Method for verifying stability of cadmium isotope standard substance based on organic matter interference evaluation

Abstract

The application discloses a kind of based on organic matter interference evaluation cadmium isotope standard substance stability verification method, belongs to environmental monitoring and geology reference material analysis technical field, the method first from the mixed to be evaluated Cd standard reference material large sample Randomly equal amount takes two samples;Two samples are respectively subjected to acid digestion and Cd separation and purification, then MC-ICP-MS measurement is carried out, obtains the δ 114 / 110 Cd value of each sample;Finally, the difference of the δ 114 / 110 Cd value of two samples is calculated and compared with threshold value to judge the homogeneity and stability of the Cd isotope composition of the standard substance, and the effectiveness of the method is verified by the fact that the measurement results of the control sample are within the known demonstration interval. The verification method directly separates the sample when taking the solid powder sample, classifies and evaluates it based on its inherent physical and chemical properties, and provides a reliable reference standard substance screening method for Cd isotope research of environmental samples.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring and geological reference material analysis technology, specifically involving a method for verifying the stability of cadmium isotope standard materials based on organic interference assessment. This method is used to screen uniform and stable standard reference materials for Cd isotope research, ensuring the accuracy and reliability of related analytical results. Background Technology

[0002] In the fields of environmental monitoring and geological reference material analysis, Cd isotope analysis is a core technical means to trace Cd pollution sources and study the migration and transformation patterns of Cd in the environment. Among them, cadmium isotope standard materials serve as the "benchmark reference" in the analytical process, and the uniformity and stability of their isotopic composition directly determine the accuracy of the analytical data. If the standard materials are unstable, it will lead to a lack of comparability of analytical results from different laboratories and different batches, which will seriously hinder the progress of Cd isotope research.

[0003] In the field of stability assessment of cadmium (Cd) isotope reference materials, the existing technology generally adopts the determination scheme of "single sample dissolution followed by sample division": that is, first prepare a solid sample of twice the amount and completely dissolve it into liquid, then divide the liquid into two equal parts for subsequent isotope measurement, and determine the stability of the reference material by the measurement difference between the two liquids.

[0004] However, this scheme has a fundamental flaw: liquids are fluid, and after the sample dissolves into a fluid, even if the isotope distribution in the solid stage is uneven (e.g., due to differences in the binding of organic matter and Cd), it will further homogenize in the liquid, resulting in a smaller difference in the Cd isotope composition between the two liquid samples. This fails to truly reflect the isotopic composition homogeneity and stability of the solid standard material itself, and easily leads to the misjudgment of actually unstable samples (especially those with high organic matter content) as stable, seriously affecting the accuracy of Cd isotope reference material screening. In practice, it has been found that even for some internationally recognized standards, implicit biases still exist when measured using the existing scheme, resulting in a long-standing lack of a reliable method for assessing the stability of Cd isotope standards. Summary of the Invention

[0005] This invention addresses the problems in existing cadmium isotope standard material stability assessment methods, such as the "liquid sample separation" approach which easily leads to artificial homogenization of isotopes, fails to accurately reflect the stability of solid samples, and makes it difficult to capture the influence of organic matter. It provides a method for verifying the stability of cadmium isotope standard materials based on organic interference assessment. With "direct sample separation in the solid stage" as the core, it accurately determines the true stability of the standard material and provides reliable reference materials for cadmium isotope research.

[0006] To address the aforementioned technical problems, the present invention provides a method for verifying the stability of cadmium isotope standard materials based on organic interference assessment. This method, centered on "parallel sampling - independent measurement - difference determination," eliminates the influence of interference factors such as organic matter on the stability assessment. The method includes the following steps:

[0007] (1) First, thoroughly mix the large sample of the Cd standard reference material to be evaluated to ensure the representativeness of the sample, and then randomly take two samples of equal amount from it; the sampling amount should meet the requirements of Cd content detection to ensure that the subsequent measurement signal is stable and reliable.

[0008] (2) After the two samples were independently subjected to completely identical acid digestion and Cd separation and purification, MC-ICP-MS was performed to obtain their respective Cd isotopic compositions, expressed as δ¹⁸O. 114 / 110 Cd value represents;

[0009] (3) Calculate δ for the two samples 114 / 110 The difference in Cd values;

[0010] (4) Compare the difference with the threshold: If the difference is less than the threshold, the isotopic composition of the Cd standard reference material is determined to be uniform and stable, and it can be used as a Cd isotopic reference material; if the difference is greater than or equal to the threshold, the isotopic composition of the Cd standard reference material is determined to be unstable and it is not suitable as a Cd isotopic reference material.

