Method for testing the content of alkali elements in a binder

Abstract

The application provides a testing method of the content of alkali metal elements in a binder, comprising the following steps: 1) sequentially performing dry ashing treatment, pre-digestion treatment and microwave digestion treatment on the binder to obtain a digestion solution; the binder comprises alkali metal elements, and the alkali metal elements comprise sodium elements and / or lithium elements; the temperature of the microwave digestion treatment is higher than that of the pre-digestion treatment; 2) testing the peak intensity of the alkali metal elements in the digestion solution by using an inductively coupled plasma emission spectrometer; 3) drawing a standard curve based on an external standard method, and calculating the content of the alkali metal elements in the binder according to the peak intensity of the alkali metal elements in the digestion solution based on the standard curve. The testing method of the content of alkali metal elements in the binder provided by the application can improve the accuracy of the testing result, since the pretreatment process comprises dry ashing treatment, pre-digestion treatment and microwave digestion treatment in sequence.

Description

Technical Field

[0001] This invention belongs to the field of analytical technology, and in particular relates to a method for testing the content of alkali metal elements in adhesives. Background Technology

[0002] Sodium-ion and lithium-ion batteries, as core materials for next-generation energy storage technologies, are widely used in new energy vehicles, energy storage systems, and consumer electronics. In battery manufacturing, binders (such as styrene-butadiene rubber, SBR) are crucial components of the negative electrode material, and their performance directly affects the battery's initial coulombic efficiency, cycle life, and energy density. Adding sodium or lithium to the binder can help capture free acid (H+) in the electrolyte. + This process mitigates the damage of acid to the cathode material while reducing the loss of active sodium or lithium, thereby improving the battery's capacity and stability. Therefore, accurately detecting the content of alkali metal elements in the binder is particularly important.

[0003] The content of alkali metal elements in adhesives, such as those in SBR, can be detected using inductively coupled plasma optical emission spectrometry (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS). The core steps are as follows:

[0004] 1) Sample pretreatment: The sample is digested by methods such as wet oxidation, dry ashing-acid digestion or organic solvent dissolution.

[0005] Wet oxidation: The sample is digested by heating a mixed acid (such as nitric acid-perchloric acid) with a hot plate, but it has problems such as low digestion temperature (<200℃), more residues, and incomplete digestion.

[0006] Dry ashing-acid digestion: This method not only requires burning the sample at high temperatures, but also takes a long time to completely remove organic matter. It is prone to causing the loss of volatile elements (such as Hg, Cd, Li, Na), especially alkali metal elements, leading to inaccurate test results.

[0007] Organic solvent dissolution: The sample can be dissolved directly with solvents such as water or ethanol. However, electrode binders such as SBR polymers are difficult to dissolve in common solvents, resulting in incomplete digestion and significant solvent background interference, which affects the detection accuracy.

[0008] 2) ICP-OES / ICP-MS detection: After adjusting the volume of the pretreated solution, the sample is directly injected and quantitative analysis is performed using characteristic wavelengths (e.g., Na: 589.592nm, Li: 670.776nm).

[0009] In the existing technology, the test methods for the content of alkali metal elements in adhesives have poor accuracy. Summary of the Invention

[0010] The main objective of this invention is to provide a method for testing the content of alkali metal elements in adhesives, which yields highly accurate test results.

[0011] In a first aspect, the present invention provides a method for testing the content of alkali metal elements in an adhesive, comprising the following steps:

[0012] 1) The binder is subjected to dry ashing treatment, pre-digestion treatment and microwave digestion treatment in sequence to obtain digestion solution; the binder includes alkali metal elements, including sodium and / or lithium elements; the temperature of microwave digestion treatment is higher than the temperature of pre-digestion treatment.

[0013] 2) The peak intensity of the alkali metal element in the digestion solution was measured using inductively coupled plasma atomic emission spectrometry;

[0014] 3) Plot a standard curve based on the external standard method, and calculate the content of the alkali metal element in the binder based on the peak intensity of the alkali metal element in the digestion solution according to the standard curve.

[0015] As described above, the dry ashing treatment includes: carbonizing the adhesive at 280-320°C for 20-40 minutes, and then ashing at 580-620°C for 20-40 minutes to obtain inorganic ash.

[0016] The test method described above includes the pre-digestion treatment of the inorganic ash under the action of concentrated nitric acid and hydrogen peroxide solution to obtain a mixed solution.

[0017] In the test method described above, the concentration of the concentrated nitric acid is 65-70%.

[0018] And / or, the concentration of the hydrogen peroxide solution is 30.0~32.0%;

[0019] And / or, the volume ratio of the concentrated nitric acid to the hydrogen peroxide solution is (2.0~4.0):1.

[0020] In the test method described above, the total volume of the concentrated nitric acid and the hydrogen peroxide solution to the mass ratio of the adhesive is (30~100) mL:1g.

[0021] As described above, the pre-digestion treatment is performed at a temperature of 140-160°C for 20-40 minutes.

[0022] As described above, the microwave digestion process includes: under microwave action, maintaining the mixed solution at 120-140°C for 3-5 minutes, at 160-180°C for 3-5 minutes, and at 190-210°C for 30-60 minutes to obtain a digestion solution.

[0023] The test method described above includes particulate matter in the digestion solution, and the digestion process further includes filtering the digestion solution.

[0024] The filtration process uses ashless filter paper.

[0025] As described above, the concentration of the alkali metal element in the digestion solution is >5 mg / L, and the digestion process further includes: diluting the digestion solution.

