Method for detecting hexavalent chromium in organic packaging

Abstract

The application discloses a detection method of hexavalent chromium in organic packaging, and belongs to the technical field of hexavalent chromium detection. The detection method provides a solution for organic packaging detection and a gold nano growth solution, and the gold nano growth solution is obtained by using a seed growth method. BSA, CTAB, hydrochloric acid and potassium bromide are sequentially added into the gold nano growth solution to obtain a hexavalent chromium test solution. The solution for organic packaging detection is added into the test solution for reaction, and the hexavalent chromium is detected through color change after the reaction or detected through an ultraviolet spectrophotometer. The use of the double protective agents bovine serum albumin (BSA) and cetyltrimethylammonium bromide (CTAB) ensures the salt resistance and acid resistance of gold nanoparticles, greatly improves the agglomeration of gold nanoparticles caused by the solution detection environment (acidity and alkalinity) and salt concentration of the actual sample after pretreatment, and thus better detection effect is obtained.

Description

Technical Field

[0001] This invention relates to the field of hexavalent chromium testing technology, and in particular to a method for detecting hexavalent chromium in organic packaging materials. Background Technology

[0002] Compared to chromium ions in other valence states, hexavalent chromium, due to its extreme toxicity and carcinogenicity, can cause significant damage to the limbs, mental state, and liver and kidney function. For paper packaging, excessive hexavalent chromium in inks and paper not only poses a significant threat to the health of printing workers, but also, if these products are used in food packaging, can cause immeasurable harm to consumers, thereby affecting brand image. Therefore, the detection of hexavalent chromium in paper packaging has extremely important social significance.

[0003] Visualization detection, as an intuitive detection method, allows for direct qualitative or semi-quantitative analysis of analytes. When combined with instruments such as ultraviolet spectrophotometers, infrared spectrophotometers, fluorescence spectrophotometers, and near-infrared spectrophotometers, it enables precise quantitative analysis. Due to its ease of operation, significant effectiveness, and low cost, this detection method is particularly suitable for high-throughput screening and rapid detection. Therefore, utilizing visualization technology in conjunction with ultraviolet spectrophotometers for the qualitative and quantitative detection of hexavalent chromium has significant application value. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for detecting hexavalent chromium in organic packaging materials.

[0005] To achieve the above and other related objectives, one aspect of the present invention provides a method for detecting hexavalent chromium in organic packaging materials, comprising the following steps:

[0006] S1. Provide solutions for testing organic packaging materials;

[0007] S2. Provide a gold nanoparticle growth solution, wherein the gold nanoparticle growth solution is obtained by a seed growth method;

[0008] S3. Bovine serum albumin, CTAB, hydrochloric acid solution and potassium bromide solution are added sequentially to the gold nanoparticle growth solution in step S2 to obtain a hexavalent chromium test solution.

[0009] S4. Add hexavalent chromium test solution to the organic packaging material detection solution to induce a colorimetric reaction. Qualitatively determine the hexavalent chromium in the organic packaging material detection solution by colorimetric method, and / or quantitatively determine the hexavalent chromium in the organic packaging material detection solution by spectrophotometry.

[0010] In some embodiments of the present invention, in step S3, the hexavalent chromium test solution includes one or more of the following technical features:

[0011] A1. The concentration of gold nanoparticles in the solution is 0.05 mmol / L to 0.25 mmol / L, which is estimated through characterization or preparation.

[0012] A2. The concentration of BSA is 5 mmol / L to 15 mmol / L;

[0013] A3. The concentration of CTAB is 0.05 mol / L to 0.2 mol / L;

[0014] A4. The concentration of the hydrochloric acid is 0.5 mol / L ~ 1.5 mol / L.

[0015] A5. The concentration of potassium bromide is 0.1 mol / L to 1 mol / L.

[0016] In some embodiments of the present invention, in step S3, bovine serum albumin, CTAB solution, hydrochloric acid solution and potassium bromide solution are added sequentially to the gold nanoparticle growth solution in step S2, and the mixture is reacted at 50°C to 100°C for 10 min to 30 min.

[0017] In some embodiments of the present invention, the method for obtaining the gold nanoparticle growth solution in step S2 is as follows:

[0018] S21. Chloroauric acid solution and sodium borohydride solution are added sequentially to CTAB solution to obtain gold nano-seed solution.

