Ionization emitter for iron isotope analysis and preparation and testing method thereof

Abstract

This invention discloses an ionizing emissive for iron isotope analysis and its preparation and testing methods. The ionizing emissive comprises a silicon nanoparticle suspension, a phosphoric acid solution, and an aluminum nitrate solution, wherein the phosphoric acid solution and aluminum nitrate solution are used as emissive excipients. In the iron isotope analysis testing method, the silicon nanoparticle suspension is used as a high-sensitivity emissive to enhance the ionization efficiency of the iron sample. Simultaneously, the phosphoric acid solution and aluminum nitrate solution assist ionization, and a high-purity rhenium filament is used as the sample carrier to test trace amounts of iron isotopes. The filament ionization temperature is 1350–1450℃. This invention has the advantages of high sensitivity, simple operation, and low cost. Compared with the traditional thermal ionization mass spectrometry method which requires 4000–50000 ng of sample, this invention only requires 400–4000 ng to obtain good iron isotope testing accuracy (<0.02%, RSE), significantly reducing the amount of iron sample used while improving testing sensitivity.

Description

Technical Field

[0001] This invention relates to the field of iron isotope analysis technology, specifically to an ionizing emissive for iron isotope analysis and its preparation and testing methods, and more particularly to an ionizing emissive for high-precision iron isotope analysis of trace samples and its preparation and testing methods. Background Technology

[0002] Iron is the most important metallic element in terrestrial planets. In terrestrial planetary systems, iron-based alloys form the planet's core, and iron is also a major element in the mantle and crust. Iron is mainly found in olivine, pyroxene, amphibole, and basic silicate minerals. Due to its prominent role and application potential in high- and low-temperature geological processes, iron has received widespread attention from the isotope geology community since the early 1990s. However, due to the limitations of the accuracy of thermal ionization mass spectrometry (TIMS) analysis technology at that time, related applied research was not common.

[0003] Until the early 2000s, breakthroughs in multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) greatly advanced the applied research of iron isotopes. Since 2000, a large number of influential research results have been published in authoritative journals in Earth and environmental sciences. Related research progress mainly focuses on the early evolution of the solar system, the iron isotopic composition of Earth's major reservoirs, iron isotopic fractionation in magmatic processes, the genesis of mineral deposits, tracing paleooceanic oxygen fugacity, early life evolution, and iron isotopic fractionation behavior in major low-temperature processes. In summary, the study of iron isotopes has opened up new perspectives for Earth science and greatly promoted the development of isotope geology and related disciplines.

[0004] The prerequisite for conducting the aforementioned applied research is the establishment of a high-precision Fe isotope analysis method. Currently, isotope geochemistry laboratories both domestically and internationally have established Fe isotope analysis techniques based on MC-ICP-MS testing, with their δ¹² values... 56 Fe analysis accuracy can reach 0.04–0.12‰, that is, using MC-ICP-MS. 56 Fe / 54 Fe isotope ratio testing typically achieves an internal precision better than 0.004% (2RSE) for a single analysis and an external precision better than 0.012% (2RSD) for long-term measurements. However, TIMS (thermal ionization mass spectrometry), the primary analytical instrument for metal isotope testing, has not produced any Fe isotope data since 2004. This is because Fe has a high ionization potential (7.902 eV), making it difficult to ionize on TIMS. Currently, there is a lack of effective emitters to improve Fe ionization efficiency, resulting in poor testing accuracy. For example, the natural abundance of Fe isotopes varies considerably. 56 The natural abundance of Fe reaches 91.66%, while54 The abundance of Fe is only 5.85%. Therefore, for accurate determination 56 Fe / 54 Fe ratio, 56 The signal intensity of Fe should be at least greater than 5 volts. Using medium-resolution MC-ICP-MS in medium-resolution mode, a Fe solution of approximately 3 ppm can generally easily achieve a signal intensity greater than 10 volts. Each MC-ICP-MS analysis consumes only 300–400 μL of sample solution (approximately 1 μg of Fe). However, for TIMS, due to the extremely poor ionization of Fe, a sample volume of 4–50 μg is typically required. Even with a sample volume of 4 μg, existing emissives can only achieve a signal intensity of around 3 volts. 56 Because of the limited Fe signal, the accuracy of Fe isotope testing using TIMS is not high. The best reported accuracy is only about 0.3‰, and most published Fe isotope analyses have an accuracy greater than 0.5‰. Therefore, TIMS cannot meet the requirements of practical research applications, and since 2000, all Fe isotope analysis work has been completely replaced by MC-ICP-MS.

