Method for detecting content of ferric ammonium citrate in table salt by using K-g-C3N4 (at) PDA nano-enzyme and application

Abstract

The invention relates to the technical field of chemical analysis and detection, and aims to provide a high-sensitivity and strong-specificity ferric ammonium citrate detection method aiming at the defect of determining the content of ferric ammonium citrate in a high-salt system so as to improve the detection precision of the content of ferric ammonium citrate in table salt. The K-g-C3N4 (at) PDA nano-enzyme is prepared by adopting a two-step sylvite-assisted thermal copolymerization strategy, the nano-enzyme has peroxidase-like activity and can catalytically oxidize a substrate ABTS and H2O2 to generate a blue-green oxidation product (ox-ABTS) and generate maximum absorption at the wavelength of 416 nm under an acidic condition, ammonium ferric citrate can enhance the peroxidase-like activity of the K-g-C3N4 (at) PDA nano-enzyme, and the K-g-C3N4 (at) PDA nano-enzyme can be used for preparing the nano-enzyme. The concentration of the ferric ammonium citrate in the sample can be measured according to the linear relationship between the concentration of the ferric ammonium citrate and the increase of the absorbance of the ox-ABTS, so that the green color of the ox-ABTS is deepened, and the concentration of the ferric ammonium citrate in the sample can be measured according to the linear relationship. The K-g-C3N4-coated PDA nano enzyme is good in stability and high in salt tolerance, and various ions in the table salt have almost no influence on the detection result, so that the K-g-C3N4-coated PDA nano enzyme has good selection specificity and wider applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical analysis and detection, and in particular to a method and application of detecting the content of ammonium ferric citrate in table salt by utilizing Kg-C3N4@PDA nanoenzyme. Background Art

[0002] Ammonium ferric citrate is a mixture of ferric citrate and ammonium citrate, but the content of these substances in the product is not fixed and can vary depending on the synthesis conditions. According to GB 2760-2024, "National Food Safety Standard for the Use of Food Additives," ammonium ferric citrate can be added to salt and salt substitutes as an anti-caking agent to prevent clumping during storage and use, which could affect the product's usability. The dosage should not exceed 25 mg / kg. Furthermore, according to GB 14880-2012, "National Food Safety Standard for the Use of Food Nutrient Fortifiers," ammonium ferric citrate can also be added to foods as a nutritional fortifier to increase the nutritional value of iron. It is widely used in the production of green food edible salt. However, excessive levels of ammonium ferric citrate can cause irritation to the gastric mucosa, leading to adverse symptoms such as nausea, vomiting, and stomach pain. Therefore, testing for ammonium ferric citrate is an important measure to ensure the safety of salt products.

[0003] According to the provisions of QB / T 5776 light industry standard "Determination of anti-caking agent ammonium ferric citrate in edible salt", the conventional detection method for ammonium ferric citrate in edible salt is the spectrophotometric method, which uses a known iron standard solution (ferric sulfate) to prepare solutions of different concentrations, and measures its absorbance by a spectrophotometer. A standard curve is made based on the positive correlation between absorbance and iron ion content, and then the absorbance of the unknown solution iron ion is measured. The iron ion content is checked on the standard curve based on the absorbance, and finally the content of ammonium ferric citrate is calculated based on the iron ion content. However, the entire detection process of this method is in a high salt system, and ferric sulfate will coexist with the Na + , K + Mg 2+ 、Fe 2+ 、[Fe(CN)6] 4- , Ca 2+ 、Cl - , I - IO3 - 、SO4 2- Side reactions may occur, and even insoluble matter may be produced, resulting in a low detection content of ammonium ferric citrate and a lower detection accuracy.

[0004] Therefore, in view of the defects of the existing technology in determining the content of ammonium ferric citrate in a high salt system, it is necessary to propose a new method for detecting the content of ammonium ferric citrate in table salt, so as to improve the detection accuracy of the content of ammonium ferric citrate in table salt and provide a new detection idea for the setting of industry standards.

[0005] The above content is only used to assist in understanding the technical solution of the present invention and does not constitute an admission that the above content is prior art. Summary of the Invention

[0006] The main purpose of the present invention is to provide a method and application for detecting the content of ammonium ferric citrate (FAC) in table salt using Kg-C3N4@PDA nanozyme. It aims to address the influence of coexisting ions in high salt systems on the determination of ammonium ferric citrate content, and proposes a method and application for detecting the content of ammonium ferric citrate in table salt using Kg-C3N4@PDA nanozyme, so as to improve the detection accuracy of the content of ammonium ferric citrate in table salt and provide a new detection idea for the setting of industry standards.