[0019] S22. Chloroauric acid solution, AgNO3 solution and ascorbic acid solution are added to CTAB solution in sequence and mixed. Then, the gold nanoparticle seed solution from step S21 is added to react and a gold nanoparticle growth solution is obtained.

[0020] In some embodiments of the present invention, step S21 includes one or more of the following technical features:

[0021] B1. The volume ratio of the CTAB solution, chloroauric acid solution, and sodium borohydride solution is 1:(1~2):(0.1~0.5).

[0022] B2. The concentration of CTAB is 0.1 mol / L ~ 0.4 mol / L;

[0023] B3. The concentration of the chloroauric acid is 0.1 mol / L ~ 1 mol / L;

[0024] B4. The concentration of the sodium borohydride is 0.01 mol / L ~ 0.05 mol / L;

[0025] B5. The particle size of the gold nanoparticles in the gold nanoseed solution is 3~10nm.

[0026] In some embodiments of the present invention, step S22 includes one or more of the following technical features:

[0027] C1, Ag + The solution is AgNO3 solution;

[0028] C2, CTAB solution, chloroauric acid solution, Ag + The volume ratio of the solution to the ascorbic acid solution is 1:(1~2):(0.01~0.06):(0.01~0.1).

[0029] The concentration of C3 and CTAB solutions is 0.05 mol / L ~ 0.2 mol / L;

[0030] C4, the concentration of chloroauric acid solution is 0.05 mmol / L ~ 0.2 mmol / L;

[0031] C5, Ag + The concentration of the solution is 0.1 mmol / L ~ 2 mmol / L;

[0032] C6. The concentration of ascorbic acid solution is 0.01 mmol / L ~ 0.1 mmol / L;

[0033] C7. The volume ratio of seed solution to gold nanoparticle growth solution is 10^ -4 ~10^ -3 .

[0034] In some embodiments of the present invention, the particle size of the gold nanoparticles in the gold nanoparticle growth solution is 30 nm to 40 nm.

[0035] And / or, the absorption wavelength of gold nanoparticles in the gold nanoparticle growth solution is 400 nm ~ 780 nm.

[0036] In some embodiments of the present invention, the solution for detecting organic packaging materials is obtained by wet digestion, microwave digestion, or oscillation extraction of the organic packaging materials. Wet digestion, microwave digestion, or oscillation extraction all utilize acid dissolution and acid removal processes.

[0037] In some embodiments of the present invention, the wet digestion includes the following steps:

[0038] S11. Add concentrated sulfuric acid to the organic packaging material to carry out a carbonization reaction to obtain a reaction solution. Add concentrated nitric acid dropwise to the reaction solution until a colorless and transparent solution is obtained. The temperature needs to be strictly controlled in the above process. Add concentrated sulfuric acid dropwise at 140℃~200℃ to carbonize the organic packaging material. Raise the temperature to 180℃~250℃ and add concentrated nitric acid to the reaction solution to continue the reaction. When the system no longer emits yellow smoke, raise the temperature to 250℃~300℃ and continue to add concentrated nitric acid dropwise until the reaction solution becomes colorless and transparent. Raise the temperature again to 300℃~350℃. Evaporate the solution of the reaction system. Generally, the evaporation is 0.5 mL~3 mL.

[0039] S12. A colorless and transparent solution undergoes an acid removal treatment. Specifically, the evaporated system is added to deionized water, cooled, and then subjected to the acid removal treatment. The acid removal treatment temperature is controlled at 150 ℃~250 ℃.

[0040] S13. Add alkaline solution to adjust the pH to 5-8.

[0041] In some embodiments of the present invention, one or more of the following technical features are included:

[0042] D1. Organic packaging material g: concentrated sulfuric acid volume mL: concentrated nitric acid volume mL = 1: (1~50): (1~40);

[0043] D2. Acid removal treatment to concentrate the solution to 0.5~3 mL;

[0044] D3. The carbonization reaction temperature is 140 ℃~ 350 ℃;

[0045] D4. The temperature for acid removal treatment is 150 ℃~ 250 ℃;

[0046] D5. The alkaline solution is ammonia water, and the concentration of the ammonia water is 10%~50%.