[0026] In the test method described above, step 3), the step of plotting the standard curve based on the external standard method includes:

[0027] Standard solutions with different contents of alkali metal elements were prepared, and the standard solutions were tested using an inductively coupled plasma atomic emission spectrometer to establish a curve relating the peak intensity of the alkali metal element to the concentration of the alkali metal element in the standard solution.

[0028] The present invention provides a method for testing the content of alkali metal elements in adhesives. The pretreatment process includes dry ashing treatment, pre-digestion treatment and microwave digestion treatment in sequence. Combined with inductively coupled plasma atomic emission spectrometry (ICP-AES) testing method and based on the external standard method, the content of alkali metal elements in adhesives can be measured, which can improve the accuracy of the final test results.

[0029] In step 1), the pretreatment process for the binder includes sequential dry ashing, pre-digestion, and microwave digestion. The dry ashing process, combined with two specific digestion steps, allows the dry ashing to be performed at a lower temperature, thus more completely removing organic matter from the binder and avoiding interference from organic matter in subsequent digestion processes, achieving a more complete dissolution of alkali metal elements. The lower temperature of the dry ashing also reduces the volatilization of alkali metal elements, improving the accuracy of the test results.

[0030] The digestion process includes pre-digestion and microwave digestion. Pre-digestion dissolves most of the inorganic ash first, followed by microwave digestion to further dissolve the undissolved inorganic ash. This can further improve the completeness of alkali metal element dissolution and increase the accuracy of the final alkali metal element content test results.

[0031] The temperature of microwave digestion is higher than that of pre-digestion. The high temperature is conducive to the further dissolution of alkali metal elements, thereby improving the accuracy of the final test results of alkali metal element content. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 The spectrum of sodium obtained by ICP-OES testing provided by this invention;

[0034] Figure 2 The spectrum of lithium obtained by ICP-OES testing provided by this invention;

[0035] Figure 3 The standard curve of sodium element provided for this invention;

[0036] Figure 4 A standard curve of lithium provided for this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0038] The inventors of this application have discovered through research that if the sample pretreatment process includes dry ashing, pre-digestion, and microwave digestion in sequence, the accuracy of the final alkali metal element test results can be significantly improved.

[0039] Based on this, in a first aspect, the present invention provides a method for testing the content of alkali metal elements in an adhesive, comprising the following steps:

[0040] 1) The binder is subjected to dry ashing treatment, pre-digestion treatment and microwave digestion treatment in sequence to obtain digestion solution; the binder includes alkali metal elements, including sodium and / or lithium elements; the temperature of microwave digestion treatment is higher than the temperature of pre-digestion treatment.

[0041] 2) The peak intensity of alkali metal elements in the digestion solution was measured using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0042] 3) Plot a standard curve based on the external standard method. Based on the standard curve, calculate the content of alkali metal elements in the binder according to the peak intensity of alkali metal elements in the digestion solution.

[0043] The method for testing the content of alkali metal elements in adhesives provided by this invention includes a pretreatment process that sequentially comprises dry ashing treatment, pre-digestion treatment, and microwave digestion treatment. This process can remove organic matter in the adhesive to a large extent and achieve relatively complete dissolution of alkali metal elements. Combined with inductively coupled plasma atomic emission spectrometry (ICP-AES) and based on the external standard method, the content of alkali metal elements in the adhesive can be measured, thereby improving the accuracy of the final test results for the content of alkali metal elements.

[0044] Specifically, in step 1), the pretreatment process for the binder includes sequential dry ashing, pre-digestion, and microwave digestion. The dry ashing process, combined with two specific digestion steps, allows the dry ashing to be performed at a lower temperature, thus more completely removing organic matter from the binder and avoiding interference from organic matter in subsequent digestion processes, achieving more complete dissolution of alkali metal elements. The lower temperature of the dry ashing also reduces the volatilization of alkali metal elements, improving the accuracy of the test results.

[0045] The digestion process includes pre-digestion and microwave digestion. Pre-digestion dissolves most of the inorganic ash first, followed by microwave digestion to further dissolve the undissolved inorganic ash. This can further improve the completeness of alkali metal element dissolution and increase the accuracy of the final alkali metal element content test results.

[0046] The temperature of microwave digestion is higher than that of pre-digestion. The high temperature is conducive to the further dissolution of alkali metal elements, thereby improving the accuracy of the final test results of alkali metal element content.

[0047] In step 2), the peak intensities of alkali metal elements in the digestion solution were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The peak intensities of alkali metal elements in the blank experiment were measured simultaneously.

[0048] In step 3), the content of alkali metal elements in the binder is calculated based on the peak intensity of alkali metal elements in the digestion solution, according to the standard curve.

[0049] Therefore, the method for testing the content of alkali metal elements in adhesives provided by the present invention includes a pretreatment process that sequentially includes dry ashing treatment, pre-digestion treatment, and microwave digestion treatment. This process can remove organic matter in the adhesive to a large extent and achieve relatively complete dissolution of alkali metal elements. Combined with inductively coupled plasma atomic emission spectrometry (ICP-AES) and based on the external standard method, the content of alkali metal elements in the adhesive can be measured, thereby improving the accuracy of the final test results for the content of alkali metal elements.

[0050] In some embodiments of the present invention, the dry ashing treatment includes: carbonizing the binder at 280~320℃ for 20~40 min, and then ashing at 580~620℃ for 20~40 min to obtain inorganic ash.

