Method for detecting heavy metals in water by combining membrane evaporation drying and monochromatic aggregation X-ray fluorescence spectrophotometer

Abstract

The invention relates to the technical field of heavy metal detection, in particular to a method for detecting heavy metal in water by combining membrane evaporation drying and a monochromatic aggregation X-ray fluorescence spectrophotometer, which comprises the following steps: (1) taking a certain volume of water sample, and adding an internal standard; (2) placing a polyamide membrane at the pretreatment position, and carrying out evaporation drying treatment, so that heavy metal elements in the water sample are enriched on the polyamide membrane in the form of solid residues; (3) taking out the polyamide membrane, performing X-ray radiation on solid residues on the polyamide membrane, and collecting fluorescence signals of heavy metal elements; and (4) carrying out qualitative and quantitative analysis on the heavy metals in the water sample by combining an internal standard algorithm with a fluorescence signal. According to the method disclosed by the invention, the heavy metals in the water are detected by combining membrane evaporation drying and a monochromatic gathering X-ray fluorescence spectrometer, and the 0.1 ppb-level analysis level of the heavy metals in the water sample can be realized by combining a membrane enrichment method.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal detection, and in particular to a method for detecting heavy metals in water by combining membrane evaporation and monochromatic focusing X-ray fluorescence spectrometer. Background Art

[0002] The content of heavy metals in surface water is at the ppb level. Because of its insufficient detection limit, X-ray fluorescence spectrometry is generally used for ppm-level analysis, which cannot meet the analysis needs of surface water. In this case, different manufacturers have adopted various means and methods to solve this problem, such as various methods based on the principle of enrichment of anion and cation exchange resins, using large volumes of aqueous solutions, which can solve the rapid analysis needs of heavy metals in surface water to a certain extent. However, because it is based on the principle of ion resins, it is affected by various external factors such as pH, high salinity, and colloidal adsorption in water bodies, and cannot completely meet the analysis needs. Traditional XRF analysis manufacturers have also tried to use evaporation to analyze, but because the conventional XRF accuracy is not enough, a large volume of evaporation is required, resulting in the inability to meet the on-site timeliness and not being realistic. Therefore, in order to achieve the goal of rapid on-site detection of low-content heavy metal elements in water bodies, it is necessary to simultaneously achieve a rapid, broad-spectrum, and anti-interference pretreatment method and a breakthrough in the method of new XRF analysis technology.

[0003] Traditional heavy metal water quality analysis instruments, such as anodic stripping voltammetry, use electrode enrichment methods. Different electrodes target different elements. When analyzing unknown elements in water samples, they will be relatively passive and require multiple analyses. At the same time, soluble state analysis is performed. The use of ion exchange resins needs to be applied according to the characteristics of the resin. They are divided into anions and cations. Different resins are required for different forms. At the same time, during analysis, particulate matter in the sample needs to be filtered out in advance to avoid clogging. There are relevant experimental data. The traditional ion resin analysis method is affected by pH. The suitable pH range is 3-10. Strong acids or strong bases cannot be analyzed. At the same time, different pH values ​​also affect the results, and the relative error is generally around 30%.

[0004] Most of the existing heavy metal enrichment technologies are ion resin exchange methods, and some technologies involve evaporation, but the evaporation is performed on a silicon wave plate; and the only method related to membrane evaporation is laser evaporation. For example, the Chinese invention patent with application number 202110666288.6 discloses a high-sensitivity X-ray fluorescence detection method for elements such as cadmium in water, which is easy to operate, has high detection accuracy, and reduces detection costs; it includes the following steps: S1. Collect the water sample to be detected and filter it with a 0.45um membrane for detection; S2. Add the water sample to be detected drop by drop onto the adsorption material; S3. Use a laser to evaporate the water sample to be detected on the adsorption material so that the heavy metal elements in the water sample are enriched on the adsorption material in the form of residual solid salts; S4. X-ray the residual solid salt on the adsorption material, and receive the characteristic X-ray fluorescence released by the residual solid salt to obtain X-ray fluorescence spectrum data; S5. According to the X-ray fluorescence spectrum data, qualitative and quantitative analysis of the heavy metals in the water sample to be detected. This patent uses a peristaltic pump to deliver samples. The laser method is to illuminate from top to bottom, directly irradiate the water sample, vaporize the sample on the surface, so that the residual solid or metal in the liquid remains on the membrane surface, and then test the membrane. The laser membrane evaporation method mentions polymer material membranes, some of which are polysulfone membranes, tris(butylene) acetate membranes, tetras(butylene) acetate membranes, cellulose acetate membranes, aromatic polyhydrazide membranes, and aromatic polyamide membranes. At present, this technology is still in the theoretical stage and has not been maturely applied. In addition, in the laser evaporation method, the required water sample volume is relatively large, about 10-50mL, and the accuracy and efficiency of actual use are insufficient. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies in the prior art, the object of the present invention is to provide a method for detecting heavy metals in water by combining membrane evaporation and monochromatic focusing X-ray fluorescence spectrometer.

