A method for determining the two-dimensional distribution of available magnesium content

Abstract

The present application relates to the field of environmental monitoring and analytical chemistry technology, and discloses a method for determining the two-dimensional distribution of effective magnesium content. The method combines gradient diffusion film technology and computer imaging density method, and the specific steps include: deploying R-GDC type DGT adsorption film in the environment medium to be measured to enrich magnesium ions in situ; then using magnesium reagent I to carry out color reaction under alkaline conditions to form a color gradient corresponding to the magnesium content; using a flatbed scanner to obtain a color film image, and converting the image gray value into magnesium accumulation amount through ImageJ software, and finally reconstructing the two-dimensional concentration distribution map of magnesium ions. The present application realizes in-situ, high-resolution, rapid and low-cost two-dimensional imaging of magnesium ions in the environment medium, and overcomes the technical defects of the traditional method, such as dependence on complex pretreatment and expensive instruments, and inability to obtain spatial distribution information.

Description

Technical Field

[0001] The technical field of this invention is environmental monitoring and analytical chemistry, specifically relating to a method for determining the two-dimensional distribution of available magnesium content. Background Technology

[0002] Magnesium is an important element in the environmental system and a key indicator for assessing the quality of water bodies, soil, and other environmental elements. In the fields of agriculture and environmental science, accurately determining the content and spatial distribution of available magnesium in environmental media is crucial for understanding nutrient migration and transformation, pollutant behavior, and ecological processes.

[0003] Currently, the conventional method for detecting magnesium in environmental media is to collect batches of samples (such as soil solutions or water bodies), pre-treat them, and then perform quantitative analysis using atomic absorption spectrometry (AAS) or inductively coupled plasma atomic emission spectrometry / mass spectrometry (ICP-OES / MS). However, these methods are destructive sampling methods, and the results obtained only represent the average concentration of the samples, failing to reflect the true distribution of magnesium ions at the micro-interface. Furthermore, the process is cumbersome and time-consuming, making it difficult to meet the needs of real-time, in-situ monitoring.

[0004] To overcome the aforementioned limitations, gradient diffusion in thin-films (DGT) technology is widely used as a passive sampling technique. Based on Fick's first diffusion law, DGT technology can enrich target substances in situ and obtain their time-integrated average concentration, effectively avoiding the random errors of traditional instantaneous sampling. In existing DGT applications, after collecting the adsorbed membrane containing magnesium ions (typically a Chelex-100 resin gel membrane with a particle size of approximately 100 µm or an SPR-IDA resin gel membrane with a particle size of approximately 0.2 µm), it is still necessary to bring it back to the laboratory for acid elution and other steps, and then use ICP-OES / MS for quantitative analysis of the eluent. Although this process improves the detection sensitivity, it still does not eliminate the complex sample pretreatment steps and cannot directly obtain the spatial distribution information of magnesium ions. To obtain the two-dimensional distribution information of target elements on the DGT adsorbed membrane, existing techniques typically use laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for scanning imaging. For example, Wagner et al. ( In situSpatiotemporal solute imaging of metal corrosion on the example of magnesium. Analytica Chimica Acta, 2022, 1212) reported the use of DGT coupled with LA-ICP-MS for two-dimensional imaging of magnesium ion release during the corrosion process of magnesium alloys, achieving sub-millimeter resolution. Although LA-ICP-MS can provide high-precision two-dimensional images, it has significant drawbacks: the equipment is extremely expensive, the operation procedure is complex and cumbersome, it requires a high level of expertise from laboratory personnel and laboratory staff, and it is difficult to perform rapid on-site analysis. These factors severely restrict the widespread application of this technology in large-scale environmental monitoring in the field or in conventional laboratories.

[0005] Therefore, there is an urgent need in this field to develop a new technology that integrates in-situ enrichment, rapid color development, and low-cost imaging to achieve simple, efficient, and visual analysis of the two-dimensional distribution of available magnesium content in environmental media. Summary of the Invention

[0006] The purpose of this invention is to overcome the limitations of existing technologies that cannot obtain spatial distribution information in situ and rely on expensive equipment, and to provide a method for determining the two-dimensional distribution of available magnesium content. This method combines gradient diffusion thin film technology (DGT) with computer imaging density method (CID) to achieve in-situ, rapid, low-cost and high-resolution two-dimensional chemical imaging of magnesium ions in environmental media.

[0007] This invention provides a method for determining the two-dimensional distribution of available magnesium content, employing the following technical solution: A method for determining the two-dimensional distribution of available magnesium content includes the following preparation steps: S1. Dissolve magnesium reagent I in dimethyl sulfoxide to prepare a colorimetric reagent stock solution, and store it away from light.