[0047] In some embodiments of the present invention, a method for detecting hexavalent chromium in organic packaging materials includes step S4, in which a standard curve method is used to quantify hexavalent chromium in the solution for detecting organic packaging materials, wherein the linear range of the standard curve is 0.05 mg / L to 5 mg / L. Attached Figure Description

[0048] Figure 1 Visual images of solutions containing different concentrations of hexavalent chromium. Detailed Implementation

[0049] This invention addresses the problem of unclear visualization by controlling the absorption wavelength of light within the 400-780 nm range through the adjustment of gold nanoparticle size. Different concentrations of hexavalent chromium are added, resulting in color variations. The use of bovine serum albumin (BSA) and cetyltrimethylammonium bromide (CTAB) as dual protectants ensures the gold nanoparticles' resistance to salt and acid. BSA provides protection through electrostatic repulsion and steric hindrance, while CTAB further stabilizes the BSA-modified gold nanoparticles, thus resolving the issue of gold nanoparticle aggregation caused by varying solution conditions (acidity / alkalinity) and salt concentration. Furthermore, a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid is used for digestion, addressing the issue of the solution color affecting detection. Based on these principles, this invention was completed. The following explanation uses paper packaging as an example, but it is also applicable to other organic packaging materials, such as plastics, inks, and plants, for heavy metal detection.

[0050] The first aspect of this invention provides a method for detecting hexavalent chromium in paper packaging, used for the visual qualitative detection of hexavalent chromium or other similar heavy metals in paper packaging, and combined with quantitative detection using an ultraviolet spectrophotometer. Specifically, it includes the following steps: First, a wet digestion method is used to provide a solution for testing the paper packaging. Then, a gold nanoparticle growth solution is obtained using a seed growth method. BSA, CTAB, hydrochloric acid, and potassium bromide are added sequentially to the gold nanoparticle growth solution to obtain a hexavalent chromium test solution, which is used to prepare a standard curve. During the testing process, the hexavalent chromium test solution is added to the packaging test solution for reaction. The reaction is generally carried out at 50℃~100℃ (oven) for 10 min~30 min. After the reaction, hexavalent chromium is detected by color change or by measuring absorbance using an ultraviolet spectrophotometer, and the concentration of hexavalent chromium is calculated by substituting the values ​​into the standard curve.

[0051] The detection principle of this method utilizes the strong oxidizing property of hexavalent chromium to oxidize gold nanoparticles into an ionic state. Different concentrations of hexavalent chromium consume varying degrees of gold nanoparticles, thus the number of residual nanoparticles in the solution changes with the concentration of hexavalent chromium, resulting in a color change. Paper packaging undergoes pretreatment before testing, typically wet digestion, microwave digestion, or ultrasonic extraction. These methods all use acid, and a large amount of salt is generated in the solution after acid removal, affecting the stability of the gold nanoparticles, causing them to aggregate and increasing the wavelength of light absorption beyond the range detectable by the human eye. To address this issue in this method, a dual protective agent (BSA and CTAB) is added to the preparation of the hexavalent chromium test solution. By using the dual protective agents bovine serum albumin (BSA) and cetyltrimethylammonium bromide (CTAB), the salt and acid resistance of the gold nanoparticles is ensured. BSA provides protection through electrostatic repulsion and steric hindrance, while CTAB can further stabilize BSA-modified gold nanoparticles, thus solving the problem of gold nanoparticle aggregation caused by solution detection environments (acidity / alkalinity) and salt concentration.