[0011] The stability verification method for cadmium isotope reference materials based on organic interference assessment of this invention is centered on "parallel sampling, independent measurement, and difference determination". It is simple and efficient to operate and does not require a complex interference correction model. By performing independent and consistent pretreatment and measurement on two samples, interference such as organic matter can be effectively eliminated, ensuring the accuracy of the results. Relying on a clear difference threshold, the stability of cadmium isotope reference materials can be quickly and accurately determined, which greatly improves the efficiency and reliability of reference material screening and provides a reliable reference benchmark for cadmium isotope research.

[0012] As a further description of the above technical solution: the Cd content of the large sample of the Cd standard reference material to be evaluated is greater than 0.3 μg / g, ensuring that the standard material to be evaluated contains sufficient Cd, which can stabilize the subsequent MC-ICP-MS measurement signal, reduce measurement errors at low contents, provide a reliable data basis for the accurate determination of isotope composition differences, and ensure that the screened standard material meets the accuracy requirements of cadmium isotope analysis.

[0013] As a further description of the above technical solution: the acid digestion process in step (2) is as follows: firstly, the sample is digested at high temperature in a sealed container using a mixture of concentrated nitric acid and concentrated hydrofluoric acid until no black precipitate is found, in order to dissolve the silicate minerals in the sample and ensure complete decomposition of the sample; then, depending on the situation, it is transferred to a polytetrafluoroethylene (PFA) container with a screw cap (washed with superior pure nitric acid and hydrochloric acid in sequence and then evaporated to dryness before use), evaporated to wet salt state, and then aqua regia or anti-aqua regia is added to further digest the organic matter; after evaporation to remove fluoride, concentrated hydrochloric acid is added and heated to dissolve in order to change the solution medium, and then a double diluent (mass ratio of 2:1 to the sample) is added and heated to fully mix the isotopes, which is suitable for the subsequent cadmium separation and purification process, and can also use the double diluent method to accurately correct the mass spectrometry mass discrimination effect; finally, after evaporation to dryness, 6 N hydrochloric acid (diluted with high-purity water) is added and heated to dissolve, and then evaporated to dryness again for subsequent Cd separation and purification and MC-ICP-MS measurement.

[0014] As a further description of the above technical solution: In step (2), the Cd separation and purification uses anion exchange resin, loaded with digested Cd sample (dissolved in 2 mL of 6N hydrochloric acid), and rinsed sequentially with dilute nitric acid and dilute hydrochloric acid to remove matrix elements. Then, it is rinsed with dilute nitric acid containing a small amount of hydrogen bromide (prepared on-site in the dark before use to prevent hydrogen bromide from decomposing in light) to further remove residual interference. Finally, the Cd fraction is collected by directional rinsing with dilute nitric acid, ensuring efficient separation of Cd from impurities while maximizing the retention of target elements. Finally, it is evaporated to dryness to obtain a purified Cd sample, which can be directly adapted to subsequent MC-ICP-MS measurements, effectively reducing matrix interference and background effects, and providing a δ¹² range. 114 / 110 Accurate measurement of Cd values ​​provides a basis for high-purity samples, further ensuring the reliability of the stability determination results of standard substances.

[0015] As a further description of the above technical solution: the MC-ICP-MS measurement in step (2) is performed in a cleanroom of class 1000 or higher, effectively reducing external pollution from trace amounts of cadmium and other impurities in the air; a multi-receiver inductively coupled plasma mass spectrometer is used to determine the stable isotope composition of Cd in the purified Cd sample, and the container used is an acid-washed PFA container to avoid contamination of the sample by residual impurities in the container; the Cd standard of NIST SRM 3108 is used as a reference standard to obtain the δ¹⁸O values ​​of each sample. 114 / 110 Cd value, ensuring δ 114 / 110 The Cd value measurement is consistent and comparable, avoiding measurement deviations caused by differences in the benchmark, and ultimately providing key measurement conditions to accurately obtain the Cd isotope composition of the sample and reliably determine the stability of the standard material.

