Method for determining ultra-trace Os in geochemical sample

Abstract

The invention provides a method for determining ultra-trace Os in a geochemical sample. The method comprises the following steps: preparing Sb2O3 by adopting antimony chloride; sb2O3 is used as a trapping agent to prepare a geochemical sample Sb assaying ingredient; putting half of the ingredients into a high-purity quartz crucible, and then dropwise adding a 190Os isotope diluent; adding the rest half of the ingredients, and paving a covering agent; preparing an Sb button, and performing soot blowing on the Sb button to obtain Sb combined particles; and for the Sb combined particles, determining the 189Os / 190Os by adopting KED-ICP-MS or LA-ICP-MS, correcting the quality discrimination effect of the 189Os / 190Os, and calculating the content of the Os in the geochemical sample by adopting an isotope dilution method. The method has the advantages of low process blank value, short pretreatment time, small test memory effect, no isobaric interference of osmium isotope and the like, and is applied to test of Os in a standard geochemical sample, and a measured value is consistent with a reference value.

Description

Technical Field

[0001] This invention relates to a method for determining trace amounts of Os in geochemical samples, specifically a method for determining trace amounts of Os in geochemical samples using antimony assay enrichment separation (Sb-FA) isotope dilution-inductively coupled plasma mass spectrometry (ID-ICP-MS). Background Technology

[0002] Os (O3) belongs to the platinum group elements and is widely used in industry and laboratories. In particular, the Re-Os isotope system is widely used to study the genesis of mineral deposits, magma formation, mantle evolution, celestial evolution, and isotope dating. Therefore, accurately analyzing the Os content in geochemical samples is of great significance for prospecting for strategic platinum group element minerals and for Earth system science research. However, the abundance of Os in natural geochemical samples is very low and its distribution is uneven, exhibiting a nugget effect. In addition, the Os(VIII) / Os(IV) system has a relatively low potential, and during conventional acid dissolution and decomposition, it will be oxidized to OsO4 to varying degrees, resulting in volatilization loss. Therefore, accurately determining its content has always been a challenge in analysis.

[0003] Traditional methods for analyzing oxygen (Os) in geochemical samples generally employ distillation-separation spectrophotometry. This method is extremely cumbersome and carries certain risks, failing to meet the requirements of rapid and safe analytical chemistry. Dissolving the sample in aqua regia in Carius tubes followed by distillation is also commonly used for Os analysis. This method produces very low Os blank values, but requires small sample sizes (less than 5g), has poor representativeness, and carries certain risks. Specialized training is required for operators, making it unsuitable for large-scale sample analysis. Currently, the popular method for analyzing Os in geochemical samples is nickel matte assay-ICP-MS. However, a major drawback of this method is that the Os blank value in nickel oxide, used as the Os collector, is too high, making direct application to nickel matte assay unsuitable. Purification of nickel oxide is necessary, which is complex. While some methods use nickel carbonyl with lower blank values ​​as a collector, nickel carbonyl is highly toxic, posing risks to environmental protection and the health of analysts. In addition, the time required for dissolving and filtering matte nickel test gold buckles with hydrochloric acid is relatively long. During the process of dissolving Os sulfide precipitate by heating with aqua regia, Os will still form OsO4 and partially volatilize even in a closed digestion vessel or microwave digestion vessel. Summary of the Invention

[0004] This invention proposes a method for determining trace amounts of Os in geochemical samples, which has advantages such as low process blank value, short pretreatment time, small test memory effect, and no interference from isotopes of osmium. When this method is applied to the determination of Os in standard geochemical samples, the measured values ​​are consistent with the reference values.

[0005] The technical solution of this invention is achieved as follows: a method for determining trace amounts of Os in geochemical samples, comprising the following steps:

[0006] (1) Dissolve antimony chloride in water, hydrolyze to produce a precipitate, filter, wash, dry and grind the precipitate to obtain Sb2O3;

[0007] (2) Based on the mineral composition of the geochemical sample, the Sb2O3 prepared in step (1) is used as a collector to prepare the ingredients for Sb assay of the geochemical sample.

