Method and device for determining the content of metal elements in airborne particulate matter

Abstract

The application discloses a method for determining the content of metal elements in air particulate matters, comprising: filter membrane sampling, automatic acid adding, single-tube microwave digestion, cooling, water adding and constant volume operation in a full-automatic microwave digestion instrument, and then sample determination through an inductively coupled plasma mass spectrometer; the method can avoid the influence of human factors on the digestion process, can avoid cross contamination between samples, is favorable for the accuracy and reliability of ICPMS analysis, and is used for detecting the content of metal elements in different air particulate matters; and the method can also eliminate the mass spectrum interference of oxides and divalent ions by using the inductively coupled plasma mass spectrometer, so that a lower detection limit is obtained, and the source of the air particulate matters can be analyzed.

Description

Technical Field

[0001] This application relates to the field of metal element determination technology, and in particular to a method and apparatus for determining the metal element content in airborne particulate matter. Background Technology

[0002] Metal elements in airborne particulate matter are important indicators for environmental quality assessment and health risk assessment. Existing standard methods for determination mostly employ hot plate digestion or traditional microwave digestion, but these methods have the following problems: 1. Large human error: The volume of acid added, heating time, and transfer process rely on human experience, easily leading to poor batch-to-batch reproducibility; 2. High risk of cross-contamination: When processing multiple samples in parallel, acid mist and residues in containers can easily cause elemental contamination; 3. Cumbersome and inefficient process: Multiple transfers and volume adjustments are required, making it difficult to meet the needs of large-scale sample analysis; 4. Limited detection limits: Insufficient sensitivity for trace heavy metals (such as Cd, Hg, and Tl).

[0003] Inductively coupled plasma mass spectrometry (ICPMS) is a key instrument for elemental analysis, boasting advantages such as high sensitivity, low interference, wide dynamic range, good stability, and the ability to simultaneously determine multiple elements. A crucial step in ICPMS analysis is ensuring complete digestion of the analytes into the sample test solution during sample pretreatment, without loss or contamination of the analytical elements. However, sample pretreatment can present numerous challenges and demands highly skilled operators. For instance, the environmental industry standard HJ1315 recommends microwave digestion as the pretreatment method. The specified method for environmental samples (soil) involves adding 10 mL of hydrochloric acid to the sample, heating to initiate initial decomposition, and then adding 15 mL of nitric acid when approximately 5 mL remains (visual observation is required). This is followed by heating until no obvious particles are visible, then adding 5 mL of hydrofluoric acid and heating until the contents reach a non-flowing viscous state. However, the sample test solutions obtained by different operators using this method can vary considerably, especially due to differences in heating time. This can easily lead to the formation of colloids (small particles with diameters of tens of micrometers) in the solution, resulting in inconsistent analytical results. Microwave digestion allows for pre-setting of heating temperature and reaction time, eliminating human error. However, the final transfer and volume adjustment processes still present opportunities for error introduction. The final removal and volume adjustment processes require considerable operator experience; improper operation can lead to sample loss or contamination. Therefore, there is an urgent need for a fully automated, pollution-free, high-throughput, and highly sensitive method for analyzing metal elements in airborne particulate matter.

[0004] To address the aforementioned issues, this application provides a method and apparatus for determining the content of metal elements in airborne particulate matter. By using a fully automated microwave digestion-inductively coupled plasma mass spectrometer, it solves the problems of significant human interference, high pollution risk, and low efficiency in existing technologies. Summary of the Invention

[0005] The purpose of this application is to provide a method and apparatus for determining metal elements in airborne particulate matter. The method employs single-tube microwave digestion, using a fully automated microwave digester to complete the entire process of acid addition, microwave digestion, cooling, volume adjustment, and sample injection. The entire sample digestion process is fully automated, and the volume-adjusted sample solution is directly introduced into an ICP-MS for analysis. Only one sample tube remains open throughout the entire process, completely avoiding cross-contamination between samples. Furthermore, the entire process requires no human intervention, eliminating the influence of human factors, ensuring analytical quality, and fully leveraging the technical advantages of ICP-MS. This allows for the completion of all analytical operations with only sampling, yielding accurate determination results.

