A method for determining iodate content in salt based on apple carbon dot fluorescence inner filter effect

Abstract

The application relates to a method for determining iodate content in salt based on apple carbon dot fluorescence inner filter effect, which comprises the following steps: step A, preparing apple carbon dots; step B, drawing a standard curve of iodate in sodium chloride through the apple carbon dots, and obtaining a linear equation of the standard curve as △I=10608X-15.608, then X=(△I+15.608) / 10608; wherein △I is a fluorescence intensity change value of the apple carbon dot solution before and after adding iodate in the standard curve, and X is the iodate concentration; step C, pretreating a to-be-measured salt sample; step D, detecting the pretreated to-be-measured salt sample and calculating to obtain △I; and step E, substituting the △I obtained in step D into the formula X=(△I+15.608) / 10608. The application is simple, rapid, high in sensitivity, good in selectivity and low in cost, the established method is higher in sensitivity than a transmittance method, the advantages of a traditional method are retained, and iodate content determination with a lower concentration can be realized.

Description

Technical Field

[0001] This invention relates to the field of salt detection, specifically to a method for determining the iodate content in salt based on the internal filtration effect of apple carbon dot fluorescence. Background Technology

[0002] Iodine is one of the essential trace elements for maintaining human health, playing a vital role in growth and metabolism. Insufficient iodine can affect children's intellectual development, while excessive iodine can lead to conditions such as hypothyroidism. Maintaining a certain level of iodine in the body is crucial for health. Currently, iodine supplementation in my country primarily occurs through iodized salt. The national standard GB26878-2011 clearly stipulates that the potassium iodate content in iodized salt should range from 14-39 mg / kg (calculated as I), indicating that domestic iodized salt mainly uses iodate as its iodine source. Therefore, the iodate content in iodized salt directly impacts human health. Determining the iodate content in table salt is therefore crucial for guiding the rational use of iodized salt and safeguarding human health.

[0003] The reported studies mainly focus on titration and photometry as standard analytical methods for determining iodate in table salt. Wang Min et al., in their article "Research Progress on Iodine Content Detection Methods and Influencing Factors in Iodized Salt," pointed out that the currently effective standards for iodine detection include: "National Food Safety Standard for Determination of Salt Indicators" (GB 5009.42—2016), "General Test Method for Iodine Determination in Salt Industry" (GB / T13025.7—2012), and "Test Method for Iodine in Imported and Exported Iodized Salt" (SN / T0929—2000). Among these, GB 5009.42—2016 only includes redox titration, while GB / T 13025.7—2012 includes direct titration, redox titration, and photometry (using a dedicated iodometer). The volumetric method provided in GB / T13025.7-2012, which uses sodium thiosulfate titration, is suitable for determining iodine in iodized salt with directly added iodate, but its efficiency is low. The spectrophotometric method provided in GB / T13025.7-2012 involves reducing iodate to elemental iodine with a reducing agent, followed by starch color development, and then measurement using a dedicated iodometer. While this method is rapid, it requires specialized equipment, is costly, and has limited sensitivity. Other titration methods and absorption spectrophotometry are similar in principle to those in GB / T13025.7-2012, and their sensitivity is only comparable to the aforementioned methods. In addition, other reported methods include electrochemical methods, such as the electrochemical analysis method reported by Li Yongmei et al. in "Determination of Iodine Content in Table Salt by Electrochemical Analysis." However, electrochemical methods are susceptible to interference and have poor reproducibility, thus their application has not been widespread. Therefore, establishing a rapid, simple, sensitive, and low-cost analytical method for iodine content in table salt remains essential. Summary of the Invention

[0004] In summary, to overcome the shortcomings of existing technologies in determining iodate in table salt, such as cumbersome operation, high cost, and low sensitivity, the technical problem to be solved by this invention is to provide a method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence, which is low-cost, simple, fast, and highly sensitive.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence, comprising the following steps:

[0006] Step A: Prepare apple carbon dots;

[0007] Step B: Plot a standard curve of iodate in sodium chloride using apple carbon dots, and obtain the linear equation of the standard curve as ΔI = 10608X - 15.608, then X = (ΔI + 15.608) / 10608; where ΔI is the change in fluorescence intensity of the apple carbon dot solution before and after the addition of iodate in the standard curve, and X is the concentration of iodate.

[0008] Step C: Pre-treat the salt sample to be tested;

[0009] Step D: Detect the pretreated salt sample and obtain the fluorescence value I. x Through I x △I is calculated;

[0010] Step E: Substitute the ΔI obtained in step D into the following formula in step B to calculate the iodate content in the salt sample to be tested:

[0011] X = (△I + 15.608) / 10608.

