Low-temperature separation sampling process for metal elements in fluoropolymers

Abstract

The present application relates to the technical field of material analysis, and relates to a low-temperature separation sampling process for metal elements in fluorine-containing polymers, and aims to solve the problems that the separation sampling of metal elements in fluorine-containing polymer particles is difficult to be fully digested and avoid loss and interference. The low-temperature separation sampling process for metal elements in fluorine-containing polymers provided by the present application comprises the following steps: placing a fluorine-containing polymer sample, a grinding ball and a digestion solution in a digestion tank and sealing the tank; starting a ball milling digestion program; after the program is ended, filtering and constant-volume processing the reaction liquid to obtain a to-be-tested liquid for metal element content determination; the digestion solution comprises a main digestion solution and an additive, the main digestion solution comprises nitric acid and hydrogen peroxide, and the additive comprises ammonium nitrate, pyridine dicarboxylic acid and boric acid. The low-temperature separation sampling process for metal elements in fluorine-containing polymers provided by the present application is based on the synergistic effect of mechanical ball milling and chemical digestion, and can fully digest fluorine-containing polymer particles at a relatively low temperature, and the closed condition of the digestion tank can avoid the introduction of impurities.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material analysis, and particularly relates to a low-temperature separation sampling process of metal elements in fluorine-containing polymers. BACKGROUND

[0002] The fluorine-containing polymer is a core supporting material in key technology fields such as semiconductors, new energy and biological medicine, and is mostly applied to semiconductor crystal boats, brackets, baskets, pipe valves and filters of electronic chemical conveying systems and equipment in the semiconductor field. The fluorine-containing polymer particles are raw materials for producing fluorine-containing polymer products (pipes, valves, containers, etc.), but the existence of metal elements in the material will affect the chemical stability, thermal stability, mechanical properties and product appearance of the material, and further affect the value and application field of the fluorine-containing polymer product. Due to the excellent chemical stability of the fluorine-containing polymer, fluorine, as the most electronegative element, can form a C-F bond with a very high bond energy (about 485 kJ / mol), and the high electron cloud density of fluorine atoms can form a fluorine atom protection layer around the carbon chain, so that it cannot be completely digested by conventional means, and thus the specific situation of the types and contents of metal elements in the fluorine-containing polymer particles cannot be accurately obtained, affecting the optimization of fluorine-containing polymer production process, product production process control and final product quality control.

[0003] At present, the low-concentration metal elements in the fluorine-containing polymer particles are mainly analyzed by inductively coupled plasma mass spectrometry by dissolving the metal elements in the solution for sampling analysis. Therefore, in order to obtain the related information such as the types and contents of metal elements in the fluorine-containing polymer particles, the first step and the biggest technical difficulty is the separation and sampling of metal elements in the fluorine-containing polymer particles. The conventional method includes immersion method or ultrasonic immersion method, which can digest and sample the metal ions on the surface and shallow layer of the plastic particles, but cannot leach out the metal ions combined closely or in the material. The fluorine-containing polymer particles are only intermediate products of fluorine-containing plastic products, which need to be injection molded into plastic containers, plastic pipelines, pipe valves and other products for application. Sampling and analyzing the metal ions on the surface of the fluorine-containing plastic particles cannot effectively control the content of metal ions in the fluorine-containing plastic products by controlling the product quality of the fluorine-containing plastic particles, and the fluorine-containing polymer particles must be completely digested to obtain all types and content information of metal ions in the particles. High-temperature digestion or microwave digestion are the main methods for polymer digestion at present. Since the fluorine-containing polymer has strong corrosion resistance, it cannot be completely digested in strong acid solution by high temperature or microwave. The ash method is to calcine the polymer into ash at high temperature, and then digest the ash to realize the separation and sampling of metal elements. The ash method has complex processing process and environmental factor interference, and the sample will be lost during the processing, which will lead to the fact that the sampling results of metal elements cannot reflect the true performance of the fluorine-containing polymer particles.