[0006] In a first aspect, this application provides a method for determining the content of metal elements in airborne particulate matter, comprising: (1) Select a filter membrane, dry the filter membrane to constant weight, and place it in a sampler to collect air particulate matter samples; (2) After the air particulate matter has been collected for a preset time, the filter membrane containing the air particulate matter sample is removed and dried to constant weight; (3) The sample membrane is placed in the sample tube of the fully automated microwave digester. Using the robotic arm of the fully automated microwave digester, the sample tube is subjected to acid addition, closed microwave digestion, cooling and volume adjustment in sequence to obtain the sample solution to be tested. Then, the sample tube containing the volume-adjusted sample solution to be tested is moved to the injection position of the inductively coupled plasma mass spectrometer and the sample solution to be tested is injected into the inductively coupled plasma mass spectrometer for testing. The inductively coupled plasma mass spectrometer uses a collision reaction cell and has an electronic dilution function. (4) Based on the correspondence between the mass concentration of different metal element standard samples and the signal intensity measured by ICPMS, an external standard working curve is prepared; then, the signal intensity of the test sample solution is obtained by measuring the test sample solution by ICPMS using the electronic dilution method, and the mass concentration of metal elements in the test sample solution is calculated according to the external standard working curve; and the metal element content in the air particulate matter is determined by calculation based on the mass of the air particulate matter sample, the fixed volume of the test sample solution and the mass concentration of metal elements in the test sample solution. The content of metal elements in airborne particulate matter is calculated according to the following formula (1): Concentration of metal element in the sample solution * Volume of the sample solution / Mass of air particulate matter sample * 100% (1) In step (1), the filter membrane is a quartz fiber filter membrane or a polytetrafluoroethylene filter membrane suitable for sampling PM10 and PM2.5 micron particles. The filter membrane is dried in an oven at 75℃-85℃, preferably 80℃, for 20-40 minutes, preferably 30 minutes, and then weighed; then it is kept in the oven for another 5-6 minutes and weighed again. The difference between the two weights is not greater than 0.5mg, which is considered constant weight. Otherwise, the drying step is repeated. The constant weight filter membrane mass is the blank membrane mass.

[0007] In step (2), the collection time for airborne particulate matter is no less than 120 hours, preferably 120-240 hours. The sample membrane containing airborne particulate matter is placed in an oven at 75-90℃, preferably 80℃, for 20-40 minutes, preferably 30 minutes, and weighed. Then, it is kept in the oven for another 5-6 minutes and weighed again. The weight difference between the two weighings is no more than 0.5mg, which is considered constant weight. Otherwise, the drying step is repeated. The constant weight is the mass of the sample membrane.

[0008] The terms "filter membrane for airborne particulate matter samples" and "sample membrane for airborne particulate matter" have the same meaning and can be used interchangeably; they are simply referred to as "sample membrane".

[0009] The difference between the mass of the sample membrane and the mass of the blank membrane from step (1) is the mass of the air particulate matter sample. The mass of the air particulate matter sample is preferably 0.1 g to 0.5 g. If it is higher than 0.5 g, the sample membrane can be divided in two, because if the filter membrane is overloaded, it may not be completely digested; if it is less than 0.1 g, sampling continues, because if the sample amount is too small, the elemental signal is weak and the method detection limit deteriorates.

[0010] In step (3), the acid addition operation involves sequentially adding nitric acid and hydrofluoric acid. The nitric acid has a purity of superior grade or higher and a concentration of not less than 65%. The hydrofluoric acid has a purity of superior grade or higher and a concentration of not less than 40%. The volume ratio of the nitric acid to the hydrofluoric acid is 5:1 to 1:2, preferably 3:1.

[0011] The closed microwave digestion operation employs a stepped temperature ramp. After the microwave digester is shut down, the sample is subjected to fully automated microwave digestion according to the following temperature ramping and holding procedure: a) Keep warm at 110-130℃ for 2-3 minutes; b) Keep warm at 140-160℃ for 5-6 minutes; c) Keep warm at 180-200℃ for 6-8 minutes.

