A secondary standard sample and calibration method for carbonate cluster isotope calibration

Abstract

This application relates to a secondary standard sample and a calibration method for carbonate cluster isotope calibration in the field of stable isotope analysis and testing technology, including: preparing a secondary standard sample and a sample; obtaining secondary standard sample CO2 and sample CO2; obtaining the cluster isotope measurement values of the secondary standard sample CO2 and the sample CO2 and performing calibration respectively to obtain the secondary standard sample cluster isotope calibration value and the sample cluster isotope calibration value; comparing the secondary standard sample cluster isotope calibration value with the recommended value of the secondary standard sample cluster isotope to establish a secondary empirical conversion function; substituting the sample cluster isotope calibration value into the secondary empirical conversion function to obtain the final cluster isotope calibration value of the sample. The calibration method of this application can reduce the differences in measurement results among different laboratories and reduce the fluctuations of data in different test periods in the same laboratory, improve the comparability of data among different laboratories and the long-term stability of data in the same laboratory, and meet the needs of the cluster laboratory for daily test calibration data.

Description

Technical Field

[0001] The present application relates to the technical field of stable isotope analysis and testing, and in particular to a secondary standard sample and a calibration method for carbonate cluster isotope calibration. Background Art

[0002] Carbonate cluster isotopes are a new type of geological thermometer that measures the CO generated by the acidolysis of carbonates. 2 Two heavy isotopes in the gas 13 C and 18 O combines to generate an isotope molecule with a mass number of 47, and the difference in the thousandth of the ion beam intensity ratio corresponding to the random distribution of C and O isotopes in each isotope molecule of the sample, that is, the Δ47 value. The Δ47 value is only related to the temperature of carbonate formation and has nothing to do with the oxygen isotope composition of the parent water from which the carbonate crystallizes. It is a single mineral thermometer that overcomes the requirement of assuming the oxygen isotope of the parent water when calculating the temperature of the traditional carbonate oxygen isotope thermometer, while the oxygen isotope composition of the parent water in the geological history is often difficult to obtain accurately. Therefore, the carbonate cluster isotope temperature measurement method has received great welcome and attention. Accurately obtaining temperature information is of great significance and has broad application prospects for in-depth research on paleoclimate, paleoenvironment and paleoecology.

[0003] Since Ghosh made the first empirical equation for the fitting curve of the temperature and Δ47 value measured by temperature-controlled synthetic calcite in 2006 (the fitting temperature range is 1-50℃), we can calculate the formation temperature of unknown samples by measuring the Δ47 value of unknown samples and inserting it into the fitting empirical equation. Since then, different laboratories and scholars have conducted many carbonate temperature-controlled sedimentation experiments, or measured natural carbonate samples with known formation temperatures. In different laboratories, different pre-treatment devices, different test instruments and different data correction methods have been used to fit many different temperature T-Δ47 empirical formulas. However, according to these different T-Δ47 empirical formulas, the same Δ47 value can be used to calculate very different formation temperature values. Even the data from the same laboratory at different test periods may fluctuate greatly, resulting in huge differences in the measurement results between different laboratories or the same laboratory at different test periods. Moreover, the current number of international carbonate standards is very limited. For example, a set of international carbonate standards distributed to various laboratories by Professor Bernasconi of the Swiss Federal Institute of Technology in Zurich contains only about 0.5-1g, which is insufficient for daily use in the laboratory. Some international carbonate standards used for cluster isotope correction, such as NBS19, have been exhausted and are no longer available. Summary of the invention

[0004] In view of the problems existing in the background technology, the present application provides a secondary standard sample and calibration method for carbonate cluster isotope calibration, which can reduce the differences in measurement results of different laboratories and reduce the fluctuation of data in different test periods of the same laboratory, improve the comparability of data from different laboratories and the long-term stability of data from the same laboratory, and meet the needs of cluster laboratories for routine testing and calibration data.

[0005] In order to achieve the above object, the present invention provides a secondary standard sample and a calibration method for carbonate cluster isotope calibration, comprising the following steps: preparing a secondary standard sample and a sample to be measured; acid hydrolyzing the secondary standard sample and the sample respectively to obtain a secondary standard sample CO 2 and sample CO 2 ; Obtain the secondary standard CO 2 and sample CO 2 The cluster isotope measurement values ​​are taken and corrected respectively to obtain the secondary standard cluster isotope correction value and the sample cluster isotope correction value; the secondary standard cluster isotope correction value is compared with the secondary standard cluster isotope recommended value to establish a secondary empirical conversion function; the sample cluster isotope correction value is brought into the secondary empirical conversion function to obtain the final cluster isotope correction value of the sample.

[0006] In some embodiments of the present invention, the secondary standard sample cluster isotope recommended value is obtained by the following steps: preparing an international carbonate standard sample; performing acid hydrolysis on the international carbonate standard sample to obtain an international carbonate standard sample CO 2 ; Obtain the international carbonate standard CO 2 The cluster isotope measurement value of the international carbonate standard CO 2 The cluster isotope measurement value of the secondary standard is compared with the recommended cluster isotope value of the international carbonate standard to establish an empirical conversion function; the cluster isotope correction value of the secondary standard is brought into the empirical conversion function to obtain the recommended cluster isotope value of the secondary standard.

