A method for measuring the oxygen isotope of hematite based on secondary ion mass spectrometry

Abstract

The application discloses a method for measuring hematite oxygen isotope based on secondary ion mass spectrometry, and comprises the following steps: using a secondary ion mass spectrometer, a hematite standard sample with known oxygen isotope is bombarded by a cesium ion source with a beam spot diameter of 15-25 mu m, 50 groups of measurements are performed, each group contains 40 times of 2-second cycles, the standard sample inter-group standard deviation and the standard sample inter-group average value are calculated; when the 2 times of the standard sample inter-group standard deviation is less than a preset threshold, the hematite standard sample with known oxygen isotope delta 18 O value and the standard sample inter-group average value are used to determine the instrument mass fractionation IMF; after the same depth measurement is performed on an unknown hematite sample, the instrument mass fractionation IMF and the unknown sample inter-group average value are used to calculate the hematite sample with unknown oxygen isotope delta 18 O value. Through comparative analysis of the fractionation characteristics and the instrument stability, the hematite oxygen isotope can be accurately measured. The method is rapid, efficient and reliable, and greatly improves the determination precision of the hematite oxygen isotope.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical detection, and more particularly relates to a method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry. BACKGROUND

[0002] Hematite is a common iron oxide mineral and the main source of iron ore. It plays an important role in global iron ore resources and has a significant impact on economic development. At the same time, hematite has wide research value in the fields of earth science and environmental science. In particular, the study of the oxygen isotopes of this mineral has important applications in the fields of paleoclimate temperature reconstruction, planetary science, and environmental science. Therefore, in-depth study of the oxygen isotopes of hematite not only has important scientific significance but also has significant economic value.

[0003] Currently, the main techniques for precise analysis of hematite oxygen isotopes include laser fluorination and secondary ion mass spectrometry (SIMS). Laser fluorination generates oxygen by heating the sample with a laser and reacting with bromine pentafluoride, and then uses a mass spectrometer to determine the oxygen isotope ratio. Although this method has high precision, the sample preparation process is complex, which limits its widespread application. In contrast, secondary ion mass spectrometry (SIMS) is a micro-area analysis technique with high spatial resolution, capable of oxygen isotope analysis on a micrometer scale, particularly suitable for studying the isotopic distribution within minerals. In addition, SIMS has the characteristic of extremely small sample size, and the sample remains intact after analysis, which can be used for subsequent research.

[0004] The working principle of SIMS technology is to use a primary ion beam (such as cesium ions, intensity about 1-2 nA, beam spot about 10 μm) to bombard the surface of a solid sample, sputtering out secondary ions. These secondary ions are separated by a mass analyzer under the action of an acceleration voltage (usually 10 kV), and finally reach the receiver. The receiver system measures the absolute intensity or ratio of the signal by measuring the ion current intensity of a specific mass (usually the measurement time is about 1 minute). In oxygen isotope analysis, two Faraday cup receivers simultaneously measure the ion current intensity of 16 O and 18 O, get the ratio R = 18 O / 16 O, and express it in the form of δ 18 O (δ 18 O = (R / 0.0020052-1) x 1000). For oxygen isotope analysis of oxygen-containing minerals, the typical precision of SIMS is about 0.2‰-0.3‰ (1SD).

[0005] However, as early as 15 years ago, Huberty et al. found that SIMS has a crystal orientation effect in the analysis of hematite oxygen isotopes, resulting in poor analysis accuracy (SD>1‰), which seriously limits the application of hematite oxygen isotopes in geochemical research. Crystal orientation effect refers to the phenomenon that due to the difference in atomic arrangement and chemical bond direction of mineral crystals on different crystallographic planes, ion yield and isotopic fractionation change in secondary ion mass spectrometry (SIMS) analysis.

[0006] Currently, there are methods for correcting the influence of the crystal orientation effect of hematite on SIMS oxygen isotope analysis using electron backscatter diffraction, and reducing the emission voltage of secondary ions (from 10 kV to 5 kV) to alleviate the influence of the crystal orientation effect. However, this method requires re-adjusting the instrument, which is difficult to operate, and will cause the beam spot to increase and the spatial resolution to decrease.

[0007] Therefore, it is an urgent need to develop a method that can improve the analysis accuracy of hematite oxygen isotopes without sacrificing spatial resolution, while reducing technical difficulty and enhancing operability. SUMMARY

[0008] In view of the above defects or improvement needs of the prior art, the present application provides a method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry, which aims to weaken the significant difference in isotopic ratio that may occur in different surface regions of hematite oxygen isotopes, and avoid affecting the reliability of the test.