[0012] After microwave digestion, cool the sample tube to a temperature not exceeding 30°C, preferably to room temperature, and then add water to make up the volume.

[0013] The inductively coupled plasma mass spectrometer uses a collision reaction cell and has an electronic dilution function.

[0014] In step (4), the metal elements of different contents in the sample solution to be tested are differentiated by electronic dilution. By electronic dilution of different multiples, the analysis of the main content elements and trace elements can be realized at the same time, and the quantitative analysis of all elements can be completed in one injection.

[0015] The different amounts of metallic elements include major metallic elements (mass concentration range of 0.5-500 mg / L), trace metallic elements (mass concentration range of 50-5000 ng / mL), and other trace metallic elements (mass concentration range of 0.05-10 ng / mL). The major metallic elements include potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), and aluminum (Al); the trace metallic elements include copper (Cu), zinc (Zn), and lead (Pb); the other trace metallic elements include chromium (Cr), nickel (Ni), cadmium (Cd), thallium (Tl), arsenic (As), beryllium (Be), selenium (Se), silver (Ag), and mercury (Hg). The electronic dilution factor of the major metallic elements is greater than that of the trace metallic elements. Preferably, the major metallic elements are diluted 1000-5000 times electronically; the trace metallic elements are preferably diluted 10-50 times electronically; the other trace metallic elements are not diluted.

[0016] Secondly, this application provides a device for determining the content of metal elements in airborne particulate matter, comprising: A sampler is used to hold a filter membrane to collect airborne particulate matter. A fully automated microwave digestion system is used to perform microwave digestion of the airborne particles in the sample tube, and then transfers the sample tube containing the microwave-digested sample solution to an inductively coupled plasma mass spectrometer; and Inductively coupled plasma mass spectrometry is used to determine the metal element content in the airborne particulate matter based on the sample test solution.

[0017] In one possible implementation, the filter membrane is selected from quartz fiber filter membranes or polytetrafluoroethylene filter membranes suitable for PM10 and PM2.5 particulate matter sampling.

[0018] In one possible implementation, the fully automated microwave digester includes a robotic arm that automatically performs acid addition, closed-loop microwave digestion, cooling, volume adjustment, and sample injection. All four operations—acid addition, closed-loop microwave digestion, cooling, volume adjustment, and sample injection—use the same sample tube, ensuring that the sample tube is only opened once during the entire analysis process, effectively preventing cross-contamination between samples.

[0019] In one possible implementation, the fully automated microwave digester includes multiple sets of independent microwave digestion tubes, and under the control of the robotic arm, multiple sample tubes are transferred to different microwave digestion tubes for microwave digestion.

[0020] The multiple independent microwave digestion tubes can perform microwave digestion, cooling, and volume adjustment operations on multiple samples simultaneously, thereby significantly improving sample processing throughput and system operating efficiency, and realizing truly fully automated continuous analysis. It effectively solves the problem that traditional microwave digesters can only process samples synchronously in batches and cannot process them asynchronously. While ensuring that each tube is independent and avoids cross-contamination, it significantly increases the number of samples processed per unit time, meeting the actual needs of large-scale, high-frequency monitoring of ambient air particulate matter.

[0021] In one possible implementation, the inductively coupled plasma mass spectrometer employs a collision reaction cell and has an electronic dilution function.

[0022] The inductively coupled plasma mass spectrometer is connected to a fully automated microwave digester to form a fully automated microwave digestion-inductively coupled plasma mass spectrometer system. This system automatically completes acid addition, single-tube microwave digestion, cooling, volume adjustment, and sample injection. The volume-adjusted sample solution is then introduced into the inductively coupled plasma mass spectrometer, which performs the metal element content analysis.