[0007] To achieve the above object, on the one hand, the present invention provides a method for detecting the content of ammonium ferric citrate in salt using Kg-C3N4@PDA nanozyme, the method comprising the following steps:

[0008] S1, prepare standard solution

[0009] Preparation of ammonium ferric citrate standard sample solution: within the concentration range of 0-6 μg / mL, nine groups of ammonium ferric citrate standard solutions with different concentrations were taken according to an arbitrary concentration gradient and added to nine colorimetric tubes respectively; then, Kg-C3N4@PDA nanozyme solution, 2,2'-hydrazino-bis-3-ethylbenzothiazoline-6-sulfonic acid and H2O2 were added to the colorimetric tubes respectively, and the volume was adjusted to 4 mL with NaAc-HAc buffer solution of pH 4.0, mixed well, and allowed to stand for 5-10 minutes to obtain nine groups of different standard sample solutions.

[0010] Blank standard solution: Add Kg-C3N4@PDA nanozyme solution, 2,2'-hydrazino-bis-3-ethylbenzothiazoline-6-sulfonic acid, and H2O2 to a colorimetric tube, dilute to 4 mL with pH 4.0 NaAc-HAc buffer solution, mix well, and let stand for 5-10 minutes to obtain a blank standard sample solution.

[0011] S2, prepare standard curve

[0012] Determine the absorbance of the standard solution at the maximum absorption wavelength, with the concentration of the ammonium ferric citrate standard solution as the horizontal coordinate and the corresponding absorbance difference ΔA as the vertical coordinate, ΔA=A-A0; draw a standard curve and calculate the regression equation of the standard curve.

[0013] A is the absorbance of the ammonium ferric citrate standard sample solution at the maximum absorption wavelength;

[0014] A0 is the absorbance of the blank standard solution at the maximum absorption wavelength;

[0015] S3, detection of the content of ammonium ferric citrate in table salt

[0016] Prepare salt sample solution: prepare salt sample solution with a concentration of 0.2 g / mL;

[0017] Take 0.5 mL of the salt sample solution into a colorimetric tube, then add Kg-C3N4@PDA nanozyme solution, 2,2'-hydrazine-bis-3-ethylbenzothiazoline-6-sulfonic acid and H2O2 into the colorimetric tube, dilute to 4 mL with NaAc-HAc buffer solution with pH 4.0, mix well, let stand for 5-10 minutes, measure the absorbance at the maximum absorption wavelength, and calculate the content of ammonium ferric citrate in the sample using the standard curve regression equation.

[0018] Optionally, the concentration of the Kg-C3N4@PDA nanozyme solution is 25 μg / mL, and the added amount is 50 to 100 μL; the concentration of the 2,2'-hydrazine-bis-3-ethylbenzothiazoline-6-sulfonic acid is 5 mmol / L, and the added amount is 50 to 100 μL; the concentration of the H2O2 is 50 mmol / L, and the added amount is 50 to 100 μL.

[0019] Optionally, the amount of the Kg-C3N4@PDA nanozyme solution added is 100 μL; the amount of the 2,2'-hydrazine-bis-3-ethylbenzothiazoline-6-sulfonic acid added is 100 μL; and the amount of the H2O2 added is 100 μL.

[0020] Optionally, the maximum absorption wavelength is 416 nm.

[0021] On the other hand, the present application also proposes a method for preparing the Kg-C3N4@PDA nanozyme solution as described in the above method, the preparation method comprising the following steps:

[0022] 1) Preparation of KCN nanomaterials: 3.0-3.5 g of melamine, 1.0-1.5 g of KCl and an appropriate amount of ethanol were ground and mixed, and the mixture was transferred to a corundum boat with a lid and heated at 5 °C / min under nitrogen atmosphere. -1 After the temperature is raised to 550°C at a heating rate of 1000 nm, the material is calcined at a constant temperature for 3 to 4 hours; then cooled to room temperature, and the material is ground into powder to obtain KCN nanomaterials;

