Method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination

Abstract

The invention discloses a method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination, and relates to the technical field of isotope analysis. According to the method, the Sr double-charge interference in the in-situ Ca isotope measurement is accurately deducted through an iteration method, the Ca isotope measurement result can be simply and quickly corrected, and high-resolution, low-detection-limit and high-flux Ca isotope measurement is realized; ca single-charge fractionation factors are calculated through an iterative method, and instrument quality discrimination correction and accurate deduction of Sr double-charge interference are simultaneously realized through formulas 1-5 in combination with the Sr isotope ratio; the method breaks through the application limitation of in-situ Ca isotope measurement, is suitable for high-Sr and low-Sr samples, solves the technical problems of in-situ Ca isotope analysis accuracy and analysis precision, fills the technical blank of Ca isotope measurement in the Sr-rich sample in laser in-situ detection, and provides a firm technical support for application in the field of geoscience.

Description

Technical Field

[0001] The present invention relates to the technical field of isotope analysis, and particularly relates to a method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination. Background Art

[0002] Calcium (Ca) is an alkaline metal widely distributed in the Earth's lithosphere and hydrosphere, and is a major rock-forming, fluid-mobile, and biologically essential element. Ca has six stable isotopes, 40 Ca (96.941%), 42 Ca (0.647%), 43 Ca (0.135%), 44 Ca (2.086%), 46 Ca (0.004%) and 48 Ca (0.187%). Among them, 40 Ca and 44 Ca with a relative mass difference of up to 10% can cause a fractionation of up to 4‰ in the stable Ca isotope composition (δ 44 / 40 Ca) in each reservoir. The Ca isotope compositions of rock, mineral, and biological samples have been widely applied in various disciplines, including cosmochemistry, geochemistry, archaeology, climatology, and biomedicine, etc.

[0003] Currently, the analysis of stable Ca isotopes mainly focuses on the determination of the overall composition of rock or mineral samples. Traditional methods usually grind the samples into powders and perform mass spectrometry analysis after chemical digestion and resin purification. The solution injection method mainly includes two techniques: one is to measure stable Ca isotopes (expressed as δ 44 / 40 Ca or δ 44 Ca) by using a thermal ionization mass spectrometer (TIMS) with a double-diluent technique; the other is to use a solution nebulization multi-collector inductively coupled plasma mass spectrometer (SN-MC-ICP-MS) and combine the bracketing method for mass discrimination correction. However, due to the 40 Ar + interference caused by the cooling gas of the plasma, this method usually measures the 44 Ca / 42 Ca ratio (expressed as δ 44 / 42Ca). The solution method analysis ignores the variation of the Ca isotope composition of the sample at the micron scale. As an important means of in-situ micro-area analysis, laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) can not only avoid the cumbersome chemical separation process, but also has the advantages of high resolution, low detection limit, low sample consumption, etc., and can reveal the geochemical characteristics of the micro-area of mineral and rock samples. However, in-situ Ca isotope analysis is inevitably affected by mass spectrometry interference generated from laser ablation samples and background gas. Among them, the interference of strontium (Sr) double-charged ions is the main factor restricting high-precision in-situ Ca isotope measurement. It cannot be separated by a high-resolution slit and can only rely on effective mathematical methods for deduction.

[0004] However, the current methods for in-situ Ca isotope measurement are mainly applicable to special samples with low Sr content (Sr / Ca ≤ 0.0058), that is, the existing methods can achieve relatively accurate Ca isotope measurement through mathematical deduction. For Sr-rich samples, such as marine carbonates, aragonite, carbonates in magmas and metasomatic carbonatites, the variation of their Sr content can cause the Sr / Ca ratio to range from 10 -6 to 10 -1 . Therefore, there is still a lack of effective means to accurately deduct the Sr double-charge interference in in-situ Ca isotope measurement of Sr-rich samples. Summary of the Invention

[0005] The main object of the present invention is to propose a method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination, aiming to solve the problem of Sr double-charge interference in in-situ Ca isotope measurement of Sr-rich samples in the prior art.