[0012] The beneficial effects of this invention are as follows: This invention utilizes the property that iodate is reduced to elemental iodine, reacts with starch to develop color, and can quench the fluorescence of apple carbon dots, to establish a linear relationship between iodate concentration and fluorescence change, and directly determine the iodate content. The determination system is simple, rapid, highly sensitive, selective, and inexpensive. The method established by this invention has higher sensitivity than the spectrophotometric method, while retaining the advantages of traditional methods, and can achieve the determination of iodate content at lower concentrations.

[0013] Based on the above technical solution, the present invention can be further improved as follows:

[0014] Further, step A prepares apple carbon dots as follows:

[0015] Weigh 10g of fresh apples, add 50mL of water, and crush them with a grinder to obtain apple pulp. Place the apple pulp in a 50mL polytetrafluoroethylene reaction vessel and keep it at 240 degrees Celsius in an oven for 12 hours. Then, let it cool naturally and filter the apple pulp to obtain filtrate. Encapsulate the filtrate with a dialysis membrane with a molecular weight pore size of 500 and dialyze it in ultrapure water for 10 hours. After dialysis, concentrate and dry the solution, and add water again to prepare a 0.5mg / mL carbon dot solution. This solution is the apple carbon dot.

[0016] Furthermore, the filter membrane used for apple pulp filtration has a pore size of 0.25 μm.

[0017] Further, in step B, a standard curve of iodate ions in sodium chloride is plotted as follows:

[0018] Add 100 μL each of 1 mol / L sodium chloride solution, 0.8 mol / L sulfuric acid solution, 12 mmol / L KI solution, and 1 mg / L starch solution to nine 2 mL sample tubes, respectively. Then, add 0, 10, 20, 40, 60, 80, 100, 150, and 200 μL of 1 μg / L iodate solution sequentially, and react for 15 minutes. The iodate solution uses potassium iodate as the iodate source. Label the nine sample tubes as 0, 1, 2, 3, 4, 5, 6, 7, and 8, and then add 100 μL of [unspecified solution] to each sample tube. 0.5 mg / mL of apple carbon dots and ultrapure water were used to make the total reaction volume of the solution in each sample tube 1000 μL. The fluorescence intensity of the solution in each sample tube was measured using a fluorescent cuvette, and the fluorescence emission spectrum curves from 380 nm to 650 nm were collected to obtain observable quantitative fluorescence spectrum curves and intensity change trends. A graph was plotted with the iodate concentration X as the abscissa and the fluorescence change value ΔI at the emission wavelength Em = 440 nm as the ordinate, and linear regression was performed to obtain the standard curve of iodate in sodium chloride. The linear equation is ΔI = 10608X - 15.608.

[0019] Furthermore, the fluorescence intensity of the solution in each sample tube was measured using a 1 mL fluorescent cuvette. The measurement parameters were set as follows: voltage 750 V, slit 10 nm, and excitation wavelength Ex = 360 nm.

[0020] Further, step C involves pretreating the salt sample to be tested as follows:

[0021] Weigh 0.1g of the salt sample to be tested and dilute it to 1000mL. After dilution, the salt sample solution is prepared. Add 100μL each of 0.8mol / L sulfuric acid solution, 12mmol / L KI solution and 1mg / L starch solution to the sample tube. Then add 50μL of the salt sample solution and react for 15min. Finally, add 100μL of 0.5mg / mL apple carbon point and 550μL of water to make the total volume 1000μL.

[0022] Further, after diluting 10 times, the resulting solution is the salt sample solution to be tested.

[0023] Further, in step D, the pretreated salt sample is tested to obtain the fluorescence value I using the following method. x and through I in the following manner x The calculated value of △I is:

[0024] The pretreated salt sample was detected using a fluorescent cuvette, and the fluorescence value at 440 nm was measured and recorded using a fluorophotometer. x The excitation wavelength is 360nm;

[0025] Replacing the salt sample solution with 50 μL of 10 μg / L sodium chloride solution, proceed with steps C and D. The fluorescence value I0 at 440 nm is obtained, and therefore ΔI = I0. x -I0.

