Low-temperature separation and sampling process for metal elements in fluorine-containing polymer

Abstract

The invention relates to the technical field of material analysis, relates to a low-temperature separation and sampling process for metal elements in a fluorine-containing polymer, and aims to solve the problem that the metal elements in fluorine-containing polymer particles are difficult to fully digest and avoid loss and interference during separation and sampling. The low-temperature separation and sampling process for the metal elements in the fluorine-containing polymer comprises the following steps: putting a fluorine-containing polymer sample, a grinding ball and a digestion solution into a digestion tank, and sealing; starting a ball milling digestion program; after the reaction is finished, filtering the reaction liquid, and fixing the volume to obtain a to-be-measured liquid for measuring the content of the metal elements; the digestion solution comprises a main digestion solution and an additive, and the main digestion solution comprises nitric acid and hydrogen peroxide; the additive comprises ammonium nitrate, dipicolinic acid and boric acid. According to the low-temperature separation and sampling process for the metal elements in the fluorine-containing polymer, provided by the invention, on the basis of the synergistic effect of mechanical ball milling and chemical digestion, fluorine-containing polymer particles can be fully digested at a relatively low temperature, and meanwhile, impurities can be prevented from being introduced under the closed condition of the digestion tank.

Description

Technical Field

[0001] This invention relates to the field of materials analysis technology, and in particular to a low-temperature separation and sampling process for metal elements in fluoropolymers. Background Technology

[0002] Fluoroplastics are core supporting materials in key technology fields such as semiconductors, new energy, and biomedicine. In the semiconductor field, they are mostly used in semiconductor boats, electronic chemical delivery systems and equipment, such as brackets, baskets, pipes, valves, and filters. Fluoroplastics particles are raw materials for producing fluoropolymer components (pipes, valves, containers, etc.). However, the presence of metal elements in the material affects its chemical stability, thermal stability, mechanical properties, and product appearance, thus impacting the value and application areas of fluoropolymer products. Due to the excellent chemical stability of fluoropolymers, fluorine, as the most electronegative element, bonds with carbon atoms to form CF bonds with extremely high bond energy (approximately 485 kJ / mol). Furthermore, the high electron cloud density of fluorine atoms forms a protective layer of fluorine atoms around the carbon chain, making it impossible to completely eliminate the metal elements through conventional methods. This makes it difficult to accurately determine the specific types and contents of metal elements in fluoropolymer particles, affecting the optimization of fluoropolymer production processes, product manufacturing process control, and final product quality control.

[0003] Currently, low-concentration metal elements in fluoropolymer particles are mainly analyzed using inductively coupled plasma mass spectrometry (ICP-MS), which involves dissolving the metal elements in a solution for sample introduction. Therefore, the primary step and the most challenging aspect in obtaining information on the types and contents of metal elements in fluoropolymer particles is the separation and sampling of these elements. Conventional methods include immersion or ultrasonic immersion, which can dissolve and sample metal ions on the surface and in the shallow layers of the plastic particles. However, these methods cannot leach tightly bound metal ions or those located within the material. Since fluoropolymer particles are merely an intermediate product in the production of fluoroplastic components, ultimately requiring injection molding into plastic containers, pipes, valves, and other applications, simply sampling and analyzing the surface metal ions is insufficient to effectively control the metal ion content in fluoroplastic components by controlling the product quality. Therefore, the fluoropolymer particles must be completely dissolved to obtain information on the types and contents of all metal ions within the particles. High-temperature digestion or microwave digestion are currently the main methods for polymer digestion. However, due to the extremely strong corrosion resistance of fluoropolymers, they cannot be completely digested directly in strong acid solutions using high-temperature or microwave methods. The ash method involves calcining the polymer at high temperature to produce ash, then digesting the ash to separate and sample the metal elements. However, the ash method is complex, susceptible to environmental interference, and involves sample loss during processing. Therefore, the metal element sampling results may not accurately reflect the true properties of the fluoropolymer particles.