[0006] To achieve the above object, the present invention proposes a method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination, including the following steps:

[0007] S10. Provide a standard sample with a matrix matching the sample to be measured, perform laser ablation on the standard sample to form aerosol particles under the action of laser, ionize the aerosol particles to form charged ions, detect the charged ions by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), and record the ion current intensities at mass-to-charge ratios of 42, 43, 43.5, and 44, respectively denoted as I 42 , I 43 , I 43.5 and I 44 ;

[0008] S20. Obtain the natural mass ratio constant of 88 Sr to 86 Sr ([[]] 88 Sr / 86 Sr)[[]] true= 8.375209, and 84 Sr and 86 The natural mass ratio constant of Sr ( 84 Sr / 86 Sr) true = 0.05654,, and the ratio of Sr to 86 Sr and 87 Sr ( 86 Sr / 87 Sr) standard sam ; Calculate the stable Ca isotope ratio ( 44 Ca / 42 Ca) standard corr1 after the first calibration of the standard sample according to formula 1, and calculate the stable Ca isotope ratio ( 43 Ca / 42 Ca) standard corr1 ;

[0009]

[0010] where M88, M87, M86 and M84 are respectively 88 Sr, 87 Sr, 86 Sr and 84 Sr mass numbers, is the Ca single-charge fractionation factor for the i-th calibration, ( 44 Ca / 42 Ca) standard corri 、( 43 Ca / 42 Ca) standard corri where i is the calibration number, and the value range of i is a positive integer; when calibrating for the first time, i = 1, is 0;

[0011] After S30 and the first calibration are completed, update through formula 3 to obtain

[0012] where M44 and M42 are respectively 44 Ca and 42 Ca mass numbers, ( 44 Ca / 42 Ca) true is 44 Ca and 42Ca natural mass ratio constant 3.2241;

[0013] S40. Calculation The ratio with When this ratio is far from 1, Substitute it back into Formulas 1 and 2 to calculate the ( Ca / 44 Ca) 42 Ca) standard corri+1 and ( 43 Ca / 42 Ca) standard corri+1 ; when this ratio tends to 1, stop the iterative calculation to obtain the stable Ca isotope ratio ( 44 Ca / 42 Ca) standard and ( 43 Ca / 42 Ca) standard ;

[0014] S50. Replace the standard sample in Steps S10 to S40 with the sample to be measured, and repeat Steps S10 to S40 to calculate the stable Ca isotope ratio ( 44 Ca / 42 Ca) sample and ( 43 Ca / 42 Ca) sample ;

[0015] S60. Calculate the final Ca stable isotope composition δ 44 / 42 Ca 915a and δ 43 / 42 Ca 915a ;

[0016]

[0017] wherein, δ 44 / 42 Ca standard / 915a and δ 43 / 42 Ca standard / 915a are the Ca stable isotope compositions of the standard sample measured by the solution method relative to NIST SRM 915a.

[0018] In one embodiment, the standard sample can be a sample with low Sr or high Sr content.

[0019] In one embodiment, the sample to be measured includes marine carbonate, carbonate minerals derived from aragonite, carbonate minerals derived from magma, or carbonate minerals derived from metasomatic carbonatite.

[0020] In one embodiment, the laser ablation instrument includes a Resonetics 193nm ArF excimer laser ablation system.

[0021] In one embodiment, before the step of laser ablating the standard sample, it further includes:

[0022] Adjust the laser ablation parameters to avoid incomplete ionization and ensure 44 Ca + The measurement signal intensity of is greater than 9V.

[0023] In one embodiment, the multi-collector inductively coupled plasma mass spectrometer includes Nu Plasma II MC-ICP-MS.

[0024] In one embodiment, the instrumental drift and matrix effect of the sample to be measured are corrected by the standard-sample bracketing method.

[0025] In one embodiment, in step S20, the standard deviation range of the 86 Sr to 87 Sr ratio measured multiple times in the same sample depends on the sample Sr / Ca ratio.

[0026] In one embodiment, the mass resolution mode in the multi-collector inductively coupled plasma mass spectrometry is the low-resolution mode.

[0027] In the technical solution of the present invention, a method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination is proposed. This method can simply and quickly correct the Ca isotope measurement results, achieving high-resolution, low-detection limit, and high-throughput Ca isotope measurement; the Ca single-charge fractionation factor is calculated by the iteration method, combined with the Sr isotope ratio, and the instrumental mass discrimination correction and the accurate deduction of Sr double-charge interference are simultaneously achieved through formulas 1 to 5; this method breaks through the application scope of in-situ Ca isotope measurement, is applicable to high-Sr and low-Sr samples, solves the technical problems of the accuracy and precision of in-situ Ca isotope analysis, and fills the blank of laser in-situ detection of the Ca isotope composition in Sr-rich samples, providing a strong technical support for applications in the field of earth science. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0029] Figure 1 This is the blank scan result in the low-quality resolution mode in Embodiment 1 provided by the present invention;

