A chromium ion form analysis method based on electrochemical and raman dual-mode detection signals

Abstract

The application relates to a chromium ion form analysis method based on electrochemical and Raman bimodal detection signals. Au-Ag Janus NPs solution is added dropwise on the surface of a glassy carbon electrode, the DPV signal value and the Raman signal value of a to-be-detected solution containing Cr 6+ and Cr 3+ are detected, the concentration of Cr 6+ in the to-be-detected solution is obtained, Cr 6+ in the to-be-detected solution containing Cr 3+ and Cr 3+ is oxidized into Cr 6+ under the conditions of strong alkalinity and heating by using potassium permanganate, then a reducing agent is added to obtain a mixed solution, the concentration of Cr 6+ in the mixed solution is detected through the DPV signal value and the Raman signal value, Cr 3+ is completely converted into Cr 6+ , the total chromium concentration is measured, finally the concentration of Cr 3+ is obtained by subtraction, and finally the chromium ion form analysis is realized. The method improves the accuracy and efficiency of Cr ion form detection, and is suitable for rapid analysis of Cr ion forms in environment and biological samples.

Description

Technical Field

[0001] This invention relates to the field of environmental monitoring and heavy metal ion analysis technology, and in particular to a method for chromium ion speciation analysis based on electrochemical and Raman dual-mode detection signals. Background Technology

[0002] Chromium (Cr) is a common heavy metal element, mainly existing in the environment as trivalent chromium (Cr). 3+ ) and hexavalent chromium (Cr 6 + It exists in two forms, with significant differences in toxicity, migration, and bioavailability. Among them, Cr... 6+ It possesses strong oxidizing properties and high toxicity, easily entering the human body through the respiratory tract, digestive tract, and skin, causing serious harm to the liver, kidneys, nervous system, and genetic material, and is listed as a priority pollutant for control; while Cr 3+ Cr is an essential trace element for the human body, with low toxicity. It is more likely to form precipitates or be adsorbed in the environment, and its migration ability is weak. Therefore, accurately distinguishing and quantitatively detecting the specific forms of Cr ions in environmental samples is of great significance for environmental pollution risk assessment, ecological protection, and human health protection.

[0003] Currently, methods for detecting Cr ion speciation mainly include spectroscopic methods, chromatographic methods, and electrochemical methods. Among spectroscopic methods, ultraviolet-visible spectrophotometry is widely used due to its ease of operation, but it is easily affected by sample matrix interference and has poor selectivity. Atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS), while highly sensitive, require pretreatment to achieve speciation separation, and the instruments are expensive and complex to operate. Chromatographic methods (such as ion chromatography) can separate Cr ions of different valence states, but they require coupling with detection instruments, resulting in a long detection process that is difficult to meet the needs of rapid on-site analysis.

[0004] Electrochemical methods have attracted much attention in heavy metal detection due to their advantages such as rapid response, low cost, and ease of miniaturization. They achieve quantification through the redox reaction of Cr ions on the electrode surface. However, the single electrochemical signal is easily affected by factors such as coexisting ions and electrode surface conditions, making it difficult to accurately distinguish Cr. 3+ With Cr 6+ The chemical form of Cr ions. Raman spectroscopy is based on the characteristic peaks of molecular vibration to achieve qualitative identification of substances. It can distinguish the form by the difference in characteristic peaks after Cr ions bind to specific ligands. However, the Raman signal intensity is relatively weak, the detection sensitivity for low concentration samples is insufficient, and it is easily affected by fluorescence background interference.

[0005] In existing technologies, a single detection method cannot simultaneously meet the requirements of high selectivity, high sensitivity, and accurate qualitative and quantitative analysis of Cr ion speciation. Therefore, developing a Cr ion speciation analysis method that can integrate the advantages of different detection technologies and achieve complementary synergy has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for chromium ion speciation analysis based on electrochemical and Raman dual-modal detection signals. This invention utilizes Au-Ag Janus nanoparticles as the sensing substrate. Hexavalent chromium etches silver into the particles, reducing the differential pulse voltammetry (DPV) signal, while the Raman enhancement effect weakens, leading to a decrease in the Raman signal. After pre-oxidizing trivalent chromium in the sample to hexavalent chromium, the changes in dual-modal signals before and after oxidation are compared to achieve separate quantification and speciation of trivalent and hexavalent chromium. This method combines the high sensitivity and specificity of electrochemical and Raman methods, improving the accuracy and efficiency of Cr ion speciation detection, and is suitable for rapid analysis of Cr ion speciation in environmental and biological samples.