[0023] 2) Preparation of Kg-C3N4-COOH nanomaterial: 1.0-1.5 g of the KCN nanomaterial was mixed with 4.0-4.5 g of potassium thiocyanate and ground into powder; the powder was placed in a corundum boat with a lid and heated at 5°C / min under nitrogen atmosphere. -1 The temperature was raised to 400°C at a heating rate of 0.1°C, kept constant at that temperature for 1 to 2 hours, then continued to be raised to 500°C, kept constant at that temperature for 30 to 40 minutes, and then cooled to room temperature. The calcined powder was dispersed in 40 to 60 mL of HNO3 solution, stirred at room temperature for 2 to 3 hours, centrifuged, and the precipitate was collected and washed with ethanol for 3 to 4 times. The washed precipitate was vacuum dried to obtain Kg-C3N4-COOH nanomaterials.

[0024] 3) Preparation of Kg-C3N4@PDA nanozyme: 0.1-0.2 g of the Kg-C3N4-COOH nanomaterial was added to 50-100 mL of Tris buffer and ultrasonically treated for 40-60 min to obtain solution A; 4-5 mg of dopamine hydrochloride was added to 1-2 mL of Tris buffer at pH 8.5 and ultrasonically treated for 5-10 min to obtain solution B; solution B was added dropwise to solution A, stirred for 2-3 h, centrifuged, and the precipitate was collected and washed with deionized water and ethanol 3-4 times each; the washed precipitate was vacuum dried to obtain Kg-C3N4@PDA nanozyme; finally, the Kg-C3N4@PDA nanozyme was dissolved in deionized water to obtain a Kg-C3N4@PDA nanozyme solution;

[0025] Optionally, the concentration of the HNO3 solution in 2) is 1.5 to 2.0 mol / L.

[0026] Optionally, the centrifugal speed is 6000-8000 r / min, and the time is 5-10 min.

[0027] Principle of the invention:

[0028] In a high-salt system, the prepared Kg-C3N4@PDA nanozyme has peroxide-like activity, high stability and salt tolerance, and can react with the substrate 2,2′-hydrazino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and H2O2 to produce blue-green compounds. Ammonium ferric citrate can enhance the activity of the nanozyme. A method for the determination of ammonium ferric citrate in table salt was established. The method has the characteristics of high sensitivity, strong specificity, simple operation and rapidity.

[0029] Kg-C3N4@PDA nanozyme not only has enzymatic activity, but also has photothermal effect, stable fluorescence and fluorescence conversion properties, and very significant photocatalytic efficiency. Therefore, Kg-C3N4@PDA nanozyme can be used as a new type of fluorescent marker and can also be used in biological imaging.

[0030] Basic principles for making linear curves (UV spectrophotometry):

[0031] In the present invention, Kg-C3N4@PDA nanozyme has peroxidase-like activity. Under acidic conditions, it can act as a catalyst to cause 2,2′-hydrazine-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) to undergo an oxidation reaction with H2O2 to generate a blue-green oxidation product (ox-ABTS). The color-developing oxidation product (ox-ABTS) has a maximum absorption at a wavelength of 416 nm and can be quantitatively analyzed by ultraviolet spectrophotometry. 3+ It can coordinate with the catechol of polydopamine, and the addition of ammonium ferric citrate can enhance the peroxidase-like activity of Kg-C3N4@PDA nanozyme, making the blue-green oxidation product (ox-ABTS) produced by the Kg-C3N4@PDA nanozyme catalyzing the oxidation of ABTS and H2O2 deepen in green and increase in absorbance. In addition, the concentration of the ammonium ferric citrate standard solution is linearly related to the increase in the absorbance of ox-ABTS. Therefore, by measuring the absorbance of different concentrations of ammonium ferric citrate standard solutions at the maximum absorption wavelength of 416nm, according to the quantitative relationship between the concentration of ammonium ferric citrate and the absorbance, a standard working curve can be drawn, and the regression equation of the standard curve can be obtained. Then, the absorbance of the sample at 416nm can be measured, and the concentration of ammonium ferric citrate in the sample can be calculated by the regression equation, thereby realizing the quantitative analysis of the ammonium ferric citrate content in the salt sample.