[0016] As a further description of the above technical solution: each sample shall be measured by MC-ICP-MS at least 3 times, and data with a standard deviation (2SD) less than 0.06‰ shall be selected as valid data (if 2SD ≥ 0.06‰, measurement shall be repeated), and the average value of the valid data shall be taken as the final δ of the sample. 114 / 110 The Cd value reduces measurement bias and makes the Cd isotopic composition data of each sample closer to the true value. This provides a high-precision data basis for subsequent calculation of the difference between two samples and reliable determination of the stability of the standard material, avoiding misjudgment of stability due to measurement error of a single sample.

[0017] As a further description of the above technical solution: both steps (1) and (2) are performed in a cleanroom of ≥1000 class, and the Cd separation and purification described in step (2) is performed in a Class 100 fume hood. A cleanroom of ≥1000 class can significantly reduce the particulate concentration of cadmium and other interfering elements in the air, avoid environmental impurities from contaminating the sample during sampling, acid digestion, Cd separation and purification, and measurement, and ensure the authenticity of the initial state of the sample; while a Class 100 fume hood can provide a higher cleanliness environment in the key matrix element removal process, reduce secondary pollution of trace amounts of cadmium or interfering substances during separation, reduce background interference throughout the entire process from sample acquisition to purification, and ensure that the measurement difference between two parallel samples truly reflects the stability of the standard substance itself.

[0018] As a further description of the above technical solution: the acid used in step (2) must be at least of analytical grade and must be purified by at least two distillations before use. The water used is high-purity water. This can deeply remove trace amounts of cadmium and interfering elements remaining in the reagent, eliminating the influence of the reagent background on isotope measurements from the source.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention replaces the existing "liquid sampling" with "direct solid-stage sampling," fundamentally avoiding the problem of artificial isotope homogenization caused by liquid fluidity, and ensuring that the δ¹⁸O values ​​of the two samples are homogenized. 114 / 110 The difference in Cd values ​​can truly reflect the uniformity and stability of the isotopic composition of the solid standard material itself. By performing solid sampling and independent processing, it is ensured that the measurement difference comes only from the standard material itself, rather than from human interference from the sampling method. Combined with the previous discovery and verification of the latent bias of international standards, it is further proved that this method can accurately identify stability problems that cannot be detected by existing methods, providing a reliable reference material basis for Cd isotope pollution source apportionment and environmental migration research, and ensuring the accuracy and comparability of subsequent analytical data. Attached Figure Description

[0021] Figure 1 This is a distribution map of Cd isotope measurements after multiple samples were divided into two parts. Detailed Implementation

[0022] The claims of the present invention will be further described in detail below with reference to specific embodiments, but this does not constitute any limitation on the present invention. Any limited modifications made by any person within the scope of protection of the claims of the present invention are still within the scope of protection of the claims of the present invention.

[0023] Cadmium (Cd) has eight stable isotopes: 106 Cd, 108 Cd, 110 Cd, 111 Cd, 112 Cd, 113 Cd, 114 Cd and 116 Cd, of which the most abundant in nature is 110 Cd (12.49%) and 114 Cd (28.73%). Cd isotopic composition is usually expressed as δ¹⁸. 114 Cd, defined as the concentration of cadmium in the sample 114 Cd / 110 Cd relative to standard materials (such as NIST SRM 3108) 114 Cd / 110 The thousandths deviation of the Cd ratio:

[0024] .

[0025] Cd isotope measurements often employ multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) with a spike-sample double-spike method for mass discrimination correction to improve accuracy and repeatability. Commonly used isotope pairs are... 114 Cd / 110 Cd is the most commonly used ratio combination in Cd isotope research due to its high abundance, low interference, and stable signal.

[0026] In the environmental field, determining the sample types to be selected can provide indicative significance for different environmental types. The sample selection of this invention mainly uses samples included in the catalogs of the China National Center for Standard Materials, the National Institute of Standards and Materials of the United States, and the European Organization for Standardization, ensuring that the selected samples are authoritative and recognized. In addition, the selected sample types generally have certain requirements for Cd concentration (greater than 0.3 μg / g), ensuring that the establishment of methods for them can provide indicative significance for scientific research.

[0027] The Cd isotope stability of the selected samples was verified using the verification method of the present invention. The specific steps are as follows:

[0028] (1) In a clean laboratory of grade ≥1000, the selected Cd standard reference material sample (Cd content greater than 0.3 μg / g) to be evaluated is thoroughly mixed to ensure the representativeness of the sample. Two samples are randomly taken out in equal amounts to meet the requirements for Cd content detection.