[0005] Although MC-ICP-MS offers higher sensitivity and analytical efficiency, its strong memory effect, complex molecular ion peak interference, and secondary ion background interference are major problems hindering its analysis. These challenges faced by MC-ICP-MS do not exist for TIMS. However, a major issue with TIMS is the low ionization efficiency of Fe. If the problem of Fe ionization efficiency in TIMS analysis can be overcome, the advantages of TIMS—low instrument memory effect, minimal molecular ion peak interference, and low mass fractionation—would be an important complement to Fe isotope analysis techniques.

[0006] In summary, the key to Fe isotope analysis using TIMS lies in developing highly sensitive emissive agents. Emissive agents are the core driving force for enhancing the ionization efficiency of Fe samples and a prerequisite for achieving high-precision Fe isotope analysis. The choice of emissive agent and filament material directly determines the test sensitivity and accuracy. Currently, there are very few reported emissive agents for improving iron ionization efficiency, only six types, all using silica gel as the main emissive: 1. Silica gel + boric acid + aluminum nitrate; 2. Silica gel + phosphoric acid + aluminum chloride; 3. Silica gel + phosphoric acid + aluminum oxide; 4. Sodium silicate + phosphoric acid; 5. Barium fluoride + silver fluoride; 6. Graphite + phosphoric acid. However, the sensitivity of these emissive agents is not high, requiring a large sample volume (approximately 50 micrograms) for each test. This large sample volume significantly restricts the application of iron isotopes in Earth sciences.

[0007] In summary, no ionizing emitter suitable for trace samples (<4 micrograms) of iron isotopes has yet been developed. Therefore, the development of highly sensitive ionizing emitters and the advancement of techniques for analyzing iron isotopes in trace samples are urgently needed. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide an ionizing emissive for iron isotope analysis and its preparation and testing method. The ionizing emissive is suitable for high-precision iron isotope analysis of trace samples and has high sensitivity, which can optimize the existing iron isotope thermal ionization mass spectrometry analysis technology.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides an ionizing emissive for iron isotope analysis, the ionizing emissive comprising a silicon nanopowder suspension, phosphoric acid and aluminum nitrate solution, wherein the phosphoric acid and aluminum nitrate solution serve as emissive auxiliary materials.

[0011] Since solid silicon nanopowder cannot be coated, this invention uses a suspension to spot onto the sample carrier, while phosphoric acid and aluminum nitrate solutions are used as excitation auxiliary materials.

[0012] In this invention, dilute phosphoric acid is added for two reasons: firstly, as a binder, it helps the silicon nanoparticle emitter to be better coated and firmly fixed to the rhenium filament surface; secondly, it assists in ionization, moderately enhancing the ionization efficiency of the sample. Preferably, the concentration of the phosphoric acid solution is 0.2–0.4 mol / L.

[0013] The addition of aluminum nitrate solution in this invention can further significantly improve the ionization efficiency of Fe. This is because under high temperature and vacuum conditions, Si-Al sintering and melting can form a porous ceramic structure, in which Fe can be encapsulated and sintered. The Si-Al porous ceramic structure can slow down the evaporation rate of Fe during thermal ionization, thereby improving the utilization rate of the sample.

[0014] Furthermore, the silicon nanopowder suspension is prepared by the following method: first, high-purity silicon nanopowder is washed with hydrochloric acid and high-purity deionized water alternately 6 to 8 times to reduce the sample bottom; then, the treated silicon nanopowder is added to deionized water to prepare a silicon nanopowder suspension of a preset concentration.

[0015] Furthermore, the concentration of the silicon nanopowder suspension is calculated based on the dosage of silicon nanopowder emissive and the amount of silicon nanopowder suspension required for each test; the dosage of high-purity silicon nanopowder required for each test is 5 ± 0.2 micrograms, the amount of silicon nanopowder suspension required is 1 to 2 μL, and the concentration of silicon nanopowder suspension is 5 to 2.5 mg / mL.