[0032] The embodiment of the present invention provides a method for detecting the content of ammonium ferric citrate in salt using Kg-C3N4@PDA nanozyme, which has at least the following beneficial effects:

[0033] 1. The present invention utilizes Kg-C3N4@PDA nanozyme with peroxidase-like activity. Under acidic conditions, it can catalyze the oxidation of ABTS and react with H2O2 to generate a blue-green oxidation product (ox-ABTS), and produce maximum absorption at a maximum wavelength of 416nm. The addition of ammonium ferric citrate can enhance the peroxidase-like activity of Kg-C3N4@PDA nanozyme, making the green color of ox-ABTS deepen and the absorbance increase. Therefore, based on the principle that the concentration of ammonium ferric citrate is linearly related to the absorbance of ox-ABTS, a new method for detecting the content of ammonium ferric citrate in a sample is established, which has high sensitivity and strong selectivity.

[0034] 2. The Kg-C3N4@PDA nanozyme prepared in the present invention adopts a two-step potassium salt-assisted thermal copolymerization strategy to introduce K + ion and carboxylation of Kg-C3N4-COOH, and amide bond connection with the amino group of dopamine to prepare Kg-C3N4@PDA, K + The introduction of can increase the high crystallinity of the material, promote carrier separation and bulk charge migration, -COOH provides an amide bond that can be connected with the amino group in dopamine to prepare Kg-C3N4@PDA and groups, while Fe 3+ The carboxyl group in citric acid can coordinate with the catechol in polydopamine and produce hydrogen bonds. Based on this, a new method for detecting ammonium ferric citrate in table salt using Kg-C3N4@PDA nanozyme was established. The detection time only takes 10 minutes, with fast detection speed, high sensitivity and simple operation.

[0035] 3. In a high-salt system, the Kg-C3N4@PDA nanozyme prepared by the present invention has good stability and salt tolerance. When detecting the content of ammonium ferric citrate in table salt, the spiked recovery rate reaches 94.09% to 105.17%, with high detection accuracy.

[0036] 4. The standard sample solution was tested by specific investigation test. Compared with the traditional QB / T 5776 light industry standard method, the present invention has a better understanding of the Na + , K + Mg 2+ 、Fe 2+ 、[Fe(CN)6] 4- , Ca 2+ 、Cl - , I - IO3 - 、SO4 2- There is almost no influence on the detection results, so the present invention has very good selection specificity and wider applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 These are transmission electron microscopy (TEM) images of Kg-C3N4@PDA nanozymes of different sizes in Example 1 (a, b).

[0038] Figure 2 This is the UV-vis absorption spectrum of Kg-C3N4@PDA nanozyme catalyzing ABTS and ABTS+H2O2 in Example 1.

[0039] Figure 3 The UV-vis absorption spectra of the peroxidase chromogenic substrates ABTS and H2O2 catalyzed by Kg-C3N4@PDA and Kg-C3N4@PDA+FAC in Example 1.

[0040] Figure 4 (ad) are the Michaelis-Menten plots of ABTS and H2O2 fitted by Kg-C3N4@PDA and Kg-C3N4@PDA+FAC in Example 1 of the present invention.

[0041] Figure 5 This is the linear fitting curve of Kg-C3N4@PDA detecting FAC in the range of 0.056 to 5.63 μg / mL in Example 1 of the present invention.

[0042] Figure 6 FAC selectivity results detected by Kg-C3N4@PDA.

[0043] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0044] To better understand the above technical solutions, exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0045] Preparation principle of Kg-C3N4@PDA nanozyme:

[0046] The present invention adopts a two-step potassium salt-assisted thermal copolymerization strategy to introduce K + ion and carboxylation of Kg-C3N4-COOH, and amide bond connection with the amino group of dopamine to prepare Kg-C3N4@PDA, K + The introduction of high crystallinity of the material promotes carrier separation and bulk charge migration, and -COOH provides an amide bond that can be connected with the amino group in dopamine to prepare Kg-C3N4@PDA and groups, while Fe 3+ The carboxyl group in citric acid can coordinate with the catechol in polydopamine and produce hydrogen bonds. Based on this, a method for detecting ammonium ferric citrate in table salt by Kg-C3N4@PDA nanozyme was established.

[0047] Principle of Michaelis-Menten catalytic kinetic parameters determination:

[0048] With other parameters unchanged, steady-state kinetic analysis of the catalytic activity of FAC at different concentrations of ABTS and H2O2 was performed. The Michaelis-Menten kinetic equation was obtained by plotting the reciprocal of the reaction rate (V) against the reciprocal of the substrate concentration [S].