[0023] In the method of this application, ICPMS employs an external standard method with a working curve for quantitative determination. Through electronic dilution at different folds, the quantitative analysis of all elements is completed in a single measurement. Throughout the entire measurement process, except for sampling, there is no human intervention, completely avoiding the influence of human factors on the digestion process and preventing cross-contamination between samples. This improves the accuracy and reliability of inductively coupled plasma mass spectrometry (ICP-MS) analysis and can be used with various types and apertures of filter membranes to detect the metal element content in different airborne particulate matter. The method of this invention leverages the ability of ICP-MS to eliminate mass spectrometric interference from oxides and divalent ions, resulting in a low detection limit, and can be used for the analysis of the sources of airborne particulate matter. Detailed Implementation

[0024] The present application will now be described in detail through embodiments. The above and other objects, features, and advantages of the present application will become more apparent from the description of the embodiments. It should be understood that the embodiments described are only some embodiments of the present application, and not all embodiments, and the present application is not limited in any way by the described embodiments. The embodiments provide a description of the disclosed aspects to enable any person skilled in the art to implement or use the present application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the present application.

[0025] The sampler used in this embodiment was a ZR-3922 ambient air particulate matter comprehensive sampler. The filter membranes were high-flow PM10 / PM2.5 quartz fiber filter membranes (Beijing Saifulaibo Technology Co., Ltd.) and EMPM2.5-47 polytetrafluoroethylene filter membranes (produced by Hangzhou Kebote Filter Material Co., Ltd.). The sampling location was within the applicant's company premises.

[0026] The fully automated microwave digester is a P3 fully automated microwave digester (manufactured by Shanghai Yiyao Instrument Technology Development Co., Ltd.); the inductively coupled plasma mass spectrometer is an iQuad2300P series mass spectrometer (manufactured by Hengsheng Mass Spectrometry (Beijing) Instrument Co., Ltd.), which uses a collision reaction cell and has an electronic dilution function. The inductively coupled plasma mass spectrometer is connected to the fully automated microwave digester to form a fully automated microwave digestion-inductively coupled plasma mass spectrometry system.

[0027] The P3 fully automated microwave digester includes a robotic arm, three sets of independent microwave digestion tubes, four independent acid / water inlet lines, and six sets (16 per set, 96 in total) of sample rack supports. Each set of microwave digestion tubes corresponds to one digestion position, each acid / water inlet line corresponds to one acid addition position, and each sample rack support corresponds to one sample position.

[0028] After air particulate matter sampling is completed, the filter membrane is cut into small pieces. Cutting the filter membrane ensures that the filter fibers are fully dispersed, increases the contact area with the digesting acid, avoids incomplete digestion, ensures the complete extraction of sparingly soluble silicate components, and avoids physical interference of the whole filter membrane with the sample introduction system.

[0029] The robotic arm of the fully automated microwave digester removes the sample tube from the sample position, completing the sample tube opening operation. Shredded filter membrane is placed into the sample tube, and the robotic arm moves the sample tube to the acid addition position, where nitric acid and hydrofluoric acid are automatically added. After acid addition, the robotic arm moves the sample tube to the digestion position, where microwave digestion is performed using a stepped temperature ramp. After microwave digestion, the robotic arm moves the sample tube back to the sample position for programmed cooling to a safe temperature. Then, the robotic arm moves the sample tube back to the acid addition position, and water is added to bring the volume to 50 mL. Finally, the robotic arm moves the sample tube to the injection position of the inductively coupled plasma mass spectrometer.

[0030] The sample tube is moved to the acid addition position using a robotic arm. 4.5 mL of nitric acid (concentration greater than 65%) and 1.5 mL of hydrofluoric acid (concentration greater than 40%) are added to the sample tube through the acid / water inlet line. The sample tube is then capped using the robotic arm to prepare for the subsequent closed-loop microwave digestion. After acid addition, the sample tube is moved to the digestion position using the robotic arm. The sample tube is heated to 120°C in the microwave digestion tube using a stepped heating method and held for 2 minutes. The temperature is then increased to 150°C and held for 5 minutes, followed by a further increase to 190°C and held for 6 minutes. Each heating step lasts for 2 minutes, thus completing the closed-loop microwave digestion process.

