On-site in-situ detection method for gaseous methyl arsenic based on surface enhanced Raman spectroscopy

Abstract

The invention provides an on-site in-situ detection method for gaseous methyl arsenic based on surface enhanced Raman spectroscopy. The method comprises the following steps: fixing a copper-silver SERS (Surface Enhanced Raman Scattering) substrate in a polytetrafluoroethylene filter membrane clamp; the air pump is connected with an air bag containing methyl arsenic gas, and the air pump is started to extract the gas; taking out the copper-silver SERS substrate which adsorbs the gaseous target object from the filter membrane clamp; a Raman spectrometer is used for detecting the copper-silver SERS substrate adsorbing the gaseous target object, and laser spots are focused on the surface of the copper-silver SERS substrate to obtain an SERS spectrogram; in-situ qualitative and quantitative analysis of gaseous methyl arsenic is carried out based on an SERS spectrogram, and SERS is surface enhanced Raman spectroscopy.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental analysis, and in particular relates to a method for on-site in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy (SERS). Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Mono-, di-, and trimethylarsenic (MMA, DMA, and TMA) are trivalent gaseous arsenic compounds with some toxicity. Compared to other arsenic compounds adsorbed in water or soil, gaseous methylarsenic is more mobile and bioavailable. Exposure to methylarsenic gas can harm human health, necessitating both qualitative and quantitative testing for gaseous methylarsenic.

[0004] Existing methods for detecting gaseous methylarsenic mainly include gas chromatography-mass spectrometry (GC-MS), gas chromatography-atomic fluorescence spectrometry (GC-AFS), and gas chromatography-electron capture detection (GC-EDC). However, these methods have the following shortcomings:

[0005] (1) If on-site testing is carried out, sophisticated instruments and high costs are required. The instrument gas cylinders cannot be transported by airplane, and professional personnel are required to tune the instrument on-site and prevent the instrument gas line from being contaminated.

[0006] (2) If samples are collected first and then transported to the laboratory for qualitative and quantitative analysis, a large number of sampling points need to be set up, making it impossible to efficiently conduct a site pollutant distribution survey.

[0007] (3) Gaseous methylarsenic is unstable and may be lost or deteriorated during sampling, transportation and analysis, affecting the accuracy of the test results.

[0008] Therefore, it is urgent to develop a method for on-site real-time detection of gaseous methylarsenic.

[0009] Currently, there are laboratory methods for detecting gaseous methylarsenic, and reports on the use of SERS technology for detecting arsenic in water. However, there is a lack of research on in-situ detection of gaseous methylarsenic. When portable Raman spectroscopy is combined with SERS technology, its unique advantages and performance overcome the shortcomings of existing methods for detecting gaseous methylarsenic, providing a powerful tool for real-time on-site detection of trace gaseous methylarsenic in the environment. Summary of the Invention

[0010] To overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for on-site in-situ detection of gaseous methylarsenic based on surface-enhanced Raman spectroscopy, which can perform in-situ detection of methylarsenic gas in a real environment without the need for pretreatment of the gas sample. The gas in the atmosphere can be directly extracted, thereby achieving specific qualitative and quantitative analysis of methylarsenic in the air.

[0011] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0012] In a first aspect, a method for in-situ detection of gaseous methylarsenic based on surface-enhanced Raman spectroscopy is disclosed, comprising:

[0013] The copper-silver SERS substrate was fixed in a polytetrafluoroethylene filter holder;

[0014] Connect the polytetrafluoroethylene filter membrane clamp to the air pump with a hose and start the air pump to extract gas;

[0015] Take out the copper-silver SERS substrate after adsorbing the gaseous target from the filter membrane holder;

[0016] A portable Raman spectrometer was used to detect the copper-silver SERS substrate after adsorbing the gaseous target. The laser spot was focused on the surface of the copper-silver SERS substrate to obtain the SERS spectrum.

[0017] In situ qualitative and quantitative analysis of gaseous methylarsenic was performed based on SERS spectra, where SERS stands for surface enhanced Raman spectroscopy.