[0004] Due to the high bond energy of C-F bond in fluoropolymers (about 485 kJ / mol), it is one of the strongest chemical bonds known. Fluorine atom has extremely high electronegativity, and its outer electron cloud densely wraps the carbon chain, forming a "fluorine atom protection layer", which greatly enhances the chemical stability and corrosion resistance of the polymer. Conventional acids (such as nitric acid, sulfuric acid) or oxidizing agents (such as hydrogen peroxide) are difficult to effectively attack and break the C-F bond at low temperature, resulting in the inability to release the metal elements wrapped inside the polymer. To achieve effective digestion, the temperature needs to be above 200℃.

[0005] In summary, the separation and sampling of metal elements in fluoropolymer particles in the prior art are difficult to fully digest at low temperature and avoid loss and interference. SUMMARY

[0006] The purpose of the present application is to provide a low-temperature separation and sampling process of metal elements in fluoropolymers to solve the problem that the separation and sampling of metal elements in fluoropolymer particles are difficult to fully digest and avoid loss and interference.

[0007] To solve the above technical problems, the technical solution provided by the present application is:

[0008] A low-temperature separation and sampling process of metal elements in fluoropolymers, comprising the following steps: placing fluoropolymer samples, grinding balls and digestion solution in a digestion tank and sealing; starting the ball milling digestion program, and carrying out synchronous mechanical ball milling and chemical digestion reaction at a temperature of 60-80℃, and the reaction time is 2.5-3.5 hours; after the end, cooling to room temperature, filtering and constant volume of the reaction liquid to obtain a test solution for metal element content determination; the digestion solution comprises a main digestion solution and an additive, the main digestion solution comprises nitric acid and hydrogen peroxide, and the additive comprises ammonium nitrate, pyridine dicarboxylic acid and boric acid. The low-temperature separation and sampling process is based on the synergistic effect of mechanical ball milling and chemical digestion, and can fully digest fluoropolymer particles at a relatively low temperature, and the closed condition of the digestion tank can avoid the introduction of impurities.

[0009] In some optional embodiments, the main digestion solution is prepared by mixing nitric acid solution and hydrogen peroxide solution, the volume concentration of the nitric acid solution is 65-70%, and the volume concentration of the hydrogen peroxide solution is 30-35%.

[0010] Further, the volume ratio of the nitric acid solution to the hydrogen peroxide solution is (8-12):3.

[0011] Further, 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.

[0012] Further, when preparing the digestion solution, the additive is first dissolved in the nitric acid solution, and then the hydrogen peroxide solution is added.

[0013] In some alternative embodiments, the grinding ball is made of zirconium oxide, has a diameter of 6-10 mm, and the number is 3-8.

[0014] In some alternative embodiments, the fluoropolymer is one or more of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetrafluoroethylene copolymer (ETFE).

[0015] In some alternative embodiments, the pyridine dicarboxylic acid is 2,6-pyridine dicarboxylic acid.

[0016] In some alternative embodiments, in the ball milling digestion process, the rotation speed of the digestion tank is 800-1200 rpm.

[0017] In some alternative 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 volume is adjusted to 25 mL or 50 mL in a volumetric flask.

[0018] Before the digestion step, pretreatment is also required. The sampling tool, grinding ball and digestion tank are soaked with nitric acid solution, and then rinsed with deionized water. Subsequently, it can be naturally dried, or dried by blowing high-purity gas, wherein the air gun and air pipe are made of PFA and other plastic materials.

[0019] In this embodiment, in order to avoid the introduction of impurities caused by the collision of the grinding ball with the digestion tank and the dissolution of the acid solution in the digestion tank, an inner liner is provided on the inner wall of the digestion tank, and the fluoropolymer sample, the grinding ball and the digestion solution are all added to the inner liner. Specifically, the inner liner is made of polytetrafluoroethylene. Although polytetrafluoroethylene is also a fluoropolymer, it is not directly impacted by the grinding ball and will not be digested. Even if a collision occurs, it will be slowed down due to its own buffering capacity. The fluoropolymer particles are subjected to extrusion and impact between the grinding balls during the ball milling process.

[0020] In this embodiment, nitric acid and hydrogen peroxide are used as the basic system, and three key additives, ammonium nitrate, pyridine dicarboxylic acid and boric acid, are introduced to form a precise system that works together and synergistically, providing a guarantee for the rapid and accurate digestion of fluoropolymers at low temperatures.