[0030] Figure 2 This is a schematic diagram of the Ca isotope composition results of the sample before and after Sr double-charge correction in Embodiment 2 provided by the present invention;

[0031] Figure 3 This is for different 87 Sr / 86 Sr values in Embodiment 3 provided by the present invention, showing the influence on the Ca isotope measurement;

[0032] Figure 4 This is a schematic diagram of the Ca isotope composition results of the sample with an Sr to Ca mass ratio (Sr / Ca) of 0.057 in Comparative Example 1 provided by the present invention;

[0033] Figure 5 In (a), this is a schematic diagram of the Ca isotope composition results of the sample with Sr / Ca = 0.00022 obtained by the iterative correction strategy in Embodiments 2 and 4 provided by the present invention; Figure 5 In (b), this is a schematic diagram of the Ca isotope composition results of the sample with Sr / Ca = 0.028 obtained by the iterative correction strategy in Embodiments 2 and 4 provided by the present invention; Figure 5 In (c), this is a schematic diagram of the Ca isotope composition results of the sample with Sr / Ca = 0.057 obtained by the iterative correction strategy in Embodiments 2 and 4 provided by the present invention.

[0034] The realization, functional features and advantages of the object of the present invention will be further described with reference to the embodiments and the drawings. Detailed implementation manners

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase. In addition, the meaning of "and / or" appearing throughout the text includes three parallel scenarios. Taking "A and / or B" as an example, it includes Scenario A, or Scenario B, or the scenario where both A and B are satisfied simultaneously. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0036] Currently, the methods for in-situ Ca isotope measurement are limited to special samples with low Sr content (Sr / Ca ≤ 0.0058). That is, the existing methods can achieve relatively accurate Ca isotope measurement through mathematical deduction. For Sr-rich samples, such as marine carbonates, aragonite, magmatic and metasomatic carbonate minerals, the Sr content changes in them can cause the Sr / Ca ratio to range from 10 -6 to 10 -1 . Therefore, there is still a lack of effective means to accurately deduct the Sr double-charge interference in the in-situ Ca isotope measurement of Sr-rich samples.

[0037] In view of this, the present invention proposes a method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination, including the following steps:

[0038] S10. Provide a standard sample with a matrix matching the sample to be measured, perform laser ablation on the standard sample to form aerosol particles under the action of the laser, ionize the aerosol particles to form charged ions, and detect the charged ions by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Record the ion current intensities at mass-to-charge ratios of 42, 43, 43.5, and 44, which are denoted as I 42 、I 43 、I 43.5 and I 44 ;

[0039] S20. Obtain 88 the natural mass ratio constant of 86 Sr to 88 Sr ( 86 Sr / true ) = 8.375209, and 84 the natural mass ratio constant of86 The natural mass ratio constant of Sr ( 84 Sr / 86 Sr) true = 0.05654, and the ratio of 86 Sr to 87 Sr ( 86 Sr / 87 Sr) standard sam ; Calculate the stable Ca isotope ratio after the first calibration of the reference sample according to Formula 1 ( 44 Ca / 42 Ca) standard corr1 , and calculate the stable Ca isotope ratio after the first calibration of the reference sample according to Formula 2 ( 43 Ca / 42 Ca) standard corr1 ;

[0040]

[0041] Among them, M88, M87, M86, and M84 are respectively 88 Sr, 87 Sr, 86 Sr, and 84 Sr mass numbers, is the Ca single-charge fractionation factor for the i-th calibration, ( 44 Ca / 42 Ca) standard corri , ( 43 Ca / 42 Ca) standard corri where i is the calibration number, and the value range of i is a positive integer; when calibrating for the first time, i = 1, is 0;

[0042] After the first calibration is completed, update through Formula 3 to obtain

[0043] Among them, M44 and M42 are respectively 44 Ca and 42 Ca mass numbers, ( 44 Ca / 42 Ca) true is 44 Ca and 42 Ca natural mass ratio constant 3.2241;

[0044] S40. Calculate the ratio of to When the ratio is far from 1, substitute back into Formulas 1 and 2 to calculate the ( 44 Ca / 42 Ca) standard corri+1 and ( 43 Ca / 42 Ca) standard corri+1 of the reference sample after the next calibration; when the ratio tends to 1, stop the iterative calculation and obtain the stable Ca isotope ratio ( 44 Ca / 42 Ca) standard and ( 43 Ca / 42 Ca) standard of the reference sample after the i-th calibration;