[0016] In this invention, the concentration of the silicon nanopowder suspension mainly depends on the dosage of silicon nanopowder emitter required for each test. Preferably, the dosage of high-purity silicon nanopowder required for each test is 5 ± 0.2 micrograms, and should not exceed 6 micrograms. Otherwise, it will significantly affect the test of iron samples, such as the following problems: 1. Sample detachment; 2. Contamination of the ion source; 3. Unstable signal emission.

[0017] In addition, since the sample volume of silicon nanopowder suspension is too large for each test, the sample will evaporate very slowly and there is a risk of sample diffusion. Therefore, the sample volume of silicon nanopowder suspension is generally controlled at 1 μL, and at most 2 μL. Consequently, the concentration of silicon nanopowder suspension is generally 5 to 2.5 mg / mL, which is calculated based on the dosage of silicon nanopowder emissive and the sample volume of silicon nanopowder suspension required for each test.

[0018] Preferably, the high-purity silicon nanopowder has a purity greater than 99.9%.

[0019] Preferably, the particle size of the high-purity silicon nanoparticles is <100nm.

[0020] Secondly, the present invention also provides a method for preparing the above-mentioned ionizing emissive for iron isotope analysis. The preparation method includes the preparation of a silicon nanopowder suspension, the preparation of a phosphoric acid solution, and the preparation of an aluminum nitrate solution. The method for preparing the silicon nanopowder suspension is as follows:

[0021] S1. Pretreatment of silicon nanopowder, as detailed below:

[0022] S11. Hydrochloric acid cleaning: Weigh high-purity silicon nanoparticles, add hydrochloric acid according to the ratio, seal, keep warm at 80-100℃ for 0.5-1 hour, and continuously shake to clean the silicon nanoparticles with hydrochloric acid to reduce the sample bottom.

[0023] S12. Deionized water cleaning: Cool the silicon nanopowder after hydrochloric acid cleaning to room temperature, remove the upper hydrochloric acid solution, add high-purity deionized water, seal again and shake for 5-6 minutes, let stand to separate into layers, and aspirate the upper clear liquid again.

[0024] The high-purity silicon nanopowder was washed 6-8 times with alternating washing of S13, hydrochloric acid and high-purity deionized water. The final precipitate phase obtained is the pretreated silicon nanopowder.

[0025] S2. Weigh the silicon nanoparticles pretreated in step S13, add deionized water, and prepare a silicon nanoparticle suspension of a preset concentration.

[0026] Furthermore, the concentration of the silicon nanopowder suspension is calculated based on the dosage of silicon nanopowder emissive and the amount of silicon nanopowder suspension required for each test; the dosage of high-purity silicon nanopowder required for each test is 5 ± 0.2 micrograms, the amount of silicon nanopowder suspension required is 1 to 2 μL, and the concentration of silicon nanopowder suspension is 5 to 2.5 mg / mL.

[0027] Furthermore, the method for preparing the phosphoric acid solution is as follows: weigh concentrated phosphoric acid solution, add deionized water in proportion, and prepare a phosphoric acid solution with a concentration of 0.2-0.4 mol / L.

[0028] Furthermore, the method for preparing the aluminum nitrate solution is as follows: a high-purity aluminum nitrate standard solution with a concentration of 1000 ppm is first passed through LN Spec resin to remove iron, so as to further reduce the sample floor of Fe, and at the same time the purified aluminum nitrate solution is recovered, thus obtaining the solution.

[0029] Preferably, the concentration of hydrochloric acid used for cleaning in step S11 is 3-6 mol / L.

[0030] Preferably, the amount of hydrochloric acid and high-purity deionized water used for cleaning is generally 3 to 10 mL.

[0031] Thirdly, the present invention also provides a method for analyzing and testing trace iron isotopes in a sample. Specifically, a silicon nanopowder suspension is used as an ionization emitter to enhance the ionization efficiency of the iron sample. At the same time, dilute phosphoric acid and aluminum nitrate solutions are used to assist ionization, and a high-purity rhenium filament is used as a sample carrier to test trace iron isotopes.

[0032] Furthermore, the method for analyzing iron isotopes in trace samples specifically includes the following steps:

[0033] C1. Take an appropriate amount of silicon nanopowder suspension, dilute phosphoric acid and aluminum nitrate solution to form an ionizing emissive and apply it to the surface of a high-purity rhenium filament. After the emissive is dried, spot the iron sample on the filament surface. Then adjust the current to 1.2 amperes to dry the iron sample. After that, continue to increase the current until the filament turns dark red and hold for 3 to 5 seconds. Then return the current to zero.