[0007] The purpose of this invention is to provide a method for chromium ion speciation analysis based on electrochemical and Raman dual-mode detection signals, comprising the following steps:

[0008] Provides an Au-Ag Janus NPs solution and multiple samples containing Cr 6+ and Cr 3+ The solution to be tested;

[0009] The Au-Ag Janus NPs solution was dropped onto the surface of a glassy carbon electrode to detect the presence of Cr. 6+ and Cr 3+ The DPV and Raman signal values ​​of the test solution were used to obtain the Cr content in the test solution. 6+ The concentration;

[0010] Using potassium permanganate under strongly alkaline and heated conditions, Cr-containing compounds are... 6+ and Cr 3+ Cr in the test solution 3+ Oxidized to Cr 6+ Then, a reducing agent was added to remove excess potassium permanganate oxidant, resulting in a mixed solution. The Cr content of the mixed solution was detected by dual-signal DPV and Raman signal values. 6+ The concentration of Cr; 3+ All converted to Cr 6+ The total chromium concentration was measured, and the total chromium concentration was subtracted from the Cr concentration in the mixed solution. 6+ The concentration of Cr was obtained 3+ The concentration was determined to ultimately achieve speciation analysis of chromium ions.

[0011] The DPV signal detection steps include: detecting the blank DPV signal value of a glassy carbon electrode with Au-Ag Janus NPs solution added; and using a series of known Cr... 6+ A standard curve was prepared using standard solutions to detect the presence of Cr. 6+ and Cr 3+ The DPV signal value of the test solution was subtracted from the blank DPV signal value to obtain the final Cr. 6+ and Cr 3+ Cr in the test solution 6+ The concentration;

[0012] The Raman signal detection procedure is as follows: The blank Raman signal value of a glassy carbon electrode with Au-Ag Janus NPs added is detected; and a series of known Cr concentration gradients are used to detect the signal. 6+ A standard curve was prepared using standard solutions; then, the presence of Cr was detected. 6+ and Cr 3+ The Raman signal value of the test solution is subtracted from the blank Raman signal value to obtain the final Cr value. 6+ and Cr 3+ Cr in the test solution 6+ The concentration.

[0013] In some embodiments of the present invention, the Au-Ag Janus NPs in the Au-Ag Janus NPs solution are prepared by the following method:

[0014] Provide an Au NPs dispersion;

[0015] NaOH solution and 2-mercaptobenzimidazole-5-carboxylic acid solution were added to the Au NPs dispersion and mixed; the mixture was then heated and incubated to form a dense ligand layer on the surface of the Au NPs.

[0016] The reducing agent and silver nitrate solution were added and mixed thoroughly. The mixture was then allowed to stand at room temperature to allow Ag+ to be reduced and deposited in the ligand layer to form Ag islands, thus obtaining the Au-Ag Janus NPs.

[0017] In some embodiments of the present invention, the concentration of the 2-mercaptobenzimidazole-5-carboxylic acid is 0.8–1.2 mM; and the concentration of the NaOH solution is 18–20 mM.

[0018] In some embodiments of the present invention, the heating and incubation temperature is 55-60°C, and the time is 2-2.5 hours;

[0019] The concentration of silver nitrate solution is 0.8–1.2 mM.

[0020] In some embodiments of the present invention, the reducing agent is selected from hydroquinone, ascorbic acid, and sodium borohydride; the concentration of the reducing agent is 0.8–1.2 mM.

[0021] In some embodiments of the present invention, the concentration of the Au-Ag Janus NPs solution is 0.25–0.3 mM.

[0022] In some embodiments of the present invention, the pH value of the strongly alkaline solution is 10 to 12.

[0023] In some embodiments of the present invention, the heating temperature is 90-95°C and the heating time is 30-60 minutes.

[0024] In some embodiments of the present invention, the reducing agent is selected from sodium nitrite, sodium sulfite, sodium thiosulfate, and oxalic acid; the mass-volume concentration of the reducing agent is 0.5-1% w / v.

[0025] In some embodiments of the present invention, the Cr 6+ and Cr 3+ Cr in the test solution 6+ The concentration of Cr is 0–100 μM. 3+ The concentration is 0–100 μM, not 0 at the same time.