[0029] (2) The two selected samples were acid digested to convert them into Cd sample solutions. The acid used for acid digestion was GR or higher purity acid, and was purified by distillation at least twice before use. The water used was high purity water. All dilute acids were prepared on-site with high purity water before use. The inner liner of the high pressure jar and the PFA container (equipped with screw caps) were boiled in 1:1 nitric acid and 1:1 hydrochloric acid solutions at 120°C for at least 6 hours. After tightening the caps, they were refluxed in 1:1 nitric acid and ultrapure water solutions at 120°C for 6 hours. Finally, the water was evaporated and the container was used. The reagent bottles, pipette tips and other experimental equipment were soaked in 10% nitric acid solution for 48 hours, washed with ultrapure water, and finally dried in a Class 100 fume hood before use.

[0030] The acid digestion process is as follows:

[0031] In a cleanroom of ≥1000 grade, the selected sample was placed in the inner liner of a high-pressure sealed container. A mixture of concentrated nitric acid and concentrated hydrofluoric acid was added using a pipette to dissolve the silicate minerals in the sample. The container was then sealed and placed in an oven at 190°C for at least 3 days to digest until no black precipitate remained. The sample was then transferred to a PFA container with a screw cap and evaporated to dryness at 125°C. When the sample was in a wet salt state, it was removed from the hot plate. 5–10 mL of aqua regia or its anti-aqua regia was added to further digest the organic matter. The container was then sealed and allowed to stand for 1–10 hours. After the reaction slowed down slightly, the sample was transferred to a hot plate and heated to 125°C until completely dissolved. Evaporation was first carried out at a low temperature of 40–60°C. After no obvious bubbles were produced, the temperature was raised to 125°C. When only a small amount of sample remained, the temperature was adjusted to 70–90°C and evaporated to dryness. 2 mL of aqua regia or its anti-aqua regia was added to the hot plate. Dissolve 2 mL of concentrated hydrochloric acid at 120°C by heating, then add a double diluent (dose ratio 2:1, m / m) and evaporate to dryness at 125°C; add 2 mL of 6N hydrochloric acid (diluted with high-purity water), dissolve by heating at 120°C, and evaporate to dryness at 125°C.

[0032] The purpose of acid digestion is to convert a solid sample into a fluid solution, which allows for the precise separation of Cd using anion exchange resin. The advantages of reagent selection, purification, and operation in a clean laboratory include reducing background levels throughout the process and minimizing experimental errors.

[0033] (3) In a Class 100 fume hood, add 2 mL of 6N hydrochloric acid to the evaporated acid digestion sample to dissolve it. The amount of Cd in the sample is generally not less than 20 ng, and it is ready for separation and purification.

[0034] The specific process is as follows:

[0035] First, refill the resin with 5 mL of water, wash with 10 mL of 1N HNO3, then change the resin environment with 2 mL of 6N HCl and equilibrate the column with 2 mL of 6N HCl.

[0036] Sample loading: 2 mL sample (6N HCl);

[0037] The matrix was then removed by rinsing sequentially: 2 mL 6 N HCl + 2 mL 6 N HCl (discard), 10 mL 0.3 N HCl + 15 mL 0.3 N HCl (discard); then residual interference was removed by rinsing with 0.5 N HNO3 + 0.1 N HBr (10 mL first, then 20 mL, discard); finally, the sample was rinsed with 10 mL 2 N HNO3 and the Cd fraction was collected, then evaporated to dryness to obtain the purified Cd sample. To remove any organic resin that may have leaked out during purification, 200 μL HNO3 + 200 μL HCl could be added and evaporated to dryness, followed by a change of medium with 400 μL HNO3 and then evaporation to dryness for easier instrument loading.

[0038] If the Cd content in the purified Cd sample is less than 0.2 μg / g, the separation and purification process should be repeated twice to ensure complete removal of the matrix element.

[0039] (4) The Cd purified samples were measured by MC-ICP-MS using a multi-receiver inductively coupled plasma mass spectrometer to obtain the stable isotopic composition of Cd in the Cd purified samples, providing essential data for analyzing whether the Cd isotopic composition in the samples is homogeneous. Each Cd purified sample was measured at least 3 times, and data with a two-fold standard deviation (2SD) less than 0.06 were selected as valid data (if 2SD is greater than 0.06, the data is invalid and needs to be measured again). The valid δ 114 / 110 The average Cd value is used as the final δ of the sample. 114 / 110 Cd value.

