A method for detecting dichromate based on surface-enhanced Raman spectroscopy

Abstract

This invention provides a method for detecting dichromate ions based on surface-enhanced Raman spectroscopy, belonging to the field of analytical chemistry. The method includes: mixing the sample to be tested with a solution containing a thiol compound, adjusting to acidic conditions to allow dichromate ions (Cr(VI)) to undergo a redox reaction with the thiol-containing compound; constructing a SERS substrate, i.e., preparing a ZnO / Ag heterostructure substrate; mixing a suspension of the ZnO / Ag heterostructure substrate with the reaction system to obtain a mixed solution, allowing the ZnO / Ag heterostructure substrate to adsorb the thiol-containing compound and enhance the Raman signal; dropping the mixed solution onto the surface of a solid support, acquiring the Raman spectral signal using a Raman spectrometer, and quantifying the Cr(VI) concentration by the change in signal intensity. This invention achieves rapid and highly sensitive detection of Cr(VI), exhibiting strong selectivity and anti-interference capabilities, and is suitable for detection in fields such as environmental monitoring, food safety, and pharmaceutical analysis.

Description

Technical Field

[0001] This invention relates to the field of analytical chemistry, and in particular to a method for detecting dichromate based on surface-enhanced Raman spectroscopy. Background Technology

[0002] Heavy metal ion pollution is a major problem threatening human health and ecological security. Among them, hexavalent chromium [Cr(VI)] has attracted much attention due to its strong oxidizing properties and high toxicity. Traditional detection methods such as inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS) have high accuracy, but they rely on expensive equipment and are difficult to implement for rapid on-site detection.

[0003] Surface-enhanced Raman spectroscopy (SERS) has shown promise for trace detection due to its high sensitivity; however, existing SERS methods generally suffer from poor selectivity and weak resistance to interference, especially in complex matrices such as traditional Chinese medicine extracts, where they are easily affected by background signals. Furthermore, existing SERS detection methods based on redox reactions suffer from slow reaction kinetics, with reaction times often exceeding 30 minutes or even several hours, and have high detection limits, making them unsuitable for the rapid detection of trace Cr(VI).

[0004] Therefore, there is an urgent need to develop a SERS detection method that combines rapid response, ultra-low detection limit and strong anti-interference capability, so as to lay a theoretical foundation for detection in fields such as environmental monitoring and food safety. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a method for detecting dichromate based on surface-enhanced Raman spectroscopy, which achieves rapid and highly sensitive detection of Cr(VI), with strong selectivity and anti-interference ability, and is suitable for detection in fields such as environmental monitoring, food safety and drug analysis.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A method for detecting dichromate based on surface-enhanced Raman spectroscopy includes the following steps:

[0008] S1. Mix the sample to be tested with a solution containing a thiol compound and adjust to acidic conditions to allow the dichromate ion Cr(VI) to undergo a redox reaction with the thiol compound.

[0009] S2. Construct the SERS substrate, i.e., prepare the ZnO / Ag heterostructure substrate;

[0010] S3. The suspension of the ZnO / Ag heterostructure substrate is mixed with the reaction system of step S1 to obtain a mixed solution, so that the ZnO / Ag heterostructure substrate adsorbs mercapto-containing compounds and enhances the Raman signal.

[0011] S4. The mixed solution is dropped onto the surface of a solid support, and Raman spectroscopy is used to collect Raman spectral signals. The concentration of Cr(VI) is quantified by the change in signal intensity.

[0012] Preferably, in S1, the pH value of the acidic condition is 1.0, and the redox reaction time is 1 minute.

[0013] Preferably, the thiol-containing compound is 2-mercaptoimidazole.

[0014] Preferably, in S3, the adsorption time of the ZnO / Ag heterostructure substrate for the mercapto-containing compound is no more than 2 minutes.

[0015] Preferably, in S3, the mixing time between the suspension of the ZnO / Ag heterostructure substrate and the reaction system is 2 minutes.