[0031] After microwave digestion, the sample tube is moved to the sample position using a robotic arm. Forced air cooling and temperature monitoring are initiated, with the sample tube temperature monitored in real time. The subsequent volume adjustment operation can only be performed after the temperature has dropped to room temperature (25±2℃). By setting a controlled cooling step, volume errors and safety hazards caused by direct volume adjustment at high temperatures are avoided, ensuring the accuracy and precision of the analytical results. After cooling, the sample tube is moved to the acid addition position using a robotic arm. Deionized water is added to the sample tube through the acid / water inlet line, and the volume is adjusted to 50 mL to obtain the sample test solution. After volume adjustment, the sample tube is moved to the injection position of the inductively coupled plasma mass spectrometer using a robotic arm.

[0032] A robotic arm moves the sample tube containing the final volume of the test solution to the inductively coupled plasma mass spectrometer (ICP-MS) injection position. The ICP-MS's automatic injection needle directly pierces the sample tube to draw up the test solution, completing the sample loading process without manual transfer, thus avoiding sample contamination and loss.

[0033] Based on the external standard working curves of each metal element, the mass concentration of each metal element in the sample test solution is calculated from the measured signal intensity. Then, combined with the constant volume and the mass of the air particulate matter sample, the content of each metal element in a unit mass of air particulate matter is calculated. Example 1

[0034] Weigh several pieces of EMPM2.5-47 polytetrafluoroethylene filter membrane, place them in an 80℃ oven for half an hour, weigh them, and then continue to keep them in the 80℃ oven for 5 minutes and weigh them again, so that the difference between the two weighings is no more than 0.5mg, to obtain a blank PTFE filter membrane with constant weight.

[0035] A constant-weight blank PTFE filter membrane was placed into the collector to collect airborne particulate matter. Samples were taken twice, at 120 hours and 168 hours. The filter membranes sampled at 120 hours were designated as PTFE sample membrane 1-1 and PTFE sample membrane 1-2, respectively, and the filter membranes sampled at 168 hours were designated as PTFE sample membrane 2-1 and PTFE sample membrane 2-2, respectively. The sample membrane was placed in an 80℃ oven for half an hour and weighed. Then, it was kept in the 80℃ oven for another 5 minutes and weighed again to obtain a sample membrane of constant weight. The mass of the air particulate matter sample is the mass of the sample membrane minus the mass of the blank membrane. The measured masses of the air particulate matter samples are as follows: PTFE sample membrane 1-1 is 0.3309g, PTFE1-2 is 0.3247g, PTFE2-1 is 0.3502g and PTFE2-2 is 0.3432g.

[0036] Cut the sample membrane into small pieces and place them into the sample tube of the fully automated microwave digester. Add 4.5 ml of 65% analytical grade nitric acid and 1.5 ml of 40% analytical grade hydrofluoric acid sequentially, shake to mix, and then perform fully automated microwave digestion according to the heating and holding procedures shown in Table 1 below. After digestion, cool the sample tube to room temperature and bring the volume to 50 ml with deionized water to obtain the sample solution to be tested.

[0037] Table 1: Heating and holding procedures for fully automated microwave digestion of samples ; Based on the typical concentration distribution of metal elements in airborne particulate matter, differentiated concentration gradients were established, and standard solutions for working curves of each metal element were prepared according to Table 2 below. The mass concentration range for the working curves of major metal elements (K, Na, Ca, Mg, Al) was 5 to 500 mg / L; the mass concentration range for the working curves of major metal elements (Mn, Fe) was 0.5 to 50 mg / L; the mass concentration range for the working curves of trace metal elements (Cu, Zn, Pb) was 50 to 5000 ng / mL; and the mass concentration range for the working curves of other trace metal elements was 0.05 to 10 ng / mL.

[0038] Table 2. Preparation of standard solutions for working curves of various metal elements ; The series of standard solutions were introduced into an inductively coupled plasma mass spectrometer (ICPMS) to establish the correspondence between the signal intensity measured by ICPMS and the mass concentration of each metal element standard. Based on multiple sets of signal intensity and mass concentration data, the external standard working curve was obtained by fitting the curve.