[0009] To achieve the above-mentioned purpose, according to one aspect of the present application, a method for measuring hematite oxygen isotopes based on secondary ion mass spectrometry is provided, the method comprising:

[0010] Using a secondary ion mass spectrometer, a hematite standard sample with known oxygen isotopes is bombarded with a cesium ion source with a beam spot diameter of 15-25 μm, 50 groups of measurements are performed, each group contains 40 times of 2 second cycles, the standard sample group standard deviation and the standard sample group average value are calculated;

[0011] When the 2 times of the standard sample group standard deviation is less than a preset threshold value, the δ 18 O value of the hematite standard sample with known oxygen isotopes is determined as the instrument mass fractionation IMF;

[0012] After the same depth measurement of unknown hematite samples, the δ 18 O value of unknown hematite samples is calculated by instrument mass fractionation IMF and the average value between unknown sample groups.

[0013] Preferably, the method comprises:

[0014] The stability test of the instrument is performed before the beam spot bombards the hematite standard sample with known oxygen isotopes, which uses at least 3 glass standard samples, and if the δ 18 The range of the δ

[0015] Preferably, more than two crystal faces of the hematite particle sample are alternately tested during the measurement.

[0016] Preferably, the calculation method of the instrument mass fractionation IMF comprises:

[0017] The arithmetic mean of each group of 40 2-second cycle data is calculated to obtain the arithmetic mean within the standard sample group, and the standard deviation within the standard sample group is calculated;

[0018] The average value between standard sample groups and the standard deviation between standard sample groups of multiple particle groups are calculated based on the arithmetic mean within the standard sample group and the standard deviation within the standard sample group.

[0019] If the standard deviation between standard sample groups is less than a preset threshold, the current group is taken, and the δ 18 O value of the standard sample is calculated to calculate the IMF.

[0020] Preferably, the method further comprises:

[0021] The unknown hematite sample needs to maintain the same ion beam sputtering time window as the known oxygen isotope hematite standard sample during the measurement.

[0022] Preferably, the method further comprises:

[0023] The glass standard sample, the known oxygen isotope hematite standard sample and the unknown hematite sample are fixed on a glass sheet by double-sided tape, and after vacuum curing with epoxy resin, a test target is formed, and the surface of the test target is flat.

[0024] Preferably, the δ 18 O value of the known oxygen isotope hematite standard sample is -1.12±0.14‰.

[0025] Preferably, when measured by a secondary ion mass spectrometer, the measurement time of each group is 2-3 minutes, and the interval between adjacent two groups is ≤5 minutes.

[0026] Preferably, the hematite standard sample based on known oxygen isotope δ 18 The method for determining instrument mass fractionation IMF from the average value of the standard sample group includes:

[0027] The instrument mass fractionation IMF is the δ 18 O value of the standard sample based on known oxygen isotope minus the average value of the standard sample group.

[0028] Preferably, after the same depth measurement is performed on the unknown hematite sample, the δ 18 O value of the unknown hematite sample is calculated by the instrument mass fractionation IMF and the average value of the unknown sample group, and the method includes:

[0029] The δ 18 O value of the unknown hematite sample is the instrument mass fractionation IMF plus the average value of the unknown sample group.

[0030] Overall, compared with the prior art, the above technical solutions conceived by the present application have the following beneficial effects:

[0031] The present application provides a method for measuring hematite oxygen isotope based on secondary ion mass spectrometry, which can accurately determine the oxygen isotope of the sample to be measured through comparative analysis of the fractionation characteristics and the instrument stability. The method is fast and efficient, has strong reliability, and greatly improves the determination precision of hematite oxygen isotope. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0033] Figure 1 is a flowchart of a method for measuring hematite oxygen isotope based on secondary ion mass spectrometry provided by the present embodiment one;

[0034] Figure 2 (a) of is a graph of the change of the hematite standard sample oxygen isotope measurement value with measurement depth in the present embodiment one using SIMS test, Figure 2 (b) of is a graph of the change of the precision of the hematite standard sample oxygen isotope measurement value with measurement depth in the present embodiment one using SIMS, Figure 2 (c) of is a graph of the change of the hematite sample oxygen isotope measurement value with measurement depth in the present embodiment one using SIMS test;