[0049] 1 / V=(Km / Vmax)(1 / [S])+1 / Km

[0050] V is the reaction rate / (mol / (L·s));

[0051] Km is the Michaelis constant / (mmol / L);

[0052] Vmax is the maximum reaction rate / (mol / (L·s));

[0053] [S] is the concentration of substrate H2O2 / (mmol / L).

[0054] The catalytic reaction increased significantly with the increase of H2O2 substrate concentration. Kg-C3N4@PDA nanozyme first reacted with H2O2 to produce hydroxyl radicals, which further oxidized the substrate ABTS to generate blue-green ox-ABTS.

[0055] The reason for detecting hydroxyl radicals (·OH) is that ·OH reacts with benzoic acid to form hydroxybenzoic acid, which emits fluorescence at an excitation wavelength of 330 nm. Under acidic conditions, the Kg-C3N4@PDA nanozyme catalyzes H2O2 to produce hydroxyl radicals, which further oxidize the substrate. Detecting ·OH allows for the investigation of the nanozyme's catalytic activity.

[0056] Based on the above description, the present invention proposes a method and application embodiment for detecting the content of ammonium ferric citrate in table salt using Kg-C3N4@PDA nanozyme.

[0057] First embodiment

[0058] 1. Preparation of Kg-C3N4@PDA nanozyme:

[0059] 1) Preparation of KCN nanomaterials: A mixture of 3.0 g melamine, 1.0 g KCl and an appropriate amount of ethanol was ground, transferred to a corundum boat, and heated at 5 °C min under a nitrogen atmosphere. -1 The material was calcined at 550 °C for 3 h at a heating rate of 0.5 ℃ and then cooled to room temperature, and then ground into powder to obtain KCN nanomaterials.

[0060] 2) Preparation of Kg-C3N4-COOH nanomaterials: 1.0 g of the prepared KCN nanomaterials was ground together with 4.0 g of potassium thiocyanate (KSCN), placed in a corundum boat with a lid, and stirred at 5 °C min in a nitrogen atmosphere. -1The powder was heated at 400°C for 1 h at a heating rate and then heated at 500°C for another 40 min. After cooling to room temperature, the collected powder was dispersed in 40 mL of 2.0 mol / L HNO3 solution and then stirred at room temperature for 2 h. The mixture was centrifuged and the precipitate was collected. The precipitate was washed with ethanol 3-4 times and dried in vacuo to obtain Kg-C3N4-COOH nanomaterials.

[0061] 3) Preparation of Kg-C3N4@PDA nanomaterial: 0.1g Kg-C3N4-COOH nanomaterial was dispersed in 50mL of pH 8.5 Tris buffer and ultrasonically treated for 40min to obtain a uniform solution, recorded as liquid A. Then, 4mg of dopamine hydrochloride was uniformly dispersed in 1mL of pH 8.5 Tris buffer and ultrasonically treated for 5-10min, recorded as liquid B. Liquid B was added dropwise to liquid A, stirred for 2h, centrifuged, and the precipitate was collected and washed with deionized water and ethanol 3-4 times each. Finally, Kg-C3N4@PDA nanozyme was obtained after vacuum drying; deionized water was added to obtain Kg-C3N4@PDA nanozyme solution; according to the needs of subsequent experiments, the above-mentioned Kg-C3N4@PDA nanozyme can be prepared into a Kg-C3N4@PDA nanozyme solution of a specific concentration.

[0062] 2. The obtained Kg-C3N4@PDA nanozyme was subjected to transmission electron microscopy (TEM) analysis, and the TEM image showed that the nanospheres were aggregated on the nanosheets.

[0063] 3. Determination of Kg-C3N4@PDA nanozyme activity: 100 μL of 1 mg / mL nanozyme Kg-C3N4@PDA or 100 μL of 1 μg / mL ammonium ferric citrate (FAC) + 100 μL of 25 μg / mL nanozyme solution Kg-C3N4@PDA, 100 μL of 5 mmol / L ABTS, and 100 μL of 50 mmol / L H2O2 were added to 2.7 mL of pH 4.0 NaAc-HAc buffer solution, mixed thoroughly, and incubated at room temperature for 5 min. The absorbance was measured at 416 nm using a UV-visible spectrophotometer. Each sample was measured 3 times and the average value was taken. Figure 2 As shown, ABTS, ABTS+H2O2 or ABTS+Kg-C3N4@PDA had no absorption in the visible light region, while a clear absorption peak was observed at 416 nm for ABTS+H2O2+Kg-C3N4@PDA, revealing the intrinsic POD-like catalytic activity of Kg-C3N4@PDA nanozyme. Figure 3 It shows that the addition of FAC will enhance the enzyme activity of Kg-C3N4@PDA.