[0026] The principle of this invention: Utilizing the silver component in Au-Ag Janus NPs to influence Cr... 6+ Specific etching, directly identifying Cr through synchronous changes in both DPV and Raman signals. 6+ ;

[0027] Potassium permanganate is a strong oxidizing agent; under alkaline and heated conditions, it can oxidize trivalent chromium ions in solution to hexavalent chromium ions. Reaction formula: 3MnO4 - +2Cr 3+ +2H₂O→3MnO₂+2CrO₄ 2- +4H + (In an alkaline environment, H) + It will be neutralized.

[0028] Sodium nitrite is a reducing agent; its role is to reduce excess potassium permanganate remaining in the solution after the chromium oxidation step (excess potassium permanganate can interfere with subsequent determination of hexavalent chromium). Reaction formula: 2MnO4 - +5NO2 - +6H + →2Mn 2+ +5NO3 - +3H₂O (This reduction step is usually carried out under slightly acidic conditions). Combined with Cr 3+ Data after oxidation transformation, realizing Cr 3+Cr 6 + It also enables precise differentiation and quantification of total Cr, solving the problem of difficult morphological identification.

[0029] In this invention, dual-modal detection technology combines the signal characteristics of two detection principles, leveraging the advantages of each while overcoming the limitations of single methods, providing a new approach for the precise analysis of Cr ion speciation. Cross-validation using electrochemical and Raman signals reduces interference from single signals and improves result reliability. The nano-effect of Au-Ag Janus NPs enhances reactivity, significantly improving detection sensitivity and making it suitable for trace analysis. No complex pretreatment is required; the oxidation-conversion combined with dual-signal detection process is simple and can be rapidly applied to multi-matrix detection in food, water, soil, etc., demonstrating strong practicality. The heterostructure of Au-Ag Janus NPs balances stability (Au) and reactivity (Ag), improving signal stability and etching efficiency, facilitating widespread adoption.

[0030] The technical solution of the present invention has the following advantages compared with the prior art:

[0031] This invention utilizes Au-Ag Janus nanoparticles as a sensing substrate. Hexavalent chromium etches silver into the particles, reducing the differential pulse voltammetry (DPV) signal. Simultaneously, the weakened Raman enhancement effect leads to a decrease in the Raman signal. After pre-oxidizing trivalent chromium in the sample to hexavalent chromium, the changes in the dual-modal signals before and after oxidation are compared to achieve separate quantification and speciation of trivalent and hexavalent chromium. This method combines the high sensitivity and specificity of electrochemistry and Raman spectroscopy, improving the accuracy and efficiency of Cr ion speciation detection, and is suitable for rapid analysis of Cr ion speciation in environmental and biological samples. Attached Figure Description

[0032] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0033] Figure 1 These are the ultraviolet absorption spectra of Au-Ag Janus NPs at different hexavalent chromium concentrations according to the present invention.

[0034] Figure 2 This invention presents the DPV, Raman spectra, and standard curves of Au-Ag Janus NPs with different hexavalent chromium concentrations.

[0035] Figure 3 This invention relates to the DPV and Raman spectra of Au-Ag Janus NPs for hexavalent chromium and other metal ions: hexavalent chromium-specific analysis.

[0036] Figure 4This invention relates to the DPV and Raman detection of actual samples containing hexavalent and trivalent chromium. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0038] Example

[0039] This embodiment provides a method for chromium ion speciation analysis based on electrochemical and Raman dual-mode detection signals, as detailed below:

[0040] I. Preparation of Au-Ag Janus NPs, the specific steps are as follows:

[0041] Step 1: First, synthesize AuNPs using the citrate reduction method: Add 0.5 mL of 1% chloroauric acid (HAuCl4) to 49.5 mL of ultrapure water and heat to boiling; quickly inject 0.5 mL of 1% sodium citrate solution, maintain boiling for 15 minutes with vigorous stirring, cool naturally to room temperature, and add water to make up to 50 mL to obtain citrate-stabilized AuNPs.