[0018] As a further technical solution, the copper-silver SERS substrate is prepared as follows:

[0019] (1) Immersing the copper mesh in a culture dish containing AgNO3 solution for a certain period of time to allow in-situ growth of silver nanodendrites;

[0020] Copper and Ag in AgNO3 solution + A replacement reaction occurs, and Ag + Reduced to Ag element, Ag + Silver nanodendrites were grown in situ on the surface of the copper mesh to adsorb gaseous methylarsenic.

[0021] (2) The copper mesh covered with silver nanodendrites was removed and dried to be used as a SERS substrate.

[0022] As a further technical solution, the SERS intensity of the characteristic peak is obtained by Raman spectroscopy, and the concentration of DMA gas in the gas is calculated by the linear relationship (1);

[0023] Log 10 (Raman Intensity) = 0.89 × Log10 (Concentration)+1.78 (1)

[0024] Raman Intensity refers to the Raman intensity, which generally refers to the height of the characteristic peak in the Raman spectrum; Concentration refers to the concentration of the target object.

[0025] As a further technical solution, the mesh number of the copper mesh is 100-1000 meshes and the diameter is 0.1-10 cm.

[0026] As a further technical solution, the concentration of the AgNO3 solution is 5-100 mM and the volume is 1-100 mL.

[0027] As a further technical solution, the copper mesh is immersed in the AgNO3 solution for 2-120 minutes.

[0028] As a further technical solution, the diameter of the polytetrafluoroethylene filter membrane clip is 5-100 mm and the height is 5-100 mm.

[0029] As a further technical solution, the air pump flow rate is 10-5000 mL / min.

[0030] As a further technical solution, the laser wavelength of the Raman spectrometer is 300-800 nm, the power is 1-600 mW, and the integration time is 1-10 s.

[0031] In the second aspect, a system for rapid on-site in-situ detection of gaseous methylarsenic based on surface-enhanced Raman spectroscopy is disclosed, comprising: a copper-silver SERS substrate, a polytetrafluoroethylene filter holder, an air pump, a portable Raman spectrometer, and a processor;

[0032] The copper-silver SERS substrate is fixed in a polytetrafluoroethylene filter membrane holder;

[0033] The polytetrafluoroethylene filter membrane clamp is connected to an air pump via a hose, and the air pump is started to extract gas from the target location;

[0034] The portable Raman spectrometer detects the copper-silver SERS substrate after adsorbing the gaseous target, focuses the laser spot on the surface of the copper-silver SERS substrate to obtain a SERS spectrum and transmits it to the processor;

[0035] The processor performs in-situ qualitative and quantitative analysis of gaseous methylarsenic based on SERS spectra, wherein SERS stands for surface enhanced Raman spectroscopy.

[0036] One or more of the above technical solutions have the following beneficial effects:

[0037] The present invention uses a silver dendrite film grown in situ on a copper mesh as a surface-enhanced Raman spectroscopy (SERS) substrate, fixes it in a polytetrafluoroethylene filter membrane holder, and connects the filter membrane holder to a portable air pump via a PVC plastic hose. When the air pump is turned on, it begins to filter the air, and the highly toxic methylarsenic gas, a trace pollutant in the air, is transported by the air pump to the surface of the copper-silver SERS substrate in the filter membrane holder and adsorbed on the substrate, and then the Raman signal is detected by a portable Raman spectrometer.

[0038] The present method for detecting gaseous methylarsenic can be used for in-situ detection of methylarsenic gas in a real-world environment. No pretreatment of the gas sample is required, and atmospheric gas can be directly extracted, thereby enabling specific qualitative and quantitative analysis of methylarsenic in the air. The filter membrane is lightweight, inexpensive, compact, and easy to carry and store, making it suitable for on-site surveys of methylarsenic outlet distribution and for subsequent laboratory research.

[0039] In the examples presented in this invention, dimethylarsenic (DMA) gas was used as an example, with a detection limit of 4.8 μg / L. This invention combines the advantages of a SERS substrate for efficient adsorption of the target pollutant methylarsenic from gases extracted by a gas pump with the rapid, in-situ detection capabilities of a portable Raman spectrometer, achieving the integration of gaseous arsenic sampling and rapid, on-site detection.

[0040] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0042] Figure 1 Schematic diagram of the SERS process for in situ detection of gaseous methylarsenic.