[0004] Because the CF bond in fluoropolymers has an extremely high bond energy (approximately 485 kJ / mol), it is one of the strongest known chemical bonds. Fluorine atoms are extremely electronegative, and their outer electron clouds densely enclose the carbon chain, forming a "fluorine atom protective layer," which greatly enhances the chemical stability and corrosion resistance of the polymer. Conventional acids (such as nitric acid and sulfuric acid) or oxidants (such as hydrogen peroxide) are unable to effectively attack and break the CF bond at low temperatures, preventing the release of the metal elements encased within the polymer. Effective dissolution requires temperatures above 200°C.

[0005] In summary, existing technologies make it difficult to fully digest and avoid loss and interference when separating and sampling metal elements from fluoropolymer particles at low temperatures. Summary of the Invention

[0006] The purpose of this invention is to provide a low-temperature separation and sampling process for metal elements in fluoropolymers, so as to solve the problem that it is difficult to fully digest and avoid loss and interference when separating and sampling metal elements in fluoropolymer particles.

[0007] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: A low-temperature separation and sampling process for metal elements in fluoropolymers includes the following steps: placing the fluoropolymer sample, grinding balls, and digestion solution in a digestion vessel and sealing it; starting the ball milling digestion program, simultaneously performing mechanical ball milling and chemical digestion reactions at a temperature of 60-80℃ for 2.5-3.5 hours; after completion, cooling to room temperature, filtering and adjusting the volume of the reaction solution to obtain the test solution for metal element content determination; the digestion solution includes a main digestion solution and an additive, wherein the main digestion solution includes nitric acid and hydrogen peroxide, and the additive includes ammonium nitrate, pyridine dicarboxylic acid, and boric acid. This low-temperature separation and sampling process, based on the synergistic effect of mechanical ball milling and chemical digestion, can achieve sufficient digestion of fluoropolymer particles at a lower temperature, while the sealed condition of the digestion vessel can avoid the introduction of impurities.

[0008] In some optional embodiments, the main digestion solution is prepared by mixing a nitric acid solution and a hydrogen peroxide solution, wherein the volume concentration of the nitric acid solution is 65-70% and the volume concentration of the hydrogen peroxide solution is 30-35%.

[0009] Furthermore, the volume ratio of nitric acid solution to hydrogen peroxide solution is (8-12):3.

[0010] Furthermore, the concentrations of ammonium nitrate, pyridine dicarboxylic acid, and boric acid in the digestion solution are 0.2-0.5 mol / L, 0.005-0.02 mol / L, and 0.05-0.2 mol / L, respectively.

[0011] Furthermore, when preparing the digestion solution, the additive is first dissolved in nitric acid solution, and then hydrogen peroxide solution is added.

[0012] In some optional embodiments, the grinding balls are made of zirconium oxide, have a diameter of 6-10 mm, and are numbered 3-8.

[0013] In some optional embodiments, the fluoropolymer is one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetrafluoroethylene copolymer (ETFE).

[0014] In some optional embodiments, the pyridine dicarboxylic acid is 2,6-pyridine dicarboxylic acid.

[0015] In some optional embodiments, the ball milling digestion process involves a digestion vessel rotating at 800–1200 rpm.

[0016] In some optional embodiments, when filtering the reaction solution, a polytetrafluoroethylene filter membrane with a pore size of 0.22 μm or 0.45 μm is used, and the solution is brought to a volumetric flask with a volumetric volume of 25 mL or 50 mL.

[0017] Before the digestion step, pretreatment is required. The sampling tools, grinding balls, and digestion vessel are soaked in nitric acid solution and then rinsed with deionized water. They can then be air-dried or dried with high-purity gas. The air gun and tubing are made of PFA and other plastics.

[0018] In this embodiment, to avoid the introduction of impurities and the dissolution of the digestion vessel by collision between the grinding balls and the digestion vessel, an inner lining is provided on the inner wall of the digestion vessel. The fluoropolymer sample, grinding balls, and digestion solution are all added to the lining. Specifically, the lining is made of polytetrafluoroethylene (PTFE). Although PTFE is also a fluoropolymer, it is not directly impacted by the grinding balls and will not undergo digestion. Even if a collision occurs, its own buffering capacity reduces the impact. The fluoropolymer particles are subjected to compression and impact between the grinding balls during the ball milling process.