[0051] For example, the carbonization temperature can be a range of 280°C, 290°C, 300°C, 305°C, 310°C, 320°C or any combination thereof; the carbonization time can be a range of 20 min, 25 min, 30 min, 35 min, 40 min or any combination thereof; the ashing temperature can be a range of 580°C, 585°C, 590°C, 600°C, 610°C, 620°C or any combination thereof; and the ashing time can be a range of 20 min, 25 min, 30 min, 35 min, 40 min or any combination thereof.

[0052] In this invention, the dry ashing process includes carbonization and ashing, which differs from the traditional single high-temperature ashing method. It achieves precise temperature-controlled pyrolysis tailored to the characteristics of the binder's organic polymer matrix, thus removing the organic matrix to obtain pure inorganic ash while avoiding the loss of volatile elements such as sodium and lithium. Simultaneously, it improves ashing efficiency and ensures ash uniformity. The inorganic ash is then digested.

[0053] If the organic binder is directly heated at high temperatures, the rapid evaporation of the internal solvent can cause sample expansion and splashing, resulting in the loss of target elements and contamination of the platinum crucible, affecting the accuracy of the test results. Slow carbonization at low temperatures of 280~320℃ allows the solvent to escape gradually and steadily, eliminating the risk of expansion and splashing. The sample maintains a stable shape throughout, ensuring the accuracy of the test results while avoiding contamination of the platinum crucible and reducing safety hazards in experimental operations. In practical applications, the binder solvent is water or NMP (N-methylpyrrolidone) solution; no specific limitation is made here.

[0054] In some embodiments of the present invention, the pre-digestion treatment includes: pre-digesting inorganic ash under the action of concentrated nitric acid and hydrogen peroxide solution to obtain a mixed solution.

[0055] Concentrated nitric acid is a strong oxidizing inorganic acid that can directly react with alkali metal oxides, carbonates, and other inorganic compounds in ash to generate soluble alkali metal nitrates, thus achieving the initial dissolution of the target elements. Hydrogen peroxide is a strong oxidizing agent that can release active oxygen in acidic systems. On the one hand, it can oxidize and dissolve trace carbon-based residues in ash that were not completely removed by dry ashing, avoiding the consumption of acid reagents in subsequent microwave digestion and reducing digestion efficiency. On the other hand, it can destroy trace amounts of insoluble organically bound alkali metal impurities that may exist in the ash, converting them into easily soluble inorganic forms. This allows the inorganic ash to be fully dispersed and dissolved in the pre-digestion stage, resulting in a homogeneous mixed solution, which lays the foundation for thorough digestion in subsequent microwave digestion.

[0056] Pre-digestion uses a concentrated nitric acid and hydrogen peroxide solution system to dissolve inorganic ash, which can achieve full dispersion of inorganic ash under mild conditions, leaving no dense solid particles in the inorganic ash. At the same time, the oxidative decomposition of trace carbon-based residues by hydrogen peroxide can avoid the explosion accident caused by the violent oxidation reaction between carbon-based residues and concentrated nitric acid under closed high pressure during subsequent microwave digestion, which would generate a large amount of gas.

[0057] In some embodiments of the present invention, the concentration of concentrated nitric acid is 65-70%, for example, it can be a range of 65%, 66%, 67%, 68%, 69%, 70%, or any two of these. This concentrated nitric acid possesses sufficient hydrogen ion concentration and oxidizing power to rapidly react with alkali metal oxides and carbonates in the ash to form soluble nitrates.

[0058] In some embodiments, the concentration of the hydrogen peroxide solution is 30.0% to 32.0%, for example, it can be a range of 30.0%, 30.5%, 31.0%, 31.5%, 31.7%, 32.0%, or any combination thereof. This hydrogen peroxide solution has moderate oxidizing activity and, at the pre-digestion temperature, can slowly decompose and release active oxygen, efficiently oxidizing trace carbon-based residues and sparingly soluble organically bound alkali metal impurities in the ash.

[0059] In some embodiments, the volume ratio of concentrated nitric acid to hydrogen peroxide solution is (2.0~4.0):1, for example, it can be a range of 2.0:1, 2.5:1, 3.0:1, 3.5:1, 3.8:1, 4.0:1 or any two of them.

[0060] This volume ratio allows for a better match between the acid dissolution effect of concentrated nitric acid and the oxidation effect of hydrogen peroxide. Under mild conditions, the ash can achieve both the full dissolution of inorganic ash and the complete oxidation of organic residues, resulting in a homogeneous mixed solution free of solid particles, which lays the reaction foundation for subsequent microwave digestion.

[0061] In some embodiments of the present invention, the total volume of concentrated nitric acid and hydrogen peroxide solution to the mass ratio of the binder is (30~100) mL:1g, for example, it can be a range of 30mL:1g, 40mL:1g, 50mL:1g, 70mL:1g, 80mL:1g, 100mL:1g or any two of these.

[0062] The above ratio can make the pre-disintegration of the binder more complete and avoid the increase in process cost caused by excessive reagent.

[0063] In some embodiments of the present invention, the temperature of the pre-digestion treatment is 140~160°C, for example, it can be a range of 140°C, 145°C, 148°C, 150°C, 155°C, 160°C or any two of these; the time is 20~40 min, for example, it can be a range of 10 min, 25 min, 30 min, 35 min, 40 min or any two of these.

[0064] The temperature of the pre-digestion treatment described above can quickly evaporate the free water in the mixed system, effectively increasing the effective concentration of nitric acid in the mixed solution, which is beneficial for subsequent microwave digestion treatment.