[0006] The object of the present invention is achieved by the following technical solution: A method for detecting heavy metals in water by combining membrane evaporation and monochromatic focusing X-ray fluorescence spectrometer, comprising the following steps:

[0007] (1) Take a certain volume of water sample and add internal standard;

[0008] (2) placing a polyamide membrane at a pretreatment position, gradually heating the polyamide membrane with a ceramic heating plate, and gradually dripping a water sample on the polyamide membrane with a high-precision metering pump for evaporation until all the water samples have been dripped, so that the heavy metal elements in the water sample are enriched on the polyamide membrane in the form of solid residues;

[0009] (3) taking out the polyamide membrane, subjecting the solid residue on the polyamide membrane to X-ray radiation, and collecting the fluorescence signal of the heavy metal elements;

[0010] (4) The internal standard algorithm is combined with the fluorescence signal to perform qualitative and quantitative analysis of heavy metals in water samples.

[0011] Preferably, in step (1), the volume of the water sample is 0.5-1.0 mL. The method of the present invention can achieve an analysis level of 0.1 ppb level for heavy metals in the water sample by dripping only 0.5-1.0 mL of the water sample.

[0012] Preferably, in step (2), the thickness of the polyamide film is 5-15 μm. When a ceramic heating plate is used to heat the film, some films are too thick to conduct heat, the efficiency is too low, and too thin to melt. Therefore, considering the thermal conductivity and the difficulty in melting, the film is improved. A polyamide film is used, and its thickness is controlled to be 5-15 μm, so that the physical properties of the film will not change when it is heated, and the liquid sample on the surface of the film can be evaporated well.

[0013] Preferably, in step (2), the ceramic heating plate is gradually heated from room temperature to 110-130° C. at a heating rate of 1-2° C. / second. The ceramic heating plate is gradually heated from room temperature to 110-130° C. at a heating rate of 1-2° C. / second, so that the connection between the flow rate of evaporation and titration can be well controlled, and a minimum automated titration of 10uL can be achieved.

[0014] Preferably, in step (2), the dripping precision of the water sample is 0.01-0.05 mL, and the dripping speed is 0.01-0.03 mL / min. In order to control the connection between the flow rate of evaporation and titration, high-precision flow rate control is required, and the minimum automated titration of 10 uL can be achieved.

[0015] Preferably, in step (2), internal standard correction is used during evaporation. During evaporation, some splashing is inevitable, and internal standard correction can improve the accuracy of quantitative analysis by X-ray fluorescence spectrometer, and can also improve work efficiency and reliability of analysis results through computer-assisted calculation.

[0016] Preferably, in step (3), the solid residue on the polyamide membrane is focused into a light spot with a size of 5-10 mm. By focusing the solid salt and metal elements on the polyamide membrane into a light spot within 10 mm, the detection accuracy is improved.

[0017] Preferably, in step (3), the X-ray is a monochromatic focused X-ray. By using monochromatic focused X-ray, an analysis level of 0.1 ppb level of heavy metals in water samples can be achieved.

[0018] Preferably, in step (4), the detection limit of heavy metals in the water sample is at the 0.1 ppb level.

[0019] Preferably, in step (4), heavy metals detected in the water sample include manganese, iron, tin, cobalt, copper, zinc, chromium, nickel, lead, cadmium, mercury and non-metallic arsenic.

[0020] The beneficial effects of the present invention are as follows: the method of the present invention gradually heats the membrane by using a ceramic heating plate, and by using a polyamide membrane, the physical properties of the membrane will not change when heated, and the liquid sample on the surface of the membrane can be evaporated well. At the same time, a high-precision metering pump is used for gradual dripping at a microliter level, and the dripping accuracy can be controlled to be 0.01-0.05mL, the solid residue is relatively enriched, the volatilization is less, and the enrichment efficiency is higher. After only 0.5-1.0mL of sample is gradually evaporated, the solid salt and metal elements therein will be focused in a light spot within 10mm, so that the metal or solid salt that is itself dispersed in the liquid in trace amounts will be gathered together; a monochromatic focusing X-ray fluorescence spectrometer is used to radiate the light spot, and the fluorescence signal of the heavy metal elements is collected for qualitative and quantitative analysis.