[0016] Preferably, in S4, the surface of the solid support is a silicon wafer, and the Raman spectrometer uses a 785nm laser wavelength.

[0017] Preferably, in S4, the Cr(VI) concentration is quantified by the change in signal intensity, specifically by using a 1232 cm⁻¹ signal intensity meter. -1 The change in peak intensity at a given location is used to quantify the Cr(VI) concentration.

[0018] Preferably, the detection limit of this method is 1.6 fmol / L, and the linear range is 1.0 × 10⁻⁶. -14 ~1.0×10 -4 mol / L.

[0019] The present invention also provides an application of the above-mentioned method for detecting dichromate based on surface-enhanced Raman spectroscopy, which is suitable for rapid detection of Cr(VI) in the fields of environmental monitoring, food safety and drug analysis.

[0020] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0021] (1) This invention significantly shortens the detection time by constructing a redox reaction system of Cr(VI) and 2-mercaptoimidazole under acidic conditions and combining it with a ZnO / Ag heterostructure substrate. The oxidation reaction of Cr(VI) and 2-mercaptoimidazole can reach equilibrium within 1 minute. Combined with the characteristic of the ZnO / Ag heterostructure substrate to rapidly adsorb probe molecules within 2 minutes, the entire detection process takes no more than 5 minutes. This solves the problems of slow reaction kinetics and excessively long detection time in existing SERS methods, laying the foundation for rapid on-site detection.

[0022] (2) This invention exhibits extremely high detection sensitivity and a wide linear detection range. Its detection limit is as low as 1.6 fmol / L, which is 9 orders of magnitude lower than the US Environmental Protection Agency's drinking water safety standard (1.0 μmol / L), while its linear range covers 1.0 × 10⁻⁶. -14 ~1.0×10 -4 The concentration of mol / L enables this method to detect trace amounts of Cr(VI) in the environment and food, thus meeting the requirements for trace detection.

[0023] (3) This invention utilizes the strong conditional potential of 1.19V for Cr(VI) at pH = 1.0 to effectively eliminate Hg. 2+ Ag + The influence of interfering ions is mitigated. An acidic environment not only inhibits the deposition of coexisting ions but also enhances the binding between the substrate and the probe through stable S-metallic bonds, thereby improving anti-interference performance. Furthermore, this method is suitable for rapid detection of Cr(VI) in environmental monitoring, food safety, and pharmaceutical analysis. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a flowchart of a method for detecting dichromate based on surface-enhanced Raman spectroscopy according to the present invention;

[0026] Figure 2 SERS signal variation curves of 2-MI and ZnO / Ag substrate at different mixing times provided by the present invention;

[0027] Figure 3 This invention provides a comparison of SERS spectra and selectivity of the reaction between 2-MI and Cr(VI); wherein, Figure 3 In the figure, A represents the SERS plot of 2-MI under different conditions. Figure 3 B in the chart represents a selective contrast chart;

[0028] Figure 4 The present invention provides SERS signal variation curves under different conditions; wherein, Figure 4 In the figure, A represents the SERS signal variation curves under different pH conditions. Figure 4 In the figure, B represents the SERS signal variation curves under different mixing ratios. Figure 4 C in the figure represents the SERS signal variation curves under different temperature conditions. Figure 4D in the figure represents the SERS signal variation curves under different concentration conditions;

[0029] Figure 5 The linear relationship between Cr(VI) concentration and SERS signal intensity provided by this invention; wherein, Figure 5 In the diagram, A represents the SERS plots for different Cr(VI) concentrations. Figure 5 In the figure, B represents the linear fitting curve of Cr(VI) concentration versus SERS signal intensity in different concentration ranges.

