A method for detecting heavy metals in water by using membrane evaporation and monochromatic aggregate X-ray fluorescence spectrometer

Abstract

The present application relates to the technical field of heavy metal detection, and particularly relates to a method for detecting heavy metals in water by using membrane evaporation and monochromatic X-ray fluorescence spectrometer, comprising the following steps: (1) taking a certain volume of water sample and adding an internal standard; (2) placing a polyamide membrane in a pretreatment position and performing evaporation 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 the solid residues on the polyamide membrane, and collecting fluorescence signals of the heavy metal elements; (4) performing qualitative and quantitative analysis on the heavy metals in the water sample by using an internal standard algorithm combined with the fluorescence signals. The method can realize the analysis level of 0.1 ppb of the heavy metals in the water sample by using membrane evaporation and monochromatic X-ray fluorescence spectrometer to detect the heavy metals in water, and further combining the membrane enrichment method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heavy metal detection, and particularly relates to a method for detecting heavy metals in water by combining membrane evaporation and monochromatic aggregation X-ray fluorescence spectrometer. BACKGROUND

[0002] The content of heavy metals in surface water is in ppb level. The X-ray fluorescence spectrometry cannot meet the analysis requirement of surface water because its detection lower limit is not enough, and is generally applied to the analysis requirement of ppm level. In this case, different manufacturers take various means and ways to solve this problem. For example, various methods based on the principle of enrichment of cation and anion exchange resins, and large volume of water solution are used to solve the rapid analysis requirement of heavy metals in surface water to a certain extent. However, because the methods are based on the principle of ion resin, they are affected by various external factors such as pH, high salinity and colloid adsorption in water, and cannot completely solve the analysis requirement. The traditional XRF analysis manufacturers have also tried to use evaporation method for analysis, but because the precision of conventional XRF is not enough, a large volume of evaporation is needed, which cannot meet the on-site time requirement, and is not practical. Therefore, in order to achieve the goal of rapid detection of low content heavy metal elements in water, a pretreatment method with rapid, wide spectrum and strong anti-interference ability and a new XRF analysis technology are needed to break through.

[0003] The traditional heavy metal water quality analyzer such as anodic stripping voltammetry is an electrode enrichment method, different electrodes are used for different elements, and when unknown elements in water samples are analyzed, it is passive and needs to be analyzed multiple times. Meanwhile, it is soluble state analysis. The ion exchange resin needs to be applied according to the characteristics of the resin, and is divided into anion and cation. Different forms need to use different resins, and at the same time, the particulate matters in the sample need to be filtered in advance to avoid blockage. There are relevant experimental data. The traditional ion resin analysis method is affected by pH, and the suitable pH range is 3-10. Strong acid or strong alkali cannot be analyzed. At the same time, different pH has an influence on the result, and the relative error is generally about 30%.

[0004] Most of the existing heavy metal enrichment technologies are ion resin exchange methods, and some technologies involve evaporation methods, but the evaporation is carried out on a silicon wave plate; and only laser evaporation is related to membrane evaporation, such as the Chinese invention patent with the application number 202110666288.6, which discloses a high-sensitivity X-ray fluorescence detection method for cadmium and other elements in water, which is convenient to operate, high in detection accuracy, and low in detection cost; comprising the following steps: S1, collecting the water sample to be detected, filtering with a 0.45um membrane for detection; S2, adding the water sample to be detected drop by drop to the adsorption material; 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; S4, X-ray radiation is performed on the residual solid salt on the adsorption material, and the characteristic X-ray fluorescence released by the residual solid salt is received to obtain X-ray fluorescence spectrum data; S5, according to the X-ray fluorescence spectrum data, the heavy metals in the water sample to be detected are qualitatively and quantitatively analyzed. The patent uses a peristaltic pump to send the sample, and the laser method is from top to bottom, directly radiating the water sample, vaporizing the sample on the surface, and leaving the residual solid or metal in the liquid on the membrane surface, and then testing the membrane. In the laser membrane evaporation method, the high molecular material film is mentioned, including some examples of polysulfone film, triacetyl cellulose film, tetracetyl cellulose film, cellulose acetate film, aromatic polyhydrazide film and aromatic polyamide film. At present, this technology is still in the theoretical stage and has not been maturely applied. In the laser evaporation method, the required water sample volume is large, about 10-50mL, and the actual use precision and efficiency are insufficient. SUMMARY

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

[0006] The purpose of the present application is achieved by the following technical scheme: a method for detecting heavy metals in water by combining membrane evaporation with a monochromatic X-ray fluorescence spectrometer, comprising the following steps:

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

[0008] (2) Place the polyamide membrane in the pretreatment position, use the ceramic heating sheet to gradually heat the polyamide membrane, and use the high-precision metering pump to gradually drip the water sample above the polyamide membrane for evaporation treatment until all the water sample is 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) Take out the polyamide membrane, perform X-ray radiation on the solid residues on the polyamide membrane, and collect the fluorescence signal of the heavy metal elements;

[0010] (4) Qualitative and quantitative analysis of heavy metals in water samples is performed by combining the internal standard algorithm with fluorescence signals.