[0035] Figure 3Fig. 1 is a side view of a sample target provided in Example 1, Figure 3 Fig. 2 is a distribution diagram of a glass standard sample, a hematite standard sample and a sample to be tested on the surface of the sample target in Example 1. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0037] In the prior art, the isotopic ratio of different surface regions of hematite oxygen isotope may have significant differences, which may affect the reliability of the test. Researchers have proposed various solutions. For example, Huberty suggested combining SIMS and electron backscatter diffraction (EBSD) techniques to evaluate the effect of crystal orientation; and tried to reduce the crystal orientation effect by reducing the incident intensity of primary ions. However, these methods still have a large repeatability problem in practical application, resulting in significant intra- or inter-grain variations in the hematite oxygen isotope test results based on SIMS.

[0038] Since the measurement of hematite oxygen isotope is affected by the crystal orientation effect, it is necessary to study the distribution of the internal oxygen isotope in order to establish a correction method and improve the precision of the test results.

[0039] Example 1

[0040] Example 1 provides a method for measuring hematite oxygen isotope based on secondary ion mass spectrometry, which comprises the following steps, as shown in Figure 1

[0041] S101: Using secondary ion mass spectrometry, bombard a hematite standard sample with known oxygen isotope with a cesium ion source with a beam spot diameter of 15-25 μm, perform 50 groups of measurements, each group containing 40 times of 2 second cycles, and calculate the inter-group standard deviation and inter-group standard average.

[0042] Before bombarding the hematite standard sample with known oxygen isotope with a beam spot, perform a stability test of the secondary ion mass spectrometer.

[0043] Use a glass standard sample with known oxygen isotope value to test the stability of the secondary ion mass spectrometer, use at least 3 glass standard samples, and if the δ 18 O distribution range is less than 1 ‰, it means that the instrument passes the stability test. For example: collect the oxygen isotope values of 10 groups of glass standard samples Nist610, denoted as δ 18 ​O Measured-Nist610-1 δ 18 O Measured-Nist610-2 ,…,δ 18 O Measured-Nist610-10 ).

[0044] When using a secondary ion mass spectrometer, each measurement session should last 2-3 minutes, with an interval of ≤5 minutes between adjacent measurement sessions.

[0045] Calculate the glass standard deviation (SD) of the above 10 sets of data. 玻璃 , denoted as SD Nist610 If satisfied

[0046] SD Nist610 If the value is less than 0.5‰, proceed to the next step; otherwise, the secondary ion mass spectrometer needs to be adjusted and the first step repeated until the condition is met.

[0047] Oxygen isotopes were collected from standard hematite samples. 18 O and 16 The instrument signal of O was collected, and its oxygen isotope ratio data were calculated using the Vienna Standard Mean Seawater (VSMOW). 18 O / 16 Normalization is performed on O = 0.0020052, using the following formula: Measured δ 18 O VSMOW =(( 18 O / 16 O)Measured value / 0.0020052-1)×1000. For example:

[0048] 2000 measurements were performed on 10 particles of a hematite standard sample (SH9264) with known oxygen isotope values.

[0049] The ratio of the first measurement of the first particle is denoted as D. -SH9264-p1-C1 ,

[0050] The ratio of the k-th measurement of the first particle is denoted as D. -SH9264-p1-Ck , where k = 1, 2, ..., 2000.

[0051] The ratio of the first measurement of the j-th particle is denoted as D. -SH9264-pj-C1 Where j = 1, 2, ..., 10

[0052] The ratio of the k-th measurement of the j-th particle is denoted as D. -SH9264-pj-Ck , where j = 1, 2, ..., 10, k = 1, 2, ..., 2000.

[0053] The measurement results for each particle were grouped into sets of 40 consecutive measurements.

[0054] Group 1: Measurements 1 through 40.

[0055] Group 2: 41st to 80th measurement.

[0056] Group i: kth to k+39th measurement.

[0057] where i = 1, 2, …, 50; k = (i-1)*40+1, the value results are (1, 41, 81, …, 1961) respectively.

[0058] Last group: 1961st to 2000th measurement.

[0059] The standard sample group average and the standard sample group standard deviation are calculated by taking the arithmetic average of each group of 40 2-second cycle data.

[0060] The inter-standard sample group average and the inter-standard sample group standard deviation of the same group of multiple particles are calculated based on the standard sample group average and the standard sample group standard deviation.