[0034] C2. The high-purity rhenium filament holder containing the iron sample is then placed into a thermal ionization mass spectrometer for testing to obtain high-precision iron isotope analysis data. It is important to note that during sample spotting, the ionizing emissive must be loaded / coated onto the surface of the high-purity rhenium filament.

[0035] Furthermore, when the ionizing emissive is actually applied to the surface of the rhenium filament, the prepared phosphoric acid solution, silicon nanopowder suspension, and aluminum nitrate solution are first applied to the surface of the rhenium filament in sequence by spotting.

[0036] Specifically, the coating process of the emissive in step (1) is as follows:

[0037] Take 1-2 μL of a 0.2-0.4 mol / L phosphoric acid solution and apply it to the surface of a high-purity rhenium filament. Adjust the filament current to evaporate the phosphoric acid solution to dryness. Then, take 1-2 μL of a certain concentration of silicon nanopowder suspension and cover it with the evaporated phosphoric acid coating. After the silicon nanopowder suspension has evaporated to dryness, cover it with 1-2 μL of aluminum nitrate solution. After the aluminum nitrate solution has evaporated to dryness, finally spot the iron sample onto the filament surface.

[0038] Specifically, the concentration of the silicon nanopowder suspension is calculated based on the dosage of silicon nanopowder emissive and the sample volume of the silicon nanopowder suspension required for each test. Specifically, the dosage of high-purity silicon nanopowder powder required for each test is 5 ± 0.2 micrograms, and the sample volume of the silicon nanopowder suspension is 1–2 μL, thus corresponding to a concentration of 5–2.5 mg / mL. This concentration is calculated based on the dosage of silicon nanopowder emissive and the sample volume of the silicon nanopowder suspension required for each test. Excessive amounts of phosphoric acid and aluminum nitrate solution can easily contaminate the ion exchange lens; generally, the sample volume for each test is 1 μL, and should not exceed 2 μL.

[0039] Preferably, the sample volume of the silicon nanopowder suspension, phosphoric acid and aluminum nitrate solution used in the test is 2 μL, and correspondingly, the concentration of the silicon nanopowder suspension is preferably 2.5 mg / mL.

[0040] Furthermore,

[0041] In step C1, the amount of iron sample used is 400–4000 ng. Preferably, it is 1000–2000 ng, and usually 1000–2000 ng is sufficient to obtain high-precision Fe isotope analysis data.

[0042] Furthermore,

[0043] In step C2, the ionization temperature of the high-purity rhenium filament during the thermal ionization mass spectrometry test is 1350–1450 °C.

[0044] According to the Langmuir-Kingdom empirical formula, the higher the work function of the metal wire surface, the higher the ionization efficiency of positive ions. This invention uses high-purity (purity higher than 99.8%) rhenium filament as the sample carrier. During sample application, a silicon nanoparticle suspension provided by this invention is added as a highly sensitive emitter. Simultaneously, phosphoric acid and aluminum nitrate solutions are used as emitter auxiliary materials to assist ionization. This significantly improves the ionization efficiency of iron, indirectly increasing the surface work function of the rhenium filament, thereby enhancing the ionization efficiency and analytical sensitivity of iron, and ultimately reducing the amount of iron sample required.

[0045] The beneficial effects of this invention are as follows:

[0046] 1. Traditional ionizing emitters used for iron isotope analysis include six types: silica gel + boric acid + aluminum nitrate; silica gel + phosphoric acid + aluminum chloride; silica gel + phosphoric acid + aluminum oxide; sodium silicate + phosphoric acid; barium fluoride + silver fluoride; and graphite + phosphoric acid. High-purity rhenium or tungsten filaments are typically used as sample carriers. However, due to the high ionization potential of Fe (7.902 eV), it is difficult to ionize during thermal ionization mass spectrometry. Traditional emitters cannot obtain a high-intensity, stable ion current signal for low sample amounts (<4000 ng) of iron isotopes, thus failing to achieve satisfactory testing accuracy for trace iron samples.