[0065] The aforementioned pre-digestion treatment time allows for more thorough dissolution of inorganic ash and carbon-based oxidation.

[0066] In some embodiments of the present invention, the microwave digestion process includes: under microwave action, maintaining the mixed solution at 120-140°C (e.g., a range of 120°C, 125°C, 130°C, 135°C, 138°C, 140°C, or any combination thereof) for 3-5 minutes (e.g., a range of 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, or any combination thereof), and at 160-180°C (e.g., 160°C, 165°C, 170°C, 175°C, 178°C, 180°C, or any combination thereof). The solution is kept at 190-210°C (e.g., 190°C, 195°C, 200°C, 205°C, 208°C, 210°C, or any two of these ranges) for 30-60 minutes (e.g., 30 minutes, 40 minutes, 45 minutes, 50 minutes, 60 minutes, or any two of these ranges) to obtain the digestion solution.

[0067] The aforementioned phased microwave digestion process enables stable and deep digestion of the microwave digestion reaction, improves digestion efficiency, reduces microwave power consumption of the equipment, reduces matrix interference in subsequent ICP-OES detection, and further improves the accuracy of alkali metal element test results.

[0068] In some embodiments of the present invention, the digestion solution includes particulate matter, and the digestion process further includes: filtering the digestion solution; the filtration process uses ashless filter paper.

[0069] Filtration removes solid particles from the digestion solution, preventing clogging of the ICP-OES detection path and protecting precision instruments. It also eliminates light scattering from particles and interference with the background, improving the signal purity and accuracy of ICP-OES detection.

[0070] Using ashless filter paper, such as Whatman 540 ashless filter paper, will not introduce target elements (e.g., sodium) and interfering metal ions into the digestion solution. This ensures the purity of the digestion solution after filtration from the material level, eliminates blank value interference caused by the filter paper itself, and allows the test results to truly reflect the actual content of alkali metal elements in the binder, enabling more accurate quantification of elements.

[0071] In some embodiments of the present invention, the concentration of alkali metal elements in the digestion solution is >5 mg / L, for example, it can be a range of 5.1 mg / L, 5.5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 10 mg / L, 20 mg / L, 30 mg / L, 50 mg / L, 100 mg / L or any two of these. The digestion treatment further includes: diluting the digestion solution.

[0072] When the concentration of alkali metal elements in the digestion solution is too high, the peak intensity of the alkali metal elements will exhibit a plateau effect as the concentration increases, disrupting the linear correlation between concentration and signal (correlation coefficient R). 2 When the concentration of the alkali metal element is less than 0.995, direct detection will result in a calculated concentration that is far lower than the actual value, leading to a nonlinear systemic bias. Dilution treatment allows the concentration of the test solution to better match the linear detection range of the instrument, restoring a good linear relationship between concentration and peak intensity. This eliminates nonlinear bias at the detection principle level, improves the accuracy of quantitative calculation using the external standard method, and ensures that the detection results accurately reflect the actual concentration of alkali metal elements in the digestion solution.

[0073] In some embodiments of the present invention, step 3) involves plotting a standard curve based on the external standard method, including:

[0074] Standard solutions with different contents of alkali metal elements were prepared, and inductively coupled plasma atomic emission spectrometry was used to test the standard solutions to establish the relationship curve between the peak intensity of alkali metal elements and the concentration of alkali metal elements in the standard solutions.

[0075] In this invention, when plotting the standard curve, at least six standard solutions with different concentrations of alkali metal elements can be prepared. The standard solutions can be obtained by gradually diluting the high-concentration standard solution containing alkali metal elements.

[0076] When testing for sodium in the adhesive, the alkali metal element is sodium; when testing for lithium in the adhesive, the alkali metal element is lithium; when testing for both sodium and lithium simultaneously, the alkali metal elements are both sodium and lithium.

[0077] The establishment of this standard curve makes the quantitative calibration of the external standard method more accurate and the error smaller, thereby improving the accuracy of the calculation of the content of alkali metal elements in the final adhesive.

[0078] In this invention, the binder is placed in a platinum crucible, which is then placed in a muffle furnace for dry ashing to remove a large amount of organic matter from the binder, yielding inorganic ash. The crucible is then cooled to room temperature in the furnace. A small amount of deionized water is added to the platinum crucible to wet the remaining inorganic ash, followed by a small amount of concentrated nitric acid solution (65-70%) to initially dissolve the inorganic ash. The nitric acid solution containing the dissolved inorganic ash is then transferred to a digestion vessel for microwave digestion, such as a polytetrafluoroethylene (PTFE) digestion vessel, and evaporated at 140-160°C until essentially solvent-free. Concentrated nitric acid and hydrogen peroxide solutions are added, and the digestion vessel is placed in an acid-removing apparatus for pre-digestion. After pre-digestion, the vessel is removed and cooled to room temperature. The digestion vessel is then sealed and placed in a microwave digestion apparatus for microwave digestion. After microwave digestion, the digestate is washed into a volumetric flask with deionized water and brought to a final volume. A blank experiment is performed simultaneously, in which no binder is added to the platinum crucible. When calculating the content of alkali metal elements in the adhesive, the content of alkali metal elements in the blank experiment should be deducted to further improve the accuracy of the results of the content of alkali metal elements in the adhesive.

