A method for detecting copper isotope in coal

Abstract

The application discloses a method for detecting Cu isotopes in coal. The method of the application is characterized in that: a coal sample is subjected to microwave digestion, the microwave digestion method has the advantages of less time consumption (4 hours for a single microwave), no external pollution and complete digestion; then, the sample is subjected to reverse aqua regia digestion and hydrochloric acid digestion; finally, the digested sample is separated and purified through a double-column method, and then subjected to mass spectrometric analysis of copper isotope composition by MC-ICP-MS. The method greatly simplifies the digestion process of the coal sample, reduces the digestion cost, thereby shortens the digestion time of the sample, improves the digestion efficiency, and realizes efficient and accurate detection of the copper isotope composition in the coal by combining the subsequent purification and mass spectrometric analysis steps.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis technology, specifically to a method for detecting Cu isotopes in coal. Background Technology

[0002] Organically rich samples refer to geological samples with a total organic carbon (TOC) content significantly higher than that of ordinary rocks (typically TOC > 0.5%). Essentially, they are geological carriers formed by the enrichment and preservation of the remains of ancient aquatic organisms (such as algae and plankton, forming "saprophytic" organic matter) or terrestrial higher plants (such as roots, stems, and leaves, forming "humic" organic matter) under specific geological conditions. Common types include sedimentary rocks, combustible minerals, and modern sediments, specifically shale, oil shale, coal, peat, deep lacustrine mudstone, and deep-sea sedimentary mud. They are not only core source rocks for oil and natural gas (saprophytic type for oil generation, humic type for gas generation), but also "natural archives" recording paleoecology (source of organic matter) and paleoredox environments (preservation conditions). They are also direct carriers of special minerals such as coal and oil shale, and play a crucial role in the geological carbon cycle by fixing carbon through burial (carbon sink) or releasing carbon through weathering (carbon source), thus maintaining the Earth's carbon balance.

[0003] Isotopes are atoms that have the same number of protons but different numbers of neutrons, and occupy the same position in the periodic table. For example, the three main isotopes of carbon are... 12 C 13 C 14 Carbon (C) has 6 protons, but the number of neutrons varies from 6 to 8. Stable isotopes are atoms of the same element that are physically stable and do not exhibit radioactivity or radiation effects; there are currently over 300 known stable isotopes. Conversely, unstable isotopes or radioactive isotopes are those that do not exhibit these properties. Taking carbon isotopes as an example... 12 C 13 C is a stable isotope, while 14 C is a radioactive isotope. The differences in physicochemical properties between isotopes cause variations in the isotopic composition of reactants and products; this is known as the isotope effect, which forms the basis of scientific research using isotopes.

[0004] Stable isotopes are non-radioactive, safe, accurate, and do not interfere with nature. They possess the ability to synthesize long-term geochemical changes and connect components of different systems, playing a unique role as liaisons between time and space. Their analytical techniques have important applications in geochemistry and source tracing. Today, isotope composition determination techniques are widely used in geochemistry, geology, space science, nuclear science, archaeology, biology, and many other fields. Thermal ionization mass spectrometry (TIMS) with hot surface ionization sources was an early isotope determination technique, mainly used for solid-state isotope analysis. Since the 1990s, the application of multiple receiver inductively coupled plasma mass spectrometry (MC-ICP-MS) has enabled the rapid development of high-precision methods for determining stable metal isotopes. Compared to other methods, MC-ICP-MS offers advantages such as faster analysis speed, higher sensitivity, and the ability of ICP ion sources to ionize metallic and some non-metallic elements.

[0005] Before using MC-ICP-MS, separating and purifying the sample to meet the analytical requirements is crucial for metal isotope analysis. Sample pretreatment mainly includes sample digestion and separation and purification of the analyte elements. Two requirements must be met during the pretreatment process: (1) no elements that may cause interference should be introduced, i.e., the background generated by the pretreatment should be reduced to the lowest level; (2) no analyte elements should be lost, i.e., the recovery rate should be as high as possible, i.e., 100% should be achieved.