[0021] The method of the present invention adopts membrane evaporation, and the background of the membrane itself is relatively clean. The monochromatic focusing X-ray fluorescence spectrometer adopts monochromatic light radiation, and its spectral background is also relatively clean, and the background signal value is also very low. The traditional XRF signal can be increased from the ppm level to the 0.01ppm level. Combined with the membrane enrichment method, the analysis level of heavy metals in water samples can be achieved at the 0.1ppb level.

[0022] The membrane evaporation method of the present invention takes advantage of the broad spectrum of XRF and realizes a one-time full analysis of all elements. It solves the problem that the traditional method needs to use different electrodes or different ion resins for pretreatment of different elements, and solves the interference of various factors such as pH and high salinity. It can realize full-quantity, soluble multi-element analysis, and the experimental data can be controlled to a relative error of 10%. Before sampling, it can also be simply filtered and analyzed in a soluble state; even without filtering, the total amount of heavy metals can be directly determined. At the same time, there is no need to adjust the pH for on-site analysis, and rapid and accurate quantitative analysis of heavy metals in different matrices such as surface water, enterprise wastewater discharge, and high-salt seawater can be achieved. DETAILED DESCRIPTION

[0023] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments, and the contents mentioned in the implementation modes are not intended to limit the present invention.

[0024] Example 1

[0025] A method for detecting heavy metals in water by combining membrane evaporation and monochromatic X-ray fluorescence spectrometer comprises the following steps:

[0026] (1) Take a certain volume of water sample and add internal standard;

[0027] (2) placing a polyamide membrane at a pretreatment position, gradually heating the polyamide membrane with a ceramic heating plate, and gradually dripping a water sample on the polyamide membrane with a high-precision metering pump for evaporation until all the water samples have been dripped, so that the heavy metal elements in the water sample are enriched on the polyamide membrane in the form of solid residues;

[0028] (3) taking out the polyamide membrane, subjecting the solid residue on the polyamide membrane to X-ray radiation, and collecting the fluorescence signal of the heavy metal elements;

[0029] (4) The internal standard algorithm is combined with the fluorescence signal to perform qualitative and quantitative analysis of heavy metals in water samples.

[0030] In the step (1), the volume of the water sample is 0.5 mL.

[0031] In the step (2), the thickness of the polyamide film is 5 μm.

[0032] In the step (2), the ceramic heating plate is gradually heated from room temperature to 110° C. at a heating rate of 1° C. / s.

[0033] In the step (2), the dripping accuracy of the water sample is 0.01 mL, and the dripping speed is 0.01 mL / min.

[0034] In the step (2), internal standard correction is used during evaporation to dryness.

[0035] In the step (3), the solid residue on the polyamide film is focused into a light spot, and the size of the light spot is 5-10 mm.

[0036] In the step (3), the X-ray is a monochromatic focused X-ray.

[0037] In the step (4), the detection limit of heavy metals in the water sample is at the 0.1 ppb level.

[0038] In the step (4), the heavy metals detected in the water sample include manganese, iron, tin, cobalt, copper, zinc, chromium, nickel, lead, cadmium, mercury and non-metallic arsenic.

[0039] Example 2

[0040] The difference between this embodiment and the above-mentioned embodiment 1 is that in step (1), the volume of the water sample is 0.8 mL.

[0041] In the step (2), the thickness of the polyamide film is 10 μm.

[0042] In the step (2), the ceramic heating plate is gradually heated from room temperature to 120° C. at a heating rate of 1.5° C. / s.

[0043] In the step (2), the dripping accuracy of the water sample is 0.03 mL, and the dripping speed is 0.02 mL / min.

[0044] Example 3

[0045] The difference between this embodiment and the above-mentioned embodiment 1 is that in step (1), the volume of the water sample is 1.0 mL.

[0046] In the step (2), the thickness of the polyamide film is 15 μm.

[0047] In the step (2), the ceramic heating plate is gradually heated from room temperature to 130° C. at a heating rate of 2° C. / s.

[0048] In the step (2), the dripping accuracy of the water sample is 0.05 mL, and the dripping speed is 0.03 mL / min.