[0021] Firstly, nitric acid provides a strong acidic environment required for the reaction as the basic acid. Its core role is to protonate and attack the carbon chain skeleton of fluoropolymers, initially destroying their structural integrity. At the same time, nitrate ions themselves have oxidizing properties and work synergistically with subsequent oxidizing agents to lay a continuous oxidizing atmosphere for the entire digestion process.

[0022] Secondly, hydrogen peroxide as the core oxidant, under the high-energy collision condition produced by mechanical milling, is activated to generate a large number of highly reactive hydroxyl radicals. These radicals can indiscriminately attack the carbon chain and C-F bond weakened by the acid, and achieve the oxidation cleavage of the polymer chain, which is the key driving force to achieve rapid digestion.

[0023] The introduction of ammonium nitrate is the key to replace the high-risk hydrofluoric acid, which plays the role of a mild attacker. Under the joint activation of heat and mechanical force, ammonium ions can effectively react with fluorine atoms to form ammonium fluoride, thereby gently stripping and breaking the strong C-F bond. The use of ammonium nitrate fundamentally avoids the safety risk of using HF and the subsequent difficult-to-handle metal fluoride precipitate problem, clearing the biggest obstacle to the accuracy of the results. At the same time, the nitrate ion further strengthens the oxidation environment of the system.

[0024] Pyridine dicarboxylic acid is the core guardian that ensures accuracy in the entire system, playing the role of an all-purpose bodyguard, instantly protecting to ensure that all target elements are completely retained in the solution for detection. Specifically, pyridine dicarboxylic acid is a highly efficient and broad-spectrum complexing agent that can maintain structural stability under strong acid, strong oxidant, and heating conditions. Its mechanism of action is to immediately chelate metal ions as soon as they are released from the polymer matrix, forming extremely stable water-soluble complexes. This process precisely solves the three major problems that lead to inaccuracy: first, it prevents metal ions from being adsorbed by the newly generated high-activity carbon surface produced by mechanical force; second, even if there is a small amount of free fluoride ion present, the metal ions tightly wrapped by pyridine dicarboxylic acid cannot come into contact with it to form fluoride precipitate; third, pyridine dicarboxylic acid has strong stability to volatile elements such as mercury and arsenic, effectively preventing their loss by volatilization under local high temperature.

[0025] Finally, boric acid serves as a safety net, with a specific and key function: any free fluoride ions that may be produced during the highly efficient complexation reaction process are converted into stable tetrafluoroborate ions. Boric acid further reduces the concentration of free fluoride ions in the solution to an extremely low level, providing double insurance for the chelation protection of pyridine dicarboxylic acid, completely eliminating the possibility of any trace amount of fluoride precipitate, greatly enhancing the reproducibility and reliability of the entire method.

[0026] In summary, this separation and sampling process constitutes a highly efficient closed loop: the nitric acid-hydrogen peroxide system is responsible for oxidizing and destroying the carbon chain skeleton, ammonium nitrate is responsible for gently and effectively breaking the C-F bond, pyridine dicarboxylic acid is responsible for instantly capturing and fixing all released metal ions, and boric acid is responsible for eliminating residual fluoride ions to ensure that nothing is missed. This synergistic design ensures that in the low-temperature rapid reaction environment provided by mechanical milling, the accuracy of the final analysis results is fundamentally guaranteed.

[0027] In addition, the synergistic enhancement mechanism of ball milling assisted heating utilizes ball milling impact to destroy the polymer crystal structure, increase the reaction contact area, and an environment of 60-80°C can accelerate molecular motion and reaction kinetics, but avoid rapid decomposition of hydrogen peroxide caused by high temperature. Mechanical fragmentation and chemical oxidation are carried out synchronously to achieve “chain breaking, oxidation, and dissolution simultaneously”. It should be noted that pure mechanical fragmentation or chemical oxidation cannot achieve the digestion effect, and both need to work together.

[0028] The separation sampling process provided in this embodiment is completed in 3 hours at 70°C, while the traditional method needs 6-12 hours and the heating temperature needs to be at 200°C. DETAILED DESCRIPTION

[0029] The following are comparative examples of different digestion liquid formulations, all groups use the same total volume of digestion liquid (10 mL), and the ball milling frequency is 30 Hz. The volume concentration of nitric acid is 65-70%, the volume concentration of hydrogen peroxide is 30-35%, and the fluorine-containing polymer is PFA. Each example can be tested multiple times.