[0006] In conducting copper isotope analysis on organic-rich samples, it is generally necessary to determine a suitable digestion method based on the composition of the organic-rich sample and the analytical objectives. To minimize the introduction of interfering elements and ensure complete sample dissolution, five common digestion methods are used for organic-rich samples: ashing, acid extraction, high-temperature and high-pressure closed digestion, microwave digestion, and alkaline dissolution. Among these, high-temperature and high-pressure closed digestion is the most widely used method in current research, extensively applied to the digestion of organic-rich samples. It offers good sample digestion results, high element recovery rates, and avoids isotope fractionation. Microwave digestion is a recently popular method for digesting organic-rich samples. Previous studies have mainly focused on using microwave digestion to detect nutrient elements in organic-rich samples (such as seaweed, feed, crops, and fruits). There are fewer studies on detecting elements in geological samples using microwave digestion, and even fewer studies on metallic elements (such as Cu) in coal. There is also a lack of research on the Cu isotope composition in coal. Previous studies have tested organic soil samples digested by dry ashing, and due to Cu volatilization and fractionation, the Cu isotope composition deviated from the true value. Summary of the Invention

[0007] The purpose of this invention is to address the problem that existing detection methods cannot accurately and efficiently detect Cu isotopes in coal, and to provide a method for detecting Cu isotopes in coal. This invention involves sequentially digesting coal samples using microwave, reverse aqua regia, and hydrochloric acid. The digested samples are then separated and purified using a dual-column method, followed by copper isotope composition analysis by MC-ICP-MS mass spectrometry. This achieves accurate determination of Cu isotopes in coal, and improves overall detection efficiency by shortening the digestion time.

[0008] The technical solution adopted in this invention is as follows:

[0009] A method for detecting Cu isotopes in coal involves digesting a coal sample, the digestion process including sequential microwave digestion, reverse aqua regia digestion, and hydrochloric acid digestion; the digested sample is then separated and purified using a dual-column method, and the purified sample is further analyzed by MC-ICP-MS mass spectrometry for copper isotope composition.

[0010] Preferably, the coal sample digestion method includes the following steps:

[0011] S1. Weigh 60 mg to 90 mg of the sample into a microwave digestion tube;

[0012] S2. First, add 5 ml of HNO3 to the microwave digestion tube and let it stand for 10 min. Then add 3 ml of HF and let the digestion tube stand to degas for 2 h.

[0013] S3. After degassing, place the sample in a microwave digester for microwave digestion. After digestion, the solution becomes clear. Pour the solution into the corresponding Beaker and rinse the digestion tube three times with HNO3. Pour the rinsing solution into the Beaker and transfer it to the clean laboratory for subsequent sample digestion.

[0014] S4. In a cleanroom, place the Beaker on a hot plate and dry it at 150-160 ℃ with the lid off.

[0015] S5. After evaporation to dryness, seal the Beaker and let it cool. Then add 3 ml of HNO3 and 1 ml of HCl. First, tighten the Beaker slightly to degas for 30 min. Then tighten the Beaker and place it on a hot plate to heat at 80 ℃. After the sample is heated to clarity, open the lid and evaporate to dryness at 80-90 ℃. After evaporation to dryness, cool.

[0016] S6. After cooling, add 4 ml of HCl to the Beaker, tighten the Beaker, place it on a hot plate and heat at 130 °C until the solution is clear, then heat at 130 °C to evaporate to dryness.

[0017] S7. After evaporation to dryness, remove the Beaker sample and cool it to room temperature. Then add 1 ml of 8 mol / L HCl to make up the volume, thus completing the digestion of the sample.

[0018] Preferably, in step S3, the microwave digestion step is as follows: the microwave digester is sealed, the instrument heating program is adjusted, the temperature is raised to 200 ℃ in 30 minutes, the temperature is kept constant at 200 ℃ for 90 minutes, and then the temperature is lowered for 120 minutes to cool down. The digestion tube is then removed and degassed for 10 minutes.

[0019] Preferably, after microwave digestion, the solution is observed. If black organic residue is present, the microwave digestion step is repeated until the digested solution is clear.

[0020] Preferably, the 1 ml of 8 mol / L HCl in S7 contains 0.001% H2O2.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. This invention provides a method for detecting Cu isotopes in coal. First, microwave energy is used to induce frictional heating of polar molecules. Combined with a sealed high-pressure environment and an auxiliary solvent, the coal sample is rapidly oxidized and dissolved, completing the microwave digestion of the coal sample. Then, reverse aqua regia digestion and hydrochloric acid digestion are performed. Finally, the digested sample is separated, purified, and analyzed by MC-ICP-MS mass spectrometry of copper isotope composition, thereby achieving accurate detection of Cu isotopes in the coal sample.

