Method for measuring carbonate sulfur isotope based on ion probe technology

Abstract

The invention discloses a method for measuring carbonate sulfur isotope based on an ion probe technology. According to the method, key problems in micro-area isotope analysis are solved by developing a carbonate micro-area sulfur isotope analysis standard sample. Blocky carbonate formed by natural deep sea is selected as an analysis object. The specific method comprises the following steps: bombarding a carbonate sample by using an ion probe and taking positive ions as an ion source; the developed standard sample is subjected to a random dotting test, and the uniformity of the sulfur isotope composition is evaluated through a long-term multi-point test to ensure that the standard deviation of the multi-point test is less than a preset threshold value. And comparing the average result of the standard sample with a total rock calibration 34S / 32S value to obtain an instrument calibration factor alpha (SIMS). An unknown sample is tested under the same condition, and the Rcorred and the delta34corred of the unknown sample are calculated in combination with alpha (SIMS). The method has the advantages of rapidness, high efficiency and high reliability, and the sulfur carbonate isotope determination precision and the application range are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical detection, specifically relating to a method for measuring sulfur isotopes in carbonates based on ion probe technology. Background Technology

[0002] Carbonates are widely distributed across various geological contexts, including igneous, metamorphic, sedimentary, hydrothermal, and biological skeleton formations. Their sulfur isotope composition is an important environmental and geochemical indicator. Studying carbonate sulfur isotopes helps reveal information about marine sulfur isotope composition, volcanic eruptions, human emissions, and biogeochemical cycles. Therefore, in-depth research on carbonate sulfur isotopes has significant scientific implications.

[0003] However, current analysis of carbonate sulfur isotopes primarily relies on whole-rock analysis techniques, including multiple receiver inductively coupled plasma mass spectrometry (MC-ICPMS) and stable isotope ratio mass spectrometry (IRMS). While these methods offer high precision, they suffer from drawbacks such as high sample consumption, cumbersome and complex sample dissolution processes, susceptibility to contamination and sample loss, and the inability to provide spatial information about the sample. This is particularly insufficient when analyzing the microstructure and alteration effects of carbonates.

[0004] Therefore, the development of micro-area sulfur isotope analysis techniques for carbonates is urgently needed. Existing micro-area analysis techniques, such as laser ablation isotope ratio mass spectrometry (LA-IRMS) and laser ablation inductively coupled plasma mass spectrometry (LA-MC-ICPMS), are mainly suitable for samples with high sulfur content, and remain challenging for carbonate samples with low sulfur content. Ion probe microanalysis (SIMS), due to its high sensitivity and high spatial resolution (micrometer level), has become an ideal technique for micro-area sulfur isotope analysis in carbonates. However, a key challenge in SIMS analysis is the lack of suitable matrix-matched standard samples. Therefore, developing a standard sample suitable for micro-area sulfur isotope analysis in carbonates and evaluating the accuracy of the method are urgent problems to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, particularly the scarcity of standard samples, this invention proposes a method for measuring carbonate sulfur isotopes based on ion probe technology. This method successfully achieves instrument mass fractionation calibration by developing standard samples suitable for micro-area sulfur isotope analysis, thereby improving the reliability and accuracy of the test.

[0006] To achieve the above objectives, the present invention provides a method for measuring carbonate sulfur isotopes based on ion probe technology, the method comprising the following steps:

[0007] (1) Standard preparation and detection: Using deep-sea bulk carbonate samples as raw materials for carbonate standard development, the bulk carbonate was crushed, and multiple random fragments were selected for ion probe detection. Specifically, random point tests were conducted at multiple time periods. Ion probes were used, with positive ions as the primary ion source and a mass spectrometry resolution ≥5000. The carbonate material was bombarded with a beam spot with a diameter of 10-25 micrometers, using two probes with different impedances (10 μm and 10 μm). 10 Ω and ≥10 12 Faraday cups (Ω) were used to detect... 32 S and 34 S-ion signal (ion current intensity), calculated 32 S and 34 The ratio of S to R SIMS (R) SIMS = 34 S / 32 S (SIMS) The relative standard deviation of multiple test points at different time periods was used to assess the sulfur isotope homogeneity and long-term stability of the material. When the relative standard deviation of multiple test points at different time periods was less than 0.35‰, it indicated that the material was suitable as a standard for carbonate micro-area sulfur isotope analysis, and the accurate sulfur isotope composition of the material was determined using whole-rock analysis. 32 S and 34 S) Perform calibration to obtain the calibrated R. actual (R) actual = 34 S / 32 S (actual) )value;

[0008] (2) Detection of unknown samples: Under the same instrument conditions as the standard sample test, the unknown carbonate sample was tested, and the average value R was compared with that of the carbonate standard sample by ion probe method test. SIMS Its calibration R actual Value, the calibration factor α of the calculation instrument. (SIMS) After measuring the unknown carbonate sample, combine the instrument's calibration factor α. (SIMS) Average R of tests with unknown carbonate samples SIMS Value, calculate the unknown carbonate sample 34 S and 32 The calibrated ratio R of S corrected and sulfur isotope δ 34 S-value.