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

[0012] Preferably, in step (2), the thickness of the polyamide film is 5-15 μm. When heating the film using a ceramic heating element, some films are too thick to conduct heat effectively, resulting in low efficiency; while films that are too thin are prone to melting. Therefore, considering both thermal conductivity and resistance to melting, the film was improved. A polyamide film is used, and its thickness is controlled within 5-15 μm, ensuring that the physical properties of the film do not change during heating, while also allowing for better evaporation of the liquid sample from the film surface.

[0013] Preferably, in step (2), the ceramic heating element is gradually heated from room temperature to 110-130°C at a heating rate of 1-2°C / second. Gradually heating the ceramic heating element from room temperature to 110-130°C at a heating rate of 1-2°C / second allows for better control of the flow rate connection between evaporation and titration, achieving a minimum automated 10µL titration.

[0014] Preferably, in step (2), the water sample is dispensed with a precision of 0.01-0.05 mL and a dispensing rate of 0.01-0.03 mL / min. To ensure proper control of the flow rate transition between evaporation and titration, high-precision flow rate control is required, which can achieve a minimum automated titration of 10 μL.

[0015] Preferably, in step (2), internal standard correction is used during evaporation. During evaporation, some splashing is unavoidable. Using internal standard correction can improve the accuracy of quantitative analysis using X-ray fluorescence spectrometry, and can also improve work efficiency and the reliability of analysis results through computer-aided calculations.

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

[0017] Preferably, in step (3), the X-rays are monochromatic focused X-rays. By using monochromatic focused X-rays, it is possible to achieve an analytical level of heavy metals in water samples at the 0.1 ppb level.

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

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

[0020] The beneficial effects of this invention are as follows: The method of this invention uses a ceramic heating element to gradually heat the membrane. By using a polyamide membrane, the physical properties of the membrane do not change during heating, while also effectively evaporating the liquid sample on the membrane surface. Simultaneously, a high-precision metering pump is used for micro-level, step-by-step dripping, with a dripping accuracy controllable to 0.01-0.05 mL. This results in a higher concentration of solid residues, less volatilization, and higher enrichment efficiency. After only 0.5-1.0 mL of sample has been gradually evaporated, the solid salts and metal elements will be focused within a light spot within 10 mm, causing the trace amounts of metals or solid salts dispersed in the liquid to aggregate. A monochromatic focused X-ray fluorescence spectrometer is used to irradiate the light spot, collecting the fluorescence signals of heavy metal elements for qualitative and quantitative analysis.

[0021] The method of this invention employs membrane evaporation, resulting in a relatively clean membrane background. The monochromatic focused X-ray fluorescence spectrometer uses monochromatic light radiation, which also has a relatively clean spectral background and very low background signal value. This can improve the traditional XRF signal from the ppm level to the 0.01ppm level. Combined with the membrane enrichment method, it can achieve the analytical level of heavy metals in water samples at the 0.1ppb level.

[0022] The membrane evaporation method of this invention leverages the broad-spectrum characteristics of XRF, enabling comprehensive analysis of all elements in a single step. It eliminates the need for pretreatment with different electrodes or ion exchange resins for different elements, a problem common in traditional methods. It also overcomes interference from factors such as pH and high salinity, achieving comprehensive, soluble multi-element analysis with experimental data controlled to a relative error of 10%. Simple filtration before sample injection allows for soluble analysis; even without filtration, total heavy metal content can be directly determined. Furthermore, on-site analysis requires no pH adjustment, enabling rapid and accurate quantitative analysis of heavy metals in various matrices, including surface water, industrial wastewater, and high-salinity seawater. Detailed Implementation

[0023] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0024] Example 1

[0025] A method for detecting heavy metals in water using membrane evaporation coupled with monochromatic focusing X-ray fluorescence spectrometry includes the following steps:

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

[0027] (2) Place the polyamide membrane in the pretreatment position, use a ceramic heating plate to gradually heat the polyamide membrane, use a high-precision metering pump to gradually drip water sample above the polyamide membrane, and perform evaporation treatment until all water sample is dripped, so that the heavy metal elements in the water sample are enriched on the polyamide membrane in the form of solid residue.