[0008] S2. Expose the DGT adsorption membrane to the test environment medium. After exposure, remove the adsorption membrane, rinse it with ultrapure water, and then immerse it in sodium hydroxide solution for pretreatment.

[0009] S3. At room temperature, mix the colorimetric reagent stock solution, sodium hydroxide solution, and pure water to prepare the colorimetric reagent. Take out the pretreated adsorption membrane and place it in the colorimetric reagent for the colorimetric reaction. At 20 minutes after the start of the colorimetric reaction, add sodium sulfite solution to the colorimetric reagent.

[0010] S4. After the color development reaction is complete, rinse the surface of the adsorption membrane with pure water. After wiping the surface of the adsorption membrane dry with a lint-free paper, immediately use a flatbed scanner to collect the grayscale value of the image.

[0011] S5. Prepare magnesium ion solutions of different concentrations, take the DGT adsorption membrane, use magnesium ion solutions of different concentrations as the test environment medium, repeat the operations of S2-S4, establish a calibration curve, and accurately convert the image grayscale values ​​in S4 into magnesium ion concentration / flux.

[0012] S6. Data processing: The color density information on the image is converted into a two-dimensional distribution of concentration / flux, and pseudo-color processing is used to make the quantitative information more intuitive.

[0013] Preferably, the concentration of magnesium reagent I in the colorimetric reagent mother liquor in step S1 is 0.5-1 g / L.

[0014] Preferably, in step S2, the DGT adsorption membrane is an R-GDC type DGT adsorption membrane, and the adsorption phase particle size is a Chelex resin gel membrane of 10µm.

[0015] Preferably, the environmental medium to be tested in step S2 can be any one of aqueous solution, soil, or sediment.

[0016] Preferably, the pH value of the sodium hydroxide solution in step S2 is 13.0-14.0, and the pretreatment time is 20-40 min.

[0017] Preferably, the color development reaction time in step S3 is 25-35 minutes.

[0018] Preferably, the concentration of the sodium hydroxide solution in step S3 is 2 mol / L.

[0019] Preferably, in step S3, the ratio of the color developer mother liquor, sodium hydroxide solution, and pure water is 1.25:1:4.

[0020] Preferably, the concentration of sodium sulfite in the colorimetric reagent in step S3 is 0.1%.

[0021] In summary, the present invention has the following beneficial technical effects: The core advantage of this invention lies in achieving in-situ, high-resolution two-dimensional imaging of available magnesium ions in environmental media. This method organically combines gradient diffusion thin film technology (DGT) with computed density imaging (CID). Magnesium ions are enriched in situ using DGT, and then converted into a visualized color density distribution through a specific colorimetric reaction. Finally, a two-dimensional concentration / flux distribution map of magnesium ions can be rapidly reconstructed using only a common flatbed scanner and image processing software. This technological approach completely eliminates the reliance on expensive and complex instruments such as LA-ICP-MS, making high spatial resolution chemical imaging simple and significantly reducing costs.

[0022] Compared with existing technologies, this invention exhibits significant comprehensive advantages: First, it can accurately reflect the spatial heterogeneity of magnesium ions in microenvironments such as the rhizosphere, sediment-water interface, and fertilizer-soil interface, precisely locating reaction "hot zones"; second, the imaging analysis process can be completed within hours, is convenient to operate, greatly improves the timeliness of monitoring, and lowers the barrier to entry for professional operators; third, the method has good anti-interference ability and sensitivity. Furthermore, this technology platform demonstrates great potential for combination with other in-situ imaging technologies, providing an efficient and economical solution for future research on simultaneous multi-parameter environmental monitoring. Attached Figure Description

[0023] Figure 1 In the image, 'a' represents the adsorption membrane after color development. Figure 1 In Figure b, the calibration curve is plotted based on standard points of magnesium ion concentration. Figure 2 Image a shows the two-dimensional distribution of magnesium sulfate heptahydrate fertilizer at the fertilizer-solution interface; Figure 2 Image b shows a three-dimensional visualization of magnesium sulfate heptahydrate fertilizer at the fertilizer-solution interface. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0025] Example A method for determining the two-dimensional distribution of available magnesium content, characterized by comprising the following steps: S1. Dissolve magnesium reagent I in dimethyl sulfoxide to prepare a colorimetric reagent stock solution, and store it in the dark; wherein, the concentration of magnesium reagent I in the colorimetric reagent stock solution is 0.5 g / L; S2. Expose the R-GDC type DGT adsorption membrane to the test environment medium. After exposure, remove the adsorption membrane, rinse it with ultrapure water, and then immerse it in a sodium hydroxide solution with a pH of 13.0-14.0 for 20-40 minutes. The adsorption phase of the R-GDC type DGT adsorption membrane is a Chelex resin gel membrane with a particle size of 10µm. The test environment medium can be any of the following: aqueous solution, soil, or sediment. S3. At room temperature, mix the colorimetric reagent stock solution obtained in step S1, 2 mol / L sodium hydroxide solution, and pure water in a mass ratio of 1.25:1:4 to prepare the colorimetric reagent. Take out the pretreated adsorption membrane from step S2 and place it in the colorimetric reagent for a colorimetric reaction. The reaction time is 25-35 min. At the 20th minute after the start of the colorimetric reaction, add a 0.1% sodium sulfite solution to the colorimetric reagent. S4. After the color development reaction is complete, rinse the surface of the adsorption membrane with pure water. After wiping the surface of the adsorption membrane with a lint-free paper, immediately use a flatbed scanner to collect the grayscale value of the image. S5. Prepare magnesium ion solutions of different concentrations, take the DGT adsorption membrane, use magnesium ion solutions of different concentrations as the test environment medium, repeat the operations of S2-S4, establish a calibration curve, and accurately convert the image grayscale values ​​in S4 into magnesium ion concentration / flux. S6. Data processing: The color density information on the image is converted into a two-dimensional distribution of concentration / flux, and pseudo-color processing is used to make the quantitative information more intuitive.