[0047] Compared to traditional ionizing emitters used in iron isotope analysis, this invention provides a novel silicon nanopowder emitter to replace the traditional silica gel-based emitter. This emitter is composed of a silicon nanopowder suspension, with phosphoric acid solution and aluminum nitrate solution as auxiliary materials. A high-purity rhenium filament is used as the sample carrier to test trace amounts of iron isotopes. This significantly improves the ionization effect of iron and increases the analytical sensitivity by at least 4 times, thereby reducing the amount of sample required. Traditional techniques require at least 4000 ng of sample per analysis, while this technique only requires 1000 ng of sample to obtain high-precision Fe isotope analysis data.

[0048] 2. The method of this invention is highly sensitive, low-cost, and easy to operate. It can effectively replace existing iron isotope thermal ionization mass spectrometry analysis methods and has great application prospects. Detailed Implementation

[0049] To better understand the above-described objects, features, and advantages of the present invention, the present invention will be further described in detail below with reference to specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may also be implemented in other ways different from those described herein, and therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0050] In the following embodiments, the raw materials used are sourced from:

[0051] Superior grade pure nano-silicon powder (purity: 99.9%, particle size less than 80 nanometers, Shanghai Chaowei Nanotechnology Co., Ltd.)

[0052] MOS pure hydrochloric acid (purified once by sub-boiling distillation, Sinopharm Chemical Reagent Co., Ltd.)

[0053] Superior grade aluminum nitrate solution (Sinopharm Chemical Reagent Co., Ltd.)

[0054] Ultrapure water (Millipore Simplicity ultrapure water system, Millipore Corporation, USA, with an output conductivity of 18.2 MΩ / cm)

[0055] Iron isotope standard IRMM524a (European Institute of Standards and Technology)

[0056] Example

[0057] This invention provides an ionizing emissive for the analysis of iron isotopes in trace samples, specifically including the following steps:

[0058] I. Preparation of Ionizing Emitting Agents for Iron Isotope Analysis

[0059] 1. Preparation of silicon nanopowder suspension

[0060] 1) Weigh 25±0.2mg of silicon nanopowder into a dissolving bottle, add 3mL of 6mol / L hydrochloric acid, seal the dissolving container, and keep it heated on an electric hot plate at 80~100℃ for 0.5~1 hour. During this period, continuously shake the dissolving container to clean the silicon nanopowder and lower the sample bottom.

[0061] 2) After the sample dissolving apparatus has cooled to room temperature, use a pipette to remove the upper layer of hydrochloric acid solution, add 3 mL of high-purity deionized water, seal the sample dissolving apparatus and shake it for 5-6 minutes, let it stand for 3 minutes, and then use a pipette to aspirate the upper layer of solution.

[0062] 3) Repeat steps 1) and 2) and wash the silicon nanopowder with hydrochloric acid and high-purity deionized water alternately 6 to 8 times. The final precipitate is the pretreated silicon nanopowder.

[0063] 4) Add the silicon nanopowder obtained in step 3) to 10 mL of high-purity deionized water to prepare a silicon nanopowder suspension with a concentration of 2.5 mg / mL for later use.

[0064] 2. Preparation of phosphoric acid solution

[0065] A 0.4 mol / L phosphoric acid solution was prepared by diluting saturated phosphoric acid (14.63 mol / L) with deionized water. This solution was used as an auxiliary material for the launcher and is ready for use.

[0066] 3. Preparation of aluminum nitrate solution

[0067] Take 2 ml of 1000 ppm aluminum nitrate solution (commercially available analytical grade, dilute nitric acid medium) and load it onto an LN Spec resin exchange column. Recover the aluminum nitrate solution and set it aside for later use. Since LN Spec resin can adsorb Fe under low acidity conditions but does not retain Al, this property can be used to purify Al.

[0068] II. Sample loading and testing

[0069] The sample loading and testing methods are as follows:

[0070] 1) Apply 1 μL of 0.4 mol / L phosphoric acid solution to the surface of a high-purity rhenium filament. Adjust the filament current to evaporate the phosphoric acid solution to dryness. Then, apply 2 μL of 2.5 mg / mL silicon nanopowder suspension to the evaporated phosphoric acid coating. After the silicon nanopowder suspension has evaporated to dryness, apply 2 μL of 1000 mg / mL aluminum nitrate solution to the evaporated coating. Finally, spot the international standard IRMM524a (4000 ng) onto the surface of the rhenium filament. Adjust the current to 2.0 amperes to evaporate the iron sample to dryness. Then, slowly increase the filament current until the filament turns dark red and hold for 3-5 seconds. Immediately return the current to zero.