[0045] S50. Replace the reference sample in Steps S10 to S40 with the sample to be measured, repeat Steps S10 to S40, and calculate the stable Ca isotope ratio ( 44 Ca / 42 Ca) sample and ( 43 Ca / 42 Ca) sample of the sample to be measured after the i-th calibration;

[0046] S60. Calculate the final Ca stable isotope composition δ 44 / 42 Ca 915a and δ 43 / 42 Ca 915a according to Formulas 4 and 5;

[0047]

[0048] wherein, δ 44 / 42 Ca standard / 915a and δ 43 / 42 Ca standard / 915a are the Ca stable isotope compositions of the reference sample measured by the solution method relative to NIST SRM 915a.

[0049] In the technical solution of the present invention, a method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination is proposed. This method can simply and quickly correct the Ca isotope measurement results, achieving high-resolution, low-detection limit, and high-throughput Ca isotope measurement; by calculating the Ca single-charge fractionation factor through the iteration method, combined with the Sr isotope ratio, the instrument mass discrimination correction and the accurate deduction of Sr double-charge interference are simultaneously achieved through formulas 1 to 5; this method breaks through the application scope of in-situ Ca isotope measurement, is applicable to high-Sr and low-Sr samples, solves the technical problems of the accuracy and precision of in-situ Ca isotope analysis, and fills the blank of laser in-situ detection of Ca isotope composition in Sr-rich samples, providing a strong technical support for applications in the field of earth science.

[0050] It can be understood that during the mass spectrometry detection process, the Sr double-charge mass spectrometry interference mentioned in the present invention includes 84 Sr 2+ , 86 Sr 2+ , 88 Sr 2+ . The ion current intensities of these are respectively superimposed on 42 Ca + , 43 Ca + , 44 Ca + , thus causing the ion current intensities of the plasma at mass-to-charge ratios of 42, 43, and 44 to be inaccurate (too large).

[0051] It should be noted that the 87 Sr / 86 Sr ratio of the standard sample or the sample to be measured is the actual value obtained by in-situ Sr isotope measurement of the standard sample or the sample to be measured before the Ca isotope experiment.

[0052] It can be understood that formulas 1 and 2 in the present invention simultaneously complete the mass discrimination correction and the Sr double-charge interference correction. Subsequently, the in formulas 1 and 2 is updated through formula 3. Specifically: using the exponential law to standardize the corrected 44 Ca / 42 Ca ratio to the known natural ratio (3.2241), repeating the correction process to calculate the Ca stable isotope ratio, and then iteratively calculating and updating until the fractionation factor tends to be stable, that is, the ratio of the fractionation factors of two adjacent times approaches 1, and the iteration is stopped to obtain the final fractionation factor. Finally, the Ca isotope composition in the final sample to be measured is calculated through formulas 4 and 5. Specifically: according to the final fractionation factor, calculate the 44 Ca / 42 Ca and 43Ca / 42 The Ca ratio. The cross-method between standard samples (SSB method) is used to correct the isotope fractionation of the Ca stable isotope ratio, and the Ca isotope composition of the final sample to be measured is obtained.

[0053] It should be noted that when correcting the test results of the standard sample, the corresponding parameters in Formulas 1 to 3 are all for the standard sample, and the corrected value is denoted as ( 44 Ca / 42 Ca) standard and ( 43 Ca / 42 Ca) standard ; when correcting the test results of the sample to be measured, the corresponding parameters in Formulas 1 to 3 are all for the sample to be measured, and the corrected value is denoted as ( 44 Ca / 42 Ca) sample and ( 43 Ca / 42 Ca) sample .

[0054] In some embodiments of the present invention, the standard sample can be a sample with low Sr or high Sr content. For example, the mass ratio of Sr to Ca in the standard sample ≤ 0.001, and the mass ratio of Sr to Ca in the sample to be measured > 0.001; or, the mass ratio of Sr to Ca in the standard sample > 0.001, and the mass ratio of Sr to Ca in the sample to be measured ≤ 0.001. That is, in the present invention, the Sr content in the standard sample and the sample to be measured can both not be limited to a low Sr content, and its correction accuracy is relatively high.