[0008] (3) Place half of the ingredients in a high-purity quartz crucible, then make grooves in the ingredients and drip the ingredients into the grooves. 190 Os isotope diluent, dried at room temperature; cover the groove with the remaining half of the ingredients, and spread a covering agent evenly on top of the ingredients, the covering agent containing Sb2O3 prepared in step (1); heat the high-purity quartz crucible to obtain a melt, pour the melt into a mold, cool and pour off the slag to obtain Sb clasp;

[0009] (4) Blow the Sb ash to the required diameter to obtain Sb granules;

[0010] (5) For the Sb aggregates from step (4), KED-ICP-MS (collision cell inductively coupled plasma mass spectrometry) or LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) was used to determine the composition of the aggregates. 189 Os / 190 The ratio of Os was corrected using a quality discrimination correction method. 189 Os / 190 Os's quality discrimination effect;

[0011] (6) Based on the corrected 189 Os / 190 The Os ratio was used to calculate the Os content in geochemical samples using the isotopic dilution method.

[0012] Furthermore, in step (3), 190 The amount of Os isotope diluent added is approximately the same as or consistent with the Os content in the corresponding standard material of the geochemical sample; or 190 The amount of Os isotope diluent added is approximately the same as or consistent with the Os content in similar geochemical samples reported in existing literature. This limitation on the amount added is to ensure... 190 The amount of Os isotope diluent added should be approximately the same as the Os content in the geochemical sample, meaning that the approximation should be on the same order of magnitude.

[0013] Furthermore, in step (2), the ingredients contain 10-20g of geochemical sample, 15-30g of borax, 15-25g of glass powder, 50-75g of Na2CO3, 10-15g of Sb2O3 prepared in step (1) and 1-5g of flour.

[0014] Further, the covering agent comprises 10-30g of borax, 15-25g of glass powder, 50-75g of Na2CO3, 10-15g of Sb2O3 prepared in step (1) and 1-5g of flour.

[0015] Further, in step (4), the specific method for obtaining Sb aggregate is as follows: the Sb granules are placed in a magnesia ash dish that has been preheated at 900℃ for more than 30 minutes to remove the skin, and then the ash blowing continues until the aggregate diameter is 2.5-3.5 mm. The magnesia ash dish is then removed and immediately immersed in water and quickly removed to allow the Sb aggregate to solidify.

[0016] Further, in step (5), KED-ICP-MS determination 189 Os / 190 The method for determining the Os ratio is as follows: Place the Sb granules from step (4) into 10 mL of 50% aqua regia (v / v), then microwave digest. After complete dissolution, soak in cold water for at least 1 hour to obtain the digestion solution. Add 1.5 mL of HCl and 3 mL of ascorbic acid solution (concentration 25 mg / mL) to 5 mL of the digestion solution, bring to a final volume, shake well, and determine the Os ratio using KED-ICP-MS. 189 Os / 190 Os ratio. The solvent for the ascorbic acid solution is water.

[0017] Furthermore, the heating method for microwave digestion is as follows: first heat for 4 minutes to reach 100°C, and hold for 3 minutes; then heat for 1 minute to reach 110°C, and hold for 5 minutes; then heat for 1 minute to reach 120°C, and hold for 5 minutes; finally, cool down to 100°C for 1 minute and hold for 5 minutes.

[0018] Further, in step (5), LA-ICP-MS determination 189 Os / 190 The method for determining the Os ratio is as follows: The Sb granules from step (4) are prepared into Sb tablets with flat and smooth surfaces; after cleaning the Sb tablets, the Os ratio is determined by LA-ICP-MS. 189 Os / 190 Os ratio.