[0071] 2) Load the sample into the Triton Plus thermal ionization mass spectrometer and use the Triton Plus thermal ionization mass spectrometer to test the international standard IRMM524a sample. The filament temperature during the test is 1350~1450℃.

[0072] 3) Adopt 57 Fe / 56 Mass fractionation correction was performed for Fe = 0.023092 using exponential law correction. 200 data sets were collected and recorded. 56 Fe / 54 Fe test results.

[0073] The concentrations of phosphoric acid solution, silicon nanopowder suspension, aluminum nitrate, and IRMM524a spotting amounts for each embodiment are shown in Table 1 below:

[0074] Table 1. Concentrations and sample volumes of phosphoric acid solution, silicon nanopowder suspension, and aluminum nitrate solution in each example, and sample volume data of IRMM524a.

[0075]

[0076] The test results of the IRMM524a standard samples in Examples 1-4 are shown in Tables 2-5 below:

[0077] Table 2. Analytical results of 4000 ng international standard IRMM524a from Example 1

[0078]

[0079]

[0080] Table 3. Analytical results of 2000 ng international standard IRMM524a in Example 2

[0081] Sample number <![CDATA[ 56 Fe / 54 Fe]]> 2SE IRMM524-2000ng-1 15.7210 0.0010 IRMM524-2000ng-2 15.7196 0.0010 IRMM524-2000ng-3 15.7206 0.0010 IRMM524-2000ng-4 15.7198 0.0008 IRMM524-2000ng-5 15.7208 0.0010 IRMM524-2000ng-6 15.7228 0.0009 IRMM524-2000ng-7 15.7170 0.0010 IRMM524-2000ng-8 15.7215 0.0008 IRMM524-2000ng-9 15.7202 0.0010 IRMM524-2000ng-10 15.7232 0.0011 IRMM524-2000ng-11 15.7206 0.0009 IRMM524-2000ng-12 15.7182 0.0010 Mean±SD 15.7204 0.0017

[0082] Table 4. Analytical results of 1000 ng international standard IRMM524a in Example 3

[0083] Sample number <![CDATA[ 56 Fe / 54 Fe]]> 2SE IRMM524-1000ng-1 15.7211 0.0011 IRMM524-1000ng-2 15.7178 0.0012 IRMM524-1000ng-3 15.7211 0.0012 IRMM524-1000ng-4 15.7212 0.0011 IRMM524-1000ng-5 15.7192 0.0013 IRMM524-1000ng-6 15.7197 0.0011 IRMM524-1000ng-7 15.7219 0.0010 IRMM524-1000ng-8 15.7176 0.0013 IRMM524-1000ng-9 15.7250 0.0013 IRMM524-1000ng-10 15.7204 0.0013 IRMM524-1000ng-11 15.7206 0.0013 IRMM524-1000ng-12 15.7191 0.0012 Mean±SD 15.7204 0.0020

[0084] Table 5. Analytical results of 400 ng international standard IRMM524a from Example 4.

[0085] Sample number <![CDATA[ 56 Fe / 54 Fe]]> 2SE IRMM524-400ng-1 15.7164 0.0020 IRMM524-400ng-2 15.7228 0.0022 IRMM524-400ng-3 15.7150 0.0016 IRMM524-400ng-4 15.7173 0.0015 IRMM524-400ng-5 15.7185 0.0020 IRMM524-400ng-6 15.7233 0.0016 IRMM524-400ng-7 15.7188 0.0018 IRMM524-400ng-8 15.7178 0.0011 IRMM524-400ng-9 15.7209 0.0016 IRMM524-400ng-10 15.7260 0.0016 IRMM524-400ng-11 15.7235 0.0014 IRMM524-400ng-12 15.7168 0.0014 Mean±SD 15.7198 0.0035

[0086] Table 6. Signal intensity and emission duration of silicon nanopowder for iron samples with different sample amounts

[0087] Sample volume (ng) <![CDATA[ 56 Fe(mV)]]> Launch duration (minutes) 4000 5500～8500 >20 2000 4000～6200 >20 1000 2700～4300 >18 400 2200～3700 >18