[0055] Preferably, in the present invention, for a sample with low Sr content or a mass ratio of Sr to Ca ≤ 0.001, the Sr / Ca value ranges from 0.000077 to 0.001; or, for a Sr-rich sample or a sample with a mass ratio of Sr to Ca > 0.001 in the present invention, the Sr / Ca value ranges from 0.028 to 0.057. The Ca isotope composition of the standard sample is evenly distributed at each position, and the homogeneity test is carried out through the measurement points evenly distributed in a cross shape. The results show that δ 4x / 42 Ca external reproducibility is better than 0.09‰ (x is 3 or 4).

[0056] In some embodiments of the present invention, the sample to be measured includes marine carbonate, carbonate minerals derived from aragonite, carbonate minerals derived from magma, or carbonate minerals derived from metasomatic carbonatite.

[0057] The method of the present invention is applicable to laser ablation instruments. Preferably, in some embodiments of the present invention, the laser ablation instrument includes a Resonetics 193nm ArF excimer laser ablation system.

[0058] The Sr / Ca value of natural carbonates usually fluctuates between 10 -6 ~10 -1 . The present invention can effectively correct the Sr double-charge mass spectrometry interference in the measurement of Ca isotopes of carbonate samples with Sr / Ca values up to 0.057. Since the Sr double-charge yield and the Sr / Ca value of the sample show a positive correlation under the same instrument state conditions in adjacent measurement stages, the accurate correction of the interference can also reduce the Sr double-charge yield of the sample to be measured by adjusting the instrument parameters, thereby improving the analysis precision. Therefore, Sr / Ca = 0.057 is not the upper limit of this method. Combining with the recommended instrument parameters, the present invention can effectively correct the interference of Sr double-charge on the measurement of Ca isotopes. In some embodiments of the present invention, before the step of laser ablation of the standard sample, it further includes: adjusting the laser ablation parameters to avoid incomplete ionization and ensuring that 44 Ca + the measurement signal intensity is greater than 9V. Through this adjustment, higher detection precision can be guaranteed. Preferably, the present invention adopts a low-resolution mode. Preferably, in some embodiments of the present invention, the multi-collector inductively coupled plasma mass spectrometer includes Nu Plasma II MC-ICP-MS. Preferably, in some embodiments of the present invention, the instrument drift and matrix effect of the sample to be measured are corrected by the standard sample-sample cross method.

[0059] 87 Sr / 86 The precision of the Sr ratio depends on the Sr / Ca value of the sample. In some embodiments of the present invention, in step S20, the standard deviation range of the Sr to 86 Sr ratio in the same sample measured multiple times is -0.005 to 0.005, that is, 87 the precision of Sr / 87 Sr / 86 Sr needs to reach ±0.005 (SD) to accurately correct the mass spectrometry interference of Sr double-charge on the measurement of Ca isotopes.

[0060] In some embodiments of the present invention, the mass resolution mode in the multi-collector inductively coupled plasma mass spectrometry is a low-resolution mode. In this mode, the detection result and the correction result are more accurate.

[0061] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0062] Example 1 Comparative analysis of Ca isotopes in low-resolution and high-resolution modes

[0063] MC-ICP-MS measurement of Ca isotopes is restricted by polyatomic ions and Sr double-charged ions interference in the plasma. Most of the polyatomic ions come from oxide ion interference composed of background gas or sample matrix elements. High-resolution mode is usually used to avoid polyatomic ion interference.

[0064] To explore the influence of mass resolution mode on Ca isotope measurement, Ca isotope analysis was carried out using low-resolution and high-resolution slits respectively in the same measurement stage, and the results were compared. The blank scan diagram under low mass resolution mode is as Figure 1 shown.

[0065] As Figure 1 can be seen, the mass spectrometry interference from the background under low-resolution mode is very small and can be deducted by background correction; under the conditions of laser parameters of 90μm, 10Hz, 3J / cm 2 the signal intensity of the 44 Ca + standard sample reaches 9V, while the 44 Ca + signal intensity under high-resolution mode decreases significantly, only 5V, and there is a significant matrix effect between different minerals, affecting the stability of measurement results. Therefore, the present invention recommends in-situ Ca isotope measurement under low-resolution mode to obtain higher signal intensity and more stable measurement results.

[0066] Example 2 Ca isotope composition of the sample before and after Sr double-charged interference correction by the iterative method

[0067] This example proposes a method for deducting Sr double-charged interference based on the iterative method to improve the accuracy of Ca isotope determination. Consistent with the steps described in the specific implementation part, the Ca single-charged fractionation factor is calculated by an iterative method while realizing instrument mass discrimination and Sr 2+ interference correction.