[0043] Figure 2 The copper mesh and copper-silver SERS substrate are real pictures. It can be seen that the surface of the copper mesh is brown and the surface of the copper-silver SERS substrate is silvery white, indicating that Ag + It is reduced by copper into a single substance and evenly covers the surface of the copper mesh.

[0044] Figure 3 This is a top view of the copper-silver SERS substrate using a scanning electron microscope. From Figure (a), we can see that Ag + The three-dimensional silver nanostructure in the form of dendrites is reduced by copper, and the multi-layer dense silver dendrites are covered on the surface of the copper mesh. As can be seen from Figure (c), the surface of the silver dendrites is relatively smooth and the size is about 320nm-370nm (width).

[0045] Figure 4 This is the XPS spectrum of the copper-silver SERS substrate after adsorbing DMA gas. It can be seen that As and C elements exist, proving that methylarsenic gas can be adsorbed by the copper-silver SERS substrate.

[0046] Figure 5 The SERS spectra (a) and the corresponding linear relationship diagram (b) were measured after the copper-silver SERS substrate adsorbed different concentrations of DMA gas (7.27-290.81 μg / L). The peak at 596.30 cm -1 The main peak at is the As-C vibration of DMA, and its intensity increases with the increase of DMA gas concentration. The linear fitting R 2 Reaching 0.987.

[0047] Figure 6 After the copper-silver SERS substrate adsorbed the same concentration of MMA, DMA, and TMA gases, the SERS spectrum (a) was measured using a portable Raman spectrometer and the result after the spectral data was analyzed using chemometric analysis (b). It can be seen that MMA, DMA, and TMA gases can be distinguished by Raman spectroscopy and chemometric analysis.

[0048] Figure 7 This is the result of Raman detection after the copper-silver SERS substrate adsorbs DMA, AsH3 and other common gases in the air (H2, CH4, SO2, H2S, etc.). From the Raman spectrum, it can be seen that the copper-silver SERS substrate has no new Raman peak after adsorbing other common gases (H2, CH4, SO2, H2S, etc.) and AsH3, but after adsorbing DMA gas, a new Raman peak appears at 596.30 cm -1 A new peak appears at , which indicates that the Cu-Ag SERS substrate is highly selective for gaseous methylarsenic.

[0049] Figure 8 After the copper-silver SERS substrate adsorbed DMA gas with a concentration of 36.4 μg / L, the Raman spectrum at 596.30 cm was measured after 10 points were evenly taken on the substrate surface. -1 The change of peak intensity at the Raman shift. As can be seen from the figure, the RSD of 10 data is 5.47%, proving that the copper-silver SERS substrate has good uniformity.

[0050] Figure 9 The Raman spectra of 596.30 cm-1 were obtained by uniformly taking three points on the surface of the five copper-silver SERS substrates prepared by the same method after the adsorption of DMA gas with a concentration of 36.4 μg / L. -1 The change of peak intensity at the Raman shift. As can be seen from the figure, the RSD of the Raman peak intensity values ​​of the five substrate surfaces is 2.56%, indicating that the copper-silver SERS substrate has good reproducibility.

[0051] Figure 10 (a) shows the Raman spectrum of the copper-silver SERS substrate at 596.30 cm after the substrate was placed in a vacuum bag for different time periods and adsorbed with DMA gas at a concentration of 36.4 μg / L. -1 The change of peak intensity at Raman shift. It can be seen from the figure that the Raman intensity does not decrease significantly with the extension of time in the first 18 days (RSD = 6.81%, n = 3). When the substrate is placed for 18-30 days, it can be seen that with the increase of days, the peak intensity of 596.30cm -1 The peak intensity at the Raman shift decreased from 1160.55 to 756.20, proving that the copper-silver SERS substrate had good stability within the first 18 days.

[0052] Figure 10 (b) shows the Raman spectra at 596.30 cm-1 measured after the copper-silver SERS substrate was adsorbed with DMA gas at a concentration of 36.4 μg / L and then placed for different periods of time. -1 The change of peak intensity at the Raman shift. As can be seen from the figure, there is no significant decrease in Raman intensity within 30 days (RSD = 5.99%, n = 3), proving that the Cu-Ag SERS substrate has good temporal stability after adsorbing DMA gas.