[0026] Furthermore, the detection voltage of the pretreated salt sample was 750V and the slit width was 10nm, using a fluorescent cuvette. Attached Figure Description

[0027] Figure 1 This is a flowchart of the steps for determining iodate in table salt according to an embodiment of the present invention;

[0028] Figure 2 Fluorescence excitation and emission spectra of apple carbon dots provided for the invention;

[0029] Figure 3 Transmission electron microscope image of apple carbon dots provided for the invention;

[0030] Figure 4 Ultraviolet-Visible absorption spectrum;

[0031] Figure 5 This is the standard curve spectrum of iodate ions in sodium chloride;

[0032] Figure 6 This is the standard curve for iodate ions in sodium chloride. Detailed Implementation

[0033] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0034] like Figure 1 As shown, a method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence includes the following steps:

[0035] Step A: Prepare apple carbon dots;

[0036] Weigh 10g of fresh apples, add 50mL of water, and crush them with a grinder to obtain apple pulp. Place the apple pulp in a 50mL polytetrafluoroethylene reaction vessel and keep it at 240 degrees Celsius in an oven for 12 hours. Then, let it cool naturally and filter the apple pulp to obtain filtrate. The filter membrane has a pore size of 0.25μm. Encapsulate the filtrate with a dialysis membrane with a molecular weight of 500 and dialyze it in ultrapure water for 10 hours. After dialysis, concentrate and dry the solution, and add water again to prepare a 0.5mg / mL carbon dot solution. This solution is the apple carbon dot.

[0037] like Figure 2As shown, the maximum fluorescence excitation wavelength of apple carbon dots is between 350 nm and 370 nm, and the maximum fluorescence emission wavelength is between 430 nm and 450 nm. Figure 3 As shown, the particle size of the apple carbon quantum dots is less than 10 nm, which is consistent with the characteristics of fluorescent carbon dots. The determination principle of this invention: iodate ions react with potassium iodide to produce elemental iodine, which then reacts with starch solution to produce a colorimetric reaction. Figure 4 The UV-Vis absorption spectra of potassium iodate and starch solutions with and without iodate are shown. With the addition of iodate, UV absorption peaks are observed at wavelengths of 350-370 nm and 430-450 nm. These peaks spectrally overlap with the maximum fluorescence excitation wavelength (350-370 nm) and maximum fluorescence emission wavelength (430-450 nm) of apple carbon dots. Therefore, the fluorescence signal of the apple carbon dots is weakened. Without iodate, no new spectral absorption occurs in the 350-470 nm wavelength range, and no fluorescence weakening occurs. Therefore, the addition of iodate causes fluorescence quenching, which is attributed to the fluorescence internal filtration effect and can be used as a basis for quantifying iodate levels. Figure 3 The transmission scanning electron microscope (SEM) images show that the particle size of the apple carbon quantum dots is less than 10 nm and the apple carbon dots are uniformly distributed. Therefore, the system belongs to a well-dispersed solution system, which can form uniform fluorescence emission, which is beneficial for detection.

[0038] Step B: A standard curve of iodate in sodium chloride is plotted using apple carbon dots, and the linear equation of the standard curve is obtained as ΔI = 10608X - 15.608, then X = (ΔI + 15.608) / 10608, where ΔI is the change in fluorescence intensity of the apple carbon dot solution before and after the addition of iodate in the standard curve, and X is the concentration of iodate.

[0039] Add 100 μL each of 1 mol / L sodium chloride, 0.8 mol / L sulfuric acid solution, 12 mmol / L KI solution, and 1 mg / L starch solution to nine 2 mL sample tubes. Then, add 0, 10, 20, 40, 60, 80, 100, 150, and 200 μL of 1 μg / L iodate solution (using potassium iodate as the iodate source) sequentially and react for 15 min. Label the nine sample tubes as “0, 1, 2, 3, 4, 5, 6, 7, 8”. Then, add 100 μL of 0.5 mg / mL carbon dot solution and an appropriate amount of ultrapure water to each sample tube, making the total reaction volume of each sample tube 1000 μL. Measure the fluorescence intensity using a 1 mL fluorescent cuvette. The instrument parameters were set to 750V voltage, 10nm slit, and excitation wavelength Ex = 360nm. Fluorescence emission spectra from 380nm to 650nm were collected to obtain observable quantitative fluorescence spectra and intensity change trends. Figure 5 This is a series of fluorescence quenching emission spectra of apple carbon dots with different concentrations of iodate. From... Figure 5 As can be seen, iodate exhibits a fluorescence emission spectrum in the 380nm-650nm range. Based on this fluorescence curve, and to maximize the sensitivity of the detection method, the selected wavelength for measuring the fluorescence signal change was 440nm. Figure 6 As shown, a standard curve for iodate was obtained by plotting the iodate concentration X (g / L) on the x-axis and the fluorescence change (ΔI) at the emission wavelength Em = 440 nm on the y-axis and performing linear regression. The linear equation was ΔI = 10608X - 15.608, and the correlation coefficient was R. 2 =0.9995. The detection limit is 0.005 g / L (signal-to-noise ratio of 3). The concentration of sodium chloride in the above 9 standard sample solutions ranges from 0.01 g / L to 0.20 g / L. The linear equation above leads to X = (ΔI + 15.608) / 10608. Adding a constant amount of sodium chloride to the standard solution completely avoids interference from chloride ions and closely approximates the actual table salt system. The resulting standard curve can be directly applied to the determination of table salt samples.