[0026] Test case Test Example 1 The specific steps for determining the binary distribution of magnesium content during a simulated magnesium fertilizer dissolution process are as follows: S1. Weigh 0.05g of magnesium sulfate heptahydrate powder and press it into dense magnesium sulfate discs with a diameter of 0.6cm using a tableting mold. These discs will serve as a simulated magnesium fertilizer source for later use.

[0027] S2. Select a 2.5cm diameter R-GDC type DGT adsorption membrane disc, rinse it with ultrapure water, and wipe the surface dry with lint-free paper. Place it flat on the bottom of a 9mm culture dish, ensuring that there are no visible air bubbles between the membrane and the culture dish.

[0028] S3. Place the prepared magnesium sulfate disc in the center of the R-GDC type DGT adsorption membrane, add a very small amount of ultrapure water to initiate the dissolution process, and cover the petri dish. Let the reaction stand at room temperature. After 70 hours, open the petri dish and use ultrapure water to quickly rinse away the remaining magnesium sulfate on the surface of the adsorption membrane. Gently blot the remaining droplets on the surface of the adsorption membrane with lint-free paper.

[0029] S4, Reference Figure 1 , Figure 1 In Figure 'a', the adsorption membrane after color development is shown. The membrane was immersed in 20 mL of a 2 mol / L sodium hydroxide solution (pH 13.0) and shaken on a shaker for 30 min. After removal, the R-GDC type DGT adsorption membrane was transferred to 20 mL of a 1.0 g / L magnesium reagent I color development solution and developed at room temperature in the dark for 20 min. Then, sodium sulfite solution was added to the color development solution until the final concentration was 0.1%, and development continued for 10 minutes. The membrane was then removed and quickly rinsed three times with pure water to remove any residual color developer. The surface moisture of the membrane was wiped dry with lint-free paper, and the membrane was placed flat in a flatbed scanner for scanning at 600 dpi resolution to acquire a color digital image.

[0030] S5. Reference Figure 1 and Figure 2 , Figure 1 In Figure b, the calibration curve is plotted based on standard points of magnesium ion concentration. Figure 2 Image a shows the two-dimensional distribution of magnesium sulfate heptahydrate fertilizer at the fertilizer-solution interface; Figure 2 Image b shows a three-dimensional visualization of magnesium sulfate heptahydrate fertilizer at the fertilizer-solution interface.

[0031] Import the scanned color image into ImageJ software. Select the RGB color channel (green) with the best contrast and convert it to an 8-bit grayscale image, then visualize the grayscale differences. Analyze the pre-established magnesium ion concentration-grayscale value correction curve to obtain a high-resolution image (100µm × 100µm resolution) of the two-dimensional diffusion distribution of magnesium ions.

[0032] The alkalization treatment is to ensure that magnesium ions in the adsorption membrane are fully precipitated and thus fully colored during the color development process. The surface of the adsorption membrane without alkalization is almost uncolored, and the gray value (green channel) of the adsorption membrane surface is reduced by 87% compared to that of the alkalized adsorption membrane. The alkalization time is determined based on the change in solution pH. After placing the adsorption membrane containing 5 mg of magnesium in 20 mL of sodium hydroxide solution with a pH of 13 for 30 minutes, if the solution pH drops by more than 0.1 units, it can be considered that the magnesium ions in the adsorption membrane have been fully precipitated.

[0033] Test Example 2 The specific steps for determining the binary distribution of magnesium content in a simulated aquatic environment are as follows: S1. Add 5µg of calcium standard material and 10µg of magnesium standard material to 20mL of aqueous solution to simulate the water environment and investigate the interference of calcium ions on this method.