[0019] Further, in step (6), the content of Os in the geochemical sample is calculated according to formula (1):

[0020]

[0021] In the formula, c represents the Os content in the sample, and M and M s The atomic masses of Os in the sample and the isotope diluent are m and m, respectively. s m is the mass of Os in the diluent, m is the mass of the sample, and A and B represent the mass of Os in the sample, respectively. 189 Os and 190 Os natural abundance, A s and B s These respectively represent the isotope diluents. 189 Os and 190 Os abundance, R true For the corrected 189 Os / 190 Os ratio.

[0022] Further, in step (1), 500g of antimony chloride is completely dissolved in 4000mL of ultrapure water, and a precipitate is generated. The precipitate is filtered, washed, dried, and ground to obtain 74-micron Sb2O3.

[0023] The beneficial effects of this invention are:

[0024] This invention uses self-made Sb₂O₃ as an O₂ trapping agent in antimony assays and replaces the clay crucibles used in traditional fire assays with high-purity quartz crucibles, significantly reducing the O₂ blank value in the fire assay process; it also incorporates [the following ingredient] into the Sb assay formula. 190 Os isotope diluent was used to achieve full exchange equilibrium between Os in the geochemical sample and Os in the isotope diluent through a high-temperature melting process with antimony assay and a blowing process with antimony ash. ICP-MS analysis was performed on the sample solution or Sb slide using both kinematic etching (KED) and laser ablation solids (LA) methods. 189 Os / 190 The ratio of O to Os was used to accurately determine the Os content in the sample using the isotope dilution method. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart illustrating the testing method of the present invention;

[0027] Figure 2 The crucibles are a clay crucible (A) and a high-purity quartz crucible (B).

[0028] Figure 3 To retain Sb for ash blowing;

[0029] Figure 4 It is an Sb film;

[0030] Figure 5 For Sb film 189 Os and 190 Os surface imaging;

[0031] Figure 6 For LA-ICP-MS testing of Sb chips 189 Os and 190 Signal diagram of Os. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] like Figure 1 As shown, a method for determining trace amounts of Os in a geochemical sample includes the following steps:

[0034] (1) Dissolve 500g of antimony chloride completely in 4000mL of ultrapure water. Hydrolysis produces a precipitate. Filter, wash, dry, and grind the precipitate to obtain 74-micron Sb2O3.

[0035] (2) Based on the mineral composition characteristics of different geochemical samples, weigh the required raw materials according to the formula in Table 1, mix them well, and obtain the ingredients for geochemical sample Sb test gold.

[0036] Table 1 Formulations of Sb assay for geochemical samples

[0037]

[0038]

[0039] (3) Place the ingredients into a 500mL mixing bottle, shake well, pour about half of the ingredients into a 400mL high-purity quartz crucible, and gently make a groove on the ingredients with a spatula. Then use a pipette to transfer the contents of the mixture into the 400mL high-purity quartz crucible. 190 Os isotope diluent (approximately the Os content in the sample, i.e., on the same order of magnitude, with a total volume not exceeding 1000 μL), 190 Os isotope diluent: 26.88 μg / mL (Oak Ridge National Laboratory, USA) was dropped into the groove and allowed to dry at room temperature;

[0040] Pour the remaining half of the ingredients into a high-purity quartz crucible and cover the groove. Spread 20g of covering agent evenly on the ingredients. Place the crucible into a high-temperature box furnace preheated to about 1000℃. Close the furnace door tightly and gradually heat to 1070℃ and maintain for 30 minutes. Then remove the crucible and pour the molten material into an iron mold. After cooling, pour off the slag and remove the Sb buckle.

[0041] The covering agent comprises 10-30g of borax, 15-25g of glass powder, 50-75g of Na2CO3, 10-15g of Sb2O3, and 1-5g of flour. The raw materials are mixed according to the above formula to obtain the covering agent.

[0042] In this embodiment, the covering agent is prepared by mixing 25g of borax, 25g of glass powder, 75g of Na2CO3, 10g of Sb2O3, and 5g of flour. Other proportions can also be used as needed.

