Method for detecting dichromate based on surface enhanced Raman spectroscopy

Abstract

The invention provides a method for detecting dichromate radicals based on surface enhanced Raman spectroscopy, and belongs to the technical field of analytical chemistry. Comprising the following steps: mixing a to-be-detected sample with a sulfydryl-containing compound solution, and adjusting to an acidic condition, so that dichromate Cr (VI) and the sulfydryl-containing compound are subjected to an oxidation-reduction reaction; constructing an SERS substrate, namely preparing a ZnO / Ag heterostructure substrate; mixing the suspension of the ZnO / Ag heterostructure substrate with a reaction system to obtain a mixed solution, so that the ZnO / Ag heterostructure substrate adsorbs a sulfydryl-containing compound and enhances a Raman signal; dropwise adding the mixed solution to the surface of a solid carrier, acquiring a Raman spectrum signal by using a Raman spectrometer, and quantifying the Cr (VI) concentration through the change of signal intensity. The method realizes rapid and high-sensitivity detection of Cr (VI), has strong selectivity and anti-interference capability, and is suitable for detection in the fields of environmental monitoring, food safety, pharmaceutical analysis and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of analytical chemistry, in particular to a method for detecting dichromate based on surface enhanced Raman spectroscopy. Background Art

[0002] Heavy metal ion pollution poses a significant threat to human health and ecological security. Hexavalent chromium (Cr(VI)) is of particular concern due to its strong oxidizing properties and high toxicity. While traditional detection methods such as inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectroscopy (AAS) are highly accurate, they rely on expensive equipment and are difficult to implement rapidly on-site.

[0003] Surface-enhanced Raman spectroscopy (SERS) technology shows potential for trace detection due to its high sensitivity. However, existing SERS methods generally suffer from poor selectivity and weak anti-interference capabilities, and are particularly susceptible to background signal interference in complex matrices such as traditional Chinese medicine extracts. Furthermore, existing SERS detection methods based on redox reactions suffer from slow reaction kinetics, often exceeding 30 minutes or even taking several hours, and have high detection limits, making them difficult to meet the needs of rapid trace Cr(VI) detection.

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

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

[0006] To achieve the above object, the present invention provides the following solutions:

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

[0008] S1, mixing the sample to be tested with a thiol-containing compound solution, adjusting the solution to an acidic condition, so that dichromate Cr(VI) undergoes an oxidation-reduction reaction with the thiol-containing compound;

[0009] S2, constructing a SERS substrate, i.e. preparing a ZnO / Ag heterostructure substrate;

[0010] S3, mixing the suspension of the ZnO / Ag heterostructure substrate with the reaction system of step S1 to obtain a mixed solution, so that the ZnO / Ag heterostructure substrate adsorbs the thiol-containing compound and enhances the Raman signal;

[0011] S4. Add the mixed solution dropwise onto the surface of the solid support, collect Raman spectral signals using a Raman spectrometer, and quantify the Cr(VI) concentration by the change in signal intensity.

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

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

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

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

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

[0017] Preferably, in S4, the concentration of Cr(VI) is quantified by the change in signal intensity, specifically by the change in 1232 cm -1 The peak intensity change at 100 nm was 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 -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 the rapid detection of Cr(VI) in the fields of environmental monitoring, food safety and drug analysis.

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

[0021] (1) The present invention achieves a significant reduction in 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 reaches equilibrium within 1 minute. Combined with the ZnO / Ag heterostructure substrate's ability 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 prolonged detection time in existing SERS methods, laying the foundation for rapid on-site detection.

[0022] (2) The present invention exhibits ultra-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 drinking water safety standard (1.0 μmol / L) stipulated by the U.S. Environmental Protection Agency. At the same time, the linear range covers 1.0×10 -14 ~1.0×10 -4 mol / L, which enables this method to detect trace amounts of Cr(VI) in the environment and food, meeting the needs of trace detection.