[0030] Example 1

[0031] Take 0.1 g of fluorine-containing polymer sample. Configure the main digestion liquid: the main digestion liquid includes nitric acid and hydrogen peroxide, the volume of the main digestion liquid is 10 mL, and the volume ratio of nitric acid to hydrogen peroxide is 50:15. Configure the additive, which includes ammonium nitrate, pyridine dicarboxylic acid, and boric acid; ammonium nitrate 240 mg, pyridine dicarboxylic acid 10 mg, and boric acid 100 mg, the additive is pre-dissolved in nitric acid, then mixed with hydrogen peroxide and added to the digestion tank. Start the ball milling digestion program, and carry out synchronous mechanical ball milling and chemical digestion reaction at a temperature of 70°C, the reaction time is 3 hours; the grinding ball is zirconia grinding ball, the diameter is 6 mm, the number is 6, after the end, cool, filter and constant volume the reaction liquid to obtain the test solution for metal element content determination.

[0032] Experimental results: digestion completion rate > 99.8%, metal recovery rate (average): 98.5%.

[0033] Mechanism analysis: nitric acid and hydrogen peroxide provide a strong acidic and strong oxidative environment, and hydrogen peroxide generates hydroxyl radicals under mechanical impact to attack the carbon chain. Ammonium ions in ammonium nitrate mildly attack the C-F bond to release fluoride ions to form NH4F, pyridine dicarboxylic acid chelates the released metal ions to prevent adsorption on the new carbon surface or the formation of fluoride precipitate, and boric acid captures free fluoride ions to generate tetrafluoroborate ions, providing double protection against fluoride precipitation.

[0034] Comparative Example 1 (without nitric acid)

[0035] Take 0.1 g of fluorine-containing polymer 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 additional agent, which includes ammonium nitrate, picolinic acid and boric acid; ammonium nitrate 240 mg, picolinic acid 10 mg and boric acid 100 mg. Start the ball milling digestion program, and perform the synchronous mechanical ball milling and chemical digestion reaction under the temperature condition of 70°C, and the reaction time is 3 hours; the grinding ball is zirconium oxide grinding ball, the diameter is 6 mm, and the number is 6. After the end, cool, filter and constant volume the reaction liquid to obtain the test solution for the determination of metal element content.

[0036] Experimental results: digestion completion rate <30%, metal recovery rate (average): 28.5%.

[0037] Principle analysis: lack of acidic environment leads to failure to protonate polymer chain, and hydrogen peroxide is difficult to effectively generate hydroxyl radicals. C-F bond is not activated, and ammonium ion cannot effectively attack fluorine atom (acidic conditions are required to promote the reaction). The metal is not released, and the complexing agent cannot play a role.

[0038] Comparative example 2 (without hydrogen peroxide)

[0039] Take 0.1 g of fluorine-containing polymer 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 additional agent, which includes ammonium nitrate, picolinic acid and boric acid; ammonium nitrate 240 mg, picolinic acid 10 mg and boric acid 100 mg. Start the ball milling digestion program, and perform the synchronous mechanical ball milling and chemical digestion reaction under the temperature condition of 70°C, and the reaction time is 3 hours; the grinding ball is zirconium oxide grinding ball, the diameter is 6–10 mm, and the number is 6. After the end, cool, filter and constant volume the reaction liquid to obtain the test solution for the determination of metal element content.

[0040] Experimental results: digestion completion rate <40%, metal recovery rate (average): 42.0%.

[0041] Principle analysis: lack of strong oxidative radicals, and the oxidation ability of HNO3 is limited, which cannot quickly break the carbon chain, and the reaction rate is extremely slow. Even if ammonium nitrate is involved in C-F rupture, the carbon skeleton is not fully oxidized, and the metal is still wrapped, and the local reducing environment may form metal elements or insoluble substances.