[0043] (4) Place the Sb particles into a magnesia ash pan that has been preheated at 900℃ for more than 30 minutes to remove the skin. Then continue blowing the ash until the particle diameter is about 3mm. Remove the magnesia ash pan and immediately immerse it in water, then quickly remove it to allow the Sb particles to solidify. Figure 3 As shown, the mass of the Sb granules is approximately 0.10 g;

[0044] Through the Sb gold fusion process and the Sb high-temperature protective ash blowing process, Os will not be lost due to OsO4 volatilization, and the Os in the geochemical sample and the Os in the isotope diluent will be fully exchanged and balanced.

[0045] (5) For the Sb granules obtained in step (4), KED-ICP-MS or LA-ICP-MS were used to determine the composition of the granules. 189 Os / 190 The ratio of Os:

[0046] KED-ICP-MS determination 189 Os / 190 The method for determining the Os ratio is as follows: Place the Sb granules from step (4) into 10 mL of 50% aqua regia (v / v), then microwave digest. After complete dissolution, soak in cold water for at least 1 hour to obtain a dissolved solution. Add 1.5 mL of HCl and 3 mL of ascorbic acid solution (concentration 25 mg / mL) to 5 mL of the digested solution, bring to a final volume, shake well, and determine the Os ratio using KED-ICP-MS. 189 Os / 190 Os ratio;

[0047] The heating method for microwave digestion is as follows: first heat for 4 minutes to reach 100℃, and hold for 3 minutes; then heat for 1 minute to reach 110℃, and hold for 5 minutes; then heat for 1 minute to reach 120℃, and hold for 5 minutes; finally, cool down to 100℃ for 1 minute and hold for 5 minutes.

[0048] The Sb particles were digested using aqua regia via microwave. Even when the microwave digester was under overpressure protection and underwent a safe pressure release, some Os particles would still be lost through OsO4 volatilization. However, the remaining Os particles in the solution... 189 Os / 190 The ratio of Os remains unchanged, so it will not affect the accurate determination of Os by the isotope dilution method.

[0049] During the microwave digestion of Sb granules with aqua regia, Os in the solution is oxidized to Os. 8+ Furthermore, preliminary experiments revealed that Os 8+ The memory effect in ICP-MS is much higher than that in Os. 4+ To reduce the memory effect, the experiment selected ascorbic acid to treat Os... 8+ Completely restored to Os 4+ Then conduct another test.

[0050] LA-ICP-MS determination 189 Os / 190 The method for determining the Os ratio is as follows: First, the Sb particles from step (4) are ground into rough Sb sheets using 120-mesh corundum abrasive cloth. Then, the rough Sb sheets are polished into smooth, flat Sb sheets suitable for LA-ICP-MS testing using 7000-mesh corundum abrasive cloth. Figure 4 As shown; the Sb tablet was placed in water and sonicated for 10 minutes, then removed and rinsed with water. The water on the Sb tablet was then completely absorbed with filter paper, and the concentration of Sb in the tablet was determined using LA-ICP-MS. 189 Os / 190 Os ratio.

[0051] In mass spectrometry, differences in transport efficiency and space charge effects among ions with different mass-to-nucleus ratios can lead to mass discrimination, causing the measured isotope ratios to deviate from the true values. This invention uses 100 ng of naturally abundant Os to prepare a blank sample formulation (excluding geochemical samples), followed by antimony assay to prepare the test solution. KED-ICP-MS is then used to analyze the solution. 189 Os / 190 Os, and then its corresponding natural abundance ratio is used to correct for the quality discrimination effect according to the linear relationship formula (2); similarly, this method is also used to correct the Sb content in LA-ICP-MS tested slices. 189 Os / 190 The quality discrimination effect of Os, as shown in formula (2), is as follows:

[0052]

[0053] (2) In the formula, R true for 189 Os / 190 The true value of Os; R obs for 189 Os / 190 The test value of Os; Δm is 189 Os and 190 The mass difference between Os; ε lin This is the linear quality bias correction factor (i.e., the bias per unit of quality).