[0053] Figure 11 The chromatogram of gaseous methyl arsenic in 100 mL of absorption liquid detected by liquid chromatography-atomic fluorescence spectrometry (LC-AFS) shows that the actual gas sample collected was dissolved in absorption liquid. It can be seen that there is only one chromatographic peak in the figure, and its retention time is the same as that of dimethyl arsenic (DMA), proving that the actual sample only contains DMA gas. DETAILED DESCRIPTION

[0054] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0055] It should be noted that the terms used herein are for describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present invention.

[0056] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0057] Surface-enhanced Raman spectroscopy (SERS) is a molecular spectroscopy technique highly suitable for on-site detection. By preparing metal nanostructures with specific adsorption and surface enhancement effects, Raman spectra containing target molecular fingerprint information can be obtained. The advantages of SERS technology include high sensitivity, high selectivity, non-destructiveness, real-time detection, and rapid response. It is not only suitable for molecular structure analysis and quantitative detection, but can also be widely used in various fields such as biomedicine and food safety. Compared with large precision instruments, portable Raman spectrometers have the advantages of miniaturization, portability, and low cost. They require little maintenance and can be transported by train, airplane, etc., and can be operated by non-professionals.

[0058] It is difficult to construct a method system based on SERS technology that is easy to operate and can detect methylarsenic gas on site. The core of the exemplary technical solution of this embodiment is to prepare a SERS substrate that has a specific adsorption effect on methylarsenic gas.

[0059] Currently, there is no instrumentation for on-site detection of gaseous methylarsenic. This example technical solution fills this gap. Currently, there are few technical solutions for gas detection using SERS, as most gases cannot adsorb on SERS materials and, therefore, fail to produce Raman spectral signals. Previous SERS detection of arsenic in water typically involved the detection of inorganic trivalent or pentavalent arsenic ions, whose structures and physicochemical properties differ significantly from those of gaseous organic arsenic.

[0060] The overall concept of the present invention:

[0061] First, the present invention uses an in-situ growth method to grow silver nanodendrites on a copper mesh surface, creating a copper-silver SERS substrate. This substrate can in-situ adsorb gaseous methylarsenic and serve as a surface-enhanced Raman substrate, enhancing the Raman signal of the target molecule. Furthermore, to improve the detection limit of gaseous methylarsenic, the SERS technique is combined with a portable air pump. By extending the pumping time and increasing the pumping volume, more targets are adsorbed on the substrate surface, thereby lowering the detection limit and enabling in-situ sampling and simultaneous qualitative and quantitative analysis of gaseous methylarsenic.

[0062] See attached Figure 1 As shown, based on the above concept, a method for in situ detection of gaseous methylarsenic based on surface enhanced Raman high-throughput includes the following steps:

[0063] Step (1) fixing the copper-silver SERS substrate in a polytetrafluoroethylene filter membrane holder;

[0064] Step (2) connecting the air pump to the air bag containing methyl arsenic gas with a PVC plastic hose;

[0065] Step (3) connecting the filter membrane holder of step (1) to an air pump using a PVC plastic hose, and starting the air pump to extract the gas in the air bag; wherein the volume of the extracted gas must be consistent with the actual volume of the gas extracted during actual testing;

[0066] Appendix of this example Figure 5 The calibration curve is generated by pumping 5L of DMA gas at varying concentrations. During actual testing, you should also pump 5L of gas and use the calibration curve to find the corresponding DMA concentration based on the Raman peak intensity. If no signal is detected after pumping 5L, extend the pumping time until a signal is detected. Then, prepare different gas concentrations in the laboratory based on the actual pumped volume, create a calibration curve, and determine the actual gas concentration.

[0067] Step (4) takes out the copper-silver SERS substrate after adsorbing the gaseous target from the filter membrane holder, detects it using a portable Raman spectrometer, focuses the laser spot on the surface of the copper-silver SERS substrate to obtain a SERS spectrum, and performs in situ qualitative and quantitative analysis of the gaseous methylarsenic.