[0064] 4. The experiment also carried out the determination of Michaelis-Menten catalytic kinetic parameters ( Figure 4 ad and Table 1), the Michaelis constant K of Kg-C3N4@PDA for substrates ABTS and H2O2 m The reaction rates were 1.460 mmol / L and 5.725 mmol / L, respectively, and the reaction rate constants were 5.670 × 10 -8 and 2.600×10 -8 mol / L·s, K of ABTS and H2O2 after adding FAC m are 0.670mmol / L and 0.941mmol / L, and the reaction rate constants are 74.31×10 -8 and 23.90×10 -8 mol / L·s, indicating that the addition of FAC greatly enhanced the affinity and reaction rate of Kg-C3N4@PDA nanozyme with substrates ABTS and H2O2.

[0065] Table 1 Michaelis-Menten catalytic kinetic parameters

[0066]

[0067] Second embodiment

[0068] The Kg-C3N4@PDA nanozyme solution prepared in the first example was used to determine the amount of ammonium ferric citrate in salt. The concentration of the Kg-C3N4@PDA nanozyme solution in this example was 25 mg / mL. The specific detection steps included:

[0069] 1. Preparation of ferric ammonium citrate (FAC) working curve:

[0070] Ammonium ferric citrate standard sample solution: Within the concentration range of 0-6 μg / mL, 100 μL of nine groups of ammonium ferric citrate standard solutions of different concentrations were taken according to any concentration gradient and added to nine colorimetric tubes respectively; then, 100 μL of 25 μg / mL Kg-C3N4@PDA nanozyme solution, 100 μL of 5 mmol / L ABTS, and 100 μL of 50 mmol / L H2O2 were added to the colorimetric tubes respectively, and the volume was made up to 4 mL with pH 4.0 NaAc-HAc buffer solution, mixed well, and allowed to stand for 5 minutes to obtain nine groups of different standard sample solutions.

[0071] Blank standard solution: Add 100 μL of 25 μg / mL Kg-C3N4@PDA nanozyme solution, 100 μL of 5 mmol / L ABTS, and 100 μL of 50 mmol / L H2O2 to a colorimetric tube, dilute to 4 mL with pH 4.0 NaAc-HAc buffer solution, mix well, and let stand for 5 minutes to obtain a blank standard solution.

[0072] The UV absorption curves of nine different standard sample solutions at 400-700 nm were measured. Figure 5 a; record the absorbance at a wavelength of 416 nm (determine the maximum wavelength, and subsequent absorbance measurements are performed at this wavelength) (ΔA = A-A0, A0 is the absorbance of the blank solution, and A is the absorbance after adding ammonium ferric citrate solution), and draw a calibration curve (standard curve) as a function of the absorbance difference and FAC concentration, see Figure 5 b, and the obtained linear equation, correlation coefficient, relative standard deviation, linear range, etc. are shown in Table 2.

[0073] Table 2 Linear equation, correlation coefficient, relative standard deviation (RSD), linear range

[0074]

[0075] Limit of detection (LOD): The lowest amount of the analyte that can be detected in the sample

[0076] Linear range: 0.056-5.63 μg / mL, but applicable to all ammonium ferric citrate standard solutions with concentrations between 0 and 6 μg / mL. In the linear equation, "c" is the concentration of ammonium ferric citrate being detected.

[0077] 2. Specificity investigation: Figure 6 Na coexisting in salt + , K + Mg 2+ 、Fe 2+ 、Fe(CN)6 4- , Ca 2+ 、Cl - , I - IO3 - 、SO4 2- The FAC concentration was 5 mg / kg, and the concentrations of all interfering substances were 100 times that of FAC. The results showed that only FAC had a significant enhancing effect, while the other substances had almost no effect, indicating that the method has good selectivity.