[0023] 2. The detection method of this invention uses microwave digestion to digest coal samples. This microwave digestion method is time-efficient (4 hours per cycle), virtually free of external contamination, and ensures thorough digestion. Furthermore, the results obtained from microwave digestion are within the error range of the high-temperature, high-pressure, closed-loop digestion method, mutually corroborating each other and demonstrating the accuracy of the microwave digestion results. Therefore, this invention, while ensuring the accuracy of MC-ICP-MS mass spectrometry analysis results of copper isotope composition, greatly simplifies the digestion process, reduces digestion costs, thereby shortening the sample digestion time and improving digestion efficiency. Attached Figure Description

[0024] Figure 1 This is a flowchart of the digestion method (including microwave digestion) in Example 1.

[0025] Figure 2 The flowchart shows the digestion method (including high-temperature and high-pressure digestion) in Comparative Example 1.

[0026] Figure 3 Comparison of Cu isotope composition of coal standard samples obtained by microwave digestion and high temperature and high pressure digestion. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] The microwave digestion instrument used in this embodiment was an ETHOS UP microwave digestion instrument. The samples were GBW11107r (bituminous coal standard), GBW11101w (bituminous coal standard), and GBW11104q (anthracite coal standard), and the organic matter content of all three coal standards was greater than 60%. In this embodiment, all acids used were purified by double sub-boiling distillation.

[0030] 1. For example Figure 1 As shown, the digestion steps for organic-rich samples (coal) are as follows:

[0031] (1) Accurately weigh 60-90 mg of coal standard sample and 20-60 mg of geological standard sample into microwave digestion tubes (the specific weighing amount is shown in Table 1, -1 and -2 represent the same sample repeated twice, w represents microwave digestion); ensure that the weighed sample contains at least 0.4 μg of copper for isotope analysis.

[0032] Table 1 Sample weighing by microwave digestion method

[0033]

[0034] (2) First add 5 ml of HNO3 to the microwave digestion tube and let it stand for 10 min. Then add 3 ml of HF and let the digestion tube stand for 2 h to degas. The ETHOS UP microwave digestion instrument used in this embodiment requires 8 ml of liquid in the digestion tube, so no heating is required during degassing.

[0035] (3) After degassing, assemble the digestion device, place it in the microwave digester, and seal the instrument;

[0036] (4) Adjust the instrument heating program, raise the temperature to 200 ℃ in 30 min, keep the temperature at 200 ℃ for 90 min, and then cool down in 120 min (one digestion takes 4 h).

[0037] (5) After the instrument has cooled down, remove the digestion tube, degas for 10 min, observe the solution, and if there is black organic residue, perform a second digestion.

[0038] (6) After the second digestion, take out the digestion tube, degas for 10 min, the solution becomes clear, pour the solution into the corresponding Beaker, and rinse the digestion tube 3 times with HNO3. Pour the rinsing solution into the Beaker and transfer it to the ultra-clean laboratory for subsequent reverse aqua regia digestion and hydrochloric acid digestion of the microwave digested sample.

[0039] (7) In a cleanroom, place the beaker on a hot plate and dry it at 150-160 ℃ with the lid off;

[0040] (8) After evaporation, seal the beaker, remove it and let it cool. After cooling, add 3 ml HNO3 and 1 ml HCl (to prepare reverse aqua regia, which has a stronger oxidizing power than aqua regia and can further dissolve organic matter). First, tighten it slightly to degas for 30 minutes, then tighten the beaker and place it on a hot plate to heat at 80 ℃.

[0041] (9) After the sample has been heated to clarity, open the lid and evaporate to dryness at 80-90 ℃. After evaporation, remove and cool.

[0042] (10) After cooling, add 4 ml of HCl to the beaker, tighten the beaker, place it on a hot plate and heat at 130 °C until the solution is clear, then heat at 130 °C to evaporate to dryness;

[0043] (11) After evaporation, remove the beaker and cool it to room temperature. Then add 1 ml of 8 mol / L HCl (+0.001% H2O2) to make up the volume and wait for column chromatography.

[0044] 2. Separation and purification

[0045] This embodiment uses a dual-column method to separate and purify copper from geological samples. Due to the large sample volume, both columns used AGMP-1M (100-200 mesh) resin (2 ml of resin filling). This method effectively separated and removed most matrix elements while ensuring recovery and reducing overall blank. The separation process is shown in Table 2.

[0046] Table 2 Separation process of copper in geological samples using the dual-column method

[0047]

[0048] 3. Copper isotope composition analysis by MC-ICP-MS mass spectrometry

[0049] The copper isotope composition was analyzed by MC-ICP-MS mass spectrometry in low-resolution mode. The methods used for instrument mass discrimination correction were SSB method and Zn internal standard method.