[0040] Step C: Pre-treatment of the salt sample to be tested:

[0041] Weigh 0.1 g of salt and dilute it to 1000 mL. Dilute 10 times to obtain the salt sample solution. Add 100 μL each of 0.8 mol / L sulfuric acid solution, 12 mmol / L KI solution, and 1 mg / L starch solution to the sample tube. Then add 50 μL of the salt sample solution and react for 15 min. Finally, add 100 μL of 0.5 mg / mL carbon dot solution and 550 μL of water to make the total volume 1000 μL.

[0042] Step D: Detect the pretreated salt sample and obtain the fluorescence value I. x Through I x The calculated value of △I is:

[0043] The sample was tested using a fluorescence cuvette and a fluorometer to measure and record the fluorescence value at 440 nm. The instrument voltage was 750 V, and the slit width was 10 nm. The excitation wavelength was 360 nm, and the fluorescence value I was obtained. x .

[0044] The procedure was performed according to "Steps C and D" using 50 μL of 10 μg / L sodium chloride solution instead of the salt sample solution. The fluorescence value I0 at 440 nm was obtained from the blank sample, and the fluorescence value I0 obtained from the salt sample was... x Subtracting I0 gives ΔI, that is, ΔI = I x -I0.

[0045] Step E: Substitute the ΔI obtained in step D into the following formula in step B to calculate the iodate content, i.e., the iodate concentration, in the salt sample to be tested.

[0046] X(IO3 - ,g / L)=(△I+15.608) / 10608(g / L)

[0047] Wherein, X(IO3) - The concentration of iodate (g / L) is calculated based on the standard curve, and ΔI is the change in fluorescence intensity of the apple carbon dot solution before and after the addition of iodate in the standard curve. This formula is derived from the linear equation in "Step B", ΔI = 10608X - 15.608.

[0048] The following specific embodiments verify the beneficial effects achieved by the present invention. The experimental methods in the embodiments are all carried out under conventional conditions.

[0049] Determination of iodate content in a certain brand of iodized salt

[0050] Standard curve of iodate in sodium chloride: Prepare a standard solution of iodate containing 0.1 g / L sodium chloride, and plot the standard curve according to "Step B". The concentration of the standard solution is 0-0.2 g / L. Measure the fluorescence change of the apple carbon dot solution after the addition of iodate in the wavelength range of 380.0 nm-650 nm. The fluorescence value at a fluorescence wavelength of 440.0 nm is used to obtain the standard curve of the fluorescence change of iodate in the 0.1 g / L sodium chloride solution at 440.0 nm: ΔI = 10608X - 15.608.

[0051] Pretreatment of the sample: Weigh 0.1 g of salt and dilute to 1000 mL, then dilute 10 times to obtain the salt sample solution. Add 100 μL each of 0.8 mol / L sulfuric acid solution, 12 mmol / L KI solution, and 1 mg / L starch solution to the sample tube, then add 50 μL of the salt sample solution and react for 15 min. Finally, add 100 μL of 0.5 mg / mL carbon dot solution and 550 μL of water to make the total volume 1000 μL.

[0052] Sample testing: The fluorescence change value of the solution at 440 nm was measured using a fluorescence cuvette and a fluorescence spectrophotometer.

[0053] The concentration of iodate in the solution was calculated to be 37.5 g / L based on the standard curve. Parallel spiked recovery experiments were performed on the samples, and the results are shown in Table 1. The recoveries ranged from 93% to 105%, and the relative standard deviation (RSD, n=5) was <3.8%, indicating that the method has high analytical accuracy. These results further confirm the reliability and feasibility of determining iodate in actual table salt samples using the apple carbon dot fluorescence method.