[0052] The inventors prepared a suitable hexavalent chromium test solution through multiple experiments. BSA, CTAB, hydrochloric acid, and potassium bromide were added sequentially to the gold nanoparticle growth solution to obtain the hexavalent chromium test solution. Stirring and other operations could be used during the addition process. Generally, bovine serum albumin (BSA) was added to the gold nanoparticle growth solution under stirring conditions. After stirring for a period of time, CTAB solution was added. After stirring for a period of time, hydrochloric acid solution and potassium bromide solution were added respectively. After stirring for a period of time, the test solution for detecting hexavalent chromium was obtained. The concentrations of gold nanoparticles, BSA, CTAB, hydrochloric acid, and potassium bromide in the above hexavalent chromium test solution were determined experimentally. The concentrations of each substance were determined experimentally as follows: The concentration of gold nanoparticles in the solution can be calculated based on the amount of chloroauric acid solution used in the preparation method. The concentration of gold nanoparticles is 0.05 mol / L to 0.25 mol / L, with options including 0.05 mol / L to 0.1 mol / L, 0.1 mol / L to 0.15 mol / L, 0.15 mol / L to 0.2 mol / L, and 0.2 mol / L to 0.25 mol / L. Uniform distribution of gold nanoparticles in the solution is ensured. The concentration of BSA in the solution is 1 mmol / L to 20 mmol / L, with options including 1 mmol / L to 5 mmol / L, 5 mmol / L to 10 mmol / L, 10 mmol / L to 15 mmol / L, and 15 mmol / L to 20 mmol / L. The concentration of CTAB in the solution is 0.01 mol / L to 0.5 mol / L, and can be selected from 0.01 mol / L to 0.02 mol / L, 0.02 mol / L to 0.05 mol / L, 0.05 mol / L to 0.1 mol / L, 0.1 mol / L to 0.2 mol / L, or 0.2 mol / L to 0.5 mol / L. The concentration of hydrochloric acid in the solution is 0.1 mol / L to 2.5 mol / L, and can be selected from 0.1 mol / L to 0.5 mol / L, 0.5 mol / L to 1.5 mol / L, or 1.5 mol / L to 2.5 mol / L. The concentration of potassium bromide in the solution is 0.02 mol / L to 2 mol / L, and can be selected as 0.02 mol / L to 0.05 mol / L, 0.05 mol / L to 0.1 mol / L, 0.1 mol / L to 0.5 mol / L, or 0.5 mol / L to 1 mol / L.

[0053] In a preferred embodiment, the method for obtaining the gold nanoparticle growth solution is as follows: Chloroauric acid solution and sodium borohydride solution are sequentially added to a CTAB solution to obtain a gold nanoparticle seed solution; chloroauric acid solution, AgNO3 solution, and ascorbic acid solution are sequentially added to a CTAB solution, mixed, and then the gold nanoparticle seed solution is added to obtain the gold nanoparticle growth solution. This method first uses a strong reducing agent to synthesize small-diameter gold nuclei as the seed solution. After aging, a weak reducing agent is used under the protection of a surfactant to reduce trivalent gold ions to monovalent gold ions, and AgNO3 can be added. + A solution (usually AgNO3 solution) is used to control the morphology of seed growth. The seed solution is then added to a growth solution for secondary growth to synthesize gold nanoparticles. The seed synthesis process conditions are as follows: the volume ratio of CTAB solution, chloroauric acid solution, and sodium borohydride solution is 1:(1~2):(0.1~0.5), optionally 1:(1~1.5):(0.1~0.3) or 1:(1.5~2):(0.3~0.5). The concentration of CTAB solution is 0.1 mol / L to 0.4 mol / L, optionally 0.1 mol / L to 0.2 mol / L or 0.2 mol / L to 0.4 mol / L. The concentration of chloroauric acid solution is 0.1 mmol / L to 1 mmol / L, optionally 0.1 mmol / L to 0.2 mmol / L, 0.2 mmol / L to 5 mmol / L, or 0.5 mmol / L to 1 mmol / L. The concentration of sodium borohydride solution is 0.01 mol / L to 0.05 mol / L, optionally 0.01 mol / L to 0.02 mol / L, 0.02 mol / L to 0.04 mol / L, or 0.04 mol / L to 0.05 mol / L. The gold nanoparticles prepared using the above method have a particle size less than 5 nm, typically 1 nm to 5 nm. The process conditions for the gold nanoparticle growth solution are CTAB solution, chloroauric acid solution, and Ag... + The volume ratio of the solution to the ascorbic acid solution is 1:(1~2):(0.01~0.06):(0.01~0.1), or alternatively 1:(1~1.5):(0.01~0.03):(0.01~0.05) or 1:(1.5~2):(0.03~0.06):(0.05~0.1). The concentration of the CTAB solution is 0.05 mol / L~0.2 mol / L, or alternatively 0.05 mol / L~0.1 mol / L or 0.1 mol / L~0.2 mol / L. The concentration of the chloroauric acid solution is 0.05 mmol / L~0.2 mmol / L, or alternatively 0.05 mmol / L~0.1 mmol / L or 0.1 mmol / L~0.2 mmol / L. Ag +The concentration of the solution is 0.1 mmol / L to 2 mmol / L, preferably 0.1 mmol / L to 0.5 mmol / L, 0.5 mmol / L to 1 mmol / L, or 1 mmol / L to 2 mmol / L. The concentration of the ascorbic acid solution is 0.01 mmol / L to 0.1 mmol / L, preferably 0.01 mmol / L to 0.05 mmol / L or 0.05 mmol / L to 0.1 mmol / L. The volume of the seed solution is approximately one-thousandth the volume of the growth solution.