[0009] Preferably, the method further includes: before testing carbonate samples, to ensure the instrument has good stability, verification is performed using a common pyrite standard; if the R of the pyrite standard... SIMS If the relative standard deviation of the distribution is less than 1‰, it indicates that the instrument is stable and in good condition.

[0010] Preferably, when performing random point testing, multiple cycles are collected for each analysis point, and the peak accumulation time for each cycle is 10 seconds.

[0011] Preferably, when testing unknown carbonate samples, they should be fixed on the same resin target as the standard sample to reduce inter-target effects and ensure that the tests are conducted under the same instrument analysis conditions.

[0012] Preferably, the pyrite standard, carbonate standard and unknown carbonate sample are all fixed on the glass slide with double-sided tape and then vacuum cured with epoxy resin to form a test target. The surface of the test target needs to be mechanically or ion polished to ensure that the surface is flat.

[0013] Preferably, the method for calculating the calibration factor of the instrument includes: performing data processing for each test point in multiple cycles (each cycle peak accumulation time is 10 seconds), calculating the average value and internal precision (standard deviation of multiple cycle tests) of the single-point test of the carbonate standard. Based on the average value and standard deviation of the multi-point test of the standard sample, the average value and external precision of the carbonate standard samples of multiple particles in the same period are calculated; and the average value R of the carbonate standard sample is used as the basis for the calculation. SIMS R calibrated by whole-rock analysis actual Value, the calibration factor for the calculation instrument.

[0014] Preferably, the instrument calibration factor is calculated as follows: Instrument calibration factor α (SIMS) = Average value R of carbonate standard tested by ion probe SIMS / Calibration value R of carbonate standard in whole-rock analysis actual .

[0015] Preferably, the developed carbonate sulfur isotope standard (carbonate standard) R actual The value is 0.045147±0.000002, and its δ 34 The S value was +22.3 ± 0.1‰. During the test, the analysis time for each test point was 2 minutes, and the interval between two adjacent measurement groups was less than 4 minutes.

[0016] Preferably, the R of the unknown carbonate sample corrected The value is calculated as follows: R corrected =Ion probe test value of unknown carbonate sample R SIMS / Instrument calibration factor α (SIMS) .

[0017] Preferably, the δ of the unknown carbonate sample 34 The S value is relative to the Vienna Gorge Diablo troilite (V-CDT). 34 S / 32 The calculation is performed using S=1 / 22.6436, and the calculation method is as follows: δ 34S value = (R of unknown carbonate sample) corrected ×22.6436-1)×1000.

[0018] Preferably, the whole-rock analysis method includes multiple receiver inductively coupled plasma mass spectrometry (MC-ICPMS) and stable isotope ratio mass spectrometry (IRMS).

[0019] The technical solution provided by this invention has the following advantages:

[0020] 1. A method for measuring sulfur isotopes in carbonates based on ion probe technology is provided, which can accurately measure sulfur isotopes in unknown samples by developing micro-area sulfur isotope analysis standard samples and calibrating the instrument by mass fractionation.

[0021] 2. This method is efficient and reliable, and can significantly improve the precision and application range of carbonate sulfur isotope determination. Attached Figure Description

[0022] Figure 1 This invention relates to the development of carbonate standards and the evaluation of their micro-region sulfur isotope homogeneity. Detailed Implementation

[0023] The following embodiments are further illustrations of the present invention, but not limitations thereof.

[0024] Example 1

[0025] To realize the application of ion probe microanalysis (SIMS) in carbonate sulfur isotope analysis, this invention addresses the matrix effect problem. The primary task of this invention is to develop standard samples for carbonate micro-region sulfur isotopes.