[0068] The above iterative method was used to analyze the Ca isotopes of calcite samples with Sr / Ca = 0.000077, and the Ca isotope compositions before and after correction were compared. The results are as Figure 2 shown. The blue dots represent the Ca isotope composition after Sr double-charged interference correction, the red triangles represent the Ca isotope composition without Sr double-charged interference correction, the error bars represent the uncertainty 2σ of a single analysis, the black solid line is the recommended value of the solution method, and the blue area within the black dotted line consists of twice the standard deviation measured by the solution method (±0.02‰, 2SD). As Figure 2It can be seen that by calculating the Ca single-charge fractionation factor through the iterative method, the Sr double-charge ion interference can be effectively corrected, significantly improving the accuracy of Ca isotope measurement. The corrected results are highly consistent with the recommended values of the solution method, indicating that this method is applicable to the precise measurement of in-situ Ca isotopes.

[0069] Example 3 87 Sr / 86 Effect of Sr /

[0070] 87 Sr / 86 The change in the Sr / 87 Sr ratio will significantly affect the accurate measurement of Ca isotopes. To evaluate this effect, this example analyzed calcite samples with different Sr / Ca ratios (ranging from 0.000077 to 0.057) and evaluated 86 the effect of the change in the Sr / Figure 3 Sr ratio on the deviation of the Ca isotope composition through numerical simulation, and the results are as Figure 3 shown. 44 / 42 In it, the ordinate Δ-δ 43 / 42 Ca and Δ-δ 87 Sr / 86 Sr refer to the deviation of the Ca isotope composition obtained after correction with an inaccurate 87 Sr / 86 Sr ratio. The green diagonal line represents the Sr double-charge ion yield corresponding to a Ca isotope composition deviation of 0.1‰ when calculated using the two critical 87 Sr / 86 Sr ratios measured (that is, the upper or lower limit of the -1 Sr /

[0071] Sr ratio range of all measured samples). The black diagonal line represents the result of the upper limit of the natural Sr / Ca ratio of 10 Figure 3 From (a) in Figure 3 and (b) in 87 Sr / 86 Sr change on the Ca isotope δ 44 / 42 Ca 915a measurement gradually increases. Similarly, the deviation trend of δ 43 / 42 Ca 915a is consistent with that of δ 44 / 42 Ca 915a . This indicates that the Sr isotope 87 Sr / 86The Sr ratio accuracy is closely related to the Sr / Ca ratio of carbonate samples. For natural samples, the upper limit of the Sr / Ca ratio is 10 -1 , 87 Sr / 86 A slight change in the Sr / Sr ratio will lead to a significant deviation in the Ca isotope measurement results. Therefore, a higher-precision 87 Sr / 86 Sr ratio correction is required to ensure the measurement accuracy.

[0072] Ca isotope compositions of calcite samples with different Sr contents measured by the iterative method correction strategy in Example 4

[0073] The iterative method correction strategy same as that in Example 2 was used to measure the Ca isotopes of calcite samples with different Sr contents (Sr / Ca range from 0.000077 to 0.057). The results show that this method can effectively correct the Sr double-charge interference, ensuring the measurement accuracy and precision, especially suitable for samples with higher Sr contents (Sr / Ca range from 0.028 to 0.057).

[0074] It should be noted that the Sr to Ca mass ratio of the measured samples is not the upper limit of the applicability of this method. As described in the "Detailed Implementation Manner" section, this method can be used for a wider range of Sr / Ca ratios to achieve high-precision Ca isotope determination of Sr-rich minerals.

[0075] Ca isotope compositions of calcite samples with different Sr contents measured by the Sr single-charge fractionation factor correction strategy in Comparative Example 1

[0076] First, Sr isotopes were measured. Referring to the content of the article "Ramos F.C., Wolff J.A., Tollstrup D.L., 2004. Measuring 87 Sr / 86 Sr variations in minerals and groundmass from basalts using LA-MC-ICPMS. Chemical Geology, 211, 135-158", the specific steps are as follows: Measure the Sr isotopes of coral reference samples and calcite samples with different Sr contents in the laser ablation cell, record the signal intensities of mass numbers 84, 85, 86, 87, and 88, and subtract the carrier gas Kr background signal to eliminate isobaric interference. Subsequently, by normalizing the measured 86 Sr / 88 Sr to the natural ratio of 0.1194 for mass discrimination correction of Rb and Sr, and finally obtain the 87 Sr / 86Sr ratio. Coral reference samples are used as monitoring samples to verify the validity of measurement data.