[0078] 3. Determination of ammonium ferric citrate in table salt

[0079] (1) Preparation of salt sample solution: Accurately weigh 10 g (accurate to 0.001 g) of sample, dissolve it in deionized water, and dilute to a 50 mL volumetric flask to prepare a salt sample solution;

[0080] (2) Sample determination: Accurately pipette 0.5 mL of salt sample solution into a colorimetric tube, and simultaneously add 100 μL of 25 μg / mL Kg-C3N4@PDA nanozyme solution, 100 μL of 5 mmol / L ABTS, and 100 μL of 50 mmol / L H2O2. The volume was made up to 4 mL with HAc-NaAc buffer solution of pH 4.0, mixed, and allowed to stand for 5 min. The absorbance was measured at a wavelength of 416 nm and substituted into the regression equation of the standard working curve to calculate the results. The results are shown in Table 3. At the same time, a spike recovery test was performed, which was between 94.09% and 105.17%, with an RSD of less than 3% (n=6, n=6 means that 6 samples were used or 6 measurements were performed when calculating the RSD%).

[0081] At the same time, the sample was detected by the o-phenanthroline spectrophotometric method specified in the light industry standard "Determination of anti-caking agent ammonium ferric citrate in edible salt" (QB / T 5776). The inspection steps were carried out in accordance with the test steps specified in the standard. The results are shown in Table 3. The content in "()" in the detection amount is the determination result of the standard. The results show that the method established by the present invention can be used for the determination of ammonium ferric citrate in edible salt.

[0082] Table 3 Determination of low sodium salt samples and spiked recovery rates (n=6)

[0083]

[0084] After analyzing the data in Table 3, it can be shown that when the salt sample is low-sodium salt, the determination result is accurate, the spiked recovery rate reaches 95.00% to 103.10%, the detection accuracy is high, the determination time is 10 minutes, and the detection efficiency is fast.

[0085] Third embodiment

[0086] In this embodiment, only the type of salt sample to be tested is changed, and seaweed iodized salt is selected for the test. The remaining steps are exactly the same as those in Example 2.

[0087] Table 4 Determination of seaweed iodine salt samples and spiked recovery rates (n=6)

[0088]

[0089]

[0090] After analyzing the data in Table 4, it can be shown that when the salt sample is seaweed iodized salt, the determination result is accurate, the spiked recovery rate reaches 94.09% to 105.13%, the detection accuracy is high, the determination time is 9 minutes, and the detection efficiency is fast.

[0091] Fourth embodiment

[0092] In this embodiment, only the type of salt sample to be tested is changed, and non-iodized salt is selected for the test. The remaining steps are exactly the same as those in Example 2.

[0093] Table 5 The present invention measures the non-iodized salt sample and the recovery rate of spiked salt (n=6)

[0094]

[0095] After analyzing the data in Table 5, it can be shown that when the salt sample is non-iodized salt, the determination result is accurate, the spiked recovery rate reaches 95.62% to 105.17%, the detection accuracy is high, the determination time is 10 minutes, and the detection efficiency is fast.

[0096] It should be noted that although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0097] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for detecting the content of ammonium ferric citrate in salt using Kg-C3N4@PDA nanozyme, characterized in that: The method The following steps are involved: S1, prepare standard solution Preparation of ammonium ferric citrate standard sample solution: within the concentration range of 0-6 μg / mL, nine groups of ammonium ferric citrate standard solutions with different concentrations were taken according to an arbitrary concentration gradient and added to nine colorimetric tubes respectively; then, Kg-C3N4@PDA nanozyme solution, 2,2'-hydrazino-bis-3-ethylbenzothiazoline-6-sulfonic acid and H2O2 were added to the colorimetric tubes respectively, and the volume was adjusted to 4 mL with NaAc-HAc buffer solution of pH 4.0, mixed well, and allowed to stand for 5-10 minutes to obtain nine groups of different standard sample solutions. Blank standard solution: Add Kg-C3N4@PDA nanozyme solution, 2,2'-hydrazino-bis-3-ethylbenzothiazoline-6-sulfonic acid, and H2O2 to a colorimetric tube, dilute to 4 mL with pH 4.0 NaAc-HAc buffer solution, mix well, and let stand for 5-10 minutes to obtain a blank standard sample solution. S2, prepare standard curve Determine the absorbance of the standard solution at the maximum absorption wavelength, with the concentration of ammonium ferric citrate standard solution as the horizontal axis and the corresponding absorbance difference ΔA as the vertical axis, ΔA=A-A0; Draw the standard curve and calculate the regression equation of the standard curve. A is the absorbance of the ammonium ferric citrate standard sample solution at the maximum absorption wavelength; A0 is the absorbance of the blank standard solution at the maximum absorption wavelength; S3, detection of the content of ammonium ferric citrate in table salt Prepare salt sample solution: prepare salt sample solution with a concentration of 0.2 g / mL; Take 0.5 mL of the salt sample solution into a colorimetric tube, then add Kg-C3N4@PDA nanozyme solution, 2,2'-hydrazine-bis-3-ethylbenzothiazoline-6-sulfonic acid and H2O2 into the colorimetric tube, dilute to 4 mL with NaAc-HAc buffer solution with pH 4.0, mix well, let stand for 5-10 minutes, measure the absorbance at the maximum absorption wavelength, and calculate the content of ammonium ferric citrate in the sample using the standard curve regression equation.