[0030] Figure 6 A bar chart showing the anti-interference experimental data provided by this invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 1 As shown, this invention provides a method for detecting dichromate ions based on surface-enhanced Raman spectroscopy, comprising the following steps:

[0034] S1. Mix the sample to be tested with a solution containing a thiol compound and adjust to acidic conditions to allow the dichromate ion Cr(VI) to undergo a redox reaction with the thiol compound.

[0035] S2. Construct the SERS substrate, i.e., prepare the ZnO / Ag heterostructure substrate;

[0036] S3. The suspension of the ZnO / Ag heterostructure substrate is mixed with the reaction system of step S1 to obtain a mixed solution, so that the ZnO / Ag heterostructure substrate adsorbs mercapto-containing compounds and enhances the Raman signal.

[0037] S4. The mixed solution is dropped onto the surface of a solid support, and Raman spectroscopy is used to collect Raman spectral signals. The concentration of Cr(VI) is quantified by the change in signal intensity.

[0038] In S1, the pH value of the acidic condition is 1.0, and the redox reaction time is 1 minute. The thiol-containing compound is 2-mercaptoimidazole.

[0039] The mixing time between the ZnO / Ag heterostructure substrate suspension and the reaction system is 2 minutes, while the reference... Figure 2 The ZnO / Ag heterostructure substrate prepared according to the above scheme exhibits an adsorption time of no more than 2 minutes for thiol-containing compounds. The solid support surface is a silicon wafer, and the Raman spectrometer uses a 785nm laser wavelength. Figure 3 As shown in B, the concentration of Cr(VI) is quantified by changes in signal intensity, specifically: through a 1232 cm⁻¹... -1 The change in peak intensity at a given location is used to quantify the Cr(VI) concentration.

[0040] In addition, in S2, the preparation method of the ZnO / Ag heterostructure substrate includes: preparing ZnO nanorods by hydrothermal method, and then depositing Ag nanoparticles on the surface of ZnO nanorods by in-situ chemical reduction method to obtain ZnO / Ag heterostructure substrate, wherein the suspension concentration of the substrate is 0.1-1 mg / mL.

[0041] Based on the above content, the following specific implementation methods will be used to experimentally verify and illustrate the content provided above.

[0042] Example 1

[0043] In this embodiment, Cr(VI) in environmental water samples is detected. The specific steps are as follows:

[0044] Sample pretreatment: A water sample from the Ganjiang River was taken and filtered through a 0.45 μm filter membrane to remove suspended solids. The pH of the filtrate was adjusted to 1.0 using a 1 mol / L hydrochloric acid solution. Figure 4 As shown in section A, the experimental results at pH=1.0 show the fastest SERS signal decay rate, thus verifying the kinetic optimization effect of the acidic environment on the oxidation of Cr(VI)2-MI. Meanwhile, referring to... Figure 6 Under the acidic conditions of pH 1.0 established in this invention, the conditional potential of Cr(VI) reaches 1.19V, which can effectively inhibit Mg. 2+ Al 3+ Deposition of interfering ions; combined with the specific adsorption capacity of the ZnO / Ag heterostructure substrate for 2-mercaptoimidazole, subsequent detection of common coexisting ions in environmental water samples (such as Na+) + K + Ca 2+ Interference from (etc.) was significantly limited, ensuring the anti-interference performance of the detection, and the final spiked recovery rate was consistent with that of the pure system.