[0054] In a preferred embodiment, the gold nanoparticles in the gold nanoparticle growth solution have a particle size of 30 nm to 40 nm and an absorption wavelength of 400 nm to 780 nm. The gold nanoparticles prepared using the above-described process meet the above requirements in terms of particle size and absorption wavelength.

[0055] In a preferred embodiment, the paper packaging testing solution is obtained by wet digestion, microwave digestion, or oscillation extraction. These methods generally involve acid, and a large amount of salt is generated in the solution after acid removal, affecting the stability of the gold nanoparticles. Therefore, this patent uses a dual protective agent to protect the gold nanoparticles and prevent the acid and salt in the pretreatment process from affecting them.

[0056] In a specific embodiment, to better pre-treat the paper packaging, this application further improves the current wet digestion process. The wet digestion includes the following steps: adding concentrated sulfuric acid to the paper packaging to carry out a carbonization reaction to obtain a reaction solution; adding concentrated nitric acid dropwise to the reaction solution until a colorless and transparent solution is obtained; subjecting the colorless and transparent solution to acid removal treatment; and adding an alkaline solution to adjust the pH to 5-8. Specifically, concentrated sulfuric acid is added dropwise at a certain temperature (140℃-200℃) to carbonize the paper packaging; the temperature is raised (180℃-250℃) and concentrated nitric acid is slowly added dropwise to the system to continue carbonization, causing the system to emit yellow fumes. When the system no longer emits yellow fumes, the temperature is raised (250℃-300℃), and concentrated nitric acid is continued to be added dropwise until the solution in the beaker becomes colorless and transparent; the temperature is raised again (300℃-350℃) to evaporate the system solution. The system was then cooled and deionized water was added for acid removal treatment at a temperature of 150℃ to 250℃. Finally, ammonia water (concentration of 10% to 50%) was used to adjust the pH to 5 to 8. The solution obtained through the above improved treatment method improved the phenomenon of slightly yellow, slightly gray, and slightly blue in the solution of the previous treatment method, ensuring the accuracy and reliability of the visual detection results.

[0057] In one specific embodiment, a paper sample was accurately weighed into a 25 mL glass beaker, concentrated sulfuric acid was added, and the beaker was heated on an electric heating plate for 10 min. The mass of the paper sample was 0.1 g to 1 g, the volume of the concentrated sulfuric acid was 1 mL to 5 mL, and the temperature of the electric heating plate was 150 ℃ to 200 ℃. After the paper base carbonized, the temperature of the heating plate was increased to continue carbonization for 10 min (the temperature of the electric heating plate was 200 ℃ to 300 ℃). Then, concentrated nitric acid (the volume of concentrated nitric acid was 0.5 mL to 2 mL) was slowly added dropwise along the wall of the beaker. A large amount of yellow fumes were emitted from the mouth of the beaker, and the carbonized material in the beaker turned yellow. After the yellow fumes stopped emitting, the temperature was increased again (the temperature of the electric heating plate was 300 ℃ to 330 ℃), and concentrated nitric acid was added dropwise until the solution in the beaker became colorless and transparent. The temperature was increased again (the temperature of the electric heating plate was 330 ℃ to 350 ℃) to evaporate the solution in the beaker. The volume of concentrated nitric acid was 0.5 mL to 2 mL. After cooling, add deionized water and place the solution back on a heating plate at 150℃~250℃ to evaporate the solution to a volume of 1~5 mL after evaporation. Transfer the solution to a centrifuge tube, add ammonia to adjust the pH, and finally bring the volume to 50 mL with deionized water to obtain the test sample solution. The ammonia concentration is 10%~50%, and the final pH range is 5~8.