[0054] The method for adding 100ng of naturally abundant Os is as follows:

[0055] 1) Preparation of Os standard solution: 100 μg / mL, weigh 0.04616 g of spectroscopically pure reagent (NH4)2OsCl6 (Johnson Matthey Chemicals) into a 250 mL glass beaker, add 100 mL of water, stir until completely dissolved, add 10 mL of hydrochloric acid, transfer to a 200 mL volumetric flask, wash the beaker with water, transfer the washing solution to the volumetric flask, make up to volume, and shake well;

[0056] 2) Then add 0.001 mL of Os standard solution to the blank sample formulation.

[0057] (6) Based on the corrected 189 Os / 190 The Os ratio is used to calculate the Os content in geochemical samples using the isotopic dilution method according to formula (1):

[0058]

[0059] In the formula, c represents the Os content in the sample, and M and M s The atomic masses of Os in the sample and the isotope diluent are m and m, respectively. s m is the mass of Os in the diluent, m is the mass of the sample, and A and B represent the mass of Os in the sample, respectively. 189 Os and 190 Os natural abundance, A s and B s These respectively represent the isotope diluents. 189 Os and 190 Os abundance, R true For the corrected 189 Os / 190 Os ratio.

[0060] Using the method of this invention, trace amounts of Os in standard geochemical samples were determined. The measured values ​​were consistent with the reference values, and the results are shown in Table 2.

[0061] Table 2. Sb-FA-ID-ICP-MS analytical data (ng g) of the certification reference material sample. -1 Comparison of the recommended values ​​(mean data ± standard deviation, n=5) and the actual values.

[0062]

[0063] The blank value of Os in fire assays is generally high, which severely limits the application of fire assays in the analysis of trace Os in geochemical samples. Using self-made Sb₂O₃ (antimony chloride) instead of commercially available Sb₂O₃ can reduce the blank value of Os in Sb assays. However, traditional fire assays generally use clay crucibles as high-temperature melting vessels, and the Os contained in the clay can be enriched by Sb, thus affecting the determination of Os in geochemical samples. To solve this problem, this invention uses a quartz crucible made of high-purity quartz material (SiO₂ > 99.99%) instead of the clay crucible commonly used in traditional fire assays. Figure 2 As shown, this significantly reduces the Os blank value in the Sb assay process, which is only 0.00075 ng / g in a 20g geochemical sample. This breaks through the bottleneck of excessively high Os blank values ​​in the fire assay process. Furthermore, the transparent high-purity quartz crucible allows for real-time observation of the sample melting status, which can better optimize the Sb assay melting temperature and time.

[0064] Table 3. Os Blank Values ​​in the Sb Trial Process

[0065]

[0066] Note: Os blank values ​​were all determined using Sb-FA-KED-ICP-MS.

[0067] Isotope dilution is a method that uses changes in isotope ratios to quantitatively determine the concentration of elements in a sample. Through the Sb assay melting process followed by high-temperature protective blowing with Sb, Os does not volatilize into OsO4, and the Os in the geochemical sample and the Os in the isotope diluent are fully exchanged and balanced. When Sb particles are digested using aqua regia via microwave digestion, even when the microwave digester is under overpressure protection and pressure is released safely, although some Os will still volatilize into OsO4, the concentration of Os in the solution remains stable. 189 Os / 190 The ratio of Os remains unchanged, so it will not affect the accurate determination of Os by the isotope dilution method.

[0068] During the microwave digestion of Sb granules with aqua regia, Os in the solution is oxidized to Os. 8+ Furthermore, preliminary experiments revealed that Os 8+The memory effect in ICP-MS is much higher than that in Os. 4+ To reduce the memory effect, this invention uses ascorbic acid to treat Os... 8+ Completely restored to Os 4+ Conduct the test.