[0050] The samples, external standards, and quality control samples all contained 100 ppb of copper and an added 200 ppb of GSB Zn, all in the same 3% HNO3 solution. Instrument parameters were optimized using a 100 ppb copper isotope standard solution (GSB Cu), while NIST 3114 Cu was diluted to 100 ppb as a quality control sample. To correct for instrument mass discrimination, 100 ppb GSB Cu was used as the copper external standard solution, and this solution was measured before and after determining the copper isotope composition of the samples. Before each sample group was tested, the injection system was cleaned with 3% HNO3, and the 3% HNO3 blank was monitored for blank subtraction. After each sample group was tested, the system was cleaned again with 3% HNO3. Each sample (including the external standard) was also cleaned with 3% HNO3 before and after testing to prevent cross-contamination between the sample and the external standard solution. To ensure the reliability of the experimental data, each sample was tested at least three times per measurement. The operating parameters of MC-ICP-MS are shown in Table 3, and the analysis results of copper isotope composition are shown in Table 4.

[0051] Table 3 Operating parameters of MC-ICP-MS

[0052]

[0053] In this embodiment, the total program blank of the microwave digestion method was ~4.5 ng. However, the data from the analysis of the samples showed that the data obtained from the pure copper solution and basalt standard after digestion by this method were consistent with the data from previous studies (reference: High-precision copper and iron isotope analysis of igneous rock standards by MC-ICP-MS) within the error range. This indicates that the digestion process can be used for copper isotope analysis of geological samples (such as coal).

[0054] Table 4. Copper isotope data of coal standard samples obtained by microwave digestion method.

[0055]

[0056] Comparative Example 1

[0057] This comparative example verifies the Cu isotope composition obtained from the microwave digestion method in Example 1 by high-temperature, high-pressure, and closed digestion of organic-rich samples (coal) and detection of Cu isotope composition in three coal standard samples.

[0058] In this comparative example, the instrument used for high-temperature and high-pressure closed digestion was a forced-air drying oven.

[0059] 1. For example Figure 2 As shown, the elimination steps in this comparative example are as follows:

[0060] (1) Accurately weigh 60~90 mg of coal standard sample and 20~60 mg of geological standard sample into the Bomb liner (the specific weighing amount is shown in Table 5, -1 and -2 represent the same sample repeated twice, and g represents high temperature and high pressure digestion); ensure that the weighed sample contains at least 0.4 μg of copper for isotope analysis.

[0061] Table 5 Sample Weighting for High Temperature and High Pressure Closed Digestion Method

[0062]

[0063] (2) Add 4 ml of HNO3 to the inner liner first, let it stand for 10 min, then add 4 ml of HF, and let the inner liner stand for 2 h to degas;

[0064] (3) After degassing, assemble the high-temperature and high-pressure digestion device, put it in the oven, seal the instrument, and heat it at 185 ℃ for 48 hours;

[0065] (4) After the instrument has cooled down, take out the inner liner and transfer it to the clean laboratory. Degas for 10 min and observe the solution. If the solution is clear, pour the solution in the inner liner into the corresponding Beaker and rinse the inner liner with HNO3 3 times. Pour the rinsing solution into the Beaker. Transfer the sample to the clean laboratory for subsequent reverse aqua regia digestion and hydrochloric acid digestion after high temperature and high pressure digestion.

[0066] (5) In a cleanroom, place the beaker on a hot plate and dry it at 150-160 ℃ with the lid off;

[0067] (6) After evaporation, seal the beaker, remove it and let it cool. After cooling, add 3 ml HNO3 and 1 ml HCl (to prepare reverse aqua regia, which has a stronger oxidizing power than aqua regia and can further dissolve organic matter). First, tighten it slightly to degas for 30 minutes, then tighten the beaker and place it on a hot plate to heat at 80 ℃.

[0068] (7) After the sample is heated to clarity, open the lid and evaporate to dryness at 80-90 ℃. After evaporation, remove and cool.

[0069] (8) After cooling, add 4 ml of HCl to the beaker, tighten the beaker, place it on a hot plate and heat at 130 °C until the solution is clear, then heat at 130 °C to evaporate to dryness;

[0070] (9) After evaporation, remove the beaker and cool it to room temperature. Then add 1 ml of 8 mol / L HCl (+0.001% H2O2) to make up to volume and wait for column chromatography.