[0077] Calculated Sr single-charge fractionation factor For Sr in Ca isotope measurement 2+ Interference correction. The Ca isotope measurement is carried out by the steps as in Example 2, and then the measured 87 Sr 2+ signal is combined with and the actual 86 Sr / 87 Sr ratio and the natural 88 Sr / 86 Sr, 84 Sr / 86 Sr ratios (8.375209 and 0.05654). The corrected 44 Ca / 42 Ca and 43 Ca / 42 Ca ratios are calculated through Formula 6 and Formula 7, and the Ca isotope composition of the final sample to be measured is obtained through Formula 4 and Formula 5.

[0078] The specific interference correction and isotope fractionation correction formulas are as follows:

[0079]

[0080] Among them, ([[]] 44 Ca / 42 Ca)[[]] corr and ([[]] 43 Ca / 42 Ca)[[]] corr are the stable Ca isotope ratios after Sr double-charge interference correction respectively, I[[[]] 44 、I[[[]] 43.5 and I[[[]] 42 are the ion current intensities of mass-to-charge ratios 44, 43.5, and 42 respectively, ([[]] 88 Sr / 86 Sr)[[]] true 、([[]] 84 Sr / 86 Sr)[[]] true and ([[]] 86 Sr / 87 Sr)[[]] sam are the natural stable Sr isotope ratio and the actual radiogenic Sr isotope ratio of the sample respectively, and M88, M87, M86, and M84 are 88 Sr, 87 Sr, 86 Sr and 84 Sr mass numbers respectively.

[0081] This strategy was adopted to measure the Ca isotope composition of calcite with different Sr contents. The Sr single-charge fractionation factor showed significant differences among different analysis stages (from April to December 2023) and samples with different Sr contents. The higher the Sr content, the smaller the value. Therefore, the of calcite samples with the lowest (0.000077) and highest (0.057) Sr / Ca ratios in the same analysis stage were used respectively for Sr double-charge interference correction. The measurement results showed that was only applicable to samples with low Sr content (Sr / Ca ≤ 0.01), but for samples with high Sr content (such as Sr / Ca = 0.057), the correction effect was limited. The measurement results were as Figure 4 shown. The squares represent the Ca isotope composition obtained by interference correction using the of the sample with the smallest Sr / Ca ratio (Sr / Ca = 0.000077), and the "X" shapes represent the Ca isotope composition obtained by interference correction using the of the sample with the largest Sr / Ca ratio (Sr / Ca = 0.057). The error bars all represent the uncertainty 2σ of a single analysis. The black solid line is the recommended value by the solution method, and the purple area within the black dashed line consists of twice the standard deviation measured by the solution method (±0.05‰, 2SD). It can be seen from Figure 4 that regardless of which is used for correction, for samples with high Sr content (Sr / Ca = 0.057), the measurement results deviate from the recommended value by the solution determination. This indicates that the correction method based on f Sr+ is not applicable to samples with high Sr content, and a more accurate correction strategy is needed to improve the accuracy of Ca isotope measurement for high-Sr-content samples.

[0082] Performance Test

[0083] It can be seen from the results of Example 4 and Comparative Example 1 that the interference correction method using the iterative method to calculate the Ca single-charge fractionation factor can significantly improve the accuracy and precision of Ca isotope measurement for Sr-rich calcite samples.

[0084] To further verify the feasibility and superiority of the iterative method correction strategy in in-situ Ca isotope analysis, Ca isotope repeated measurements were carried out on dolomite samples with Sr / Ca = 0.00022 and calcite samples with Sr / Ca = 0.028 and 0.057 at different analysis stages (from April to December 2023). The measurement results are as Figure 5 shown in (a), Figure 5 shown in (b), and Figure 5 shown in (c). The error bars represent the uncertainty 2σ of a single analysis. The black solid line is the recommended value by the solution method, and the area within the black dashed line consists of twice the standard deviation measured by the solution method (2SD).Figure 5 It can be seen that the iterative correction strategy is applicable to the Ca isotopes of carbonate samples with all different Sr contents. This method breaks through the application bottleneck of Ca isotope analysis and can be rapidly promoted and used.

[0085] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the patent protection scope of the present invention.