[0040] The advantages of reagent selection, purification, and operation in a clean laboratory are to reduce background noise throughout the process and minimize experimental errors; the advantage of using a multi-receiver inductively coupled plasma mass spectrometer to determine Cd isotopes is to improve testing accuracy and make the results more reliable.

[0041] (5) Calculate the final δ of the two samples. 114 / 110 The difference in Cd values ​​is compared with a threshold (0.1‰): if the difference is less than the threshold, the Cd standard reference material is determined to have a uniform and stable isotopic composition and can be used as a Cd isotopic reference material; if the difference is greater than or equal to the threshold, the Cd standard reference material is determined to have insufficient isotopic stability and is not suitable as a Cd isotopic reference material.

[0042] In practice, the separation and purification steps can be adjusted by adding or subtracting steps according to the properties of the sample.

[0043] Validation of low organic matter reference material:

[0044] Using the cadmium isotope standard material stability verification method based on organic interference assessment of the present invention, the low organic matter reference materials NIST SRM 1648a (urban atmospheric particulate matter), GBW07310 (aqueous sediment I), and GBW07312 (aqueous sediment II) were tested. The results are shown in Table 1 and... Figure 1 As shown, NIST SRM 1648a measured δ 114 / 110 Cd = –0.233‰ (2SD = 0.009‰) and δ 114 / 110 Cd = –0.178‰ (2SD = 0.044‰), δ measured twice. 114 / 110 The difference between Cd values ​​is 0.055‰, which is less than 0.1‰; GBW07310 measured δ respectively. 114 / 110 Cd = –0.096‰ (2SD = 0.054‰) and δ 114 / 110 Cd = –0.132‰ (2SD = 0.050‰), the difference between the two measurements is 0.036‰, which is less than 0.1‰; GBW07312 measured δ 114 / 110 Cd = –0.107‰ (2SD = 0.053‰) and δ 114 / 110 The Cd value was -0.010‰ (2SD = 0.020‰), and the difference between the two measurements was 0.097‰, which is less than 0.1‰. The isotopic differences of the three low-organic-matter samples were all less than 0.1‰, indicating that their Cd isotopic compositions were highly uniform and stable, and they could be used as Cd isotopic reference materials.

[0045] Table 1. Detection results of low organic matter reference materials

[0046]

[0047] Validation of high organic matter reference material:

[0048] The stability verification method of cadmium isotope reference materials based on organic interference assessment of this invention was used to test high organic matter reference materials NIST SRM 1573a (tomato leaves), NIST SRM 1570a (spinach leaves), NIST SRM 2781 (sewage sludge), NIST SRM 695 (fertilizer), ERM-BB186 (pig kidney), and GBW11159 (coal). The results are shown in Table 2. Since there was previous measurement data for NIST SRM 1573a and NIST SRM 1570a, only one sample was measured for comparison. The final results are compared with the literature values ​​(δ0.05 of NIST SRM 1573a). 114 / 110 Cd = -0.07‰, 2SD = 0.09‰; δ of NISTSRM 1570a 114 / 110 The difference between Cd=0.47‰ and 2SD=0.03‰ is too large (e.g., Figure 1 As shown in the figure), NIST SRM 695 (fertilizer) and GBW11159 (coal) showed multiple invalid data with 2SD > 0.06‰, indicating that the high organic matter samples could not even meet the requirement of "single sample measurement repeatability" due to the uneven binding of Cd with organic matter, thus completely ruling out their possibility as standard samples; among the other samples, the difference between the two samplings of NIST SRM 2781 and ERM-BB186 both exceeded 0.1‰, indicating that their Cd isotope composition homogeneity was poor and they were not suitable as Cd isotope reference materials.

[0049] Based on the detection results of low-organic-matter and high-organic-matter reference materials, the following conclusions can be drawn: If the organic matter content in the elemental standard sample to be developed is too high (exceeding the organic matter content levels of tomato leaves, spinach leaves, sewage sludge, fertilizer, and coal), it will significantly affect the uniformity of the Cd isotope composition in the sample, resulting in a lack of potential and stability for further development as a Cd isotope standard material. Furthermore, given the high cost of preparing elemental standard samples, the significant technical difficulties in development, and the high experimental costs required for Cd isotope analysis, in future explorations of Cd isotope standard material development, samples with low organic matter content should be prioritized. This effectively avoids development failures due to excessively high organic matter content in the samples, reducing unnecessary economic waste and resource depletion.