[0007] In some embodiments of the present invention, the secondary standard sample includes high temperature carbonate, medium temperature carbonate and low temperature carbonate.

[0008] In some embodiments of the present invention, the high-temperature carbonate is selected from Carrara marble, the medium-temperature carbonate is selected from Guizhou Wangmo Iceland spar, and the low-temperature carbonate is selected from natural travertine.

[0009] In some embodiments of the present invention, the secondary standard CO 2 and sample CO 2 The correction of cluster isotope measurements includes nonlinear correction, CO 2 Balance scale correction and acid fractionation correction.

[0010] In some embodiments of the invention, the nonlinear correction and CO 2 The equilibrium scale calibration comprises the following steps: preparing high temperature gas and equilibrium gas; obtaining nonlinear calibration results based on the pressure baseline calibration method for cluster isotope values ​​of the high temperature gas and equilibrium gas; comparing the intercept values ​​obtained after the nonlinear calibration of cluster isotope values ​​of the high temperature gas and equilibrium gas with the CO 2 The cluster isotope theoretical values ​​were compared to establish an empirical conversion function; the secondary standard CO 2 and sample CO 2 The cluster isotope measurements of CO are brought into the empirical conversion function to complete the 2 Balance scale calibration, obtain the cluster isotope balance scale calibration value of the secondary standard or sample.

[0011] In some embodiments of the present invention, the acid fractionation calibration comprises the following steps: preparing a carbonate standard sample; obtaining the CO of the carbonate standard sample at an acid hydrolysis temperature of 90° C. and at an acid hydrolysis temperature of 25° C. in a common acid bath sealed reaction vessel; 2 The Δ47 value after balance scale correction; subtracting the Δ47 value at 90°C acid hydrolysis temperature from the Δ47 value at 25°C acid hydrolysis temperature to obtain the acid fractionation correction factor between 25-90°C; adding the acid fractionation correction factor to the balance scale correction value to complete the acid fractionation correction and obtain the cluster isotope value of the secondary standard or sample at an acid reaction temperature of 25°C.

[0012] In some embodiments of the present invention, the preparation temperatures of the high temperature gas and the balance gas are 1000° C. and 25° C., respectively.

[0013] In some embodiments of the invention, the slope of the empirical transfer function is greater than 0.8 and less than 1.2.

[0014] In some embodiments of the present invention, the high temperature gas, balance gas, secondary standard sample and sample are interspersed in the test.

[0015] The embodiment of the present application provides a secondary standard sample and a calibration method for carbonate cluster isotope calibration. The method adopts a secondary standard sample, calibrates the cluster isotope measurement values ​​of the secondary standard sample and the sample respectively, establishes a secondary empirical conversion function based on the secondary standard sample cluster isotope calibration value and the secondary standard sample cluster isotope recommended value, and substitutes the sample cluster isotope calibration value into the secondary empirical conversion function to obtain the final calibration value of the sample cluster isotope, so that the final calculated result of the sample cluster isotope value is more consistent with the international recommended value, thereby reducing the difference in measurement results of different laboratories and reducing the fluctuation of data in different test periods of the same laboratory, improving the comparability of data of different laboratories and the long-term stability of data of the same laboratory, and meeting the needs of cluster laboratories for routine test calibration data, providing an experimental basis for the cluster isotope temperature measurement accuracy requirements, and the use of secondary standards greatly reduces the use and consumption of international carbonate standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only used to illustrate the preferred embodiments and are not to be considered as limiting the present application. In the accompanying drawings:

[0017] Figure 1 is a flow chart of the correction method of the present invention;

[0018] Figure 2 It is a detailed process diagram of the correction method of the present invention;

[0019] Figure 3 This is a photo of the hand specimen of the Icelandic stone in Wangmo, Guizhou;

[0020] Figure 4 This is the result of X-ray diffractometer (XRD) of Guizhou Wangmo Iceland spar;

[0021] Figure 5 This is a diagram of the pressure baseline correction process of the present invention;

[0022] Figure 6 This is a graph showing the results of the laboratory secondary internal standard calibration using an international carbonate standard sample in the present invention;

[0023] Figure 7 An empirical conversion function diagram established for the present invention using the calibration values ​​and recommended values ​​of the secondary standard;

[0024] Figure 8 This is the long-term stability diagram of the laboratory standard cluster isotope Δ47 data of the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The present application discloses a secondary standard sample and calibration method for carbonate cluster isotope calibration. Figure 1 and Figure 2 As shown, the secondary standard sample and calibration method for carbonate cluster isotope calibration include the following steps:

[0027] S1. Prepare secondary standard samples and samples to be tested.

[0028] S2. Acid hydrolyze the secondary standard sample and the sample to obtain the secondary standard sample CO. 2 and sample CO 2 .

[0029] S3. Obtain secondary standard CO 2 and sample CO 2 The cluster isotope measurement values ​​are taken and corrected respectively to obtain the secondary standard cluster isotope correction value and the sample cluster isotope correction value.

[0030] S4. Compare the secondary standard cluster isotope correction value with the secondary standard cluster isotope recommended value to establish a secondary empirical conversion function.