[0023] (3) The present invention utilizes the strong conditional potential of 1.19V of Cr(VI) at pH=1.0 to effectively eliminate Hg 2+ 、Ag + The acidic environment not only inhibits the deposition of coexisting ions but also strengthens the binding between the substrate and the probe through a stable S-metal bond, thereby improving anti-interference performance. This method is also suitable for the rapid detection of Cr(VI) in environmental monitoring, food safety, and pharmaceutical analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

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

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

[0027] Figure 3 The SERS spectrum and selectivity comparison diagram of the reaction between 2-MI and Cr(VI) provided by the present invention; wherein, Figure 3 A in the figure is the SERS image of 2-MI under different conditions. Figure 3 B in the figure is a selective comparison chart;

[0028] Figure 4 The SERS signal change curves under different conditions provided by the present invention are as follows; wherein, Figure 4 A in the figure is the SERS signal change curve under different pH conditions. Figure 4 B in the figure is the SERS signal change curve under different mixing ratio conditions. Figure 4 C in the figure is the SERS signal change curve under different temperature conditions. Figure 4D in the figure is the SERS signal change curve under different concentration conditions;

[0029] Figure 5 The linear relationship diagram of Cr(VI) concentration and SERS signal intensity provided by the present invention is shown in FIG. Figure 5 A in the figure is the SERS image of different Cr(VI) concentrations. Figure 5 B in the figure is the linear fitting curve of Cr(VI) concentration and SERS signal intensity in different concentration ranges;

[0030] Figure 6 This is a histogram of the anti-interference experimental data provided by the present invention. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

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

[0034] S1, mixing the sample to be tested with a thiol-containing compound solution, adjusting the solution to an acidic condition, so that dichromate Cr(VI) undergoes an oxidation-reduction reaction with the thiol-containing compound;

[0035] S2, constructing a SERS substrate, i.e. preparing a ZnO / Ag heterostructure substrate;

[0036] S3, mixing the suspension of the ZnO / Ag heterostructure substrate with the reaction system of step S1 to obtain a mixed solution, so that the ZnO / Ag heterostructure substrate adsorbs the thiol-containing compound and enhances the Raman signal;

[0037] S4. Add the mixed solution dropwise onto the surface of the solid support, collect Raman spectral signals using a Raman spectrometer, and quantify the Cr(VI) concentration by the change in signal intensity.

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

[0039] The mixing time of the suspension of the ZnO / Ag heterostructure substrate and the reaction system is 2 minutes, while the reference Figure 2 The ZnO / Ag heterostructure substrate prepared according to the above scheme has an adsorption time of no more than 2 minutes for mercapto compounds. The surface of the solid support is a silicon wafer, and the Raman spectrometer uses a 785nm laser wavelength. Figure 3 As shown in Figure B, the concentration of Cr(VI) is quantified by the change in signal intensity, specifically: -1 The peak intensity change at 100 nm was 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 a hydrothermal method, and then depositing Ag nanoparticles on the surface of the ZnO nanorods by an in situ chemical reduction method to obtain a ZnO / Ag heterostructure substrate, wherein the suspension concentration of the substrate is 0.1 to 1 mg / mL.

[0041] Based on the above content, the following provides an experimental verification and explanation of the above content through specific implementation methods.

[0042] Example 1

[0043] In this embodiment, Cr(VI) in environmental water samples is detected by the following specific steps:

[0044] Sample pretreatment: Take the Ganjiang River water sample, filter it with a 0.45μm filter membrane to remove suspended matter, and adjust the pH of the filtrate to 1.0 with 1mol / L hydrochloric acid solution. Figure 4 It can be found in A that the SERS signal decay rate is fastest when pH = 1.0, which further verifies the kinetic optimization effect of acidic environment on the oxidation of 2-MI by Cr(VI); Figure 6 Under the acidic condition of pH=1.0 constructed by the present invention, the conditional potential of Cr(VI) reaches 1.19V, which can effectively inhibit Mg 2+ 、Al 3+ The deposition of interfering ions such as Na + , K + , Ca 2+ The interference of the sample (such as ) was significantly limited, ensuring the anti-interference performance of the detection. The final measured spike recovery rate was consistent with that of the pure system.