[0050] Table 2 Detection results of high organic matter reference materials

[0051]

[0052] Verification by comparison with standard products:

[0053] The standard sample NIST SRM 2711a, with known stable Cd isotope compositions, was used for detection. The δ¹⁸O⁻ was measured using the cadmium isotope standard material stability verification method based on organic interference assessment of this invention. 114 / 110 Cd = 0.536‰ (2SD = 0.047‰), the measured value falls within its known indication range (0.532~0.62‰), such as Figure 1 As shown, the verification method of the present invention is effective and the measurement is accurate.

[0054] The method of this invention clarifies the correlation between "organic matter content and the development potential of Cd isotope standard materials," providing key guidance for screening high-quality Cd isotope standard materials in the fields of environmental monitoring and geological reference material analysis. This helps to improve the accuracy and comparability of Cd isotope analysis data in related fields and lays a solid foundation for the development of technologies such as cadmium pollution source apportionment and environmental migration and transformation research in the field.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; 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 of the technical features; and these modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the present invention.

Claims

1. A method for verifying the stability of cadmium isotope standard materials based on organic interference assessment, characterized in that, Includes the following steps: (1) Two samples of equal quantity were randomly taken from the well-mixed Cd standard reference material sample to be evaluated; (2) After the two samples were independently subjected to completely identical acid digestion and Cd separation and purification, MC-ICP-MS was performed to obtain their respective Cd isotopic compositions, expressed as δ¹⁸O. 114 / 110 Cd value represents; The acid digestion process is as follows: First, the sample is subjected to high-temperature sealed digestion in a high-pressure sealed container using a mixture of concentrated nitric acid and concentrated hydrofluoric acid; then, it is transferred to a polytetrafluoroethylene container, evaporated to a wet salt state, and then aqua regia or anti-aqua regia is added to further digest the organic matter; after evaporation to remove fluorides, concentrated hydrochloric acid is added and heated to dissolve, then a double diluent is added and heated to fully mix the isotopes; after evaporation to dryness again, 6 N hydrochloric acid is added and heated to dissolve, and then evaporated to dryness for later use; The Cd separation and purification process uses anion exchange resin. The sample is eluted with dilute nitric acid and dilute hydrochloric acid in sequence, followed by elution with dilute nitric acid containing hydrogen bromide to remove interference. Finally, the Cd fraction is collected by elution with dilute nitric acid, evaporated to dryness, and the purified Cd sample is obtained. (3) Calculate δ for the two samples 114 / 110 The difference in Cd values; (4) Compare the difference with the threshold: If the difference is less than the threshold, the Cd standard reference material is determined to have a uniform and stable isotopic composition and can be used as a cadmium isotope standard material; if the difference is greater than or equal to the threshold, the Cd standard reference material is determined to have insufficient isotopic composition stability and is not suitable as a cadmium isotope standard material.

2. The method for verifying the stability of cadmium isotope standard materials based on organic interference assessment according to claim 1, characterized in that: The Cd content of the large sample of the Cd standard reference material to be evaluated is greater than 0.3 μg / g.

3. The method for verifying the stability of cadmium isotope standard materials based on organic interference assessment according to claim 2, characterized in that: The high-pressure sealed container liner and polytetrafluoroethylene container are cleaned at high temperature with nitric acid and hydrochloric acid solutions before use, and then dried before use.

4. The method for verifying the stability of cadmium isotope standard materials based on organic interference assessment according to claim 2, characterized in that: The dilute nitric acid containing hydrogen bromide is prepared on-site before use and should be prepared in the dark.

5. The method for verifying the stability of cadmium isotope standard materials based on organic interference assessment according to claim 2, characterized in that: The MC-ICP-MS measurement in step (2) uses the Cd standard of NIST SRM 3108 as a reference to obtain the δ of each sample. 114 / 110 Cd value.

6. The method for verifying the stability of cadmium isotope standard materials based on organic interference assessment according to claim 5, characterized in that: Each sample should be subjected to at least three valid MC-ICP-MS measurements, and the average value should be taken as the final δ value for that sample. 114 / 110 Cd value.

7. The method for verifying the stability of cadmium isotope standard materials based on organic interference assessment according to any one of claims 1-6, characterized in that: Both steps (1) and (2) are performed in a cleanroom of ≥1000 class, and the Cd separation and purification described in step (2) is performed in a Class 100 fume hood.

8. The method for verifying the stability of cadmium isotope standard materials based on organic interference assessment according to claim 7, characterized in that: The acid used in step (2) must be of at least superior purity and must be purified by at least two distillations before use.

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