[0031] S5. Substitute the sample cluster isotope correction value into the secondary empirical conversion function to obtain the final cluster isotope correction value of the sample.

[0032] The present invention adopts a secondary standard sample, and the cluster isotope measurement values ​​of the secondary standard sample and the sample are corrected respectively. Based on the secondary standard sample cluster isotope correction value and the secondary standard sample cluster isotope recommended value, a secondary empirical conversion function is established, and the sample cluster isotope correction value is substituted into the secondary empirical conversion function to obtain the cluster isotope final correction value of the sample. If the national standard sample is used as an unknown sample for testing, the corrected cluster isotope value can be made more consistent with the international recommended value, thereby reducing the difference in the measurement results of different laboratories and reducing the fluctuation of the data of different test periods in the same laboratory, improving the comparability of different laboratory data and the long-term stability of the same laboratory data, and meeting the needs of cluster laboratory daily test correction data, providing an experimental basis for cluster isotope temperature measurement accuracy requirements, and the use of the secondary standard sample greatly reduces the use and consumption of international carbonate standards.

[0033] In some embodiments of the present invention, Figure 2As shown, the recommended cluster isotope values ​​of the secondary standard samples are obtained by the following steps:

[0034] First prepare the international carbonate standards.

[0035] The international carbonate standard was then acid-hydrolyzed to obtain the international carbonate standard CO 2 .

[0036] Then obtain the international carbonate standard CO 2 Cluster isotope measurements.

[0037] Then the international carbonate standard CO 2 The measured cluster isotope values ​​of the carbonate standard were compared with the recommended cluster isotope values ​​of the international carbonate standard, and an empirical conversion function was established.

[0038] Finally, the secondary standard cluster isotope correction value is substituted into the empirical conversion function to obtain the secondary standard cluster isotope recommended value.

[0039] In some embodiments of the present invention, the international carbonate standard can be a set of international carbonate standards ETH-1, ETH-2, ETH-3, ETH-4, ETH-MERK, IAEA-C1, and IAEA-C2 distributed to various laboratories by Professor Bernasconi of the Swiss Federal Institute of Technology in Zurich; that is, the recommended cluster isotope values ​​of the secondary standard can be obtained by calibration with the set of international carbonate standards distributed to various laboratories by Professor Bernasconi of the Swiss Federal Institute of Technology in Zurich.

[0040] In some embodiments of the present invention, the secondary standard sample includes high temperature carbonate, medium temperature carbonate and low temperature carbonate.

[0041] In this embodiment, in order to cover the cluster isotope compositions of unknown carbonate samples of high temperature, medium temperature and low temperature, a group of pure and uniform carbonates with a wide range of cluster isotope composition variation can be selected as secondary standards, that is, the secondary standard can be selected from one each of high temperature carbonate, medium temperature carbonate and low temperature carbonate.

[0042] In some embodiments of the present invention, the high-temperature carbonate can be selected from Carrara marble in Italy, such as the IAEA-C1 carbonate standard provided by the International Atomic Energy Agency or the NBS-19 limestone standard provided by the U.S. National Bureau of Standards, both of which are prepared from Carrara marble in Italy; the medium-temperature carbonate can be selected from hydrothermal Iceland spar or high-purity synthetic carbonate, such as Iceland spar from Wangmo County, Guizhou or Merck's high-purity synthetic calcium carbonate with a purity of more than 99.95%; the low-temperature standard can be selected from pure and uniform natural travertine, coral or stalagmite, such as the IAEA-C2 travertine standard provided by the International Atomic Energy Agency.

[0043] In some embodiments of the present invention, each secondary standard sample is preferably more than 100 g, each secondary standard sample is ground into a powder of less than 200 mesh using an agate mortar, and each secondary standard sample is mixed evenly, packaged in glass vials, and stored in a drying oven or a drying dish to prevent moisture absorption.

[0044] In some embodiments of the present invention, Figure 2 As shown, the secondary standard CO 2 and sample CO 2 The correction of cluster isotope measurements includes nonlinear correction, CO 2 Balance scale correction and acid fractionation correction.

[0045] In some embodiments of the present invention, Figure 2 As shown, the nonlinear correction and CO 2 Balance scale calibration includes the following steps:

[0046] First, prepare high temperature gas and balance gas.

[0047] Then, the cluster isotope values ​​of the high-temperature gas and the equilibrium gas are corrected based on a pressure baseline method to obtain nonlinear correction results.

[0048] Then, the intercept values ​​obtained after nonlinear correction of the cluster isotope values ​​of the high-temperature gas and the equilibrium gas are compared with the CO 2 The theoretical values ​​of cluster isotopes were compared and empirical conversion functions were established.

[0049] Then the secondary standard CO 2 and sample CO 2 The cluster isotope measurement value of CO is brought into the empirical conversion function to complete the 2 Balance scale calibration, obtain the cluster isotope balance scale calibration value of the secondary standard or sample.

[0050] In some embodiments of the present invention, for the pressure baseline correction method, the background signal with mass numbers of 47 and 48 can be first monitored and corrected using the 47.5 Faraday cup signal intensity. Specifically, the peak shape scanning of the dual-path injection gas source mass spectrometer can be used to obtain the working reference CO 2 The m / z (mass-to-charge ratio) of the gas under different gas pressures are respectively 44, 45, 46, 47, 47.5, 48 and 49. On the m / z 47 and 48 scans, the upper and lower background value intervals are determined, the 47 or 48 background signals within the upper and lower background intervals are averaged, and the voltage values ​​of the upper and lower background value intervals are also averaged.