2. The method according to claim 1, wherein The concentration of the Kg-C3N4@PDA nanozyme solution is 25 μg / mL, and the added amount is 50 to 100 μL; the concentration of the 2,2'-hydrazine-bis-3-ethylbenzothiazoline-6-sulfonic acid is 5 mmol / L, and the added amount is 50 to 100 μL; the concentration of the H2O2 is 50 mmol / L, and the added amount is 50 to 100 μL.

3. The method according to claim 2, wherein The amount of the Kg-C3N4@PDA nanozyme solution added is 100 μL; the amount of the 2,2'-hydrazine-bis-3-ethylbenzothiazoline-6-sulfonic acid added is 100 μL; and the amount of the H2O2 added is 100 μL.

4. The method according to claim 1, wherein The maximum absorption wavelength is 416 nm.

5. A method for preparing the Kg-C3N4@PDA nanozyme solution according to the method of claim 1, characterized in that: The preparation method comprises the following steps: 1) Preparation of KCN nanomaterials: 3.0-3.5 g of melamine, 1.0-1.5 g of KCl and an appropriate amount of ethanol were ground and mixed, and the mixture was transferred to a corundum boat with a lid and heated at 5 °C / min under nitrogen atmosphere. -1 After the temperature is raised to 550°C at a heating rate of 1000 nm, the material is calcined at a constant temperature for 3 to 4 hours; then cooled to room temperature, and the material is ground into powder to obtain KCN nanomaterials; 2) Preparation of Kg-C3N4-COOH nanomaterial: 1.0-1.5 g of the KCN nanomaterial was mixed with 4.0-4.5 g of potassium thiocyanate and ground into powder; the powder was placed in a corundum boat with a lid and heated at 5°C / min under nitrogen atmosphere. -1 The temperature was raised to 400°C at a heating rate of 0.1°C, kept constant at that temperature for 1 to 2 hours, then continued to be raised to 500°C, kept constant at that temperature for 30 to 40 minutes, and then cooled to room temperature. The calcined powder was dispersed in 40 to 60 mL of HNO3 solution, stirred at room temperature for 2 to 3 hours, centrifuged, and the precipitate was collected and washed with ethanol for 3 to 4 times. The washed precipitate was vacuum dried to obtain Kg-C3N4-COOH nanomaterials. 3) Preparation of Kg-C3N4@PDA nanozyme: 0.1-0.2 g of the Kg-C3N4-COOH nanomaterial was added to 50-100 mL of Tris buffer and ultrasonically treated for 40-60 min to obtain solution A; 4-5 mg of dopamine hydrochloride was added to 1-2 mL of Tris buffer at pH 8.5 and ultrasonically treated for 5-10 min to obtain solution B; solution B was added dropwise to solution A, stirred for 2-3 h, centrifuged, and the precipitate was collected and washed with deionized water and ethanol 3-4 times each; the washed precipitate was vacuum dried to obtain Kg-C3N4@PDA nanozyme; finally, the Kg-C3N4@PDA nanozyme was dissolved in deionized water to obtain a Kg-C3N4@PDA nanozyme solution.

6. The preparation method according to claim 5, wherein The concentration of the HNO3 solution in the above 2) is 1.5-2.0 mol / L.

7. The preparation method according to claim 5, wherein The centrifugal speed is 6000-8000 r / min, and the time is 5-10 min.

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