[0039] The method detection limits and lower limits of analysis (LDAs) for the 19 metallic elements listed in Table 2 were tested, and the results are shown in Table 3. It can be seen that, at a sample weight of 0.1 g, the method detection limits range from 0.004 to 9 mg / kg, and the LAs range from 0.02 to 36 mg / kg. In particular, the method detection limits for trace metallic elements Cd, Tl, and Hg are as low as 0.004 mg / kg, 0.01 mg / kg, and 0.01 mg / kg, respectively, significantly better than the traditional hot plate digestion method, meeting the monitoring requirements for ultra-trace heavy metals in ambient air particulate matter.

[0040] Table 3. Detection limits and lower limits of analysis for each metal element. ; Next, the diluted sample solution was injected into the inductively coupled plasma mass spectrometer (ICP-MS) for testing. The electronic dilution function of the ICP-MS was activated, automatically performing an electronic dilution of approximately 3000 times for the main metal elements (K, Na, Ca, Mg, Al, Mn, Fe) and an electronic dilution of approximately 30 times for trace metal elements (Cu, Zn, Pb). Other metal elements were not electronically diluted.

[0041] The inductively coupled plasma mass spectrometer automatically calculates the measured mass concentration of each metal element in the sample solution based on the established external standard working curve. Then, according to formula (1), the content of each metal element in the unit mass of air particulate matter is calculated based on the measured mass concentration, the constant volume, and the mass of the air particulate matter sample. The content of each metal element in the collected air particulate matter sample is shown in Table 4.

[0042] Table 4. Determination results of the content of various metals in airborne particulate matter collected in Example 1 ; Example 2 Example 1 was repeated, except that PM10 quartz fiber filter membranes were used. Quartz sample membranes collected over 120 hours were labeled Quartz Sample Membrane 1-1 and Quartz Sample Membrane 1-2, respectively, and filter membranes collected over 168 hours were labeled Quartz Sample Membrane 2-1 and Quartz Sample Membrane 2-2, respectively. The sample membranes were placed in an 80°C oven for half an hour and weighed. They were then kept in the 80°C oven for another 5 minutes and weighed again to obtain sample membranes of constant weight. The measured masses of the air particulate matter samples were as follows: Quartz Sample Membrane 1-1: 0.4009 g, Quartz Sample Membrane 1-2: 0.3953 g, Quartz Sample Membrane 2-1: 0.4100 g, and Quartz Sample Membrane 2-2: 0.4228 g.

[0043] The results of the determination of the content of each metal element in the obtained air particulate matter samples are shown in Table 5.

[0044] Table 5. Determination results of the content of various metals in airborne particulate matter collected in Example 2 ; The present application has been described above with reference to specific embodiments. It should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential. The specific details described above are for illustrative purposes and ease of understanding, and do not limit the implementation of this application to the aforementioned specific details. In this application, terms such as "comprising," "including," and "having" are open-ended terms meaning "including but not limited to," and are used interchangeably. The terms "or" and "and" refer to the words "and / or," and are used interchangeably unless the context explicitly indicates otherwise. The term "such as" refers to the phrase "such as but not limited to," and is used interchangeably. It should also be noted that in the methods and apparatus of this application, each step or component can be decomposed and / or recombined. These decompositions and / or recombinations should be considered equivalent solutions of this application.

Claims

1. A method for determining the content of metal elements in airborne particulate matter, comprising: (1) Select a filter membrane, dry the filter membrane to constant weight, and place it in a sampler to collect air particulate matter samples; The constant weight mass is the mass of the blank membrane; (2) After the air particulate matter has been collected for a preset time, the sample membrane containing the air particulate matter is taken out and dried to constant weight; the constant weight is the mass of the sample membrane. (3) The sample membrane containing air particles is placed in the sample tube of the fully automated microwave digester. The robotic arm of the fully automated microwave digester is used to sequentially perform acid addition, closed microwave digestion, cooling, and volume adjustment on the sample tube to obtain the sample solution to be tested. Then, the sample tube containing the volume adjusted sample solution to be tested is moved to the injection position of the inductively coupled plasma mass spectrometer and the sample solution to be tested is injected into the inductively coupled plasma mass spectrometer for testing. The inductively coupled plasma mass spectrometer uses a collision reaction cell and has an electronic dilution function. (4) Based on the correspondence between the mass concentration of different metal element standard samples and the signal intensity measured by ICPMS, an external standard working curve is prepared; then, the test sample solution is measured by ICPMS using the electronic dilution method. Based on the obtained signal intensity, the mass concentration of metal elements in the test sample solution is obtained by referring to the external standard working curve. Based on the mass of the air particulate matter sample, the volume of the test sample solution, and the mass concentration of metal elements in the test sample solution, the content of metal elements in the air particulate matter is calculated according to the following formula (1): metal element concentration in the test sample solution × volume of the test sample solution / mass of the air particulate matter sample × 100% (1).