[0028] (3) Remove the polyamide film, irradiate the solid residue on the polyamide film with X-rays, and collect the fluorescence signals of heavy metal elements;

[0029] (4) Qualitative and quantitative analysis of heavy metals in water samples is performed by combining the internal standard algorithm with fluorescence signals.

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

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

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

[0033] In step (2), the water sample is dispensed with a precision of 0.01 mL and a dispensing rate of 0.01 mL / min.

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

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

[0036] In step (3), the X-rays are monochromatic focused X-rays.

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

[0038] In step (4), the detection of heavy metals in the water sample includes 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 embodiment 1 is that in step (1), the volume of the water sample is 0.8 mL.

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

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

[0043] In step (2), the water sample is dispensed with a precision of 0.03 mL and a dispensing rate of 0.02 mL / min.

[0044] Example 3

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

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

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

[0048] In step (2), the water sample is dispensed with a precision of 0.05 mL and a dispensing rate of 0.03 mL / min.

[0049] Comparative Example 1

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

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

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

[0053] S3. The water sample to be tested on the adsorption material is dried by laser to make the heavy metal elements in the water sample accumulate on the adsorption material in the form of residual solid salt. The power of laser evaporation is 8KW.

[0054] S4. Expose the residual solid salt on the adsorbent material to X-ray radiation and receive the characteristic X-ray fluorescence emitted by the residual solid salt to obtain X-ray fluorescence spectral data.

[0055] S5. Based on the X-ray fluorescence spectroscopy data, perform qualitative and quantitative analysis of heavy metals in the water sample to be tested.

[0056] Examples 1-3 and Comparative Example 1 were used to detect the detection limits of four heavy metals, Cr, As, Cd and Pb, in water samples. The detection results are shown in Appendix Table 1.

[0057] detection element 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 table above, the method of detecting heavy metals in water by combining membrane evaporation with monochromatic focusing X-ray fluorescence spectrometry of the present invention has a significantly improved detection limit compared with the existing laser evaporation enrichment and detection method, and only 0.5-1.0 mL of water sample is needed to achieve the analytical level of heavy metals in water samples at the 0.1 ppb level.

[0059] The actual detection results of water sample A, water sample B, and water sample C using the methods of Examples 1, 2, and 3 of this invention are shown in the table below:

[0060]

[0061]

[0062] The method of this invention employs membrane evaporation, resulting in a relatively clean membrane background. The monochromatic focused X-ray fluorescence spectrometer uses monochromatic light radiation, which also has a relatively clean spectral background and very low background signal value. This can improve the traditional XRF signal from the ppm level to the 0.01ppm level. Combined with the membrane enrichment method, it can achieve the analytical level of heavy metals in water samples at the 0.1ppb level.

[0063] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for detecting heavy metals in water by combining membrane evaporation with monochromatic focusing X-ray fluorescence spectrometry, characterized in that: Includes the following steps: (1) Take a certain volume of water sample and add an internal standard; (2) Place the polyamide membrane in the pretreatment position, use a ceramic heating plate to gradually heat the polyamide membrane, use a high-precision metering pump to gradually drip water sample above the polyamide membrane, and perform evaporation treatment until all water sample is dripped, so that the heavy metal elements in the water sample are enriched on the polyamide membrane in the form of solid residue. (3) Remove the polyamide film, irradiate the solid residue on the polyamide film with X-rays, and collect the fluorescence signal of heavy metal elements; (4) Qualitative and quantitative analysis of heavy metals in water samples was performed by combining the internal standard algorithm with fluorescence signals; In step (1), the volume of the water sample is 0.5-1.0 mL; in step (2), the ceramic heating element is gradually heated from room temperature to 110-130 °C at a heating rate of 1-2 °C / second; in step (2), the dropping accuracy of the water sample is 0.01-0.05 mL, and the dropping speed is 0.01-0.03 mL / min; in step (2), the thickness of the polyamide film is 5-15 µm; in step (2), internal standard correction is used during evaporation; in step (3), the X-ray is monochromatic focused X-ray; in step (3), the solid residue on the polyamide film is focused into a spot with a spot size of 5-10 mm; in step (4), the detection limit for heavy metals in the water sample is at the 0.1 ppb level.

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

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