[0051] Then, a straight line was fitted between the background signal intensity value and the voltage value to obtain the fitted straight line equation of the 47 or 48 background signal intensity and voltage under different gas pressures; the signal with a mass number of 45 was used for peak centering to obtain the voltage value in the peak centering; the obtained voltage value in the peak centering was substituted into the fitted straight line equation to obtain the background signal intensity of 47 or 48 at the peak under different gas pressures; on the 47.5 peak scanning graph, the intensity I of the 47.5 peak signal under different gas pressures was obtained. 47.5peak ; The background signal intensity of 47 or 48 and the intensity of the peak signal I 47.5peak Fitted straight line, the slope of the straight line is the initial pressure baseline correction factor k1 for m / z 47 or 48 initial or k2 initial .

[0052] Then, the original 45, 46, 47, 47.5, 48 and 49 signal intensity values ​​of the high temperature gas and the equilibrium gas without pressure baseline background correction were measured by stable isotope mass spectrometer; the fitting line was fitted on the d47(raw)-Δ47(raw) or d48(raw)-Δ48(raw) graph, and its slope was the original common slope value Slope initial ; Use correction factor k1 initial and k2 initial The pressure baseline correction is performed on the 47 or 48 signal intensity of the high temperature gas and the balance gas. The correction equation is:

[0053] I 47 corrected = I 47,measured – k1 initial ×I 47.5peak (1)

[0054] I 48 corrected = I 48,measured – k2 initial ×I 47.5peak (2)

[0055] Among them, k1 initial = I 47background / I 47.5peak , k2 initial = I 48background / I 47.5peak .

[0056] In d47 (raw) -Δ47 (raw) The nonlinear correction line of high temperature gas and equilibrium gas is fitted on the d48(raw)-Δ48(raw) graph to obtain the residual common slope value Slope after preliminary pressure baseline correction. residual ; The original common slope value Slope initial , Remaining common slope value Slope residualand the initial pressure baseline correction factor k1 initial , k2 initial , the final pressure baseline correction factor K1 of the m / z 47 or 48 signal is obtained by proportional calculation method final and K2 final , the slopes of the fitted straight lines of the high temperature gas and the equilibrium gas on the d47-Δ47raw and d48-Δ48raw graphs are corrected to be close to zero, and the formula for the proportional calculation method is:

[0057] (3)

[0058] Their residual slope is preferably less than 0.001, so as to ensure that for samples with extremely large or extremely small δ47 values, the influence of nonlinear effects in the cluster isotope measurement process on the measurement data can be removed. The above pressure baseline correction method can be detailed in Chinese patent CN115980165A.

[0059] Then, the intercept difference between the high temperature gas and the equilibrium gas on the d47-Δ47raw and d48-Δ48raw graphs was used to compare the CO 2 The theoretical values ​​of cluster isotopes obtained by thermodynamic calculations were compared and empirical conversion functions were established for CO 2 Balanced scale correction: This allows cluster isotope values ​​from different laboratories and different measurement periods to be corrected to a common scale, improving data comparison and consistency.

[0060] In some embodiments of the present invention, the preparation temperatures of the high temperature gas and the balance gas are 1000° C. and 25° C., respectively.

[0061] In this embodiment, the high temperature gas is obtained by reacting carbonates with different C and O isotopic compositions with phosphoric acid, and then removing water through the pre-treatment system to obtain pure CO 2 It is sealed in a quartz tube, heated in a muffle furnace at 1000℃ for more than 3 hours, and quenched to room temperature to make the C and O isotopes in CO 2 The molecules reach a random distribution state.

[0062] The balance gas is the reaction of carbonates with different C and O isotopic compositions with phosphoric acid, and the water is removed by the pre-treatment system to obtain pure CO 2 Water with a different isotopic composition from O is sealed in a quartz tube or a Pyrex glass tube and placed in a constant temperature water bath for more than 3 days. 2 The isotope exchange with water reaches isotope equilibrium, and the resulting CO 2 To balance the gas.

[0063] The wider the composition range of δ47 and δ48 of the high temperature gas and the balance gas, the better. It is best if the composition of δ47 and δ48 of the unknown sample can be covered. This can reduce errors when calibrating secondary standards and samples with high temperature gas and balance gas.

[0064] In some embodiments of the invention, the slope of the empirical transfer function is greater than 0.8 and less than 1.2.

[0065] The closer the slope of the empirical transfer function is to 1, the better, indicating that during the sample preparation and mass spectrometry testing, water is removed more cleanly and the isotope exchange reaction of residual water has less impact. The slope value of the empirical transfer function is preferably lower than 1.2.

[0066] In some embodiments of the invention, the acid fractionation calibration comprises the following steps:

[0067] First prepare the carbonate standards.

[0068] Then, the CO of the carbonate standard sample was obtained at 90°C acid hydrolysis temperature and 25°C acid hydrolysis temperature in a common acid bath sealed reaction vessel. 2 Δ47 value after balance scale correction.