[0079] Pre-digestion before microwave digestion offers advantages such as uniform heating, reduced reagent usage, low blank count, and high efficiency and energy saving. It also effectively avoids sample component loss and the introduction of interfering substances. Furthermore, pre-digestion effectively prevents accidents like digester explosions that can occur with direct digestion, reduces digester wear, and extends its lifespan. During pre-digestion, controlling the temperature is crucial; this temperature removes some moisture from the system, facilitating subsequent microwave digestion. In other words, pre-digestion effectively increases the acid concentration in the sample solution, which is beneficial for subsequent microwave digestion. Under microwave conditions, the sample-acid mixture absorbs microwave heat, increasing oxidation reactivity, causing the sample surface layer to agitate and break down, continuously increasing contact between the sample surface and the acid, thus resulting in more thorough sample digestion.

[0080] The peak intensities of alkali metal elements in the digestion solution were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The peak intensities of alkali metal elements in a blank experiment were also measured simultaneously.

[0081] ICP-OES tests were performed on standard solutions of multiple alkali metal elements with known concentrations. The peak intensities of the alkali metal elements in the standard solutions were recorded. The standard curve of the alkali metal elements was plotted with the peak intensities of the alkali metal elements in the standard solutions as the ordinate and the concentration of the alkali metal elements in the standard solutions as the abscissa. This is the standard curve plotted by the external standard method mentioned above. A linear equation was obtained by fitting the curve.

[0082] Based on the peak intensity of alkali metal elements in the digestion solution, the mass concentration of alkali metal elements in the digestion solution can be obtained from this standard curve.

[0083] The linearity of the standard curve should be 0.995 or higher, i.e., R0. 2 ≥0.995. Verification showed that Na can be detected at a wavelength of 589.592 nm and Li at a wavelength of 670.776 nm, with no spectral interference, effectively enabling the quantification of alkali metal content in samples.

[0084] The content of alkali metal elements in the adhesive can be calculated using the following formula:

[0085] x i =(C-C0)×V×f / m,

[0086] Where, x i The content of the alkali metal element i to be tested in the binder is expressed in mg / kg.

[0087] C represents the mass concentration of alkali metal element i in the digestion solution obtained from the standard curve, in mg / L.

[0088] C0 represents the mass concentration of alkali metal element i in the blank solution obtained from the standard curve, in mg / L.

[0089] V represents the volume of the digestion solution, in mL;

[0090] f is the dilution factor. If the digestion solution is not diluted, f = 1.

[0091] m represents the mass of the adhesive, expressed in grams (g).

[0092] This invention employs ICP-OES for testing, enabling simultaneous quantitative analysis of multiple elements with detection limits down to the mg / kg level. Under these testing conditions, the detection limits for Na and Li in the digestion solution reach 0.03 mg / L and 0.01 mg / L, respectively, with spiked recoveries of 90-110%. The absolute difference between independent parallel sample tests does not exceed 5% of the arithmetic mean, allowing for precise quantification of alkali metal content in samples.

[0093] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0094] Example 1

[0095] The method for testing the sodium and lithium content in the adhesive in this embodiment includes the following steps:

[0096] 1) Sample Preparation: Weigh 0.2g (accurate to 0.0001g) of binder sample (national standard material, developed by the National Steel Materials Testing Center of Steel Research Institute NACK Testing Technology Co., Ltd.) into platinum crucibles 1, 2, 3, and 4 respectively. Add 0.1mL of GSB G 62004-90 sodium standard solution (medium: ultrapure water) with a Na element concentration of 1000mg / L and 0.1mL of GSB G 62001-90 lithium standard solution (medium: 10% HCl) with a Li element concentration of 1000mg / L to platinum crucibles 3 and 4 respectively. The theoretical spiking mass m 加标 The sample consisted of 100 μg each of Na and Li. Platinum crucibles 1 and 2 were parallel sample sets (parallel sample 1 and parallel sample 2), while platinum crucibles 3 and 4 were parallel sample recovery sets (spiked recovery sample 1 and spiked recovery sample 2). Blank experiments were conducted simultaneously in platinum crucibles 5 and 6 (blank sample 1 and blank sample 2), meaning no substance was added to the platinum crucibles.

[0097] 2) Sample pretreatment:

[0098] Dry ashing treatment: Platinum crucibles 1, 2, 3, 4, 5 and 6 from step 1) are placed in a muffle furnace, heated to 300℃ and held for 30 min for carbonization treatment, and then held at 600℃ for 30 min for ashing treatment. The furnace is then cooled to room temperature to obtain inorganic ash.

[0099] Pre-digestion treatment: Add a small amount of deionized water to platinum crucibles 1, 2, 3, 4, 5, and 6 respectively to wet the residual inorganic ash. Add 1 mL of 69.37% concentrated nitric acid solution to initially dissolve the inorganic ash, and transfer it to a PTFE digestion vessel for microwave digestion. Evaporate to near dryness at 150℃. Add 4 mL of 69.37% concentrated nitric acid solution (analytical grade) and 2 mL of 30.92% hydrogen peroxide solution (analytical grade). Place the PTFE digestion vessel in the new TK12 acid removal apparatus. Set the acid removal apparatus temperature to 150℃ and keep it at that temperature for 30 minutes for pre-digestion treatment. After the temperature is maintained, remove the apparatus and cool it to room temperature.

[0100] Microwave digestion: The PTFE digestion vessel was sealed and placed into the new TANK eco microwave digester. The microwave digester was programmed to rise to 135°C for 6 minutes, hold for 5 minutes, rise to 180°C for 4 minutes, hold for 4 minutes, rise to 210°C for 5 minutes, and hold for 30 minutes. After microwave digestion, the digestion solution was washed into a 25 mL volumetric flask with deionized water and diluted to volume. The solution diluted 5 times was used as the test solution. In some embodiments, if obvious solid insoluble matter was found in the digestion solution after microwave digestion, it was necessary to filter it and dilute it into a 25 mL volumetric flask to volume; otherwise, filtration was not required.