[0045] To construct the reaction system: Add 10 μL of a 1.0 × 10⁻⁶ solution to 1 mL of filtered water sample. -11A standard solution of Cr(VI) at mol / L was prepared, and 1 mL of a 0.5 mg / L 2-mercaptoimidazole (2-MI) solution was added. After thorough mixing, the mixture was reacted at room temperature for 1 minute. Because Cr(VI) has strong oxidizing properties under acidic conditions, it can undergo a redox reaction with the thiol group in 2-MI, leading to the destruction of the 2-MI molecular structure. (The last sentence appears to be incomplete and possibly refers to a reaction with a specific concentration of 1232 cm⁻¹.) -1 The Raman peak at 1232 cm⁻¹ is a characteristic peak of the binding of thiol groups in 2-MI to the ZnO / Ag substrate. Therefore, as the Cr(VI) concentration increases, the number of oxidized 2-MI molecules increases, and the number of 2-MI molecules that can bind to the substrate decreases, resulting in a higher Raman peak at 1232 cm⁻¹. -1 The SERS peak intensity at the reference point decreases with increasing Cr(VI) concentration. Figure 3 A in the figure shows the difference in peak intensity at this displacement between the Cr(VI)-added group and the blank group, confirming this trend; (Refer to...) Figure 4 The redox reaction can be completed by reacting C at room temperature (25°C) for 1 minute.

[0046] Preparation and mixing of the SERS substrate: ZnO nanorods were prepared using a hydrothermal method, followed by in-situ chemical reduction of Ag nanoparticles to obtain a ZnO / Ag heterostructure substrate, and a suspension was prepared. 1 mL of the substrate suspension was added to the above reaction system and mixed for 2 minutes to allow the substrate to adsorb 2-MI. (Refer to...) Figure 2 The mixing time between the substrate and 2-MI was optimized to 2 minutes, i.e. Figure 4 The signal stability is best when the mixing ratio of B in the formula is 5:1, and it is also referenced to... Figure 5 In section A, this operation ensures rapid adsorption of 2-MI by the substrate, i.e., adsorption time ≤ 2 minutes, for low concentrations of Cr(VI) (1.0 × 10⁻⁶). -12 The detection of (mol / L) provides a basis for signal enhancement.

[0047] Signal Acquisition and Analysis: The mixture was dropped onto the silicon wafer surface, and the signal was acquired using a portable Raman spectrometer equipped with a 785nm laser. The image was taken at 1232cm⁻¹. -1 Based on the change in peak intensity at that point, and referring to Figure 5 In equation A, the Cr(VI) concentration was calculated using the linear equation I = -lgC × 393.1 - 1047.4, and the spiked recovery rate was found to be 93.9%, with a relative standard deviation (RSD) of 0.1%. Furthermore, referring to... Figure 6 The interference from common ions in environmental water samples was effectively limited, and the recovery rate was consistent with that of the pure system.

[0048] Example 2

[0049] In this embodiment, the Cr(VI) in the traditional Chinese medicine sample is detected. The specific steps are as follows:

[0050] Weigh 2.0 g of Astragalus membranaceus powder, prepare acidified water with pH = 1.0 using 1 mol / L hydrochloric acid, and add 10 mL of acidified water to the Astragalus membranaceus powder. Extract by sonication for 30 minutes. Centrifuge the extract at 10000 rpm for 10 minutes and collect the supernatant. Add 0.5 g of MgO powder to the supernatant, shake for 10 minutes to adsorb pigments, filter, and adjust the pH of the filtrate to 1.0. (Refer to...) Figure 4 As shown in A, pH = 1.0 maximizes the oxidation potential of Cr(VI), φ' = 1.19 V, combined with Figure 6 Under the detection system of this invention (pH=1.0, ZnO / Ag heterostructure substrate), even if the traditional Chinese medicine matrix contains 100 times the concentration of common interfering ions (such as Fe), 3+ Cu 2+ Pb 2 + The redox reaction of Cr(VI) with 2-mercaptoimidazole can still be carried out specifically, and the Raman signal enhancement of the target product by the ZnO / Ag substrate is not interfered with. The final spiked recovery rate is ≥98%, which proves that the acidic conditions combined with the substrate characteristics of this method can effectively inhibit the influence of interfering substances in the Chinese medicine matrix.