[0069] Then, the Δ47 values ​​at 90°C acid hydrolysis temperature and 25°C acid hydrolysis temperature were subtracted to obtain the acid fractionation correction factor between 25 and 90°C.

[0070] Then, the acid fractionation correction coefficient is added to the equilibrium scale correction value to complete the acid fractionation correction and obtain the cluster isotope value of the secondary standard or sample at an acid reaction temperature of 25°C.

[0071] In some embodiments of the present invention, we simultaneously measure the CO obtained by the international carbonate standard IAEA-C2 in a common acid bath reaction vessel at 90°C acid hydrolysis temperature and in a closed reaction vessel at 25°C acid hydrolysis temperature. 2 The Δ47 values ​​after balance scale correction are subtracted to obtain an acid fractionation correction coefficient of 0.086‰ between 25-90°C, which is very close to the acid fractionation correction coefficient of 0.088‰ obtained by Petersen et al. in 2019 by measuring many carbonate standards under different acid hydrolysis temperature reaction conditions. Therefore, we recommend using the acid fractionation correction coefficient of 0.088‰ between 25-90°C obtained by Petersen et al. in 2019.

[0072] In some embodiments of the present invention, high temperature gas, balance gas, secondary standard and sample are interspersed with the test.

[0073] In this embodiment, by interleaving the testing of high temperature gas, balance gas, secondary standard and sample, the isotope signal intensity of the high temperature gas, balance gas, secondary standard and sample is measured. Not only can the high temperature gas, balance gas and secondary standard be used to calibrate the sample, but also the stability of the mass spectrometer used for isotope signal intensity measurement and the sample pretreatment system can be monitored.

[0074] In some embodiments of the present invention, a high temperature gas or a balance gas can be measured every 1-2 days, and an average of 6-8 high temperature gases and balance gases can be measured every month; 1-2 secondary standards are measured every day, and the test ratio of the secondary standard to the sample is preferably 1:1.

[0075] In some embodiments of the present invention, a dual-injection stable isotope mass spectrometer can be used to measure the signal intensities of isotopes 44, 45, 46, 47, 48, 49, and 47.5 of high-temperature gas, balance gas, secondary standard sample, and sample.

[0076] In this embodiment, the secondary standard CO 2 and sample CO 2 The acquisition of cluster isotope measurements includes the following steps:

[0077] Calculate the original values ​​of δ47, δ48, δ49 and Δ47, Δ48, Δ49 of the secondary standard or sample using the following formula:

[0078] (4)

[0079] (5)

[0080] (6)

[0081] Among them, δ47, δ48 and δ49 are the sample CO 2 The ratio of the ion beam intensity of the gas with mass numbers of 47, 48, and 49 to the ion beam intensity of mass number 44 is similar to the working reference CO 2 The thousandth difference in the corresponding ion beam intensity ratio of the gas.

[0082] (7)

[0083] (8)

[0084] (9)

[0085] Among them, Δ47raw, Δ48raw and Δ49raw are sample CO 2 Gas or secondary standard CO 2The ratio of the ion beam intensity of the gas with mass numbers of 47, 48, and 49 to the ion beam intensity of mass number 44 is the thousandth difference from the corresponding ion beam intensity ratio when the C and O isotopes of the sample are in a random distribution state in each isotope molecule.

[0086] The detailed calculation steps include:

[0087] (1) Calculation of working reference CO 2 Gas 13 C / 12 C. 17 O / 16 O and 18 O / 16 O isotope abundance ratio.

[0088] (2) Calculation of working reference CO 2 Gas 12 C. 13 C. 16 O. 17 O and 18 O isotope abundance.

[0089] (3) Calculation of working reference CO 2 Isotope abundance of gas C 44-Ref , C 45-Ref , C 46-Ref , C 47-Ref , C 48-Ref and C 49-Ref .

[0090] (4) Calculate the CO of the sample or secondary standard 2 Gas relative to the working reference CO 2 δ45, δ46, δ47, δ48 and δ49 values ​​of the gas.

[0091] (5) Calculate the CO of the sample or secondary standard 2 The overall isotopic composition of the gas R 13-Sample , R 18-Sample and R 17-Sample .

[0092] (6) Calculate the CO of the sample or secondary standard 2 R is the ratio of isotope abundance in a randomly distributed gas * 45-Sample , R * 46-Sample , R * 47-Sample , R * 48-Sample and R * 49-Sample .

[0093] (7) Calculate the CO of the sample or secondary standard 2 The Δ47raw, Δ48raw and Δ49raw values ​​of gases can be automatically calculated using the software Easotope released in 2016 by Professor Cedric John of Imperial College London.

[0094] During the calculation, most of the silicate rocks, minerals and water on Earth 17 O and 18 The O isotope composition follows a mass-dependent fractionation relationship:

[0095] λ (10)

[0096] Among them, Brand et al. proposed a set of parameters R in 2010. 13 VPDB =0.01118, R 18 VSMOW =0.0020052, R 17 VSMOW =0.00038475 and λ=0.528 are used for the calculation of Δ47raw, Δ48raw and Δ49raw, which can increase the consistency of the sample calculation results and reduce the error of the sample results.