Claims

1. A method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination, characterized in that It includes the following steps: S10. Provide a standard sample that matches the matrix and the sample to be measured. Perform laser ablation on the standard sample to form aerosol particles under the action of laser. Ionize the aerosol particles to form charged ions, and detect the charged ions by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Record the ion current intensities at mass-to-charge ratios of 42, 43, 43.5, and 44, denoted as I 42 , I 43 , I 43.5 , and I 44 ; S20. Obtain 88 the natural mass ratio constant of 86 Sr to 88 Sr ([[]] 86 Sr / true Sr)[[]] 84 is 8.375209, and 86 the natural mass ratio constant of 86 Sr to 84 Sr ([[]] 86 Sr / 86 Sr)[[]] true is 0.05654. And obtain the ratio of 86 Sr to 87 Sr ([[]] 86 Sr / 87 Sr)[[]] standardsam of the standard sample by repeatedly measuring in-situ Sr isotopes; Calculate the stable Ca isotope ratio ([[]] 44 Ca / 42 Ca)[[]] standardcorr1 after the first correction of the standard sample according to Formula 1, and calculate the stable Ca isotope ratio ([[]] 43 Ca / 42 Ca)[[]] standardcorr1 after the first correction of the standard sample according to Formula 2; wherein, M88, M87, M86, and M84 are respectively 88 Sr, 87 Sr, 86 Sr, and 84 the mass numbers of Sr, is the Ca single-charge fractionation factor for the i-th calibration, ( 44 Ca / 42 Ca) standardcorri 、( 43 Ca / 42 Ca) standardcorri where i is the number of calibrations, and the value range of i is a positive integer; when the first calibration is performed, i = 1, is 0; After the first calibration is completed, update through Formula 3 to obtain and . to obtain Among them, M44 and M42 are respectively 44 Ca and 42 the mass numbers of Ca, ([[]] 44 Ca / 42 Ca)[[]] true is 44 the natural mass ratio constant of Ca and 42 Ca, 3.2241; S40. Calculate the ratio of to When the ratio is far from 1, substitute back into Formulas 1 and 2 to calculate the ( 44 Ca / 42 Ca) standardcorri+1 and ( 43 Ca / 42 Ca) standardcorri+1 of the standard sample after the next calibration; when the ratio tends to 1, stop the iterative calculation and obtain the stable Ca isotope ratio ( 44 Ca / 42 Ca) standard and ( 43 Ca / 42 Ca) standard of the standard sample after the i-th calibration; S50. Replace the calibration sample in steps S10 to S40 with the sample to be measured, repeat steps S10 to S40, and calculate the stable Ca isotope ratio after the i-th calibration of the sample to be measured ( 44 Ca / 42 Ca) sample and ( 43 Ca / 42 Ca) sample ; S60. Calculate the Ca stable isotope compositions δ 44 / 42 Ca 915a and δ 43 / 42 Ca 915a ; where δ 44 / 42 Ca standard / 915a and δ 43 / 42 Ca standard / 915a are the Ca stable isotope compositions of the standard samples determined by the solution method relative to NIST SRM 915a.

2. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, wherein This method is applicable to samples with a relatively high Sr content in nature, and its Sr content can reach up to 10 times the highest level of natural carbonates -1 .

3. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, characterized in that, The standard sample can be a sample with low Sr or high Sr content.

4. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, characterized in that, The sample to be measured includes marine carbonate, carbonate minerals derived from aragonite, carbonate minerals derived from magma, or carbonate minerals derived from metasomatic carbonatite.

5. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, characterized in that, The instrument for laser ablation includes a Resonetics 193 nm ArF excimer laser ablation system.

6. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, characterized in that, Before the step of performing laser ablation on the standard sample, it further includes: Adjust the laser ablation parameters to avoid incomplete ionization and ensure that 44 Ca + the measured signal intensity is greater than 9V.

7. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, characterized in that, The multi-collector inductively coupled plasma mass spectrometer includes Nu Plasma II MC-ICP-MS.

8. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, characterized in that, The instrumental drift and matrix effect of the sample to be measured are corrected by the standard sample-sample cross method.

9. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, wherein In step S20, the standard deviation range of the 86 Sr to 87 Sr ratio obtained by measuring the same sample multiple times depends on the Sr / Ca ratio of the sample.

10. The method for accurately deducting Sr double-charge interference in in-situ Ca isotope determination according to claim 1, characterized in that, The mass resolution mode in the multi-collector inductively coupled plasma mass spectrometry is the low resolution mode.

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