the method is characterized in that, The nitrogen-doped graphene quantum dots are prepared by the following method: Dissolve citric acid and urea in water, stir until the solution is clear, then heat to 180℃ within 20 minutes, and keep for 8 hours, after the reaction is completed, cool to room temperature, to obtain nitrogen-doped graphene quantum dots. 3.The method according to claim 2, wherein the method is characterized in that, The concentration of the nitrogen-doped graphene quantum dot solution is 0.1 mg / mL-6 mg / mL. 4.The method according to claim 1, wherein, The 1,4-naphthoquinone solution is prepared by dissolving 1,4-naphthoquinone powder in acetonitrile / water (V:V=7:3) solvent. 5.The method according to claim 1, wherein, The standard curve is made by the following method: Formaldehyde sodium sulfite was prepared into 20 μmol / L, 30 μmol / L, 40 μmol / L, 50 μmol / L, 60 μmol / L, 70 μmol / L, 80 μmol / L, 100 μmol / L, 120 μmol / L, 150 μmol / L, 180 μmol / L standard solution with acetonitrile / water (V:V=7:3) solution, different concentrations of formaldehyde sodium sulfite standard solution and 1,4-naphthoquinone solution were added in acetonitrile / water (V:V=7:3) solution, after mixing uniformly, nitrogen-doped graphene quantum dot solution was added, mixed uniformly, after 2h reaction, the fluorescence intensity at 420nm and 440nm was measured under 360nm excitation wavelength, and the fluorescence intensity ratio I 420 / I 440 was calculated as the ratio of fluorescence response I 420 / I 440 As the ordinate, the concentration of formaldehyde sodium sulfite was taken as the abscissa, and the standard curve was drawn.

6. The method for detecting sodium sulfite formaldehyde according to any one of claims 1-5, wherein, The concentration of the 1,4-naphthoquinone solution is 10-60 μmol / L.

7. The application of the method for detecting sodium formaldehyde sulfoxylate based on the ratio fluorescence of nitrogen-doped graphene quantum dots in the detection of sodium formaldehyde sulfoxylate in food.

8. Use according to claim 7, characterized in that, The food is solid or powdered food.

9. Use according to claim 8, characterized in that, The food is at least one of vermicelli, rice noodles, dried beancurd, flour, canned food, and white sugar.

10. Use according to claim 7, characterized in that, Before detection, the sample to be measured is first crushed and made uniform, an HCl-NaCl solution is added for sample pretreatment, and the sample is extracted by oscillation, the extract is centrifuged, and the supernatant is reserved for detection. The steps are as follows: The nitrogen-doped graphene quantum dots are prepared by the following method: Dissolve citric acid and urea in water, stir until the solution is clear, then heat to 180℃ within 20 minutes, and keep for 8 hours, after the reaction is completed, cool to room temperature, to obtain nitrogen-doped graphene quantum dots. The concentration of the nitrogen-doped graphene quantum dot solution is 0.1 mg / mL-6 mg / mL. The 1,4-naphthoquinone solution is prepared by dissolving 1,4-naphthoquinone powder in acetonitrile / water (V:V=7:3) solvent. The standard curve is made by the following method: The concentration of the 1,4-naphthoquinone solution is 10-60 μmol / L.

7. The application of the method for detecting sodium formaldehyde sulfoxylate based on the ratio fluorescence of nitrogen-doped graphene quantum dots in the detection of sodium formaldehyde sulfoxylate in food. The food is solid or powdered food. The food is at least one of vermicelli, rice noodles, dried beancurd, flour, canned food, and white sugar. Before detection, the sample to be measured is first crushed and made uniform, an HCl-NaCl solution is added for sample pretreatment, and the sample is extracted by oscillation, the extract is centrifuged, and the supernatant is reserved for detection.

Images