[0069] Os has 7 isotopes, which bind in high abundance and are unaffected by isotopic interference. 190 Os isotope diluent selection 189 Os is the reference isotope and 190 Os is a labeled isotope.

[0070] The samples prepared by Sb assay contain elements such as Sb, Cu, Pb, Bi, Ni, Co, Au, Ag, Pt, Pd, Ru, Rh, Os, Ir, N, H, O, Cl, and C, along with Ar from the plasma. These coexisting elements may generate polyatomic ions. 1 H 188 Os and 1 H 189 Os to 189 Os and 190 Os causes mass spectrometry interference. To eliminate mass spectrometry interference and instrument background interference, this invention conducted tests in standard mode (STD-ICP-MS) and collision cell mode (KED-ICP-MS), and the results are shown in Table 4. Table 4 shows that solutions 1-3 have low Os content. 189 Os / 190 The two analysis modes for Os show significant deviations, for solutions 4-11. 189 Os / 190 The results were consistent with the Os values ​​and were compared with reference values; therefore, KED-ICP-MS testing was used in this experiment. 189 Os / 190 Os.

[0071] Table 4 Comparison of Standard Mode and Collision Pool Mode

[0072]

[0073]

[0074] Add the appropriate mass to the Sb assay formula 190 Os isotope diluent (the amount added is approximately the same as the Os content in the sample, meaning they are on the same order of magnitude) was used to prepare Sb slides suitable for LA-ICP-MS testing via an Sb assay process. The slides were then tested using LA-ICP-MS surface imaging technology. 189 Os and 190Distribution of Os in Sb sheets (Sb sheets prepared using standard material GBW07293 via Sb assay, with 134.4 ng of Os isotope diluent added; ablation parameters: 20*20 μm, 120 Hz, 85 μm / s). 189 Os 20.7ms, 190 OS 5.4ms, see Figure 5 ),Depend on Figure 5 It can be known that: 189 Os and 190 The distribution of Os in Sb slices is uneven, but the trend of uneven distribution is consistent.

[0075] LA-ICP-MS multi-point ablation of Sb wafers 189 Os and 190 Os (signal see) Figure 6 ), 189 Os and 190 The mass spectrometry intensities and intensity ratios of Os are shown in Table 5. Therefore, it can be concluded that despite six tests... 189 Os and 190 The mass spectrometry intensity RSDs of Os were 15.42% and 16.02%, respectively, but... 189 Os / 190 The RSD of Os was only 1.89%, which was consistent. This proves that the Sb assay process allows for sufficient exchange and equilibrium between the Os in the isotope diluent and the Os in the sample. Therefore, the Os in the sample can be analyzed by combining the isotope dilution method with LA-ICP-MS.

[0076] Table 5 shows the LA-ICP-MS test results for Sb in the chip. 189 Os and 190 Os mass spectral intensity and ratio

[0077]

[0078]

[0079] Comparison of Sb gold assay with isotope dilution and nickel matte gold assay with isotope dilution

[0080] The popular analytical method for trace Os in geochemical samples is the nickel-matte gold assay-isotope dilution method. However, this method also has its drawbacks. Compared with the nickel-matte gold assay-isotope dilution method, the Sb assay-isotope dilution method has advantages such as lower process blank value, shorter pretreatment time, smaller test memory effect, and no isotopic interference of Os isotopes (see Table 6). Therefore, this method selects the antimony assay-isotope dilution method to analyze trace Os in geochemical samples.