[0071] 2. Separation and purification

[0072] The separation and purification method of the digested sample in this comparative example is the same as that in Example 1.

[0073] 3. MC-ICP-MS mass spectrometry analysis

[0074] The copper isotope composition analysis method of the purified samples in this comparative example was the same as that in Example 1. The analytical results are shown in Table 6.

[0075] Table 6. Copper isotope data of coal standard samples measured by high temperature and high pressure closed digestion method

[0076]

[0077] In summary, the microwave digestion method in this invention is essentially free of external contamination and achieves thorough digestion. MC-ICP-MS mass spectrometry analysis shows that the Cu isotope composition is consistent with the Cu isotope composition of the coal standard sample measured by the high-temperature, high-pressure closed digestion method, indicating that the detection results of Example 1 are within the error range of Comparative Example 1, further verifying the accuracy of the detection results of Example 1. Figure 3 As can be seen, the Cu isotopic composition of the three coal standards did not change significantly, remaining largely consistent with low blank values. Compared to the high-temperature, high-pressure digestion method (48 h) in Comparative Example 1, the microwave digestion method in this invention is less time-consuming (only 4 h for a single microwave digestion; in this example, the organic matter content of the three samples was greater than 60%, so microwave digestion was performed twice, taking a total of 8 h), significantly shortening the digestion time. Therefore, this invention achieves the detection of Cu isotopes in coal samples through microwave, aqua regia, and hydrochloric acid digestion, followed by separation, purification, and MC-ICP-MS mass spectrometry analysis. Furthermore, while ensuring the accuracy of the MC-ICP-MS mass spectrometry analysis results of the copper isotope composition, it greatly simplifies the digestion process, shortens the digestion time, and improves the digestion efficiency, thereby improving the overall detection efficiency of Cu isotopes in coal samples.

[0078] The specification and drawings of this invention are intended to be illustrative rather than restrictive. Based on this invention, those skilled in the art can make substitutions and modifications to some of the technical features without creative effort, and all such modifications are within the scope of protection of this invention.

Claims

1. A method for detecting Cu isotopes in coal, characterized by, The coal sample was digested, which included microwave digestion, reverse aqua regia digestion and hydrochloric acid digestion in sequence; the digested sample was separated and purified by a dual-column method, and then copper isotope composition was analyzed by MC-ICP-MS mass spectrometry.

2. The detection method according to claim 1, characterized in that, The digestion method for coal samples includes the following steps: S1. Weigh 60 mg to 90 mg of the sample into a microwave digestion tube; S2. First, add 5 ml of HNO3 to the microwave digestion tube and let it stand for 10 min. Then add 3 ml of HF and let the digestion tube stand to degas for 2 h. S3. After degassing, place the sample in a microwave digester for microwave digestion. After digestion, the solution becomes clear. Pour the solution into the corresponding Beaker and rinse the digestion tube three times with HNO3. Pour the rinsing solution into the Beaker and transfer it to the clean laboratory for subsequent sample digestion. S4. In a cleanroom, place the Beaker on a hot plate and dry it at 150-160 ℃ with the lid off. S5. After evaporation to dryness, seal the Beaker and allow it to cool. Then add 3 ml of HNO3 and 1 ml of HCl. First, tighten the Beaker slightly to degas for 30 minutes. Then tighten the Beaker and place it on a hot plate to heat at 80 ℃. After the sample has been heated to clarity, open the lid and evaporate to dryness at 80-90 ℃. After evaporation to dryness, cool. S6. After cooling, add 4 ml of HCl to the Beaker, tighten the Beaker, place it on a hot plate and heat at 130 °C until the solution is clear, then heat at 130 °C to evaporate to dryness. S7. After evaporation to dryness, remove the Beaker sample and cool it to room temperature. Then add 1 ml of 8 mol / L HCl to make up the volume, thus completing the digestion of the sample.

3. The detection method according to claim 2, characterized in that, In S3, the microwave digestion steps are as follows: Seal the microwave digester, adjust the instrument heating program, raise the temperature to 200 ℃ in 30 min, maintain the temperature at 200 ℃ for 90 min, then cool down for 120 min, remove the digestion tube, and degas for 10 min.

4. The detection method according to claim 2, characterized in that, After microwave digestion, observe the solution. If black organic residue is present, repeat the microwave digestion process until the solution becomes clear.

5. The detection method according to claim 2, characterized in that, The 1 ml of 8 mol / L HCl in S7 contains 0.001% H2O2.

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