[0026] This invention selects massive carbonate samples collected from the deep sea as the standard sample for development. The deep-sea environment is stable, resulting in relatively simple structures and compositions of massive carbonates formed therein, making them ideal for development. This invention collects massive carbonate samples from a depth of 1386 meters in the Mariana Trench as raw materials for standard sample development. The massive carbonate is then crushed, and multiple random fragments are selected for ion probe microanalysis. Specifically:

[0027] The long-term stability and homogeneity of the material were evaluated by repeatedly testing multiple random fragments using an ion probe. The ion probe used was equipped with a positive ion source, a mass spectrometry resolution ≥5000, an ion beam diameter of 10-25 μm, and focused on the sample surface. Two Faraday cup receivers (impedance 10⁻⁶ and 10⁻⁵ μm respectively) were employed. 10 Ω and ≥10 12 Ω) Simultaneous measurement 32 S and 34 The ion current intensity of S is calculated to obtain the ion probe measurement.34 S and 32 S ratio R SIMS The test covered 209 random test points (each test point was analyzed in multiple 10-second loops), distributed across different fragments, and spanned a two-year period.

[0028] The results showed that the reproducibility (relative standard deviation) of each test was less than 0.35‰, which is within the accuracy range of conventional ion probe testing for sulfur isotopes. Therefore, this material has good homogeneity and is suitable as a matrix matching standard sample for carbonate sulfur isotope analysis.

[0029] like Figure 1 As shown, the test results for the five periods indicate that the standard deviation (i.e., precision) of the multi-point test for each period is less than 0.35‰, and the results are consistent. Specific test details are as follows:

[0030] In the first test, the standard deviation of the 27 test points was 0.34‰;

[0031] In the second test, the standard deviation of the 16 test points was 0.26‰.

[0032] In the third test, the standard deviation of 139 test points was 0.30‰;

[0033] In the fourth test, the standard deviation of the 11 test points was 0.29‰.

[0034] In the fifth test, the standard deviation of the 16 test points was 0.27‰.

[0035] In summary, the sulfur isotope composition of this material is uniform and stable over a long period of time, making it suitable as a standard sample for carbonate sulfur isotope analysis.

[0036] like Figure 1 As shown, the horizontal axis represents the number of measurement points, with each point being measured multiple times in a loop, and the vertical axis represents the measured sulfur isotopes. 34 S and 32 S ratio R SIMS ( 34 S / 32 S (SIMS) The error bars for each point represent the accuracy of the single-point analysis. σ represents the relative standard deviation of all random points measured in the same period.

[0037] The average R of carbonate standard samples was measured by SIMS. SIMS The value is 0.044431±0.000018.

[0038] The accurate sulfur isotope values ​​of the standard samples developed in this invention were calibrated using whole-rock analysis. Whole-rock analysis methods include multiple receiver inductively coupled plasma mass spectrometry (MC-ICPMS) or stable isotope ratio mass spectrometry (IRMS). This invention utilizes IRMS testing, with the specific testing procedure as follows: First, hydrochloric acid is used to dissolve carbonates, barium chloride is added to precipitate barium sulfate, and then the solid barium sulfate is subjected to high-temperature combustion (1000°C). SO2 is purified through gas separation and detected by mass spectrometry. Using this method, the R... actual ( 34 S / 32 The value of S is 0.045147±0.000002.

[0039] The instrument calibration factor is calculated as follows: Instrument calibration factor α (SIMS) = Average value R of carbonate standard tested by ion probe SIMS Calibration of carbonate standards for whole-rock analysis R actual value.

[0040] In this embodiment, the whole-rock analysis calibration value of the standard sample is R. actual =0.045147±0.000002, therefore the calibration factor of the instrument is calculated to be 0.984.

[0041] In this embodiment, carbonate samples with unknown sulfur isotopes (unknown-1 and unknown-2) were tested under the same instrument conditions as the standard samples, and the test results are as follows:

[0042] The average value R of multiple tests on the unknown-1 sample SIMS It is 0.0444329±0.00004;

[0043] The average value R of the multi-point test of the unknown-2 sample SIMS It is 0.0443950±0.00003.

[0044] According to α (SIMS) Value and formula: R for unknown carbonate samples corrected Value = Average R of ion probe tests on unknown samples SIMS Value / Instrument calibration factor α (SIMS) The corrected unknown sample R is obtained. corrected The value is:

[0045] The unknown-1 sample value was 0.0451554 ± 0.00004;

[0046] The unknown-2 sample value was 0.0451169 ± 0.00003.

[0047] According to δ 34 S-value and formula: δ value of an unknown carbonate sample 34 S corrected Value = (R of the unknown carbonate sample) corrected ×22.6436-1)×1000, we obtain the corrected δ of the unknown sample. 34 S corrected The value is:

[0048] The unknown-1 sample was 22.48±0.79‰;

[0049] The unknown-2 sample was 21.61±0.57‰.