[0058] In addition, a standard curve is provided. The preparation of the standard curve can refer to existing technologies. This embodiment provides a method for preparing the standard curve by taking 0.9 mL of multiple sets of the hexavalent chromium test solutions provided above, adding 0.1 mL of hexavalent chromium solution of different concentrations to each set of test solutions, and mixing thoroughly to obtain a series of working solutions of different concentrations. Finally, place them in an oven for reaction for several minutes, and after cooling, they can be detected. The first method uses color change for qualitative detection; multiple color changes occur from blue to purple and finally to red, with obvious visual color changes. Alternatively, an ultraviolet-visible spectrophotometer can be used to measure absorbance changes and plot a standard curve. The linear range of the standard curve is 0.05 mg / L to 5 mg / L, the limit of quantitation is approximately 0.03 mg / L, and the limit of detection is approximately 0.009 mg / L.

[0059] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0060] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Unless otherwise specified, specific experimental or operational conditions in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0061] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0062] Unless otherwise specified, all reagents, materials and instruments used in the following embodiments are commercially available.

[0063] Example 1

[0064] Synthesis of gold nanoseed solution

[0065] Prepare 2.5 mL of 0.2 mol / L CTAB solution, add 2.5 mL of 0.5 mmol / L chloroauric acid solution under magnetic stirring, continue stirring for 10 min, slowly add 0.6 mL of 0.01 mol / L sodium borohydride solution (prepared with ice water), continue stirring for 3 min, transfer to centrifuge tube, and store the gold nanoseed solution in a 30℃ constant temperature water bath.

[0066] Synthesis of gold nanoparticle growth solution

[0067] Prepare 50 mL of 0.1 mol / L LCTAB solution, add 50 mL of 1 mmol / L chloroauric acid solution under mechanical stirring, add 0.8 mL of 1 mmol / L AgNO3 solution after 10 min, continue stirring for 10 min, then add 1 mL of 0.08 mol / L ascorbic acid solution, continue stirring for 10 min, then add 150 μL of seed solution from (1), continue stirring for half an hour, and place the product at 30°C. o The gold nanoparticles were placed in a constant temperature water bath for 24 h, and then centrifuged twice (9000 r / min, 15 min) to obtain the gold nanoparticle growth solution, which was then stored in a refrigerator for later use. Characterization by electron transmission microscopy showed that the gold nanoparticles were uniformly distributed and the particle size was 30 nm ~ 40 nm.

[0068] Establishing a standard curve

[0069] Take 50 mL of gold nanoparticle growth solution in a beaker, add 10 mL of BSA (10 mmol / L BSA) under magnetic stirring. After stirring for 10 min, add 10 mL of CTAB solution (0.1 mol / L CTAB), and continue stirring for 5 min. Then add 10 mL of 1 mol / L hydrochloric acid solution and 10 mL of 0.2 mol / L potassium bromide solution, and continue stirring for 5 min to obtain the test solution for detecting hexavalent chromium. Take 0.9 mL of the above test solution, add 0.1 mL of hexavalent chromium solution of different concentrations and mix well to obtain a series of working solutions of different concentrations. Finally, place the above series of working solutions in a 70℃ oven for 20 min, and after cooling, they can be detected. Qualitative detection of hexavalent chromium can be performed by observing the color change of the solution before and after the reaction. The solution concentration is 0.05 mg / L ~ 5 mg / L. Figure 1 As shown, the concentrations of hexavalent chromium from left to right are 0.05 mg / L, 0.1 mg / L, 0.2 mg / L, 0.4 mg / L, 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, and 5 mg / L. The color change gradually changes from blue to purple and finally to red, with a clear and visible color change, overcoming the limitations of current technology. The absorbance change was measured using a UV-Vis spectrophotometer. A standard curve was plotted based on the absorbance value of the maximum absorption peak corresponding to each concentration (due to the etching mechanism, the absorption wavelength of gold nanoparticles shifts from 650 nm to 520 nm as the hexavalent chromium concentration increases), which can be used for the quantitative detection of hexavalent chromium. The limit of quantitation for this method is 0.03 mg / L, and the limit of detection is 0.009 mg / L.

[0070] The regression equation, correlation coefficient, and linear range of the standard curve are shown in Table 1.