[0045] Construct the reaction system: add 10 μL of 1.0×10 -11mol / L Cr(VI) standard solution, then add 1mL of 0.5mg / L 2-mercaptoimidazole (2-MI) solution, mix well and react at room temperature for 1 minute. Since Cr(VI) has strong oxidizing properties under acidic conditions, it can undergo redox reaction with the thiol group in 2-MI, resulting in the destruction of the molecular structure of 2-MI, and the 1232cm -1 The Raman peak at 1232 cm is the characteristic peak of the combination of thiol groups in 2-MI and ZnO / Ag substrate. Therefore, as the concentration of Cr(VI) increases, the number of oxidized 2-MI molecules increases, and the number of 2-MI molecules that can combine with the substrate decreases, making the peak at 1232 cm -1 The SERS peak intensity at the Cr(VI) decreases with the increase of Cr(VI) concentration. Figure 3 A in the figure shows the difference in peak intensity between the group with Cr(VI) and the blank group at this shift, which confirms this trend. Figure 4 For C in the sample, the redox reaction can be completed in 1 minute at room temperature (25°C).

[0046] Preparation of SERS substrate and mixing: ZnO nanorods were prepared by hydrothermal method, and then Ag nanoparticles were chemically reduced in situ to prepare ZnO / Ag heterostructure substrate and prepare its suspension; 1 mL of substrate suspension was added to the above reaction system and mixed for 2 minutes to allow the substrate to adsorb 2-MI. Figure 2 , the mixing time of substrate and 2-MI was optimized to be 2 minutes, i.e. Figure 4 The signal stability is best when the mixing ratio is 5:1 in B, and refer to Figure 5 A in the figure, this operation ensures the rapid adsorption of 2-MI by the substrate, that is, the adsorption time is ≤ 2 minutes, which is a good condition for low concentration Cr(VI) (1.0×10 -12 mol / L) provides a basis for signal enhancement.

[0047] Signal acquisition and analysis: The mixed solution was added to the surface of the silicon wafer and the signal was collected using a portable Raman spectrometer equipped with a 785 nm laser. -1 Based on the peak intensity change at Figure 5 The concentration of Cr(VI) was calculated by the linear equation I=-lgC×393.1-1047.4, and the spiked recovery was 93.9% with a relative standard deviation (RSD) of 0.1%. Figure 6 The interference of 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, Cr(VI) in a traditional Chinese medicine sample is detected, and the specific steps are as follows:

[0050] Weigh 2.0g of Astragalus powder, prepare acidified water with pH=1.0 with 1mol / L hydrochloric acid, add 10mL of acidified water to the Astragalus powder, extract by ultrasonication for 30 minutes, centrifuge the extract at 10000rpm for 10 minutes, and take the supernatant; add 0.5g of MgO powder to the supernatant, shake for 10 minutes to adsorb the pigment, filter and adjust the filtrate pH to 1.0. Figure 4 As shown in A, pH = 1.0 can maximize the oxidation potential of Cr(VI), φ' = 1.19 V, combined with Figure 6 In the detection system of the present invention (pH = 1.0, ZnO / Ag heterostructure substrate), even if there are 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 proceed specifically, and the ZnO / Ag substrate does not interfere with the Raman signal enhancement of the target product. The final spike recovery rate is ≥98%, demonstrating that the acidic conditions combined with the substrate characteristics of this method can effectively suppress the influence of interfering substances in the traditional Chinese medicine matrix.