[0068] During qualitative analysis, the Raman spectra detected in the actual environment are compared with the Raman spectra of three types of methylarsenic gases (monomethylarsenic, dimethylarsenic, and trimethylarsenic) prepared in the laboratory to identify which types of methylarsenic gases are contained in the actual gas;

[0069] According to the preferred embodiment of the present invention, in step (1), the copper-silver SERS substrate is prepared as follows:

[0070] (1-1) A copper mesh was cut into a circular shape and immersed in a plastic culture dish containing AgNO3 solution for a certain period of time to allow in situ growth of silver nanodendrites.

[0071] The shape of the copper mesh and the material of the culture dish are merely used as an example. Of course, the copper mesh can also be cut into a desired shape and culture dishes can be made of other materials according to actual conditions.

[0072] (1-2) Take out the copper mesh covered with silver dendrites and use it as a SERS substrate after drying. The preparation steps of the above method are simple, the cost is low, and the prepared substrate has stable properties and is easy to carry to the actual on-site environment for use. The copper-silver SERS substrate prepared with copper mesh as the material is breathable, and the surface of the substrate can specifically adsorb methylarsenic gas. In addition, it is easy to prepare in batches, easy to commercialize, light in weight, small in size, and its properties remain stable for a long time when stored in a vacuum bag. Please refer to the attached Figure 10 As shown in a.

[0073] In step 1), the copper mesh has a mesh size of 100-1000 and a diameter of 1-10 cm. The concentration of the AgNO solution is 1-100 mM and the volume is 1-100 mL. The diameter of the culture dish is 0.5-10 cm. The copper mesh is immersed in the AgNO solution for 2-120 minutes. In step 1), the copper mesh can be dried by blowing nitrogen or by heating in an anaerobic chamber to dry it.

[0074] The above copper mesh size and AgNO3 solution concentration and volume are selected to obtain the optimal conditions for the best Raman signal enhancement effect.

[0075] In situ detection of gaseous methylarsenic:

[0076] Preferably according to the present invention, in step 1), the diameter of the polytetrafluoroethylene filter membrane holder is 40 mm and the height is 66 mm.

[0077] Preferably according to the present invention, in step 3), the air pump flow rate is 500 mL / min.

[0078] According to the preferred embodiment of the present invention, in step 3), the surface enhanced Raman laser has a wavelength of 780-790 nm, a power of 100-110 mW, and an integration time of 3-8 s.

[0079] When selecting the above parameters, the size of the PTFE filter holder should be matched to the diameter of the copper mesh. A high flow rate from the portable air pump will cause the gas to flow too quickly, shortening the adsorption time on the substrate surface and reducing the amount of gas adsorbed for the same volume. A low flow rate will result in a longer extraction time for the same volume of gas.

[0080] The laser light source with the above wavelength is one of the commonly used light sources for Raman detectors.

[0081] Excessively high light source power and long integration times can burn the copper-silver SERS substrate, causing abnormal Raman spectra. Excessively low light source power and short integration times can lead to low Raman signal intensity, increasing the minimum detectable concentration of methylarsenic gas. Therefore, it is necessary to explore the optimal light source power and integration time.

[0082] In the preparation process of the copper-silver SERS substrate of the present invention, firstly, an AgNO3 solution is prepared, and then the cut copper mesh is immersed in the AgNO3 solution. Elemental copper is more active than elemental silver, so copper can react with Ag in the AgNO3 solution. + A replacement reaction occurs, and Ag + Reduced to Ag element. + Silver nanodendrites are in situ grown on the surface of the copper mesh and can adsorb gaseous methylarsenic. The copper-silver SERS substrate obtained by the present invention can also be used as a surface-enhanced Raman substrate to enhance the Raman signal of the adsorbed target molecules.

[0083] In summary, the present invention combines surface-enhanced Raman technology with an air pump device to achieve on-site rapid detection of gaseous methylarsenic. The combination of surface-enhanced Raman technology and an air pump device has the following advantages:

[0084] In the embodiment of the present invention, the copper-silver SERS substrate can enrich gaseous methylarsenic and adsorb methylarsenic gas in the atmosphere onto the substrate surface; as a SERS substrate, the silver nanodendrites loaded on the surface of the copper mesh can enhance the Raman signal, thereby obtaining a Raman spectrum of gaseous methylarsenic; by extending the air pumping time, the pumping volume can be increased, so that more target molecules are adsorbed on the substrate surface, thereby reducing the detection limit of gaseous methylarsenic by SERS technology.