[0051] Add Cr(VI) standard solutions of different concentrations (spiking level 1.0 × 10⁻⁶) to 1 mL of filtrate. -12 ~1.0×10 - 8 Add 1 mL of 0.5 mg / L 2-MI solution and react at room temperature for 1 minute. Add 1 mL of ZnO / Ag substrate suspension, mix for 2 minutes, and then dropwise onto a silicon wafer. Acquire the signal using the same Raman spectroscopy parameters as in Example 1. Refer to Figure 5 A and B in the formula represent concentrations that cover the low and medium concentration ranges within the linear detection interval, including 1.0 × 10⁻⁶. -10 The recovery rate was 98.7% (RSD = 2.3%) when spiked at mol / L, compared with... Figure 5 The linear fitting results for the low concentration range (A) were consistent with the detection limit of 1.6 fmol / L, and the components in the herbal extract did not affect the redox reaction between 2-MI and Cr(VI). (1232 cm⁻¹) -1 The peak intensity decay pattern is the same as that of the pure system.

[0052] The recoveries at different spiking concentrations ranged from 91.1% to 106.9%, with RSDs ≤ 4.2%. The spiking concentration was 1.0 × 10⁻⁶. -10 At mol / L, the recovery rate was 98.7%, RSD = 2.3%, and the reference value was [missing information]. Figure 4 High concentrations of Cr(VI) in D can still cause significant signal attenuation, compared to Figure 5The linear relationship in the high concentration range of B is complementary, demonstrating the applicability of the method to the detection of Cr(VI) over a wide concentration range in complex matrices of traditional Chinese medicine.

[0053] Therefore, the above-mentioned method for detecting dichromate based on surface-enhanced Raman spectroscopy achieves rapid and highly sensitive detection of Cr(VI), with strong selectivity and anti-interference ability, and is suitable for detection in fields such as environmental monitoring, food safety and drug analysis.

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0055] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for detecting a hexavalent chromium species based on surface enhanced Raman spectroscopy, characterized in that, The method comprises the following steps: S1, mixing a sample to be tested with a solution containing a thiol compound, adjusting to an acidic condition, and allowing a redox reaction between Cr(VI) and the thiol compound to occur; In S1, the pH value of the acidic condition is 1.0, the time of the redox reaction is 1 minute, and the thiol compound is 2-mercaptoimidazole; S2, constructing a SERS substrate, i.e. preparing a ZnO / Ag heterostructure substrate; S3, mixing a suspension of the ZnO / Ag heterostructure substrate with the reaction system of step S1 to obtain a mixed solution, allowing the ZnO / Ag heterostructure substrate to adsorb the thiol compound and enhance the Raman signal; S4, dropping the mixed solution onto a solid carrier surface, collecting a Raman spectrum signal by using a Raman spectrometer, and quantifying the Cr(VI) concentration through the signal intensity change.

2. The method for detecting the heavy chromate according to claim 1, characterized in that, In S3, the adsorption time of the ZnO / Ag heterostructure substrate to the thiol compound is not more than 2 minutes.

3. The method for detecting the heavy chromate according to claim 1, characterized in that, In S3, the mixing time of the suspension of the ZnO / Ag heterostructure substrate and the reaction system is 2 minutes.

4. The method for detecting the heavy chromate according to claim 1, characterized in that, In S4, the solid carrier surface is a silicon wafer, and the Raman spectrometer uses a 785 nm laser wavelength.

5. The method for detecting the heavy chromate according to claim 1, characterized in that, In S4, the Cr(VI) concentration is quantified by the signal intensity change, specifically, the Cr(VI) concentration is quantified by the peak intensity change at 1232 cm -1 .

6. The method for detecting the heavy chromate according to claim 1, characterized in that, The detection limit of the method is 1.6 fmol / L, and the linear range is 1.0 x 10 -14 ~1.0 x 10 -4 mol / L.

7. Use of a method for the detection of hexavalent chromium according to any one of claims 1 to 6 based on surface-enhanced Raman spectroscopy, characterized in that, The method is suitable for rapid detection of Cr(VI) in the fields of environmental monitoring, food safety and drug analysis.

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