[0101] 3) Preparation of standard solutions: Accurately transfer 5 mL of GSB G 62004-90 sodium standard solution (1000 mg / L Na, medium: ultrapure water) and 5 mL of GSB G 62001-90 lithium standard solution (1000 mg / L Li, medium: 10% HCl) into a 50 mL volumetric flask, and dilute to volume with deionized water. This solution is a stock solution of mixed standard solutions of 100 mg / L Na and 100 mg / L Li. Using serial dilution, prepare working standard solutions with concentrations of 0 mg / L, 0.1 mg / L, 0.5 mg / L, 1.0 mg / L, 2.0 mg / L, and 5.0 mg / L.

[0102] 4) Thermo Fisher Scientific ICAP PRO ICP-OES Detection: Under the set test conditions (as shown in Table 1), take the working standard solution from step 3) and perform ICP-OES testing to obtain the peak intensities of sodium and lithium. Plot standard curves for sodium and lithium using the external standard method, with element concentration as the x-axis and peak intensity as the y-axis. Figure 1 As shown, sodium can be detected at a wavelength of 589.592 nm; Figure 2 As shown, lithium can be detected at a wavelength of 670.776 nm. Figure 3 The standard curve for sodium has a linear fitting coefficient R0. 2=1.000, in the curve equation y=ax+b, a is -19.452 and b is 522.069; Figure 4 The standard curve for lithium has a linear fitting coefficient R. 2 =1.000, in the curve equation y=ax+b, a is 4.729 and b is 2647.086. Tests were conducted simultaneously on platinum crucibles 1, 2, 3, 4, 5, and 6.

[0103] 5) Calculation of target analyte content: The content of sodium and lithium elements was calculated according to the following formulas. The test results are shown in Table 2.

[0104] x i =(C-C0)×V×f / m,

[0105] Where, x i The content of the alkali metal element i to be tested in the binder is expressed in mg / kg.

[0106] C represents the mass concentration of alkali metal element i in the digestion solution obtained from the standard curve, in mg / L.

[0107] C0 represents the mass concentration of alkali metal element i in the blank solution obtained from the standard curve, in mg / L.

[0108] V represents the volume of the digestion solution, in mL; in this example, V is 25 mL.

[0109] f is the dilution factor. If the digestion solution is not diluted, f = 1; in this example, f is 5.

[0110] m represents the mass of the adhesive, expressed in grams; in this example, m is 0.2 g.

[0111] Table 1

[0112]

[0113] Table 2

[0114]

[0115] In Example 1, the absolute difference between the parallel sample test results did not exceed 5% of the arithmetic mean, and the spike recovery rate of the spiked recovery sample was between 90% and 105%, indicating that the test results were highly accurate.

[0116] Spiked recovery rate = ((C) 加标回收样i -C0)×V×f-(x i ×m)) / m 加标i ×100%,

[0117] Among them, C 加标回收样iThe mass concentration of alkali metal element i in the spiked recovery sample digestion solution obtained from the standard curve is expressed in mg / L.

[0118] C0 represents the mass concentration of alkali metal element i in the blank solution obtained from the standard curve, expressed in mg / L; in this example, the C0 values ​​for Na and Li were 0.005 mg / L and 0.000 mg / L, respectively.

[0119] V represents the volume of the digestion solution, in mL; in this example, V is 25 mL.

[0120] f is the dilution factor. If the digestion solution is not diluted, f = 1; in this example, f is 5.

[0121] m represents the mass of the adhesive, expressed in grams; in this example, m is 0.2 g.

[0122] x i The content of the alkali metal element i to be tested in the binder is expressed in mg / kg. In this example, the contents of Na and Li in the binder are 743.6 mg / kg and 970.0 mg / kg, respectively, which are taken as the average values ​​of the tests of parallel sample 1 and parallel sample 2.

[0123] m 加标i The amount of theoretical alkali metal element i in the spiked recovery sample is expressed in μg; in this example, m 加标Na和 m 加标Li The value is 100 μg.

[0124] Example 2

[0125] 1) Preparation and pretreatment of control blank solutions: Prepare six clean platinum crucibles, numbered A1, A2, B1, B2, C1, and C2. Except for the absence of sample binder, perform pretreatment as described in step 2) of Example 1. After digestion, A1 and A2 do not require filtration. B1 and B2 are filtered using standard Cytiva 11cm quantitative slow filter paper, and C1 and C2 are filtered using Whatman 540 ashless filter paper. Then, wash the digested solution into 25mL volumetric flasks with deionized water and dilute to volume to prepare the test solution.

[0126] 2) Preparation of standard solution: Same as step 3 in Example 1.

[0127] 3) ICP-OES detection: Same as step 4 in Example 1.

[0128] 4) Calculation of the content of the target substance: Same as step 5 in Example 1. The test results are shown in Table 3.

[0129] Table 3

[0130]

[0131] Compared to the unfiltered blank solution, the filter paper introduces different amounts of Na elements during filtration, but does not introduce Li elements. However, the amount of Na elements introduced by Whatman 540 ashless filter paper is relatively low. Therefore, when conducting Na element tests, Whatman 540 ashless filter paper should be given priority for filtering the digestion solution.