[0054] Table 1. Spike recovery results (n=5)

[0055]

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence, characterized in that, The steps include the following: Step A: Prepare apple carbon dots; Step B: Plot a standard curve of iodate in sodium chloride using apple carbon dots, and obtain the linear equation of the standard curve as ΔI = 10608X - 15.608, then X = (ΔI + 15.608) / 10608; where ΔI is the change in fluorescence intensity of the apple carbon dot solution before and after the addition of iodate in the standard curve, and X is the concentration of iodate. Step C: Pre-treat the salt sample to be tested; Step D: Detect the pretreated salt sample and obtain the fluorescence value I. x Through I x △I is calculated; Step E: Substitute the ΔI obtained in step D into the following formula in step B to calculate the iodate content in the salt sample to be tested: X = (△I + 15.608) / 10608.

2. The method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence according to claim 1, characterized in that, Step A: Prepare apple carbon dots as follows: Weigh 10g of fresh apples, add 50mL of water, and crush them with a grinder to obtain apple pulp. Place the apple pulp in a 50mL polytetrafluoroethylene reaction vessel, keep it at 240 degrees Celsius in an oven for 12 hours, then cool it naturally. Filter the apple pulp to obtain filtrate. Encapsulate the filtrate with a 500 molecular weight pore size dialysis membrane and dialyze it in ultrapure water for 10 hours. After dialysis, concentrate and dry the solution, and add water again to prepare a 0.5 mg / mL carbon dot solution, which is the apple carbon dot.

3. The method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence according to claim 2, characterized in that, The filter membrane used for apple pulp filtration has a pore size of 0.25 μm.

4. The method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence according to claim 1, characterized in that, Step B involves plotting a standard curve for iodate in sodium chloride as follows: Nine 2 mL sample tubes were filled with 100 μL each of 1 mol / L sodium chloride, 0.8 mol / L sulfuric acid, 12 mmol / L KI, and 1 mg / L starch solution, respectively. Then, 0, 10, 20, 40, 60, 80, 100, 150, and 200 μL of 1 μg / L iodate solution were added sequentially, and the mixture was reacted for 15 minutes. The iodate solution was derived from potassium iodate. The nine sample tubes were labeled 0, 1, 2, 3, 4, 5, 6, 7, and 8. Then, 100 μL of 0.5 mg / mL apple carbon dots and ultrapure water were added to each sample tube, bringing the total reaction volume in each tube to 1000 μL. The fluorescence intensity of the solution in each sample tube was measured using a fluorescent cuvette, and samples were collected at 380 nm–650 nm. The fluorescence emission spectrum curve of nm is obtained to obtain an observable quantitative fluorescence spectrum curve and intensity change trend; the standard curve of iodate in sodium chloride can be obtained by plotting the iodate concentration X as the abscissa and the fluorescence change value ΔI at the emission wavelength Em=440nm as the ordinate and performing linear regression, and the linear equation is ΔI =10608X-15.

608.

5. The method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence according to claim 4, characterized in that, The fluorescence intensity of the solution in each sample tube was measured using a 1 mL fluorescent cuvette. The measurement parameters were set as follows: voltage 750 V, slit 10 nm, and excitation wavelength Ex = 360 nm.

6. The method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence according to claim 1, characterized in that, Step C involves pretreating the salt sample to be tested as follows: Weigh 0.1g of the salt sample to be tested and dilute it to 1000mL. After dilution, the salt sample solution is prepared. Add 100μL each of 0.8mol / L sulfuric acid solution, 12mmol / L KI solution and 1mg / L starch solution to the sample tube. Then add 50μL of the salt sample solution and react for 15min. Finally, add 100μL of 0.5mg / mL apple carbon point and 550μL of water to make the total volume 1000μL.

7. The method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence according to claim 6, characterized in that, The solution is diluted 10 times to obtain the salt sample solution to be tested.

8. The method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence according to any one of claims 1 to 7, characterized in that, Step D involves detecting the fluorescence value I of the pretreated salt sample as described below. x and through I in the following manner x The calculated value of △I is: The pretreated salt sample was detected using a fluorescent cuvette, and the fluorescence value at 440 nm was measured and recorded using a fluorophotometer. x The excitation wavelength is 360 nm; Replacing the salt sample solution with 50 μL of 10 μg / L sodium chloride solution, proceed with steps C and D. The fluorescence value I0 at 440 nm is obtained, and therefore ΔI = I0. x -I0.

9. The method for determining the iodate content in table salt based on the internal filtration effect of apple carbon dot fluorescence according to claim 8, characterized in that, The detection voltage of the pretreated salt sample was 750 V and the slit width was 10 nm, which was used to detect the sample using a fluorescent cuvette.

Images