[0042] Step 2: Au-Ag Janus NPs were synthesized using a ligand-regulated growth method: 4 mL of the Au NPs solution obtained in Step 1 was centrifuged to remove sodium citrate and dispersed in 10 mL of deionized water. 400 μL of 20 mM NaOH and 200 μL of 1 mM 2-mercaptobenzimidazole-5-carboxylic acid (MBIA, soluble in ethanol) were added, and the mixture was vigorously vortexed. The mixture was incubated in a 60°C oven for 2 hours to allow MBIA to bind to the Au surface via thiol groups (-SH), forming a dense ligand layer. After the solution cooled to room temperature, 600 μL of 10 mM hydroquinone (HQ, reducing agent) and 1200 μL of 1 mM silver nitrate (AgNO3) solution were added sequentially, and the mixture was vigorously vortexed. The mixture was then allowed to stand at room temperature for at least 2 hours to allow the Ag... + At specific sites on the Au surface regulated by MBIA ligands, reduction and deposition are carried out to form Ag islands, resulting in Au-Ag Janus NPs. 200 μL of 0.025M CTAB is added dropwise with stirring to prevent aggregation, and the mixture is centrifuged and dispersed in ultrapure water for later use.

[0043] II. Dual-signal detection:

[0044] Add 0.01M HBr to the Au-Ag Janus NPs solution obtained in step one to adjust the pH to 5, and then prepare solutions containing different concentrations of Cr. 6+ Au-Ag JanusNPs solution, Cr 6+The concentrations were 0, 5, 10, 25, 50, 75, and 100 μM, respectively, to obtain the test solutions.

[0045] DPV detection: The pretreated glassy carbon electrode (GCE) was polished sequentially with 0.3 μm and 0.05 μm alumina powder, rinsed with ultrapure water, and then Au-Ag Janus NPs were added to measure the blank DPV signal. The DPV of solutions with different concentrations was then measured, and the blank DPV signal was subtracted. Finally, a standard curve was established using the Cr6+ concentration and the corresponding DPV signal. The specific linear equation is y = 34.31337 + 0.29508X, where x is the Cr(VI) concentration in μM; y is the DPV signal, and the correlation coefficient R² = 0.98886.

[0046] Raman detection: The parameters of the Raman spectrometer are as follows: excitation power 150mW, exposure time 10s; optical resolution 500x (eyepiece 10x, objective 50x); laser wavelength 785nm; Raman shift range 600–2000cm. -1 The Raman signals of the test solutions at different concentrations were measured respectively, and Cr was used to analyze the signals. 6+ A standard curve was established using the concentration of Cr(VI) and the corresponding Raman signal. The specific linear equation is y = 24423.444 - 196.2709X, where x is the concentration of Cr(VI) in μM, y is the Raman signal, and the correlation coefficient R is 1 / 2. 2 =0.99649。

[0047] II. Testing of actual samples:

[0048] Add 50 μM Cr(VI) and 50 μM Cr(III) (Sample 1) to deionized water. Adjust the pH of Sample 1 to 2 with dilute sulfuric acid. Heat the solution to 95°C and add (1 mM) potassium permanganate dropwise until a purple-red color appears. Continue stirring and maintain a distinct purple-red color throughout the heating process (indicating the presence of excess potassium permanganate, ensuring complete oxidation). If the purple-red color fades, add potassium permanganate solution dropwise until the purple-red color is stably maintained for more than one minute. Keep the solution at a gentle boil and add a small amount of 1% (w / v) sodium nitrite dropwise until the purple color just disappears. Cool to room temperature to obtain Sample 2.

[0049] Actual standard sample testing: Spiking recovery experiments were conducted by adding 50 μM Cr(VI) and 50 μM Cr(III) (Sample 1) and the treated Sample 1 (Sample 2) to deionized water, respectively. The experimental results are shown in Tables 1 and 2. The electrochemical DPV values ​​were 48.793 μM and 95.314 μM, respectively; the Raman values ​​were 50.22 μM and 97.462 μM, respectively.

[0050] Table 1 Electrochemical DPV Detection

[0051]

[0052] Table 2 Raman Detection

[0053]

[0054] As shown in Tables 1 and 2, for electrochemical DPV detection, the recovery rate of spiked sample 1 (50 μMCr(VI) + 50 μMCr(III)) was 97.692%, with a relative standard deviation (RSD) of 1.12%; and the recovery rate of spiked sample 2 after treatment was 95.314%, with an RSD of 0.86%.

[0055] Raman spectroscopy: The recovery rate of spiked sample 1 was 100.44%, with an RSD of 2.9%; the recovery rate of spiked sample 2 after treatment was 97.462%, with an RSD of 1.13%.

[0056] Both detection methods showed high recovery rates and low RSDs. This indicates that both electrochemical DPV detection and Raman detection methods have good accuracy and high precision for chromium detection, and the results exhibit good repeatability and stability.