[0085] The method of the present invention is based on a copper-silver SERS substrate, which can adsorb target pollutants in situ and serve as a surface-enhanced Raman substrate to enhance Raman signals, thereby realizing in-situ sampling and simultaneous in-situ qualitative and quantitative analysis of gaseous methylarsenic.

[0086] The method of the present invention is efficient and fast in analysis. It only takes a few seconds to obtain a Raman spectrum using a portable Raman spectrometer, which is very fast and convenient.

[0087] The method of the present invention can simultaneously detect different gaseous methyl arsenics with one spectrum data, thereby realizing in-situ qualitative analysis of gaseous methyl arsenic.

[0088] The method of the present invention is applicable to actual atmospheric environments and has strong anti-interference ability. The method of the present invention has high sensitivity, and the detection limit of DMA detected using a copper-silver SERS substrate is 4.8 μg / L.

[0089] Example 1

[0090] Suitable for the preparation of copper-silver SERS substrates:

[0091] (1) Select a copper mesh with a mesh size of 200 and cut it into a circle with a diameter of 3 cm.

[0092] (2) Place the copper mesh in a culture dish, add 5 mL of 40 mM AgNO3 solution to the dish, and soak for 20 minutes.

[0093] (3) Take out the copper mesh, blow dry it with nitrogen, and place the dried copper-silver substrate in a vacuum bag for storage.

[0094] The appearance of the copper-silver SERS substrate prepared in this embodiment is shown in FIG. Figure 2 From the appearance, it can be seen that the silver nanodendrites are loaded very evenly on the substrate surface.

[0095] The SEM top view of the copper-silver SERS substrate prepared in this embodiment is shown in FIG. Figure 3 ,from Figure 3 In (a), it can be seen that Ag+ is reduced by copper to form a three-dimensional silver nanostructure in the form of dendrites. The formed multi-layer dense silver dendrites cover the surface of the copper mesh. Figure 3 In (c), it can be seen that the surface of the silver crystal is relatively smooth and the size is about 320nm-370nm (width).

[0096] Figure 3 This is the XPS spectrum of the copper-silver SERS substrate after adsorbing DMA gas, which shows the presence of As and C elements.

[0097] Example 2

[0098] A method for rapid in-situ detection of gaseous methylarsenic based on surface-enhanced Raman spectroscopy comprises the following steps:

[0099] (1) Prepare a certain concentration of DMA gas: Prepare DMA gas and dilute it with a certain volume of nitrogen in an air bag.

[0100] (2) The copper-silver SERS substrate prepared in Example 1 was fixed in a polytetrafluoroethylene filter membrane holder, and the filter membrane holder was connected to an air pump using a PVC plastic hose.

[0101] (3) Connect the air pump to the air bag outlet with a PVC plastic hose, start the air pump, and extract the gas in the air bag for 1-30 minutes;

[0102] (4) After adsorbing the gaseous target, the copper-silver SERS substrate was removed from the filter holder and examined using a portable Raman spectrometer. The laser spot was focused onto the surface of the copper-silver SERS substrate to obtain a SERS spectrum for in-situ qualitative and quantitative analysis of gaseous methylarsenic. The laser wavelength was 785 nm, the power was 100-110 mW, and the integration time was 5 s. The SERS intensity of the characteristic peak was obtained through Raman spectroscopy, and the concentration of DMA gas in the gas was calculated using the linear relationship (1).

[0103] Log 10 (Raman Intensity) = 0.89 × Log 10 (Concentration)+1.78 (1)

[0104] Raman Intensity refers to the Raman intensity, which generally refers to the height of the characteristic peak in the Raman spectrum; Concentration refers to the concentration of the target object.

[0105] The linear relationship here is obtained based on the specific parameters in this implementation example. When the actual relevant parameters change, the constants in the linear relationship will also change accordingly.

[0106] The technical solution of this embodiment can calculate the concentration of gaseous methylarsenic in the actual sample based on the constructed linear relationship and the Raman intensity of the actual sample detected on site.