[0050] Comparing the IRMS test results of these two unknown samples with the results obtained by the method of the present invention (see Table 1), it can be seen that the results obtained by the method of the present invention are consistent with the whole-rock analysis results within the error range, indicating that the carbonate sulfur isotope testing method based on the ion probe method of the present invention is feasible.

[0051] Table 1. Accuracy assessment of sulfur isotope analysis results of carbonates in the embodiments of the present invention.

[0052] The above detailed description is a specific description of the embodiments of the present invention. These embodiments are not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included in the patent scope of this case.

Claims

1. A method for measuring sulfur isotopes in carbonates based on ion probe technology, characterized in that, Includes the following steps: (1) Standard preparation and detection: The bulk carbonate collected from the deep sea was used as the raw material for the development of carbonate standards. The bulk carbonate was crushed and multiple random fragments were selected for ion probe detection. Specifically, random point tests were conducted at multiple time periods. Ion probes were used, with positive ions as the primary ion source. The carbonate material was bombarded with a beam spot with a diameter of 10-25 micrometers. Two Faraday cups with different impedances were used for detection. 32 S and 34 The S-ion signal was used to calculate the standard deviation of multiple test points in each time period. When the relative standard deviation of multiple points in different time periods was less than 0.35‰, it indicated that the material was suitable as a standard for carbonate micro-area sulfur isotope analysis. The accurate sulfur isotope composition of the material was then calibrated using whole-rock analysis to obtain the calibration results. 34 S and 32 S ratio R actual Its calculation formula is R actual = 34 S / 32 S (actual) ; (2) Detection of unknown samples: Under the same instrument conditions as the standard sample test, the unknown carbonate sample is tested, and the results are compared with the ion probe test of the carbonate standard sample. 34 S and 32 S average ratio R SIMS Its calibration 34 S and 32 S ratio R actual Calculate the instrument calibration factor a (SIMS) The R SIMS The calculation formula is R SIMS = 34 S / 32 S (SIMS) After measuring the unknown carbonate sample, combine the instrument's calibration factor a. (SIMS) Test with unknown carbonate samples 34 S and 32 S average ratio R SIMS Calculate the R value after calibration for the unknown carbonate sample. corrected Values ​​and sulfur isotope δ 34 S-value.

2. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 1, characterized in that, The method further includes: before testing carbonate samples, to ensure the instrument has good stability, verification is performed using a common pyrite standard. If the R of the pyrite standard is... SIMS If the distribution range is less than 1‰, it indicates that the instrument is stable and in good condition.

3. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 1, characterized in that, When conducting random point testing, multiple cycles are collected for each analysis point, and the peak accumulation time for each cycle is ≥10 seconds.

4. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 1, characterized in that, When testing unknown carbonate samples, they should be fixed on the same resin target as the standard sample to reduce inter-target effects and ensure that the tests are conducted under the same instrument analysis conditions.

5. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 2, characterized in that, The pyrite standard, carbonate standard and unknown carbonate sample are all fixed on the glass slide with double-sided tape and then vacuum cured with epoxy resin to form a test target. The surface of the test target needs to be mechanically or ion polished to ensure that the surface is flat.

6. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 1, characterized in that, The method for calculating the instrument calibration factor includes: performing multiple cycles of data processing for each test point, calculating the average value and internal precision of single-point tests of the carbonate standard sample, and calculating the average value and external precision of carbonate standard samples from multiple particles in the same period based on the average value and standard deviation of multi-point tests of the standard sample; and calibrating the calibration factor using the average value of the carbonate standard sample and the calibration factor calibrated by whole-rock analysis. 34 S / 32 S ratio, calculate instrument calibration factor a (SIMS) .

7. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 1, characterized in that, The instrument calibration factor is calculated as follows: Instrument calibration factor a (SIMS) = Average value R of carbonate standard tested by ion probe SIMS Calibration of carbonate standards for whole-rock analysis R actual value.

8. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 1, characterized in that, The R after calibration of the unknown carbonate sample corrected The value is calculated as follows: R corrected =Average R of ion probe tests for unknown samples SIMS Value / Instrument calibration factor a (SIMS) The sulfur isotope δ of the unknown carbonate sample 34 The S value is calculated relative to the Diablo meteorite in Vienna Gorge, and the calculation method is as follows: δ 34 S value = (R value after calibration for unknown carbonate sample) corrected ×22.6436 -1)×1000.

9. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 1, characterized in that, The whole-rock analysis methods include multi-receiver inductively coupled plasma mass spectrometry and stable isotope ratio mass spectrometry.

10. The method for measuring carbonate sulfur isotopes based on ion probe technology according to claim 1, characterized in that, The impedances of the Faraday cups are 10. 10 Ω and ≥10 12 Ω.

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