[0049] Comparative Example 1

[0050] A method for X-ray fluorescence analysis of trace heavy metals in water, comprising the following steps:

[0051] S1. Collect 30 mL of water sample to be tested for testing;

[0052] S2. Add the water sample to be tested drop by drop onto the adsorption material at a rate of 0.1 mL / s;

[0053] S3, using laser to evaporate the water sample to be detected on the adsorption material, so that the heavy metal elements in the water sample are enriched on the adsorption material in the form of residual solid salt, and the power of laser evaporation is 8KW;

[0054] S4, irradiating the residual solid salt on the adsorption material with X-rays, and receiving characteristic X-ray fluorescence released by the residual solid salt to obtain X-ray fluorescence spectrum data;

[0055] S5. Perform qualitative and quantitative analysis on the heavy metals in the water sample to be detected according to the X-ray fluorescence spectrum data.

[0056] Examples 1-3 and Comparative Example 1 respectively tested the detection limits of four heavy metals, Cr, As, Cd, and Pb, in water samples. The test results are shown in Appendix 1.

[0057] Detection elements Example 1 Example 2 Example 3 Comparative Example 1 Nickel (μg / L) 0.3 0.2 0.1 1 Non-metallic arsenic (μg / L) 0.3 0.2 0.1 1 Cadmium (μg / L) 0.3 0.25 0.1 3 Lead (μg / L) 0.2 0.15 0.1 1

[0058] As can be seen from the above table, the method of detecting heavy metals in water by combining membrane evaporation with monochromatic focusing X-ray fluorescence spectrometer of the present invention has a significantly improved detection limit compared with the existing detection after laser evaporation and enrichment, and only 0.5-1.0mL of water sample is needed to achieve an analysis level of 0.1ppb level for heavy metals in water samples.

[0059] The actual test results of water sample A, water sample B and water sample C respectively using the methods of Example 1, Example 2 and Example 3 of the present invention are shown in the following table:

[0060]

[0061]

[0062] The method of the present invention adopts membrane evaporation, and the background of the membrane itself is relatively clean. The monochromatic focusing X-ray fluorescence spectrometer adopts monochromatic light radiation, and its spectral background is also relatively clean, and the background signal value is also very low. The traditional XRF signal can be increased from the ppm level to the 0.01ppm level. Combined with the membrane enrichment method, the analysis level of heavy metals in water samples can be achieved at the 0.1ppb level.

[0063] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention may also be implemented in other ways. Any obvious replacement without departing from the concept of the present invention is within the protection scope of the present invention.

Claims

1. A method for detecting heavy metals in water by combining membrane evaporation and monochromatic X-ray fluorescence spectrometer, characterized in that: The steps include: (1) Take a certain volume of water sample and add internal standard; (2) placing a polyamide membrane at a pretreatment position, gradually heating the polyamide membrane with a ceramic heating plate, and gradually dripping a water sample onto the polyamide membrane with a high-precision metering pump for evaporation until all the water samples have been dripped, so that the heavy metal elements in the water sample are enriched on the polyamide membrane in the form of solid residues; (3) taking out the polyamide membrane, subjecting the solid residue on the polyamide membrane to X-ray radiation, and collecting the fluorescence signal of the heavy metal elements; (4) The internal standard algorithm is combined with the fluorescence signal to perform qualitative and quantitative analysis of heavy metals in water samples.

2. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (1), the volume of the water sample is 0.5-1.0 mL.

3. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (2), the thickness of the polyamide film is 5-15 µm.

4. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic focused X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (2), the ceramic heating plate is gradually heated from room temperature to 110-130°C at a heating rate of 1-2°C / second.

5. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (2), the dripping accuracy of the water sample is 0.01-0.05 mL, and the dripping speed is 0.01-0.03 mL / min.

6. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (2), internal standard correction is used during evaporation.

7. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic focused X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (3), the solid residue on the polyamide film is focused into a light spot, and the size of the light spot is 5-10 mm.

8. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic focused X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (3), the X-ray is a monochromatic focused X-ray.

9. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic focused X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (4), the detection limit of heavy metals in the water sample is at the 0.1 ppb level.

10. The method for detecting heavy metals in water by combining membrane evaporation and monochromatic focusing X-ray fluorescence spectrometer according to claim 1, characterized in that: In the step (4), the heavy metals detected in the water sample include manganese, iron, tin, cobalt, copper, zinc, chromium, nickel, lead, cadmium, mercury and non-metallic arsenic.

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