[0061] If the inter-standard sample group standard deviation is less than the preset threshold, the current group is taken, and the inter-standard sample group average and the standard sample δ of the current group are used. 18 The O value is calculated as IMF.

[0062] The standard sample group average and the standard sample group standard deviation of the hematite standard sample are calculated:

[0063] The standard sample group average and the standard sample group standard deviation of the jth particle in the SH9264 sample in the ith group are represented as A -SH9264-pj-gi and SD -SH9264-pj-gi ,

[0064]

[0065] where j = 1, 2, …, 10; i = 1, 2, …, 50; k = (i-1)*40+1, the value results are (1, 41, 81, …, 1961) respectively.

[0066]

[0067] where j = 1, 2, …, 10; i = 1, 2, …, 50; k = (i-1)*40+1, the value results are (1, 41, 81, …, 1961) respectively.

[0068] The inter-standard sample group average and the inter-standard sample group standard deviation of all hematite standard sample particles at the same group, i.e., the same measurement depth, are calculated.

[0069] The inter-standard sample group average of the ith group is:

[0070] Where j = 1, 2, ..., 10; i = 1, 2, ..., 50;

[0071] The standard deviation between groups of the standard samples in group i is:

[0072] Where j = 1, 2, ..., 10; i = 1, 2, ..., 50.

[0073] S102: When the standard deviation between groups of the standard samples is less than twice the preset threshold, the hematite standard sample δ based on known oxygen isotopes... 18 The O value and the average value among the standard sample groups determine the instrument mass fractionation (IMF).

[0074] In this embodiment, the first preset threshold is set to 0.5‰. If 2SD -SH9264-gi If the value is less than or equal to 0.5‰, take the current value of i and proceed to S103; otherwise, continue calculating until the condition is met. The range of i is 1-50, and the first i that meets the condition is used, while the subsequent ones are discarded.

[0075] Based on the known value δ of the hematite standard sample 18 O SH9264 =-1.12‰, calculate the instrument mass fractionation IMF:

[0076] IMF = δ 18 O SH9264 -AA SH9264-gi .

[0077] S1043: After measuring the unknown hematite sample at the same depth, the δ of the unknown hematite sample was calculated using the instrument mass fractionation IMF and the average value between unknown sample groups. 18 O-value standard sample.

[0078] When measuring unknown hematite samples, the same ion beam sputtering time window must be maintained as that for hematite standard samples with known oxygen isotopes.

[0079] Calculate the mean and standard deviation of all hematite samples (UH01) with unknown oxygen isotope values ​​within the same group of unknown samples, at the same depth as the hematite standard sample particles.

[0080] The mean value between groups for the unknown samples in group i is:

[0081] Where j = 1, 2, ..., 10; i = 1, 2, ..., 50;

[0082] The oxygen isotope value δ of the unknown hematite sample was obtained by combining the instrument mass fractionation of the detection instrument and the average value between unknown sample groups. 18 O UH01 δ18 O UH01 = IMF + AA UH01-gi .

[0083] In combination with the present embodiment, there is also a preferred implementation scheme, specifically, the method for using the glass standard sample with known oxygen isotope values to test the stability of the detection instrument comprises:

[0084] Using the detection instrument to collect instrument signals of no less than 3 glass standard samples, and obtaining oxygen isotope values of each glass standard sample;

[0085] Calculating the distribution range of oxygen isotope values of all the glass standard samples;

[0086] If the distribution range is less than 1 ‰, it means that the detection instrument passes the stability test.

[0087] In the present embodiment, 10 glass standard samples are selected.

[0088] In combination with the present embodiment, there is also a preferred implementation scheme, specifically, the method for using the detection instrument to measure multiple groups of crystal faces of each hematite standard sample with known oxygen isotope values comprises:

[0089] When measuring, more than two crystal faces of the hematite particle sample need to be tested alternately.

[0090] In the present embodiment, different crystal faces of the hematite standard sample with known oxygen isotope values are measured multiple times, the variation range of the hematite measurement values in different measurement time periods is calculated, the measurement value with a variation range less than or equal to the variation range of the instrument is the best measurement result, and the corresponding sampling time and sampling range are determined as the best measurement time and sampling range of the hematite sample, thereby improving the measurement precision.

[0091] The best measurement time and sampling range are obtained by long-time measurement to obtain the interval of stable late measurement values. The performance of stable measurement values is that the SD becomes smaller. When the instrument is stable, the sampling range at the same time point is the same. In the present embodiment, the inter-group standard deviation of the standard sample is set to satisfy 2SD -SH9264-gi less than 0.5 ‰.