[0097] The secondary standard sample and calibration method for carbonate cluster isotope calibration of the present application will be further described below in conjunction with specific embodiments.

[0098] Example 1

[0099] The test of the present invention adopts Mat-253Plus high-precision stable isotope mass spectrometer of Thermo Fisher Scientific, and the pretreatment system for carbonates such as samples or secondary standards can adopt an offline manual sample preparation and purification system developed by the Qinghai-Tibet Plateau Institute of the Chinese Academy of Sciences, see Chinese patent CN113804534A for details.

[0100] The stable isotope mass spectrometer has a mass number of 44-49 and the amplifiers configured in the Faraday cup for ion intensity detection are: 3×10 8 Ω,3×10 10 Ω,1×10 11 Ω,1×10 13 Ω,1×10 13 Ω,1×10 13 Ω, especially equipped with an additional mass number of 47.5 half cup for online baseline detection, the mass number of 47.5 half cup amplifier is 1×10 13 Ω.

[0101] Cluster isotope measurements were made using a dual-path test mode, with reference to CO 2 Gas and sample CO reacted and purified by the pretreatment system 2 The gas was automatically adjusted to a mass number of 44 and a signal strength of 15000 (±100) mV, and alternately entered the ion source for analysis and testing.

[0102] Sample CO 2 Gas and working reference CO 2 Each gas sample was measured for 8 acquisitions, each acquisition was tested for 8 cycles, the integration time for each cycle was 26 seconds, and the idle time between cycles was 15 seconds. The total integration time for each replicate test signal was 1664 seconds.

[0103] The ion signal counting statistics generated by mass spectrometry conform to the Poisson distribution, and its minimum error limit is called the shot noise limit (Merritt and Hayes, 1994). Based on the ion beam signal of mass number 47 and the integration time, the shot noise limit of the measurement can be calculated to determine the internal precision that the Δ47 value can achieve in theory. The calculation formula is as follows:

[0104] Shot-noise limit = (11)

[0105] Among them, 6.24×10 18 represents the number of electrons in a current of 1 ampere per second, E represents the ion voltage signal detected by the Faraday cup (V), R represents the resistance of the amplifier (Ω), and t represents the integration time (s).

[0106] Generally, it is necessary to ensure that the measurement errors of the secondary standard and sample are as close to the shot noise limit as possible, so as to exclude the existence of stable isotope mass spectrometer instrument errors other than counting statistics. Otherwise, it will affect the external accuracy of the duplicate sample measurement to a certain extent. The shot noise limit calculated under the duplicate sample test conditions adopted in the present invention is 0.009‰.

[0107] 1) Selection and preparation of secondary standard samples

[0108] Carbonate secondary standard samples can be selected from pure and uniform natural marble, limestone, hydrothermal Iceland spar, high-purity synthetic carbonate, natural travertine, coral or stalagmite, etc.

[0109] In this example, we selected Carrara marble from Italy, Sohofen limestone from the Cretaceous period in Germany, and Iceland spar from Wangmo, Guizhou ( Figure 3As shown in the figure, high-purity carbonate synthesized by Merck or Aladdin, IAEA-C2 travertine standard provided by the International Atomic Energy Agency, natural microporous coral and cave stalagmite, etc., these secondary standard samples were ground into powders below 200 mesh with an agate mortar and pestle and mixed evenly.

[0110] The homogeneity and purity of the secondary standard samples are tested by X-ray diffractometer (XRD). X-ray diffractometer checks the purity of the samples. Generally, the calcium carbonate content of natural samples is greater than 99% ( Figure 4 ), the calcium carbonate content of the synthetic carbonate sample is greater than 99.95%.

[0111] In order to ensure that the selected secondary standard cluster isotope composition has a certain span range, it can cover the Δ47 composition of natural unknown samples and avoid the introduction of additional correction errors by extrapolating the secondary standard value to correct the Δ47 composition of unknown samples; in this embodiment, we selected a secondary standard at high temperature, medium temperature and low temperature to construct a secondary calibration curve (secondary empirical conversion function).

[0112] The high-temperature standard sample selected Carrara marble from Italy, specifically the IAEA-C1 carbonate standard sample provided by the International Atomic Energy Agency; the medium-temperature standard sample selected hydrothermal Iceland spar, specifically the Iceland spar BZ from Wangmo County, Guizhou; the low-temperature standard sample selected natural travertine, specifically the IAEA-C2 travertine standard sample provided by the International Atomic Energy Agency.

[0113] The 25°C phosphoric acid hydrolysis carbon dioxide equilibrium scale correction values ​​(Δ47_CDES_25) of the three secondary standard samples in this embodiment range from 0.3898% to 0.7289%, which basically covers geological carbonate samples of various origins and temperatures.

[0114] Each secondary standard sample is selected to be more than 100g, such as Figure 3 Shown is a photo of a hand specimen of Icelandic stone BZ from Wangmo, Guizhou.

[0115] In this embodiment, firstly, each secondary standard sample is ground into powder with a size of less than 200 mesh using an agate mortar, mixed evenly, and then sealed and packaged in glass vials to prevent moisture.