[0019] This embodiment uses nitric acid and hydrogen peroxide as the base system, and introduces three key additives: ammonium nitrate, pyridine dicarboxylic acid, and boric acid, forming a precise system in which each component performs its function and works synergistically to ensure the rapid and accurate digestion of fluoropolymers at low temperatures.

[0020] First, nitric acid, as the base acid, provides the strongly acidic environment required for the reaction. Its core role is to protonate and attack the carbon chain backbone of the fluoropolymer, initially disrupting its structural integrity. Simultaneously, nitrate ions themselves possess oxidizing properties, working synergistically with subsequent oxidants to establish a sustained oxidizing atmosphere throughout the digestion process.

[0021] Secondly, hydrogen peroxide, as the core oxidant, is activated under the high-energy collision conditions generated by mechanical ball milling, producing a large number of highly reactive hydroxyl radicals. These radicals can indiscriminately attack the carbon chains and CF bonds that have been weakened by acid, achieving oxidative cleavage of the polymer chains, which is the key driving force for achieving rapid dissolution.

[0022] The introduction of ammonium nitrate is key to replacing the high-risk hydrofluoric acid, acting as a milder aggressor. Under the combined activation of heating and mechanical force, ammonium ions can effectively react with fluorine atoms to form ammonium fluoride, thereby gently stripping and breaking the strong CF bonds. The use of ammonium nitrate fundamentally avoids the highly toxic safety risks associated with HF and the subsequent difficult-to-handle metal fluoride precipitation problem, removing the biggest obstacle to the accuracy of the results. Simultaneously, nitrate ions further enhance the oxidizing environment of the system.

[0023] Pyridine dicarboxylic acid (PDCA) is the core guardian ensuring accuracy in the entire system, acting as an all-around protector to ensure that all target elements are completely retained in solution for detection. Specifically, PDCA is a highly efficient, broad-spectrum complexing agent that maintains structural stability under strong acid, strong oxidizing agents, and heating conditions. Its mechanism of action is to immediately chelate metal ions released from the polymer matrix, forming an extremely stable water-soluble complex. This process precisely solves three major problems that lead to inaccuracies: first, it prevents metal ions from being adsorbed by the newly formed highly active carbon surface generated by mechanical force; second, even in the presence of trace amounts of free fluoride ions, the metal ions tightly bound by PDCA cannot come into contact with them to form fluoride precipitates; and third, PDCA has a strong stabilizing ability for volatile elements such as mercury and arsenic, effectively preventing their volatilization loss under localized high temperatures.

[0024] Finally, boric acid acts as a safety net, with a specific and crucial function: it converts any free fluoride ions that may be generated during the efficient complexation reaction into stable tetrafluoroborate ions. Boric acid further reduces the concentration of free fluoride ions in the solution to extremely low levels, providing double protection for the chelation of pyridine dicarboxylic acid, completely eliminating the possibility of any trace amounts of fluoride precipitation, and greatly enhancing the reproducibility and reliability of the entire method.

[0025] In summary, this separation and sampling process constitutes a highly efficient closed loop: the nitric acid-hydrogen peroxide system is responsible for oxidizing and breaking the carbon chain skeleton, ammonium nitrate is responsible for gently and effectively breaking the CF bond, pyridine dicarboxylic acid is responsible for instantly capturing and immobilizing all released metal ions, and boric acid is responsible for removing residual fluoride ions to ensure complete accuracy. This synergistic design fundamentally guarantees the accuracy of the final analytical results under the low-temperature, rapid reaction environment provided by mechanical ball milling.

[0026] Furthermore, the synergistic enhancement mechanism of ball milling-assisted heating utilizes the impact of ball milling to disrupt the polymer crystal structure, increasing the reaction contact area. The 60–80℃ environment can accelerate molecular motion and reaction kinetics, while avoiding the rapid decomposition of hydrogen peroxide due to high temperatures. Mechanical crushing and chemical oxidation occur simultaneously, achieving "chain breaking, oxidation, and dissolution simultaneously." It should be noted that neither mechanical crushing nor chemical oxidation alone can achieve the desired dissolution effect; both must be combined.