[0071] Table 1

[0072] <![CDATA[Hexavalent chromium standard solution (H2Cr2O7)]]> Y = -0.0703X + 0.7935 0.998 0.05~5

[0073] Actual sample testing

[0074] Accurately weigh 0.2 g of the paper sample into a 25 mL glass beaker, add 3 mL of concentrated sulfuric acid (96%), and place at 140 °C. o Heat the paper base with an electric heating plate for 10 minutes, then raise the temperature to 180°C after carbonization. o Continue carbonization at C for 10 minutes, then slowly add 1 mL of concentrated nitric acid (68%) dropwise along the wall of the beaker. A large amount of yellow fumes emerge from the mouth of the flask, and the carbonized material inside the beaker turns yellow. Once the yellow fumes cease, continue raising the temperature to 250°C. o C, and repeat the process of adding concentrated nitric acid dropwise until the solution in the beaker becomes colorless. Then, raise the temperature to 320°C again. oC. Evaporate the solution in the beaker to approximately 0.5 mL. After cooling, add 20 mL of deionized water and place back at 180°C. o On a heating plate, evaporate the solution to approximately 0.5 mL. Transfer the solution to a centrifuge tube, add 25% ammonia to adjust the pH to 6-7, and finally bring the volume to 50 mL with deionized water. Centrifuge at 8000 rpm to obtain the sample solution for testing.

[0075] Qualitative detection was performed by comparing the solution color with the blank color. Quantitative detection of heavy metal content was performed using a standard curve. The quantitative results were basically consistent with those of inductively coupled plasma mass spectrometry (ICP-MS), as shown in Table 2, indicating that this method has high accuracy.

[0076] Table 2

[0077] Paper base sample Not detected Not detected Paper packaging paper samples Not detected Not detected Screen printing ink 1 for paper packaging (on coated paper) 5.91 5.81 Screen printing ink 2 for paper packaging (on coated paper) 5.13 5.26

[0078] As the concentration of BSA increases from 1 mmol / L to 20 mmol / L, its absorbance increases with the increase of BSA concentration, reaching a maximum at a BSA concentration of 10 mmol / L, and then decreasing with further increases in concentration. This is because a certain concentration of BSA can adhere to the surface of gold nanoparticles, providing protection through electrostatic repulsion and steric hindrance. However, excessive BSA will hinder the contact between hexavalent chromium and gold nanoparticles. Therefore, in this embodiment, the preferred BSA concentration is 10 mmol / L. As the concentration of CTAB, the stabilizer, increased from 0.05 mol / L to 0.2 mol / L, its absorbance increased accordingly, reaching a maximum at a concentration of 10 mmol / L, and then decreasing further with increasing concentration. It reached a maximum at a concentration of 0.1 mol / L, and then decreased further with increasing concentration. This is because a certain amount of CTAB can stabilize BSA-gold nanoparticles, and CTAB is also a salt; excessive concentration can cause gold nanoparticle aggregation. Therefore, in this embodiment, a CTAB concentration of 0.1 mol / L was preferred for the experiment.

[0079] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A method for detecting hexavalent chromium in organic packaging materials, comprising the following steps: S1. Provide solutions for testing organic packaging materials; S2. Provide a gold nanoparticle growth solution, wherein the gold nanoparticle growth solution is obtained by a seed growth method; S3. Add BSA to the gold nanoparticle growth solution in step S2 and stir continuously for 10 min. Then add CTAB solution and stir for another 5 min. Finally, add hydrochloric acid solution and potassium bromide solution to react and obtain a test solution for detecting hexavalent chromium. By using dual protective agents BSA and CTAB, the salt and acid resistance of gold nanoparticles is ensured. BSA provides protection through electrostatic repulsion and steric hindrance, while CTAB can further stabilize BSA-modified gold nanoparticles. S4. Add hexavalent chromium test solution to the organic packaging material detection solution to perform a colorimetric reaction, and qualitatively detect hexavalent chromium in the organic packaging material detection solution by colorimetry, and / or quantitatively detect hexavalent chromium in the organic packaging material detection solution by spectrophotometry. In step S2, the seed growth method includes the following steps: S21. Chloroauric acid solution and sodium borohydride solution are added sequentially to CTAB solution to obtain gold nano-seed solution. S22. Add chloroauric acid solution and Ag to CTAB solution in sequence. + After mixing the solution and ascorbic acid solution, the gold nanoparticle seed solution from step S21 is added to react and a gold nanoparticle growth solution is obtained.