[0081] Table 6 Comparison of Antimony Assay-Isotope Dilution Method and Nickel Matte Assay-Isotope Dilution Method

[0082]

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining trace amounts of Os in geochemical samples, characterized in that, Includes the following steps: (1) Dissolve antimony chloride in water, hydrolyze to produce a precipitate, filter, wash, dry and grind the precipitate to obtain Sb2O3; (2) Based on the mineral composition of the geochemical sample, the Sb2O3 prepared in step (1) is used as a collector to prepare the ingredients for Sb assay of the geochemical sample. (3) Place half of the ingredients in a high-purity quartz crucible, then make grooves in the ingredients and drip the ingredients into the grooves. 190 Os isotope diluent, dried at room temperature; cover the groove with the remaining half of the ingredients, and spread a covering agent evenly on top of the ingredients, the covering agent containing Sb2O3 prepared in step (1); heat the high-purity quartz crucible to obtain a melt, pour the melt into a mold, cool and pour off the slag to obtain Sb clasp; (4) Blow the Sb ash to the required diameter to obtain Sb granules; (5) For the Sb granules obtained in step (4), KED-ICP-MS or LA-ICP-MS were used for determination. 189 Os / 190 The ratio of Os; corrected using a quality discrimination correction method. 189 Os / 190 Os's quality discrimination effect; (6) Based on the corrected 189 Os / 190 The Os ratio was used to calculate the Os content in geochemical samples using the isotopic dilution method.

2. The method for determining trace amounts of Os in geochemical samples according to claim 1, characterized in that, In step (2), the ingredients include 10-20g of geochemical sample, 15-30g of borax, 15-25g of glass powder, 50-75g of Na2CO3, 10-15g of Sb2O3 prepared in step (1) and 1-5g of flour.

3. A method for determining trace amounts of Os in a geochemical sample according to claim 1 or 2, characterized in that, The covering agent comprises 15-30g of borax, 15-25g of glass powder, 50-75g of Na2CO3, 10-15g of Sb2O3 prepared in step (1) and 1-5g of flour.

4. The method for determining trace amounts of Os in a geochemical sample according to claim 1, characterized in that, In step (4), the specific method for obtaining Sb aggregate is as follows: the Sb granules are placed in a magnesia ash dish that has been preheated at 900℃ for more than 30 minutes to remove the skin, and then the ash blowing continues until the aggregate diameter is 2.5-3.5 mm. The magnesia ash dish is then removed and immediately immersed in water and quickly removed to allow the Sb aggregate to solidify.

5. The method for determining trace amounts of Os in a geochemical sample according to claim 1, characterized in that, In step (5), the Sb granules from step (4) were placed in 10 mL of 50% aqua regia (v / v) and then microwaved for digestion. After complete dissolution, the solution was soaked in cold water for at least 1 hour to obtain a digestion solution. 1.5 mL of HCl and 3 mL of ascorbic acid solution (concentration 25 mg / mL) were added to 5 mL of the digestion solution. The solution was brought to a final volume, shaken well, and the concentration of ascorbic acid was determined using KED-ICP-MS. 189 Os / 190 Os ratio.

6. The method for determining trace amounts of Os in a geochemical sample according to claim 5, characterized in that, The heating method for microwave digestion is as follows: first heat for 4 minutes to reach 100℃, and hold for 3 minutes; then heat for 1 minute to reach 110℃, and hold for 5 minutes; then heat for 1 minute to reach 120℃, and hold for 5 minutes; finally, cool down to 100℃ for 1 minute and hold for 5 minutes.

7. The method for determining trace amounts of Os in a geochemical sample according to claim 1, characterized in that, In step (5), the Sb granules from step (4) are prepared into Sb flakes with flat and smooth surfaces; after cleaning the Sb flakes, the Sb content in the Sb flakes is determined by LA-ICP-MS. 189 Os / 190 Os.

8. The method for determining trace amounts of Os in a geochemical sample according to claim 1, characterized in that, In step (6), the content of Os in the geochemical sample is calculated according to formula (1): In the formula, c represents the Os content in the sample, and M and M s The atomic masses of Os in the sample and the isotope diluent are m and m, respectively. s m is the mass of Os in the diluent, m is the mass of the sample, and A and B represent the mass of Os in the sample, respectively. 189 Os and 190 Os natural abundance, A s and B s These respectively represent the isotope diluents. 189 Os and 190 Os abundance, R true For the corrected 189 Os / 190 Os ratio.

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