[0027] The separation and sampling process provided in this embodiment can complete efficient digestion at 70°C in 3 hours, while traditional methods require 6–12 hours and a heating temperature of 200°C. Detailed Implementation

[0028] The following are comparative examples of different digestion solution formulations. All groups used the same total volume of digestion solution (10 mL) and a ball milling frequency of 30 Hz. The volume concentration of nitric acid was 65–70%, the volume concentration of hydrogen peroxide was 30–35%, and the fluoropolymer was PFA. Each example can be tested multiple times.

[0029] Example 1 Take 0.1g of fluoropolymer sample. Prepare the main digestion solution: the main digestion solution includes nitric acid and hydrogen peroxide, with a volume of 10mL and a volume ratio of nitric acid to hydrogen peroxide of 50:15. Prepare the additives: the additives include ammonium nitrate, pyridine dicarboxylic acid, and boric acid; 240mg of ammonium nitrate, 10mg of pyridine dicarboxylic acid, and 100mg of boric acid are dissolved in nitric acid beforehand, then mixed with hydrogen peroxide and added to the digestion vessel. Start the ball milling digestion program, and carry out simultaneous mechanical ball milling and chemical digestion reaction at 70℃ for 3 hours; use 6 zirconia grinding balls with a diameter of 6mm. After completion, cool, filter, and dilute to volume to obtain the test solution for metal element content determination.

[0030] Experimental results: Digestion completion rate >99.8%, metal recovery rate (average): 98.5%.

[0031] Mechanism analysis: Nitric acid and hydrogen peroxide provide a strong acidic and oxidizing environment. Hydrogen peroxide generates hydroxyl radicals under mechanical impact to attack the carbon chain. Ammonium ions in ammonium nitrate gently attack the CF bond, releasing fluoride ions to form NH4F. Pyridine dicarboxylic acid chelates the released metal ions, preventing adsorption on the surface of newly formed carbon or the formation of fluoride precipitates. Boric acid captures free fluoride ions to form tetrafluoroborate ions, providing double protection against fluoride precipitation.

[0032] Comparative Example 1 (without nitric acid) Take 0.1 g of the fluoropolymer sample. Prepare the main digestion solution: the main digestion solution includes hydrogen peroxide, and the volume of the main digestion solution is 10 mL. Prepare the additives: the additives include ammonium nitrate, pyridine dicarboxylic acid, and boric acid; ammonium nitrate 240 mg, pyridine dicarboxylic acid 10 mg, and boric acid 100 mg. Start the ball milling digestion program and carry out simultaneous mechanical ball milling and chemical digestion reactions at a temperature of 70℃ for 3 hours; the grinding balls are zirconia grinding balls, 6 mm in diameter, and the quantity is 6. After the reaction is completed, cool, filter, and dilute to volume to obtain the test solution for the determination of metal element content.

[0033] Experimental results: Digestion completion rate <30%, metal recovery rate (average): 28.5%.

[0034] Principle analysis: The lack of an acidic environment prevents the protonation of the polymer chain, making it difficult for hydrogen peroxide to effectively generate hydroxyl radicals. The CF bond remains unactivated, preventing ammonium ions from effectively attacking fluorine atoms (acidic conditions are required to promote the reaction). The metal is not released, rendering the complexing agent ineffective.

[0035] Comparative Example 2 (without hydrogen peroxide) Take 0.1 g of the fluoropolymer sample. Prepare the main digestion solution: the main digestion solution includes nitric acid, and the volume of the main digestion solution is 10 mL. Prepare the additives: the additives include ammonium nitrate, pyridine dicarboxylic acid, and boric acid; ammonium nitrate 240 mg, pyridine dicarboxylic acid 10 mg, and boric acid 100 mg. Start the ball milling digestion program and carry out simultaneous mechanical ball milling and chemical digestion reactions at a temperature of 70℃ for 3 hours; the grinding balls are zirconia grinding balls with a diameter of 6–10 mm, and the number of balls is 6. After the reaction is completed, cool the solution, filter it, and dilute it to a final volume to obtain the test solution for the determination of metal element content.

[0036] Experimental results: Digestion completion rate <40%, metal recovery rate (average): 42.0%.

[0037] Principle Analysis: Lacking strong oxidizing free radicals, the oxidizing power of HNO3 is limited and cannot rapidly break the carbon chain, resulting in an extremely slow reaction rate. Even with the participation of ammonium nitrate in CF cleavage, the carbon skeleton is not fully oxidized, and the metal remains encapsulated. The localized reducing environment may lead to the formation of elemental metals or insoluble substances.