2. The method for detecting hexavalent chromium in organic packaging materials according to claim 1, characterized in that, In step S3, the hexavalent chromium test solution includes one or more of the following technical features: A1. The concentration of gold nanoparticles in the solution is 0.05 mmol / L to 0.25 mmol / L; A2. The concentration of BSA in the solution is 1 mmol / L ~ 20 mmol / L; A3. The concentration of CTAB in the solution is 0.01 mol / L to 0.5 mol / L; A4. The concentration of hydrochloric acid in the solution is 0.1 mol / L ~ 2.5 mol / L; A5. The concentration of potassium bromide in the solution is 0.02 mol / L ~ 2 mol / L; A6. The reaction time is 10 min to 30 min; the reaction temperature is 50℃ to 100℃.

3. The method for detecting hexavalent chromium in organic packaging materials according to claim 1, characterized in that, Step S21 includes one or more of the following technical features: B1. The volume ratio of the CTAB solution, chloroauric acid solution, and sodium borohydride solution is 1:(1~2):(0.1~0.5). B2. The concentration of the CTAB solution is 0.1 mol / L ~ 0.4 mol / L; B3. The concentration of the chloroauric acid solution is 0.1 mmol / L ~ 1 mmol / L; B4. The concentration of the sodium borohydride solution is 0.01 mol / L ~ 0.05 mol / L; B5. The particle size of the gold nanoparticles in the gold nanoseed solution is 1 nm to 5 nm.

4. The method for detecting hexavalent chromium in organic packaging materials according to claim 1, characterized in that, Step S22 includes one or more of the following technical features: C1, Ag + The solution is AgNO3 solution; C2, CTAB solution, chloroauric acid solution, Ag + The volume ratio of the solution to the ascorbic acid solution is 1:(1~2):(0.01~0.06):(0.01~0.1). The concentration of C3 and CTAB solutions is 0.05 mol / L ~ 0.2 mol / L; C4, the concentration of chloroauric acid solution is 0.05 mmol / L ~ 0.2 mmol / L; C5, Ag + The concentration of the solution is 0.1 mmol / L ~ 2 mmol / L; C6. The concentration of ascorbic acid solution is 0.01 mmol / L ~ 0.1 mmol / L; C7. The volume ratio of seed solution to gold nanoparticle growth solution is 10^ -4 ~10^ -3 .

5. The method for detecting hexavalent chromium in organic packaging materials according to any one of claims 1-4, characterized in that, The gold nanoparticles in the gold nanoparticle growth solution have a particle size of 30 nm to 40 nm. And / or, the absorption wavelength of gold nanoparticles in the gold nanoparticle growth solution is 400 nm ~ 780 nm.

6. The method for detecting hexavalent chromium in organic packaging materials according to claim 1, characterized in that, The solution for detecting organic packaging materials is obtained by treating organic packaging materials using wet digestion, microwave digestion, or oscillation extraction. And / or, the organic packaging is organic packaging or plastic packaging.

7. The method for detecting hexavalent chromium in organic packaging materials according to claim 6, characterized in that, The wet digestion process includes the following steps: S11. Add concentrated sulfuric acid to the organic packaging material to carry out a carbonization reaction to obtain a reaction solution. Add concentrated nitric acid dropwise to the reaction solution until a colorless and transparent solution is obtained. S12, a colorless and transparent solution, is subjected to acid removal treatment; S13. Add alkaline solution to adjust the pH to 5-8.

8. The method for detecting hexavalent chromium in organic packaging materials according to claim 7, characterized in that, Includes one or more of the following technical features: D1. Organic packaging material g: concentrated sulfuric acid volume mL: concentrated nitric acid volume mL = 1: (1~50): (1~40); D2. Acid removal treatment to concentrate the solution to 0.5~3 mL; D3. The carbonization reaction temperature is 100℃~350℃; D4. The temperature for acid removal treatment is 150 ℃~ 250 ℃; D5. The alkaline solution is ammonia water, and the mass fraction of the ammonia water is 10%~50%.

9. The method for detecting hexavalent chromium in organic packaging materials according to claim 1, characterized in that, In step S4, the hexavalent chromium in the solution for detecting organic packaging materials is quantified using the standard curve method, and the linear range of the standard curve is 0.05 mg / L ~ 5 mg / L.

Images