[0092] As Figure 2 a is the relationship diagram of the test ratio of 3 different hematite standard samples SH9264 particles with the change of measurement depth. Figure 2 b is the relationship diagram of the precision (here, 2 times of the standard deviation, i.e., 2SD) of the test ratio of 3 different hematite standard samples SH9264 particles with the change of measurement depth.

[0093] For hematite samples with uniform oxygen isotope values, the precision of oxygen isotope values of 3 hematite standard samples SH9264 with known oxygen isotope values is 2SD = 0.14‰, although there is a large difference in the test of the surface of multiple particles of the hematite standard samples by SIMS, such as 40 cycles of test, test time of 3 minutes, 2SD = 1.57‰, such as Figure 2 As shown in a, the test ratio of 3 different hematite standard sample SH9264 particles gradually tends to be consistent with the increase of test depth and the extension of test time, and the precision of measurement is significantly improved. If the increase is to 1520 cycles, the test time is 54 minutes, the precision is improved to 2SD = 0.48‰. If the increase is to 2000 cycles, the test time is 76 minutes, the precision is improved to 2SD = 0.34‰.

[0094] As shown in Figure 2 a, the abscissa is the number of cycles of measurement, and a total of 2000 cycles, each cycle is 2 seconds. The ordinate is the change of hematite oxygen isotope ratio, which is represented by 2SD, i.e. 2 times the standard deviation between groups. As can be seen, with the increase of time (i.e. the number of cycles), the change range of hematite oxygen isotope ratio becomes smaller. For example, the 2SD from the first cycle to the 40th cycle is 1.57‰, which is Figure 2 the first point of b. The 2SD from the 1481st cycle to the 1520th cycle is 0.48‰, which is Figure 2 the 38th point of b. The 2SD from the 1961st cycle to the 2000th cycle is 0.34‰, which is Figure 2 the last point of b.

[0095] As shown in Figure 2 a, the relationship diagram of the measurement value of hematite standard sample oxygen isotope obtained by SIMS with the change of measurement depth. As shown in Figure 2 c, the relationship diagram of the measurement value of hematite sample oxygen isotope obtained by SIMS with the change of measurement depth. Since SIMS is a relative measurement method. It is found in experiments that the test values of different hematite samples have consistent instrument mass fractionation at the same measurement depth. The consistency of instrument mass fractionation is judged from Figure 2 a and Figure 2 c, the difference between the ordinate of the two curves is consistent. By mutual correction of hematite standard sample particles with known oxygen isotope values and hematite samples with unknown oxygen isotope values, the oxygen isotope values of the hematite samples can be accurately obtained, so as to realize high-precision measurement. This research finding provides a scientific basis for solving the measurement deviation caused by the crystal orientation effect of hematite, and lays a foundation for the correction method.

[0096] As shown in Figure 2b, the horizontal axis is the number of cycles, and the total number of cycles is 2000, and each cycle is 2 seconds. The vertical axis is the measured value of the hematite oxygen isotope ratio, denoted by δ 18 O. The calculation method is as follows: using Vienna Standard Mean Ocean Water (VSMOW; 18 O / 16 O=0.0020052) for normalization, and the formula is as follows: measured δ 18 O VSMOW =( 18 O / 16 O) measured value / 0.0020052-1) x 1000. Figure 2 a and Figure 3 c are two different hematite samples, Figure 3 a is a curve of the measured values of the three SH9264 over time; Figure 1 c is a curve of the measured values of the three UH01 over time; the difference between the average of the measured values of the three SH9264 and the average of the measured values of the three UH01 is constant over time. This is because the instrument fractionation characteristics of the two samples are the same, that is, the instrument mass fractionation of hematite is the same at the same test time / depth / cycle.

[0097] In combination with the embodiment, there is also a preferred implementation scheme, specifically, a method for obtaining the standard deviation between the standard sample groups of each hematite standard sample particle with a known oxygen isotope value in each group includes:

[0098] calculating the average of the standard sample groups of all particles at the same measurement depth from the arithmetic mean of the standard sample groups and the standard deviation of the standard sample groups of each hematite standard sample particle with a known oxygen isotope value in the subgroup;

[0099] calculating the standard deviation SD 已知 between the standard sample groups from the average of the standard sample groups.