2. The method according to claim 1, wherein in step (1), the filter membrane is dried in an oven at 75℃-85℃ for 20-40 minutes and weighed; then it is kept warm in the oven for 5-6 minutes and weighed again. When the weight difference between the two weighings is not greater than 0.5mg, it is considered as constant weight; otherwise, the drying steps are repeated until constant weight is achieved.

3. The method according to claim 1, wherein in step (2), the collection time of the air particles is not less than 120 hours; the sample membrane with air particles is placed in an oven and kept at 75-90℃ for 20-40 minutes and weighed; then it is kept in the oven for another 5-6 minutes and weighed again. When the weight difference between the two weighings is not greater than 0.5mg, it is considered as constant weight; otherwise, the drying steps are repeated until constant weight is achieved.

4. The method according to claim 1, wherein the difference between the mass of the sample membrane obtained in step (2) and the mass of the blank membrane obtained in step (1) is the mass of the air particulate matter sample, wherein the mass of the air particulate matter sample is 0.1 g to 0.5 g.

5. The method according to claim 1, wherein in step (3), the acid addition operation is to add nitric acid and hydrofluoric acid in sequence, with a volume ratio of 5:1-2:

1.

6. The method according to claim 1, wherein in step (3), the closed microwave digestion operation performs stepwise heating, and the sample is subjected to fully automated microwave digestion according to the following heating and holding program: a) Keep warm at 110-130℃ for 2-3 minutes; b) Keep warm at 140-160℃ for 5-6 minutes; c) Keep warm at 180-200℃ for 6-8 minutes; After the microwave digestion is completed, the sample tube is cooled to a temperature not exceeding 30°C, and water is added to make up the volume.

7. The method according to claim 1, wherein in step (4), the sample solution to be tested is subjected to electronic dilution to differentiate the metal elements contained therein, and all elements are quantitatively analyzed in one measurement; the metal elements of different contents include the main contents of potassium, sodium, calcium, magnesium, manganese, iron, and aluminum, the trace elements of copper, zinc, and lead, and other trace metal elements, wherein the electronic dilution factor of the main contents of the main contents is greater than the electronic dilution factor of the trace elements.

8. The method according to claim 7, wherein potassium, sodium, calcium, magnesium, manganese, iron, and aluminum are diluted 1000-5000 times electronically, copper, zinc, and lead are diluted 10-50 times electronically, and the other trace metal elements are not diluted.

9. A device for determining the content of metal elements in airborne particulate matter, characterized in that, include: A sampler is used to hold a filter membrane to collect airborne particulate matter. A fully automated microwave digestion instrument is used to perform microwave digestion of the air particles in the sample tube and to move the sample tube containing the test sample solution obtained by microwave digestion to an inductively coupled plasma mass spectrometer. An inductively coupled plasma mass spectrometer, employing a collision reaction cell and featuring electronic dilution, is used to determine the metal element content in airborne particulate matter based on the sample test solution.

10. The measuring device according to claim 9, characterized in that: The filter membrane is selected from quartz fiber filter membranes or polytetrafluoroethylene filter membranes for PM10 and PM2.5 particulate matter sampling; the fully automated microwave digestion instrument includes a robotic arm and multiple sets of independent microwave digestion tubes. The robotic arm is used to automatically perform acid addition, closed microwave digestion, cooling, volume adjustment and sample injection operations. Under the control of the robotic arm, multiple sample tubes are transferred to different microwave digestion tubes for microwave digestion.