[0038] Comparative Example 3 (without ammonium nitrate) Take 0.1g of the fluoropolymer sample. Prepare the main digestion solution: the main digestion solution includes nitric acid and hydrogen peroxide, with a volume of 10mL and a volume ratio of nitric acid to hydrogen peroxide of 50:15. Prepare the additives: the additives include pyridine dicarboxylic acid and boric acid; 10mg of pyridine dicarboxylic acid and 100mg of boric acid are dissolved in nitric acid beforehand, then mixed with hydrogen peroxide and added to the digestion vessel. Start the ball milling digestion program, and carry out simultaneous mechanical ball milling and chemical digestion reactions at a temperature of 70℃ for 3 hours; use 6 zirconium oxide grinding balls with a diameter of 6mm. After the reaction is completed, cool the solution, filter and dilute to volume to obtain the test solution for the determination of metal element content.

[0039] Experimental results: Digestion completion rate: 60%; Metal recovery rate (average): 61.5%.

[0040] Principle Analysis: Ammonium ions can effectively react with fluorine atoms to form ammonium fluoride, thereby gently stripping and breaking the strong CF bonds. The lack of ammonium nitrate makes CF bond breaking difficult, which is the direct cause of incomplete digestion. Consequently, the metal encapsulated within the undigested polymer cannot be released, resulting in a low recovery rate.

[0041] Comparative Example 4 (without pyridine dicarboxylic acid) Take 0.1g of fluoropolymer sample. Prepare the main digestion solution: the main digestion solution includes nitric acid and hydrogen peroxide, with a volume of 10mL and a volume ratio of nitric acid to hydrogen peroxide of 50:15. Prepare the additives: the additives include ammonium nitrate and boric acid; 240mg of ammonium nitrate and 100mg of boric acid are dissolved in nitric acid beforehand, then mixed with hydrogen peroxide and added to the digestion vessel. Start the ball milling digestion program, and carry out simultaneous mechanical ball milling and chemical digestion reactions at 70℃ for 3 hours; use 6 zirconium oxide grinding balls with a diameter of 6mm. After completion, cool, filter, and dilute to volume to obtain the test solution for metal element content determination.

[0042] Experimental results: Digestion completion rate >99.8%, metal recovery rate (average): 70.2%.

[0043] Principle analysis: The high digestion completion rate indicates that the carbon chain and CF bond have been destroyed. However, the metal was not effectively protected, and the surface of the newly formed carbon has high adsorption capacity, with Al³⁺ and Fe³⁺ easily adsorbed. Free fluoride ions and aluminum ions form AlF₃ precipitate.

[0044] Comparative Example 5 (without boric acid) Take 0.1g of fluoropolymer sample. Prepare the main digestion solution: the main digestion solution includes nitric acid and hydrogen peroxide, with a volume of 10mL and a volume ratio of nitric acid to hydrogen peroxide of 50:15. Prepare the additives: the additives include ammonium nitrate and pyridine dicarboxylic acid; 240mg of ammonium nitrate and 10mg of pyridine dicarboxylic acid are dissolved in nitric acid beforehand, then mixed with hydrogen peroxide and added to the digestion vessel. Start the ball milling digestion program, and carry out simultaneous mechanical ball milling and chemical digestion reaction at a temperature of 70℃ for 3 hours; the grinding balls are zirconia grinding balls, 6mm in diameter, and 6 balls in total. After the reaction is completed, cool, filter, and dilute to volume to obtain the test solution for the determination of metal element content.

[0045] Experimental results: Digestion completion rate >99.8%, metal recovery rate (average): 85%.