[0042] Comparative example 3 (without ammonium nitrate)

[0043] Take 0.1 g of fluorine-containing polymer sample. Prepare the main digestion solution: the main digestion solution includes nitric acid and hydrogen peroxide, the volume of the main digestion solution is 10 mL, and the volume ratio of nitric acid and hydrogen peroxide is 50:15. Prepare the additive, which includes pyridinedicarboxylic acid and boric acid; pyridinedicarboxylic acid 10 mg and boric acid 100 mg, the additive is dissolved in nitric acid in advance, and then mixed with hydrogen peroxide before being added to the digestion tank. Start the ball milling digestion program, and carry out synchronous mechanical ball milling and chemical digestion reaction at a temperature of 70°C, and the reaction time is 3 hours; the grinding ball is zirconia grinding ball with a diameter of 6 mm, and the number is 6; after the reaction is completed, the reaction liquid is cooled, filtered and diluted to volume to obtain the test solution for determination of the content of metal elements.

[0044] Experimental results: digestion completion rate 60%, metal recovery rate (average): 61.5%.

[0045] Principle analysis: ammonium ions can effectively react with fluorine atoms to form ammonium fluoride, thereby gently peeling off and breaking the strong C-F bond. The lack of ammonium nitrate makes it difficult to break the C-F bond, which is the direct reason for incomplete digestion, and thus the metal wrapped in the undigested polymer cannot be released, so the recovery rate is also low.

[0046] Comparative Example 4 (without pyridinedicarboxylic acid)

[0047] Take 0.1 g of fluorine-containing polymer sample. Prepare the main digestion solution: the main digestion solution includes nitric acid and hydrogen peroxide, the volume of the main digestion solution is 10 mL, and the volume ratio of nitric acid and hydrogen peroxide is 50:15. Prepare the additive, which includes pyridinedicarboxylic acid and boric acid; pyridinedicarboxylic acid 10 mg and boric acid 100 mg, the additive is dissolved in nitric acid in advance, and then mixed with hydrogen peroxide before being added to the digestion tank. Start the ball milling digestion program, and carry out synchronous mechanical ball milling and chemical digestion reaction at a temperature of 70°C, and the reaction time is 3 hours; the grinding ball is zirconia grinding ball with a diameter of 6 mm, and the number is 6; after the reaction is completed, the reaction liquid is cooled, filtered and diluted to volume to obtain the test solution for determination of the content of metal elements.

[0048] Experimental results: digestion completion rate >99.8%, metal recovery rate (average): 70.2%.

[0049] Principle analysis: high digestion completion rate indicates that the carbon chain and C-F bond have been broken. However, the metal is not effectively protected, the newly generated carbon surface has high adsorption, Al³⁺ and Fe³⁺ are easily adsorbed, and free fluoride ions form AlF3 precipitate with aluminum ions.

[0050] Comparative Example 5 (without boric acid)

[0051] Take 0.1 g of fluorine-containing polymer sample. Configure the main digestion solution: the main digestion solution includes nitric acid and hydrogen peroxide, the volume of the main digestion solution is 10 mL, and the volume ratio of nitric acid and hydrogen peroxide is 50:15. Configure the additive, which includes ammonium nitrate and pyridine dicarboxylic acid; ammonium nitrate 240 mg and pyridine dicarboxylic acid 10 mg, the additive is dissolved in nitric acid in advance, and then mixed with hydrogen peroxide and added to the digestion tank. Start the ball milling digestion program, and carry out synchronous mechanical ball milling and chemical digestion reaction at a temperature of 70°C, and the reaction time is 3 hours; the grinding ball is zirconia grinding ball with a diameter of 6 mm, and the number is 6. After cooling, filter and dilute the reaction solution to obtain the test solution for metal element content determination.

[0052] Experimental results: digestion completion rate > 99.8%, metal recovery rate (average): 85%.

[0053] Principle analysis: ammonium nitrate releases fluoride ions, and pyridine dicarboxylic acid can partially resist interference, but cannot completely prevent the formation of AlF3, ZrF4 and other precipitates. Zr 4+ combined with free F - to form ZrF4 precipitate, which consumes free fluoride ions in the solution, although this reduces the F - available for forming target metal fluoride precipitates such as AlF3 to some extent, but this consumption is uncontrollable and incomplete. More importantly, the newly generated ZrF4 precipitate itself can adsorb target metal ions in the solution, or block the filter membrane, causing these metals to be unable to enter the final test solution. At the same time, there is still enough F - in the solution to combine with Al 3+ , Fe 3+ and other target ions to form AlF3 and FeF3 precipitates, and pyridine dicarboxylic acid may not be able to completely prevent the formation of these precipitates, especially in areas with high local F - concentration. Therefore, the combination of these factors leads to a decrease in metal recovery rate and poor reproducibility, a decrease in reproducibility after the absence of boric acid, and a large fluctuation in the recovery rate of low-concentration metals.