[0100] If the standard deviation SD 已知 between the standard sample groups satisfies 2SD 已知 < first preset threshold, it indicates that the sampling range of the hematite standard sample particle with a known oxygen isotope value passes the test.

[0101] In the first embodiment, the arithmetic mean of the standard sample groups and the standard deviation of the standard sample groups of the hematite standard sample are calculated as follows:

[0102] The arithmetic mean of the standard sample groups and the standard deviation of the standard sample groups of the jth particle in the ith group of the hematite standard sample SH9264 are denoted as A -SH9264-pj-gi and SD -SH9264-pj-gi ,

[0103]

[0104] wherein j = 1, 2, …, 10; i = 1, 2, …, 50; k = (i-1)*40+1, the value results are (1, 41, 81, …, 1961) respectively.

[0105]

[0106] wherein j = 1, 2, …, 10; i = 1, 2, …, 50; k = (i-1)*40+1, the value results are (1, 41, 81, …, 1961) respectively.

[0107] The first average value of all hematite standard sample particles in the same group, i.e., the same measurement depth, and the standard sample group inter-standard deviation are calculated again.

[0108] The standard sample group inter-standard average value of the i-th group is:

[0109] wherein j = 1, 2, …, 10; i = 1, 2, …, 50;

[0110] The standard sample group inter-standard deviation of the i-th group is:

[0111] wherein j = 1, 2, …, 10; i = 1, 2, …, 50.

[0112] The first preset threshold is set to 0.5‰, if 2SD -SH9264-gi <0.5‰, the current i value is taken, and the next step is entered; otherwise, the calculation is continued until the condition is met. The range of i is 1-50.

[0113] In the first embodiment, the value of i is 38, the standard sample group inter-standard average value of the i = 38-th group is -61.92‰, and the standard sample group inter-standard deviation of the i = 38-th group is 0.48‰.

[0114] In combination with the present embodiment, there is also a preferred implementation scheme, specifically, the instrument mass fractionation calculation method of the detection instrument is:

[0115] The known oxygen isotope value of the hematite standard sample is subtracted from the standard sample group inter-standard average value meeting the sampling range test.

[0116] The instrument mass fractionation IMF = the δ 18 O value of the hematite standard sample based on the known oxygen isotope is subtracted from the standard sample group inter-standard average value.

[0117] In the first embodiment, the known value of the hematite standard sample is δ 18 O SH9264= -1.12 ‰, Instrumental mass fractionation of the instrument IMF: IMF = δ 18 O SH9264 -AA SH9264-gi In this embodiment, the value of the IMF is 60.80 ‰

[0118] In combination with this embodiment, there is also a preferred implementation scheme, in particular, in combination with the method for obtaining the oxygen isotope value of the hematite sample from the instrument mass fractionation of the detection instrument, comprising:

[0119] The unknown sample group inter mean value of all particles at the same measurement depth is calculated from the unknown sample group intra mean value and the unknown sample group intra standard deviation of each unknown oxygen isotope value hematite sample in the unknown sample group.

[0120] In this embodiment, the unknown sample group intra mean value and the unknown sample group intra standard deviation of the unknown oxygen isotope value hematite sample (UH01) are calculated:

[0121] The unknown sample group intra mean value and the unknown sample group intra standard deviation of the i-th group of the j-th particle in the unknown oxygen isotope value hematite sample UH01 are denoted as A -UH01-pj-gi and SD -UH01-pj-gi ,

[0122]

[0123] Where j = 1, 2, …, 10; i = 1, 2, …, 50; k = (i-1)*40+1, the value results are (1, 41, 81, …, 1961) respectively.

[0124] When i = 38, the unknown sample group intra mean value of the j = 1 UH01 particle is -61.25 ‰; when i = 38, the unknown sample group intra mean value of the j = 2 UH01 particle is -62.71 ‰; when i = 38, the unknown sample group intra mean value of the j = 3 UH01 particle is -62.98 ‰, and the unknown sample group intra standard deviation is calculated again.

[0125]

[0126] Where j = 1, 2, …, 10; i = 1, 2, …, 50; k = (i-1)*40+1, the value results are (1, 41, 81, …, 1961) respectively.

[0127] The unknown sample group inter mean value of all hematite standard sample particles at the same group, i.e., the same measurement depth, is calculated again.

[0128] The unknown sample group inter mean value of the i-th group is:

[0129] where j = 1, 2, …, 10; i = 1, 2, …, 50.