[0132] Example 3

[0133] The testing methods for sodium and lithium content in the adhesive in this embodiment are basically the same as those in Example 1, except that step 2) involves sample pretreatment:

[0134] Dry ashing treatment: Platinum crucibles 1, 2, 3, 4, 5 and 6 from step 1) are placed in a muffle furnace, heated to 280°C and held for 40 minutes for carbonization treatment, and then held at 580°C for 40 minutes for ashing treatment. The furnace is then cooled to room temperature to obtain inorganic ash.

[0135] Pre-digestion treatment: Add a small amount of deionized water to platinum crucibles 1, 2, 3, 4, 5, and 6 respectively to wet the residual inorganic ash. Add 1 mL of 69.37% concentrated nitric acid solution to initially dissolve the inorganic ash, and transfer it to a PTFE digestion vessel for microwave digestion. Evaporate to near dryness at 150℃. Add 6 mL of 69.37% concentrated nitric acid solution (analytical grade) and 2 mL of 30.92% hydrogen peroxide solution (analytical grade). Place the PTFE digestion vessel in the new TK12 acid removal apparatus. Set the acid removal apparatus temperature to 140℃ and keep it at that temperature for 30 minutes for pre-digestion treatment. After the temperature is maintained, remove the apparatus and cool it to room temperature.

[0136] Microwave digestion: The PTFE digestion vessel was sealed and placed into the new TANK eco microwave digester. The microwave digester was programmed to rise to 130°C in 6 minutes, hold for 4 minutes, rise to 170°C in 4 minutes, hold for 4 minutes, rise to 200°C in 5 minutes, and hold for 40 minutes. After microwave digestion, the digestion solution was washed into a 25 mL volumetric flask with deionized water and diluted to volume. The solution obtained by diluting the sample solution by 5 times was used as the test solution.

[0137] The test results are shown in Table 4.

[0138] Table 4

[0139]

[0140] In this example, the CO values ​​for Na and Li were 0.003 mg / L and 0.001 mg / L, respectively.

[0141] In Example 3, the absolute difference between the parallel sample test results did not exceed 5% of the arithmetic mean, and the spike recovery rate was between 90% and 105%, indicating that the test results were highly accurate.

[0142] Example 4

[0143] The testing methods for sodium and lithium content in the adhesive in this embodiment are basically the same as those in Example 1, except that step 2) involves sample pretreatment:

[0144] Dry ashing treatment: Platinum crucibles 1, 2, 3, 4, 5 and 6 from step 1) are placed in a muffle furnace, heated to 320℃ and held for 20 minutes for carbonization treatment, and then held at 620℃ for 20 minutes for ashing treatment. The furnace is then cooled to room temperature to obtain inorganic ash.

[0145] Pre-digestion treatment: Add a small amount of deionized water to platinum crucibles 1, 2, 3, 4, 5, and 6 respectively to wet the residual inorganic ash. Add 1 mL of 69.47% concentrated nitric acid solution to initially dissolve the inorganic ash, and transfer it to a PTFE digestion vessel for microwave digestion. Evaporate to near dryness at 150℃. Add 7 mL of 69.47% concentrated nitric acid solution (analytical grade) and 2 mL of 30.92% hydrogen peroxide solution (analytical grade). Place the PTFE digestion vessel in the new TK12 acid removal apparatus. Set the acid removal apparatus temperature to 160℃ and keep it at that temperature for 30 minutes for pre-digestion treatment. After the temperature is maintained, remove the apparatus and cool it to room temperature.

[0146] Microwave digestion: The PTFE digestion vessel was sealed and placed into the new TANK eco microwave digester. The microwave digester was programmed to rise to 140°C in 6 minutes, hold for 5 minutes, rise to 180°C in 4 minutes, hold for 5 minutes, rise to 210°C in another 5 minutes, and hold for 50 minutes. After microwave digestion, the digestion solution was washed into a 25 mL volumetric flask with deionized water and diluted to volume. The solution obtained by diluting the sample solution by 5 times was used as the test solution.

[0147] The test results are shown in Table 5.

[0148] Table 5

[0149]

[0150] In this example, the CO values ​​for Na and Li were 0.009 mg / L and 0.000 mg / L, respectively.

[0151] In Example 4, the absolute difference between the parallel sample test results did not exceed 5% of the arithmetic mean, and the spike recovery rate was between 90% and 105%, indicating that the test results were highly accurate.

[0152] Comparative Example 1

[0153] The testing methods for sodium and lithium content in the binder of this comparative example and Example 1 are basically the same, except that in step 1), a PTFE beaker is used instead of a platinum crucible, and in step 2), a wet oxidation method is used for sample pretreatment. Specifically, 10 mL of 69.37% concentrated nitric acid solution (analytical grade) and 4 mL of 30.92% hydrogen peroxide solution (analytical grade) are added to PTFE beakers 1, 2, 3, 4, 5, and 6, respectively. The PTFE beakers are then placed on a graphite heating plate, and the temperature is set to 150°C and held for 30 min. The temperature is then increased to 200°C and held for 30 min for digestion. After the holding period, the beakers are removed and cooled to room temperature.

[0154] The test results are shown in Table 6.

[0155] Table 6

[0156]

[0157] In this example, the CO values ​​for Na and Li were 0.010 mg / L and 0.003 mg / L, respectively.

[0158] In Comparative Example 1, the absolute difference between the parallel sample test results exceeded 5% of the arithmetic mean, and the spike recovery rate was between 100% and 120%, indicating that the accuracy of the test results was poor.