[0051] 1 mL of filtrate was added with different concentrations of Cr(VI) standard solution (spiking level was 1.0×10 -12 ~1.0×10 - 8 mol / L), then add 1mL of 0.5mg / L 2-MI solution and react at room temperature for 1 minute. Add 1mL of ZnO / Ag substrate suspension, mix for 2 minutes and then drop it onto the silicon wafer. The Raman spectrometer parameters used in Example 1 are used to collect signals. Figure 5 A and B in the above analysis, the concentration range covers the low and medium concentration segments of the linear detection interval, where 1.0×10 -10 The recovery rate was 98.7% (RSD = 2.3%) when the mol / L spike was added. Figure 5 The linear fitting result of the low concentration section of A in the HPLC-MS / MS was consistent with the detection limit of 1.6 fmol / L. The components in the Chinese herbal medicine extract did not affect the redox reaction between 2-MI and Cr(VI). -1 The peak intensity decay law is the same as that of the pure system.

[0052] The recoveries at different spike concentrations ranged from 91.1% to 106.9%, with RSDs ≤ 4.2%. -10 mol / L, the recovery rate was 98.7%, RSD = 2.3%, refer to Figure 4 In D, high concentration of Cr(VI) can still cause significant signal attenuation, which is consistent with Figure 5The linear relationship in the high concentration section of B is complementary, which proves the applicability of the method for the detection of Cr(VI) in 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 is used to achieve rapid and highly sensitive detection of Cr(VI), which has strong selectivity and anti-interference ability and is suitable for detection in the fields of environmental monitoring, food safety and drug analysis.

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

[0055] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for detecting dichromate based on surface enhanced Raman spectroscopy, characterized in that: The following steps are involved: S1, mixing the sample to be tested with a thiol-containing compound solution, adjusting the solution to an acidic condition, so that dichromate Cr(VI) undergoes an oxidation-reduction reaction with the thiol-containing compound; S2, constructing a SERS substrate, i.e. preparing a ZnO / Ag heterostructure substrate; S3, mixing the suspension of the ZnO / Ag heterostructure substrate with the reaction system of step S1 to obtain a mixed solution, so that the ZnO / Ag heterostructure substrate adsorbs the thiol-containing compound and enhances the Raman signal; S4. Add the mixed solution dropwise onto the surface of the solid support, collect Raman spectral signals using a Raman spectrometer, and quantify the Cr(VI) concentration by the change in signal intensity.

2. The method for detecting dichromate based on surface enhanced Raman spectroscopy according to claim 1, wherein: In S1, the pH value of the acidic condition is 1.0, and the time of the redox reaction is 1 minute.

3. The method for detecting dichromate based on surface enhanced Raman spectroscopy according to claim 1, characterized in that: The thiol-containing compound is 2-mercaptoimidazole.

4. The method for detecting dichromate based on surface enhanced Raman spectroscopy according to claim 1, characterized in that: In S3, the adsorption time of the mercapto-containing compound on the ZnO / Ag heterostructure substrate is no more than 2 minutes.

5. The method for detecting dichromate based on surface enhanced Raman spectroscopy 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.

6. The method for detecting dichromate based on surface enhanced Raman spectroscopy according to claim 1, characterized in that: In S4, the surface of the solid support is a silicon wafer, and the Raman spectrometer uses a laser wavelength of 785 nm.

7. The method for detecting dichromate based on surface enhanced Raman spectroscopy according to claim 1, characterized in that: In S4, the concentration of Cr(VI) was quantified by the change in signal intensity, specifically: -1 The peak intensity change at 100 nm was used to quantify the Cr(VI) concentration.

8. The method for detecting dichromate based on surface enhanced Raman spectroscopy according to claim 1, characterized in that: The detection limit of this method was 1.6 fmol / L, and the linear range was 1.0 × 10 -14 ~1.0×10 -4 mol / L.

9. An application of the method for detecting dichromate based on surface enhanced Raman spectroscopy according to any one of claims 1 to 8, characterized in that: This method is suitable for the rapid detection of Cr(VI) in the fields of environmental monitoring, food safety and drug analysis.

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