[0107] Figure 4 The SERS spectra (a) and the corresponding linear relationship diagram (b) were measured after the copper-silver SERS substrate adsorbed different concentrations of DMA gas (7.27-290.81 μg / L). The peak at 596.30 cm -1 The main peak is the As-C vibration of DMA, and its intensity increases with the increase of DMA gas concentration. The linear fitting R 2 Reaching 0.987.

[0108] Example 3

[0109] Detection of gaseous methylarsenic in actual sampling in Yangbajing area of ​​Tibet:

[0110] (1) The copper-silver SERS substrate prepared in Example 1 was fixed in a polytetrafluoroethylene filter membrane holder, and the filter membrane holder was connected to an air pump using a PVC plastic hose.

[0111] (2) Start the air pump and extract air for 1-30 minutes;

[0112] (3) The copper-silver SERS substrate, after adsorbing the gaseous target, was removed from the filter holder and examined using a portable Raman spectrometer. The laser spot was focused onto the surface of the copper-silver SERS substrate to obtain a SERS spectrum for in-situ qualitative and quantitative analysis of gaseous methylarsenic. The laser wavelength was 785 nm, the power was 100-110 mW, and the integration time was 5 s. The SERS intensity of the characteristic peak was obtained from the Raman spectrum, and the concentration of DMA gas in the gas was calculated using the linear relationship (1).

[0113] Figure 11 The chromatogram of gaseous methylarsenic in the absorption liquid detected by liquid chromatography-atomic fluorescence spectrometry (LC-AFS) after dissolving an actual sample from the Yangbajing area of ​​Tibet (90.55°E, 30.08°N) in the absorption liquid shows only one chromatographic peak with the same retention time as dimethylarsenic (DMA), proving that the actual sample contains only DMA gas.

[0114] Example 4

[0115] Liquid chromatography-atomic fluorescence spectrometry (LC-AFS) was used to detect the form and content of gaseous methylarsenic in gas samples:

[0116] (1) Preparation of gaseous methyl arsenic absorption solution: 1 mL of concentrated nitric acid and 0.3 mL of 30% H2O2 were added to 100 mL of ultrapure water, mixed well, and then the absorption solution was injected into the gas bag.

[0117] (2) Draw 100 mL of gas sample into the air bag and leave it overnight to allow the gas to fully dissolve in the absorption liquid.

[0118] (3) Liquid chromatography-atomic fluorescence spectrometry (LC-AFS) was used to detect the form and content of gaseous methylarsenic in the absorption liquid, and the concentration of gaseous methylarsenic in the gas sample was calculated.

[0119] Table 1 shows the concentration of gaseous methylarsenic in the air of Yangbajing, Tibet (90.55°E, 30.08°N) in 100 mL of absorption solution detected by liquid chromatography-atomic fluorescence spectrometry (LC-AFS), as well as the Raman spectrum of the air sampled at 596.30 cm -1 The peak intensities at the Raman shifts and the theoretical Raman peak intensities calculated using the linear relationship (1) are shown in the table. The concentrations of DMA gas in the actual sampled gas are 29.1 μg / L, 29.5 μg / L, and 33.3 μg / L (RSD = 7.52%), respectively. The theoretically calculated peak intensities are similar to the actual detection results, demonstrating that the method of the present invention can be used for rapid on-site detection of gaseous methylarsenic.

[0120] Table 1

[0121]

[0122] Example 5

[0123] The method for preparing a copper-silver SERS substrate is the same as that described in Example 1, except that:

[0124] In step (2), the copper mesh was placed in a culture dish, 5 mL of a 1-100 mM AgNO 3 solution was added to the culture dish, and the mesh was soaked for 5-50 minutes.

[0125] The surface properties of the substrates prepared by immersing the copper mesh in AgNO3 solutions of different concentrations vary, and the enhancement effect on the Raman signal is also different. Therefore, it is necessary to explore the concentration condition with the best enhancement effect.