[0034] S2. Experimental System Setup and Reaction Termination: Place the R-GDC adsorption membrane in the solution and terminate the reaction after 30 hours. Quickly rinse off any remaining solution on the surface of the adsorption membrane with ultrapure water, and gently blot away any residual droplets with lint-free paper.

[0035] S3. Immerse the adsorption membrane in 20 mL of a 2 mol / L sodium hydroxide solution (pH 13.0) and shake on a shaker for 30 min. After removal, transfer the adsorption membrane to 20 mL of a 1.0 g / L magnesium reagent I colorimetric solution and develop at room temperature in the dark for 20 min. Then, add sodium sulfite solution to the colorimetric solution to a final concentration of 0.1% (w / v) and continue developing for 10 min. Remove the adsorption membrane and rinse it three times quickly with pure water to remove any residual colorimetric agent. Wipe the surface of the adsorption membrane dry with lint-free paper and place it flat in a flatbed scanner to scan and acquire a color digital image at a resolution of 600 dpi.

[0036] S4. Import the scanned color image into ImageJ software. Select the RGB color channel with the best contrast, convert it to an 8-bit grayscale image, and visualize the grayscale differences. Analyze the pre-established magnesium ion concentration-grayscale value correction curve to obtain a high-resolution image of the final two-dimensional diffusion distribution of magnesium ions.

[0037] Test Example 3 Unlike Test Example 2, the calcium standard substance in step S1 is 10g, while the rest of the steps are the same as in Test Example 1.

[0038] Test Example 4 Unlike Test Example 2, the calcium standard substance in step S1 is 20g, while the rest of the steps are the same as in Test Example 1.

[0039] The grayscale values ​​of test examples 1-4 were tested, and the test results are shown in the table below: By comparing the gray values, it was found that the experimental system of the present invention exhibits excellent resistance to calcium ion interference. Even when the concentration of calcium ions is several times that of magnesium ions, it can still achieve accurate and efficient detection of magnesium ions in aqueous solution.

[0040]

[0041] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for determining the two-dimensional distribution of available magnesium content, characterized in that, Includes the following steps: S1. Dissolve magnesium reagent I in dimethyl sulfoxide to prepare a colorimetric reagent stock solution, and store it away from light; S2. Expose the DGT adsorption membrane to the test environment medium. After exposure, remove the adsorption membrane, rinse it with ultrapure water, and then immerse it in a sodium hydroxide solution with a pH of 13.0-14.0 for 20-40 min for pretreatment. The DGT adsorption membrane is an R-GDC type DGT adsorption membrane, and the adsorption phase particle size is a Chelex resin gel membrane with a particle size of 10 μm. S3. At room temperature, the colorimetric reagent mother liquor obtained in step S1 is mixed with sodium hydroxide solution and pure water to prepare the colorimetric reagent. The pretreated adsorption membrane from step S2 is taken out and placed in the colorimetric reagent for a colorimetric reaction. At 20 minutes after the start of the colorimetric reaction, sodium sulfite solution is added to the colorimetric reagent. The concentration of sodium sulfite in the colorimetric reagent is 0.1%. S4. After the color development reaction is complete, rinse the surface of the adsorption membrane with pure water. After wiping the surface of the adsorption membrane with a lint-free paper, immediately use a flatbed scanner to collect the grayscale value of the image. S5. Prepare magnesium ion solutions of different concentrations, take the DGT adsorption membrane, use magnesium ion solutions of different concentrations as the test environment medium, repeat the operations of S2-S4, establish a calibration curve, and accurately convert the image grayscale values ​​in S4 into magnesium ion concentration / flux. S6. Data processing: The color density information on the image is converted into a two-dimensional distribution of concentration / flux, and pseudo-color processing is used to make the quantitative information more intuitive.

2. The method for determining the two-dimensional distribution of available magnesium content according to claim 1, characterized in that, In step S1, the concentration of magnesium reagent I in the colorimetric reagent mother liquor is 0.5-1 g / L.

3. The method for determining the two-dimensional distribution of available magnesium content according to claim 1, characterized in that, In step S2, the environmental medium to be tested is any one of aqueous solution, soil, or sediment.

4. The method for determining the two-dimensional distribution of available magnesium content according to claim 1, characterized in that, The color development reaction time in step S3 is 25-35 minutes.

5. The method for determining the two-dimensional distribution of available magnesium content according to claim 1, characterized in that, In step S3, the concentration of the sodium hydroxide solution is 2 mol / L.

6. The method for determining the two-dimensional distribution of available magnesium content according to claim 1, characterized in that, In step S3, the mass ratio of the colorimetric reagent mother liquor, sodium hydroxide solution, and pure water is 1.25:1:4.

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