[0057] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for chromium ion speciation analysis based on electrochemical and Raman dual-mode detection signals, characterized in that, Includes the following steps: Provides an Au-Ag Janus NPs solution and multiple samples containing Cr 6+ and Cr 3+ The solution to be tested; The Au-Ag Janus NPs solution was added dropwise to the surface of a glassy carbon electrode to detect the presence of Cr. 6+ and Cr 3+ The DPV and Raman signal values ​​of the test solution were used to obtain the Cr content in the test solution. 6+ The concentration; Using potassium permanganate under strongly alkaline and heated conditions, Cr-containing compounds are... 6+ and Cr 3+ Cr in the test solution 3+ Oxidized to Cr 6+ Then, a reducing agent was added to remove excess potassium permanganate oxidant, resulting in a mixed solution. The Cr content of the mixed solution was detected by dual-signal DPV and Raman signal values. 6+ The concentration of Cr; 3+ All converted to Cr 6+ The total chromium concentration was measured, and the total chromium concentration was subtracted from the Cr concentration in the mixed solution. 6+ The concentration of Cr was obtained 3+ The concentration was determined to ultimately achieve speciation analysis of chromium ions. The DPV signal detection steps include: detecting the blank DPV signal value of a glassy carbon electrode with Au-Ag Janus NPs solution added; and using a series of known Cr... 6+ A standard curve was prepared using standard solutions to detect the presence of Cr. 6+ and Cr 3+ The DPV signal value of the test solution was subtracted from the blank DPV signal value to obtain the final Cr. 6+ and Cr 3+ Cr in the test solution 6+ The concentration; The Raman signal detection procedure is as follows: The blank Raman signal value of a glassy carbon electrode with Au-Ag Janus NPs added is detected; and a series of known Cr concentration gradients are used to detect the signal. 6+ A standard curve was prepared using standard solutions; then, the presence of Cr was detected. 6+ and Cr 3+ The Raman signal value of the test solution was subtracted from the blank Raman signal value to obtain the final result containing Cr. 6+ and Cr 3+ Cr in the test solution 6+ The concentration.

2. The chromium ion speciation analysis method according to claim 1, characterized in that, The Au-Ag Janus NPs in the Au-Ag Janus NPs solution were prepared by the following method: Provide an Au NPs dispersion; NaOH solution and 2-mercaptobenzimidazole-5-carboxylic acid solution were added to the Au NPs dispersion and mixed; the mixture was then heated and incubated to form a dense ligand layer on the surface of the Au NPs. Add the reducing agent and silver nitrate solution, mix thoroughly, and then let stand at room temperature to allow Ag to settle. + Ag islands are formed by reduction and deposition in the ligand layer, yielding the Au-Ag Janus NPs.

3. The chromium ion speciation analysis method according to claim 2, characterized in that, The concentration of the 2-mercaptobenzimidazole-5-carboxylic acid is 0.8–1.2 mM; the concentration of the NaOH solution is 18–20 mM.

4. The chromium ion speciation analysis method according to claim 2, characterized in that, The incubation temperature is 55–60℃, and the time is 2–2.5 hours; The concentration of silver nitrate solution is 0.8–1.2 mM.

5. The chromium ion speciation analysis method according to claim 2, characterized in that, The reducing agent is selected from one or more of hydroquinone, ascorbic acid, or sodium borohydride; the concentration of the reducing agent is 0.8–1.2 mM.

6. The chromium ion speciation analysis method according to claim 1, characterized in that, The concentration of the Au-Ag Janus NPs solution was 0.25–0.3 mM.

7. The chromium ion speciation analysis method according to claim 1, characterized in that, The pH value of a strongly alkaline solution is 10 to 12.

8. The chromium ion speciation analysis method according to claim 1, characterized in that, The heating temperature is 90-95℃, and the heating time is 30-60 minutes.

9. The method for analyzing the speciation of chromium ions according to claim 1, characterized in that, The reducing agent is selected from one or more of sodium nitrite, sodium sulfite, sodium thiosulfate, or oxalic acid; the mass-volume concentration of the reducing agent is 0.5-1% w / v.

10. The method for analyzing the speciation of chromium ions according to claim 1, characterized in that, The Cr 6+ and Cr 3+ Cr in the test solution 6+ The concentration of Cr is 0–100 μM. 3+ The concentration ranges from 0 to 100 μM.

Images