[0054] Digestion completion rate calculation method:

[0055] ;

[0056] Wherein, m1 is the mass of the fluorine-containing polymer sample before digestion (unit: g), m2 is the mass of the residual solid after filtration, washing and drying after the end of the digestion reaction (unit: g)

[0057] Operation steps: accurately take 0.1 g of fluorine-containing polymer sample for digestion. After digestion is completed, the reaction liquid is filtered through a filter membrane. The residue on the filter membrane is washed with ultrapure water for 3-5 times. The filter membrane together with the residue is placed in an empty drying oven and dried to constant weight. The mass of the residue is weighed, and the digestion completion rate is calculated by substituting the formula.

[0058] Metal recovery rate calculation method:

[0059] Metal recovery rate ;

[0060] Wherein, C1 is the concentration of metal element measured by ICP-MS or ICP-OES after the sample is digested under the condition of adding metal standard solution (unit: μg / L or ppb);

[0061] C2 is the background concentration measured by digesting the blank sample (without adding metal standard solution) under the same condition;

[0062] C is the theoretical concentration of the standard metal solution added to the sample (which needs to be converted to the final constant volume).

[0063] Operation steps (take a single metal as an example): take two identical fluorine-containing polymer samples each 0.1 g, one of which adds a known amount of metal standard solution (such as Fe, Al, Hg, etc., the total added amount is controlled at 1-10 μg), mix well and then digest. Blank sample: no metal standard solution is added, and the rest of the steps are calculated for recovery.

[0064] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A process for low temperature separation sampling of metal elements in fluoropolymers, characterized by, The method comprises the following steps: placing a fluoropolymer sample, a grinding ball and a digestion solution in a digestion tank and sealing the tank; starting a ball milling digestion program to perform synchronous mechanical ball milling and chemical digestion reaction at a temperature of 60-80℃, and the reaction time is 2.5-3.5 hours; after the reaction is completed, cooling to room temperature, filtering the reaction solution, and diluting to volume to obtain a test solution for metal element content determination; the digestion solution comprises a main digestion solution and an additive, the main digestion solution comprises nitric acid and hydrogen peroxide, and the additive comprises ammonium nitrate, pyridine dicarboxylic acid and boric acid; the main digestion solution is prepared by mixing a nitric acid solution and a hydrogen peroxide solution, the volume concentration of the nitric acid solution is 65-70%, and the volume concentration of the hydrogen peroxide solution is 30-35%; the volume ratio of the nitric acid solution to the hydrogen peroxide solution is (8-12):3; the concentrations of ammonium nitrate, pyridine dicarboxylic acid and boric acid in the digestion solution are 0.2-0.5mol / L, 0.005-0.02mol / L and 0.05-0.2mol / L, respectively.

2. The process for low temperature separation sampling of metal elements in fluoropolymers according to claim 1, characterized in that, when the digestion solution is prepared, the additive is first dissolved in the nitric acid solution, and then the hydrogen peroxide solution is added.

3. The process for low temperature separation sampling of metal elements in fluoropolymers according to claim 1, characterized in that, The grinding ball is made of zirconia, has a diameter of 6-10mm, and the number is 3-8.

4. The process for low temperature separation sampling of 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).

5. The process of claim 1, wherein the process is conducted at a temperature of about - 20 °C to about 20 °C. The pyridine dicarboxylic acid is 2,6-pyridine dicarboxylic acid.

6. The process of claim 1, wherein the process is conducted at a temperature of about - 20 °C to about 20 °C. In the ball milling digestion program, the rotation speed of the digestion tank is 800-1200rpm.

7. The process of claim 1, wherein the process is conducted at a temperature of about - 20 °C to about 20 °C. When the reaction solution is filtered, a polytetrafluoroethylene filter membrane with a pore size of 0.22μm or 0.45μm is used, and the volume is diluted to 25mL or 50mL in a volumetric flask.