[0126] Example 6

[0127] The purpose of this embodiment is to provide a system for rapid on-site in-situ detection of gaseous methylarsenic based on surface-enhanced Raman spectroscopy, comprising: a copper-silver SERS substrate, a polytetrafluoroethylene filter holder, an air pump, a portable Raman spectrometer, and a processor;

[0128] The copper-silver SERS substrate is fixed in a polytetrafluoroethylene filter membrane holder;

[0129] The polytetrafluoroethylene filter membrane clamp is connected to an air pump via a hose, the air pump is connected to an air bag containing methyl arsenic gas, and the air pump is started to extract the gas in the air bag;

[0130] The Raman spectrometer detects the copper-silver SERS substrate after adsorbing the gaseous target, focuses the laser spot on the surface of the copper-silver SERS substrate to obtain a SERS spectrum and transmits it to the processor;

[0131] The processor performs in-situ qualitative and quantitative analysis of gaseous methylarsenic based on SERS spectra, wherein SERS stands for surface enhanced Raman spectroscopy.

[0132] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A method for in-situ detection of gaseous methylarsenic based on surface-enhanced Raman spectroscopy, characterized in that: include: The copper-silver SERS substrate was fixed in a polytetrafluoroethylene filter holder; Connect the polytetrafluoroethylene filter membrane clamp to the air pump with a hose and start the air pump to extract gas; Take out the copper-silver SERS substrate after adsorbing the gaseous target from the filter membrane holder; A portable Raman spectrometer was used to detect the copper-silver SERS substrate after adsorbing the gaseous target. The laser spot was focused on the surface of the copper-silver SERS substrate to obtain the SERS spectrum. In situ qualitative and quantitative analysis of gaseous methylarsenic was performed based on SERS spectra, where SERS stands for surface enhanced Raman spectroscopy.

2. The method for on-site in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy according to claim 1, characterized in that: The copper-silver SERS substrate is prepared as follows: (1) Immersing the copper mesh in a culture dish containing AgNO3 solution for a certain period of time to allow in-situ growth of silver nanodendrites; Copper and Ag in AgNO3 solution + A replacement reaction occurs, and Ag + Reduced to Ag element, Ag + Silver nanodendrites were grown in situ on the surface of the copper mesh to adsorb gaseous methylarsenic. (2) The copper mesh covered with silver nanodendrites was removed and dried to be used as a SERS substrate.

3. The method for in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy according to claim 1, wherein: The SERS intensity of the characteristic peak was obtained by Raman spectroscopy, and the concentration of DMA gas in the gas was calculated by the linear relationship (1); Log 10 (Raman Intensity)=0.89×Log 10 (Concentration)+1.78(1) Raman Intensity refers to the Raman intensity, which generally refers to the height of the characteristic peak in the Raman spectrum; Concentration refers to the concentration of the target object.

4. The method for in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy according to claim 1, wherein: The mesh size of the copper mesh is 100-1000 mesh and the diameter is 0.1-10 cm.

5. The method for on-site in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy according to claim 1, wherein: The concentration of AgNO3 solution is 5-100mM and the volume is 1-100mL.

6. The method for in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy according to claim 1, wherein: The copper mesh is immersed in the AgNO3 solution for 2-120 minutes.

7. The method for in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy according to claim 1, characterized in that: The diameter of the polytetrafluoroethylene filter membrane holder is 5-100mm and the height is 5-100mm.

8. The method for in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy according to claim 1, wherein: The air pump flow rate is 10-5000mL / min.

9. The method for in-situ detection of gaseous methylarsenic based on surface enhanced Raman spectroscopy according to claim 1, wherein: The laser wavelength of the Raman spectrometer is 300-800 nm, the power is 1-600 mW, and the integration time is 1-10 s.

10. A system for rapid in-situ detection of gaseous methylarsenic based on surface-enhanced Raman spectroscopy, comprising: Copper-silver SERS substrate, polytetrafluoroethylene filter holder, air pump, portable Raman spectrometer and processor; The copper-silver SERS substrate is fixed in a polytetrafluoroethylene filter membrane holder; The polytetrafluoroethylene filter membrane clamp is connected to an air pump via a hose, and the air pump is started to extract gas from the target location; The portable Raman spectrometer detects the copper-silver SERS substrate after adsorbing the gaseous target, focuses the laser spot on the surface of the copper-silver SERS substrate to obtain a SERS spectrum and transmits it to the processor; The processor performs in-situ qualitative and quantitative analysis of gaseous methylarsenic based on SERS spectra, wherein SERS stands for surface enhanced Raman spectroscopy.

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