[0130] In this embodiment, the unknown sample group average of the hematite sample UH01 is -62.31 ‰.

[0131] In combination with this embodiment, there is a preferred implementation scheme, specifically, the calculation method of the oxygen isotope value of the hematite sample is:

[0132] The instrument mass fraction of the detection instrument plus the unknown sample group average.

[0133] The δ 18 O value of the unknown hematite sample is:

[0134] In this embodiment, the oxygen isotope value of the hematite sample with unknown oxygen isotope value is -1.52 ‰ 18 O UH01 . 18 O UH01 = IMF + AA UH01-gi .

[0135] In this embodiment, the oxygen isotope value of the hematite sample with unknown oxygen isotope value is -1.52 ‰

[0136] In combination with this embodiment, there is a preferred implementation scheme, specifically, at least 1 glass standard sample with known oxygen isotope value, at least 1 hematite standard sample with known oxygen isotope value, and at least 1 hematite sample with unknown oxygen isotope value are tested on a flat target surface.

[0137] As shown in Figure 3 a and Figure 3 b, a plurality of hematite standard samples SH9264, a plurality of samples to be tested UH01, and a plurality of glass standard samples Nist610 are on the sample target surface.

[0138] In combination with this embodiment, there is a preferred implementation scheme, specifically, double-sided tape is adhered to the glass sheet, and the glass standard sample with known oxygen isotope value, the hematite standard sample with known oxygen isotope value, and the hematite sample with unknown oxygen isotope value are pasted on the double-sided tape.

[0139] In this embodiment, a target is first made, which contains a glass standard sample, a hematite standard sample, and a hematite sample to be tested.

[0140] Because of the stability of the instrument needs a standard sample with a known oxygen isotope results to monitor, so the choice of the United States National Institute of Standards and Technology developed glass standard sample NIST610, this standard sample has a uniform oxygen isotope value δ 18 O Nist610 =10.91±0.20‰.

[0141] Because of the matrix effect of the ion probe, it is necessary to use a sample similar to the composition of the sample to be tested as a standard sample, so a hematite sample which has been tested by traditional method is chosen as the standard sample. The hematite sample SH9264 selected in example one has an oxygen isotope value of δ 18 O SH9264 =-1.12±0.14‰ obtained by traditional method. Here, SH9264 is used as a standard sample to obtain the test time range and sampling interval of hematite, and the instrument mass fractionation of the instrument is calculated to establish the method. The sample to be tested selects a hematite sample UH01 similar to the source of the standard sample as the sample to be tested to test, and the hematite sample has an oxygen isotope of δ 18 O UH01 =-1.12±0.14‰ obtained by traditional method. The hematite sample UH01 with a known oxygen isotope value is used as a sample to be tested to verify the method.

[0142] The specific process of making the target is as follows: 10-12 glass standard samples Nist610 with a particle size of 100-250 microns, 10-12 hematite standard samples SH9264 with a known oxygen isotope and 10-12 unknown hematite samples UH01 with a particle size of 100-250 microns are pasted in a 1 cm diameter circle on the double-sided adhesive tape on a 10 cm*10 cm glass sheet. Mix the epoxy resin with the curing agent; place a smooth-surfaced 1-inch inner diameter polyethylene hollow column vertically on the double-sided adhesive tape, and place the glass and hematite particles pasted above on the middle position of the polyethylene hollow column; slowly inject the mixture of the epoxy resin and the curing agent after vacuum extraction along the inner surface of the polyethylene hollow column, vacuum again and let stand to allow the mixture to solidify, then remove the polyethylene hollow column and tear off the double-sided adhesive tape, thereby obtaining a solidified hematite standard sample sheet that can be removed from the polyethylene hollow column. In turn, use fine sandpaper and polishing discs to polish the hematite target, so that the glass standard sample Nist610 and the hematite standard sample SH9264 and the sample to be tested UH01 are exposed on one side of the target, and the entire surface is smooth and smooth. The prepared target is as shown in Figure 3 . Figure 3 a is the overall image, which is a disc, ​b is the surface topography. ​ b is ​ a distribution map of the sample target surface amplified 50 times.

[0143] In this embodiment one, hematite is tested by secondary ion mass spectrometer method (SIMS).

[0144] First, the sample target surface is cleaned with water, and the sample target is placed in a beaker containing alcohol, and the sample is ultrasonically cleaned for three minutes, and then the sample target is placed in a drying oven for one hour.