[0159] Comparative Example 2

[0160] The test method for the content of alkali metal elements in the binder of this comparative example and Example 1 is basically the same. The difference is that microwave digestion was not performed in step 2). After the pre-digestion treatment, the sample was further heat-treated in the new TK12 acid removal instrument according to the following procedure: 6 min to 135°C, hold for 5 min, 4 min to 180°C, hold for 4 min, then 5 min to 210°C and hold for 30 min. After the heat treatment, the digestion solution was washed into a 25 mL volumetric flask with deionized water and diluted to volume. The solution after diluting the sample solution by 5 times was used as the test solution.

[0161] The test results are shown in Table 7.

[0162] Table 7

[0163]

[0164] In this example, the CO values ​​for Na and Li were 0.006 mg / L and 0.001 mg / L, respectively.

[0165] In Comparative Example 2, the absolute difference between the parallel sample test results exceeded 5% of the arithmetic mean, and the spike recovery rate was between 80% and 95%, indicating that the accuracy of the test results was poor.

[0166] Comparative Example 3

[0167] The test method for the content of alkali metal elements in the binder of this comparative example and Example 1 is basically the same. The difference is that in step 2), dry ashing treatment is performed: platinum crucibles 1, 2, 3, 4, 5 and 6 in step 1) are placed in a muffle furnace, heated to 500°C and held for 2 hours for dry ashing treatment, and then cooled to room temperature with the furnace to obtain inorganic ash.

[0168] Furthermore, no microwave digestion treatment was performed. After the pre-digestion treatment, the sample was further heat-treated in the new TK12 acid removal instrument according to the following procedure: 6 minutes to 135°C, 5 minutes to hold, 4 minutes to 180°C, 4 minutes to hold, 5 minutes to 210°C, and 30 minutes to hold. After the heat treatment, the digestion solution was washed into a 25 mL volumetric flask with deionized water and diluted to volume. The solution after diluting the sample solution by 5 times was used as the test solution.

[0169] The test results are shown in Table 8.

[0170] Table 8

[0171]

[0172] In this example, the CO values ​​for Na and Li were 0.003 mg / L and 0.000 mg / L, respectively.

[0173] In Comparative Example 3, the absolute difference between the parallel sample test results did not exceed 5% of the arithmetic mean, and the spiked recovery rate was between 80% and 95%, indicating that the accuracy of the test results was poor. Furthermore, a relatively long dry ashing treatment time is required to completely remove organic matter from the binder.

[0174] As can be seen from the above, compared with the comparative example, the test method for the content of alkali metal elements in the adhesive provided by the present invention includes dry ashing treatment, pre-digestion treatment and microwave digestion treatment in sequence in the pretreatment process. Combined with the inductively coupled plasma atomic emission spectrometry test method, and based on the external standard method to determine the content of alkali metal elements in the adhesive, the accuracy of the final test results can be improved.

[0175] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for testing the content of alkali metal elements in an adhesive, characterized in that, Includes the following steps: 1) The binder is subjected to dry ashing treatment, pre-digestion treatment and microwave digestion treatment in sequence to obtain digestion solution; the binder includes alkali metal elements, including sodium and / or lithium elements; the temperature of microwave digestion treatment is higher than the temperature of pre-digestion treatment. 2) The peak intensity of the alkali metal element in the digestion solution was measured using inductively coupled plasma atomic emission spectrometry; 3) Plot a standard curve using the external standard method, and calculate the content of the alkali metal element in the binder based on the peak intensity of the alkali metal element in the digestion solution according to the standard curve.

2. The test method according to claim 1, characterized in that, The dry ashing treatment includes: carbonizing the adhesive at 280~320℃ for 20~40 minutes, and then ashing at 580~620℃ for 20~40 minutes to obtain inorganic ash.

3. The test method according to claim 2, characterized in that, The pre-digestion treatment includes: pre-digesting the inorganic ash under the action of concentrated nitric acid and hydrogen peroxide solution to obtain a mixed solution.

4. The test method according to claim 3, characterized in that, The concentration of the concentrated nitric acid is 65-70%; And / or, the concentration of the hydrogen peroxide solution is 30.0~32.0%; And / or, the volume ratio of the concentrated nitric acid to the hydrogen peroxide solution is (2.0~4.0):

1.

5. The test method according to claim 4, characterized in that, The total volume of the concentrated nitric acid and the hydrogen peroxide solution, and the mass ratio of the binder, are (30~100) mL: 1g.

6. The test method according to claim 5, characterized in that, The pre-digestion treatment is carried out at a temperature of 140~160℃ for a time of 20~40 min.

7. The test method according to claim 6, characterized in that, The microwave digestion process includes: under microwave action, maintaining the mixed solution at 120~140℃ for 3~5 min, at 160~180℃ for 3~5 min, and at 190~210℃ for 30~60 min to obtain a digestion solution.

8. The test method according to claim 7, characterized in that, The digestion solution contains particulate matter, and the digestion process further includes filtering the digestion solution. The filtration process uses ashless filter paper.

9. The test method according to claim 7, characterized in that, The concentration of the alkali metal element in the digestion solution is >5 mg / L, and the digestion process further includes: diluting the digestion solution.

10. The test method according to any one of claims 7-9, characterized in that, In step 3), the step of plotting the standard curve based on the external standard method includes: Standard solutions with different contents of alkali metal elements were prepared, and the standard solutions were tested using an inductively coupled plasma atomic emission spectrometer to establish a curve relating the peak intensity of the alkali metal element to the concentration of the alkali metal element in the standard solution.

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