[0116] 2) Determination of recommended values ​​of secondary standard samples and establishment of secondary calibration curve

[0117] The secondary standard BZ and a set of international carbonate standards ETH-1, ETH-2, ETH-3, ETH-4, ETH-MERK, IAEA-C1, IAEA-C2 distributed to various laboratories by Professor Bernasconi of the Swiss Federal Institute of Technology in Zurich were interspersed with mass spectrometry tests during a test period. A high-temperature gas or balance gas was tested every 1-2 days, and an average of 6-8 high-temperature gases and balance gases were tested every month.

[0118] The secondary standard BZ that needs to be calibrated and the international carbonate standards ETH-1, ETH-2, ETH-3, ETH-4, ETH-MERK, IAEA-C1, and IAEA-C2 were tested in turn. The high-temperature gas, balance gas, international carbonate standards, and secondary standards were tested using a dual-path injection stable isotope mass spectrometer Thermo Mat-253Plus to obtain signal intensities of isotopes 44, 45, 46, 47, 48, 49, and 47.5.

[0119] Using Easotope, a free software released by Professor Cedric John of Imperial College London in 2016, the isotope signal intensity data was automatically calculated to obtain the original values ​​of δ47, δ48, δ49 and Δ47, Δ48, Δ49 of high-temperature gas, equilibrium gas, international carbonate standards and secondary standards.

[0120] Among them, the 1000℃ high temperature gas and the 25℃ balance gas are made of 2 different compositions of water and several different compositions of CO 2 Gases prepared, O isotopes of water and CO 2 The C and O isotopic compositions are shown in Table 1:

[0121] Table 1 Water and CO used in the preparation of high temperature gas and balance gas 2 Gas isotope composition

[0122]

[0123] First, the signal intensity of the Faraday cup of 47.5 can be used to remove the nonlinear effect of the signal intensity of mass numbers 47 and 48 through pressure baseline background correction (PBL). The correction equation is:

[0124] I 47 corrected = I 47,measured – k1 initial ×I 47.5peak (12)

[0125] I 48 corrected = I 48,measured – k2 initial ×I 47.5peak (13)

[0126] Among them, k1 initial = I 47background / I 47.5peak , k2 initial = I 48background / I 47.5peak .

[0127] like Figure 5 , the common slope of high temperature gas and equilibrium gas without pressure baseline correction Slope initial is 0.00596331, after k1 initial After correction, the high temperature gas and balance gas slopes may be under-corrected or over-corrected, resulting in the remaining common slope Slope residual is -0.00206832. According to the simple proportional calculation formula, we get k1 final , the common slope of high temperature gas and equilibrium gas can be corrected to be close to 0, and the Slope is -0.0000002.

[0128] The intercepts of the two straight lines composed of 1000℃ high temperature gas and 25℃ equilibrium gas after pressure baseline correction are respectively consistent with the CO 2 The theoretical values ​​of cluster isotopes were compared (the theoretical value of high temperature gas at 1000℃ is 0.0266, and the theoretical value of equilibrium gas at 25℃ is 0.9196), and an empirical conversion function was established for CO 2 Balance scale correction.

[0129] The secondary standard sample BZ was purified by CO 2 The value obtained after equilibrium scale correction was added with the acid fractionation correction factor of 0.088‰ to obtain the cluster isotope value of the secondary standard BZ with an acid reaction temperature of 25°C.

[0130] Then, a secondary calibration curve (secondary empirical transfer function) was established using the measured values ​​and recommended values ​​of a set of international carbonate standards ETH-2, ETH-3, ETH-4, ETH-MERK, IAEA-C1, and IAEA-C2 distributed to various laboratories by Professor Bernasconi of the Swiss Federal Institute of Technology in Zurich. The recommended values ​​of this set of standards are ETH-2=0.2965‰, EHT-3=0.7012‰, ETH-4=0.5385‰, IAEA-C1=0.3898‰, IAEA-C2=0.7289‰, and MERCK=0.6015‰ (Bernasconi et al., 2021). This secondary calibration curve (secondary empirical transfer function) was used to calibrate the laboratory internal standard BZ (cluster isotope value of the secondary standard BZ with an acid reaction temperature of 25°C) to determine the recommended value of the laboratory secondary standard BZ ( Figure 6 ).

[0131] 3) Determination of unknown samples

[0132] Similar to step 2), the laboratory high temperature, medium temperature, and low temperature secondary standard samples IAEA-C1, BZ, IAEA-C2, high temperature gas, and balance gas were interspersed for mass spectrometry testing within a test period. The sample was first subjected to pressure baseline correction with high temperature gas and balance gas to remove nonlinear effects, and then CO 2 Balanced scale calibration was performed, and the acid fractionation correction factor of 0.088‰ was added to the value obtained after calibration to obtain the cluster isotope value when the sample acid reaction temperature was 25°C.

[0133] The secondary calibration curve (secondary empirical transfer function) is established by using the measured values ​​of the three internal standards IAEA-C1, BZ, and IAEA-C2 (secondary standard cluster isotope correction values) and the recommended value of the secondary standard BZ obtained in 2). Figure 7 As shown, this quadratic calibration curve is used to calibrate the cluster isotope values ​​(sample cluster isotope correction values) of the unknown samples measured interspersed therein to obtain the correction values ​​of the unknown samples.