[0046] Principle Analysis: Ammonium nitrate releases fluoride ions. While pyridine dicarboxylic acid can partially inhibit interference, it cannot completely prevent the formation of precipitates such as AlF3 and ZrF4. Zr dissolved from the grinding balls... 4+ With free F - The combination to form ZrF4 precipitate consumes free fluoride ions in the solution, although this reduces the amount of fluoride available for forming target metal fluorides such as AlF3. - However, this consumption is uncontrollable and incomplete. More importantly, the newly formed ZrF4 precipitate itself can adsorb target metal ions in the solution or clog the filter membrane, preventing these metals from entering the final test solution. Meanwhile, sufficient F2+ remains in the solution. - With Al 3+ Fe 3+ When target ions combine, AlF3 and FeF3 precipitates are formed. However, pyridine dicarboxylic acid may not completely prevent the formation of these precipitates, especially in localized F... - Areas with high concentrations of metals. Therefore, this combination leads to decreased metal recovery and poorer reproducibility; the absence of boric acid further reduces reproducibility, and low-concentration metal recovery fluctuates significantly.

[0047] Method for calculating digestion completion rate: ; Where m1 is the mass of the fluoropolymer sample before digestion (in g), and m2 is the mass of the residual solid after filtration, washing, and drying after the digestion reaction (in g). Operating Procedure: Accurately weigh 0.1g of the fluoropolymer sample for digestion. After digestion, filter the reaction solution through a filter membrane. Wash the filter membrane thoroughly with ultrapure water 3-5 times to remove any residue. Place the filter membrane and residue in an empty drying oven and dry to constant weight. Weigh the residue and substitute the mass into the formula to calculate the digestion completion rate.

[0048] Metal recovery rate calculation method: Metal recovery rate ; Wherein, C1 is the concentration of the metal element (in μg / L or ppb) measured by ICP-MS or ICP-OES after digestion of the sample under the condition of adding metal standard solution; C2 is the background concentration measured by digestion of a blank sample (without metal standard solution) under the same conditions; C represents the theoretical concentration of the standard metal solution added to the sample (which needs to be converted to the final volume).

[0049] Operating procedures (taking a single metal as an example): Take two identical 0.1g samples of fluoropolymer. Add a known amount of metal standard solution (such as Fe, Al, Hg, etc., with the total amount added controlled between 1–10 μg) to one sample, mix well, and then digest. Blank sample: Do not add metal standard solution; follow the remaining steps and calculate the recovery rate.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-temperature separation and sampling process for metal elements in fluoropolymers, characterized in that, Includes the following steps: Place the fluoropolymer sample, grinding balls, and digestion solution in a digestion vessel and seal it. Start the ball milling digestion program and carry out simultaneous mechanical ball milling and chemical digestion reactions at a temperature of 60-80℃ for 2.5-3.5 hours. After the reaction was completed, the solution was cooled to room temperature, filtered, and diluted to a final volume to obtain the test solution for determining the metal element content. The digestion solution comprises a main digestion solution and an additive. The main digestion solution includes nitric acid and hydrogen peroxide, and the additive includes ammonium nitrate, pyridine dicarboxylic acid, and boric acid.

2. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 1, characterized in that, The main digestion solution is prepared by mixing nitric acid solution and hydrogen peroxide solution, with the nitric acid solution having a volume concentration of 65-70% and the hydrogen peroxide solution having a volume concentration of 30-35%.

3. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 2, characterized in that, The volume ratio of nitric acid solution to hydrogen peroxide solution is (8-12):

3.

4. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 3, characterized in that, The concentrations of ammonium nitrate, pyridine dicarboxylic acid, and boric acid in the digestion solution are 0.2-0.5 mol / L, 0.005-0.02 mol / L, and 0.05-0.2 mol / L, respectively.

5. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 4, characterized in that, When preparing the digestion solution, the additive is first dissolved in nitric acid solution, and then hydrogen peroxide solution is added.

6. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 1, characterized in that, The grinding balls are made of zirconium oxide, with a diameter of 6-10mm, and a quantity of 3-8.

7. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 1, characterized in that, The fluoropolymer is one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetrafluoroethylene copolymer (ETFE).

8. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 1, characterized in that, The pyridine dicarboxylic acid is 2,6-pyridine dicarboxylic acid.

9. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 1, characterized in that, In the ball milling digestion process, the digestion vessel rotates at 800–1200 rpm.

10. The low-temperature separation and sampling process for metal elements in fluoropolymers according to claim 1, characterized in that, When filtering the reaction solution, use a polytetrafluoroethylene filter membrane with a pore size of 0.22 μm or 0.45 μm, and make up to a volumetric flask of 25 mL or 50 mL.