[0145] The exposed side surface of the above-mentioned cleaned wafer sample target is plated with a continuous gold film using a Q150TE model gold plating instrument from Quorum. In order to ensure good electrical conductivity of the sample, the plating thickness is 20-50 nm, for example, it can be 20 nm or only 45 nm.

[0146] The signal required for testing the oxygen isotope of hematite by secondary ion mass spectrometer is tested using a cesium ion source. The focused ion beam is irradiated onto the glass or hematite sample on the sample target, and a beam spot with a diameter of about 20 μm is used to excite the sample to generate secondary ions. Subsequently, the secondary ions released by the sample 16 O and 18 O pass through the electric and magnetic fields in turn, and finally reach the ion signal detection system. The instrument signals of the oxygen isotopes of the hematite standard sample are collected, and the oxygen isotope ratio data is calculated. The calculation method is: using Vienna Standard Mean Ocean Water (VSMOW; 18 O and 16 O is normalized, and the formula is as follows: the measured δ 18 O 16 O = 0.0020052) is normalized, and the formula is as follows: the measured δ 18 O VSMOW = ( 18 O 16 O ) measured value / 0.0020052-1) x 1000. During the detection process, two Faraday cups are used to receive the secondary ion signals simultaneously. Each test round contains at least 2000 cycles, and each cycle of test takes 2 seconds.

[0147] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for measuring the oxygen isotope composition of hematite based on secondary ion mass spectrometry, characterized in that the method The method comprises: The method further comprises: δFe2O3= δFe2O3std+ 2 * (O - Ostd) when 2 * the standard sample group standard deviation is less than a pre-set threshold value, based on known oxygen isotope of hematite standard sample δFe2O3std 18 O value and the standard sample group average value determine instrument mass fractionation IMF; After the same depth measurement of the unknown hematite sample, the δO value of the unknown hematite sample was calculated by the instrument mass fractionation, IMF, and the average value between the unknown sample groups 18 O values; The unknown hematite sample is measured with the same ion beam sputtering time window as the known oxygen isotope hematite standard sample. The method further comprises: The glass standard sample, the known oxygen isotope hematite standard sample and the unknown hematite sample are fixed on a glass sheet by double-sided tape, and a test target is formed after vacuum curing with epoxy resin, and the surface of the test target is flat. If the standard sample group standard deviation is less than a preset threshold, the current group is taken, and the standard sample group average corresponding to the current group and the delta of the standard sample are used again 18 O value calculates IMF.

2. The method of measuring the oxygen isotope of hematite based on secondary ion mass spectrometry according to claim 1, characterized by, When measured by the secondary ion mass spectrometer, each group of measurements takes 2 to 3 minutes, and the interval between adjacent two groups of measurements is ≤5 minutes. Stability tests of the instrument were performed prior to beam spot bombardment of hematite standard samples of known oxygen isotopes, using at least 3 glass standard samples, if the glass standard samples δ 18 An O distribution range of less than 1 ‰ indicates that the instrument passed the stability test.

3. The method of measuring the oxygen isotope of hematite based on secondary ion mass spectrometry according to claim 1, characterized by, ​ ​ 4. The method of measuring the oxygen isotope of hematite based on secondary ion mass spectrometry according to claim 2, characterized by, ​ ​ 5. The method of measuring the oxygen isotope of hematite based on secondary ion mass spectrometry according to claim 1, characterized by, The δ 18 O value is -1.12 ± 0.14 ‰.

6. The method of measuring the oxygen isotope of hematite based on secondary ion mass spectrometry according to claim 1, characterized by, ​ 7. The method of measuring the oxygen isotope composition of hematite by secondary ion mass spectrometry according to any one of claims 1 to 6, characterized in that, The hematite standard sample δ 18 A method for determining instrument mass fractionation (IMF) from the O values and the average value of the standard sample group comprises: Instrument mass fractionation, IMF = δ of the hematite standard sample based on known oxygen isotopes 18 O value minus the inter-standard sample set average.

8. The method of measuring the oxygen isotope of hematite based on secondary ion mass spectrometry according to claim 7, characterized in that, The δO value of the unknown hematite sample is calculated after the same depth measurement of the unknown hematite sample by instrument mass fractionation (IMF) and the average value between the unknown sample groups 18 The method for calculating the O value of the unknown hematite sample includes: The δO value for the unknown hematite sample 18 O value = instrument mass fractionation IMF + the unknown sample group mean.

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