[0134] In addition, in the present invention, international carbonate standards ETH-1, ETH-2, ETH-3 and ETH-4 with known recommended values ​​can be used as unknown samples interspersed in different test time periods (sessions) to monitor the long-term stability and precision of the test method.

[0135] Figure 8 The long-term stability results of the standards were obtained for our laboratory using the secondary standard calibration method from 2021 to the end of 2024, which is nearly 4 years and 18 test sessions. The long-term standard deviation (1SD) of the test results of nearly 1,000 international carbonate standards is less than 0.02‰ and close to 0.015‰. The long-term average value of international carbonate standards is consistent with their recommended value ( Figure 8 The data (marked with thin solid lines) are basically consistent within the error range, indicating that the long-term stability and precision of cluster isotope data obtained by the secondary standard correction method are very high.

[0136] Based on this, we established a secondary standard calibration method that can improve the accuracy and reproducibility of cluster isotope sample testing and ensure the long-term stability of test data. This method has very important application needs in paleoclimate, paleoenvironment and paleoecology, solves the problem of carbonate cluster isotope data calibration, and improves the comparability of data from different laboratories and the long-term stability of data from the same laboratory.

[0137] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A secondary standard sample and calibration method for carbonate cluster isotope calibration, characterized in that: The following steps are involved: Prepare secondary standards and samples to be tested; Acid hydrolyze the secondary standard sample and the sample to obtain secondary standard CO2 and sample CO2; Obtaining cluster isotope measurement values ​​of the secondary standard CO2 and the sample CO2, and performing corrections on them respectively to obtain a secondary standard cluster isotope correction value and a sample cluster isotope correction value; The correction of the cluster isotope measurement values ​​of the secondary standard CO2 and the sample CO2 includes nonlinear correction, CO2 equilibrium scale correction and acid fractionation correction; Compare the cluster isotope correction value of the secondary standard sample with the recommended cluster isotope value of the secondary standard sample to establish a secondary empirical conversion function; wherein the recommended cluster isotope value of the secondary standard sample is obtained by the following steps: prepare an international carbonate standard sample; acid hydrolyze the international carbonate standard sample to obtain an international carbonate standard sample CO2; obtain the cluster isotope measurement value of the international carbonate standard sample CO2; compare the cluster isotope measurement value of the international carbonate standard sample CO2 with the recommended cluster isotope value of the international carbonate standard sample to establish an empirical conversion function; bring the cluster isotope correction value of the secondary standard sample into the empirical conversion function to obtain the recommended cluster isotope value of the secondary standard sample; Substitute the sample cluster isotope correction value into the secondary empirical conversion function to obtain the final cluster isotope correction value of the sample.

2. The secondary standard sample and calibration method for carbonate cluster isotope calibration according to claim 1, characterized in that: The secondary standard sample includes high-temperature carbonate, medium-temperature carbonate and low-temperature carbonate.

3. The secondary standard sample and calibration method for carbonate cluster isotope calibration according to claim 2, characterized in that: The high-temperature carbonate is selected from Carrara marble, the medium-temperature carbonate is selected from Guizhou Wangmo Iceland spar, and the low-temperature carbonate is selected from natural travertine.

4. The secondary standard sample and calibration method for carbonate cluster isotope calibration according to claim 1, characterized in that: The nonlinear correction and CO2 balance scale correction include the following steps: Prepare high temperature gas and balance gas; Obtaining nonlinear correction results based on a pressure baseline correction method for cluster isotopes of the high-temperature gas and equilibrium gas; The intercept values ​​of the cluster isotope values ​​of the high-temperature gas and the equilibrium gas obtained after nonlinear correction are compared with the theoretical values ​​of the CO2 cluster isotope at the corresponding temperature obtained by thermodynamic calculation to establish an empirical conversion function; The cluster isotope measurement values ​​of the secondary standard CO2 and the sample CO2 are brought into the empirical conversion function to complete the CO2 balance scale correction and obtain the cluster isotope balance scale correction value of the secondary standard or the sample.

5. The secondary standard sample and calibration method for carbonate cluster isotope calibration according to claim 4, characterized in that: The acid fractionation calibration comprises the following steps: Prepare carbonate standards; Obtain the Δ47 value of the carbonate standard sample after CO2 balance scale correction at 90°C acid hydrolysis temperature and 25°C acid hydrolysis temperature in a common acid bath closed reaction vessel; The Δ47 value at 90°C acid hydrolysis temperature and 25°C acid hydrolysis temperature was subtracted to obtain the acid fractionation correction factor between 25°C and 90°C; The acid fractionation correction coefficient is added to the equilibrium scale correction value to complete the acid fractionation correction and obtain the cluster isotope value of the secondary standard or sample at an acid reaction temperature of 25°C.

6. The secondary standard sample and calibration method for carbonate cluster isotope calibration according to claim 4, characterized in that: The preparation temperatures of the high temperature gas and the balance gas are 1000° C. and 25° C. respectively.

7. The secondary standard sample and calibration method for carbonate cluster isotope calibration according to claim 4, characterized in that: The slope of the empirical transfer function is greater than 0.8 and less than 1.

2.

8. The secondary standard sample and calibration method for carbonate cluster isotope calibration according to claim 4, characterized in that: The high temperature gas, balance gas, secondary standard sample and sample are interspersed in the test.

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