[0088] Tables 2-5 list the results of multiple analyses of the international standard IRMM524a (4000 ng, 2000 ng, 1000 ng, 400 ng) using silicon nanopowder suspensions of different concentrations. The test results show that for all samples in the 4000–1000 ng range... 56 Fe / 54 The internal precision of the Fe ratio was less than ±0.0013 (2SE), and the external precision of multiple analyses was better than ±0.0020 (1SD). Even for a sample amount of 400 ng, the accuracy of all samples was excellent. 56 Fe / 54 The internal precision of the Fe ratio is better than ±0.0022 (2SE), and the external precision for multiple analyses is better than ±0.0035. The testing accuracy of this invention is superior to that obtained by most similar studies, while significantly reducing the amount of sample required.

[0089] The data above shows that even for a trace sample of 400 ng, the use of silicon nanoparticles as an emitter... 56 Fe / 54 The Fe ratio still achieves an internal precision of better than ±0.012% (RSE) and an external precision of ±0.022% (RSD), which fully demonstrates that silicon nanopowder emitters have extremely high sensitivity and high accuracy for Fe isotope analysis.

[0090] To further illustrate the sensitizing effect of the emissive provided by this invention on trace Fe samples, Table 6 lists the emission duration and emission intensity for different sample amounts. 56 Fe has the highest isotopic abundance in the Fe isotopic system, therefore... 56 The emission intensity of Fe serves as a direct benchmark for sensitivity evaluation. Table 6 above shows that the test method provided by this invention, even for a 400 ng iron sample, 56 The strength of Fe can also reach 2200-3700mV, and in this plateau area 56The Fe signal can be stably emitted for more than 18 minutes, and actual sample acquisition only requires 16 minutes (4s integration, 200 data sets) to obtain an analytical accuracy better than 0.01% (RSE). This also demonstrates that the emissive provided by this invention has extremely high sensitivity and high accuracy for Fe isotope analysis.

[0091] It should be noted that those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of this invention without departing from the spirit and scope of this invention should be covered within the scope of the claims of this invention.

Claims

1. An ionizing emissive for iron isotope analysis, characterized in that, The ionizing emissive comprises a silicon nanopowder suspension, a phosphoric acid solution, and an aluminum nitrate solution, wherein the phosphoric acid solution and the aluminum nitrate solution serve as auxiliary materials for the emissive.

2. The ionizing emissive for iron isotope analysis according to claim 1, characterized in that, The silicon nanopowder suspension is prepared by the following method: first, high-purity silicon nanopowder is washed with hydrochloric acid and high-purity deionized water alternately 6 to 8 times to reduce the sample bottom; then, the treated silicon nanopowder is added to deionized water to prepare a silicon nanopowder suspension of a preset concentration.

3. The ionizing emissive for iron isotope analysis according to claim 2, characterized in that, The concentration of the silicon nanopowder suspension is calculated based on the dosage of silicon nanopowder and the amount of silicon nanopowder suspension required for each test. The dosage of high-purity silicon nanopowder required for each test is 5 ± 0.2 micrograms, the amount of silicon nanopowder suspension required is 1 to 2 μL, and the concentration of silicon nanopowder suspension is 2.5 to 5 mg / mL.

4. The ionizing emissive for iron isotope analysis according to any one of claims 2 to 3, characterized in that, The high-purity silicon nanopowder has a purity greater than 99.9%; The particle size of the high-purity silicon nanopowder is <100nm; The concentration of the phosphoric acid solution is 0.2–0.4 mol / L.

5. The method for preparing an ionization emitter for iron isotope analysis according to any one of claims 1 to 4, characterized in that, The preparation methods include the preparation of a silicon nanopowder suspension, a phosphoric acid solution, and an aluminum nitrate solution. The method for preparing the silicon nanopowder suspension is as follows: S1. Pretreatment of silicon nanopowder, as detailed below: S11. Hydrochloric acid cleaning: Weigh high-purity silicon nanopowder, add hydrochloric acid according to the ratio, seal, keep warm at 80-100℃ for 0.5-1 hour, and continuously shake to clean the silicon nanopowder with hydrochloric acid to reduce the sample bottom. S12. Deionized water cleaning: Cool the silicon nanopowder after hydrochloric acid cleaning to room temperature, remove the upper hydrochloric acid solution, add high-purity deionized water, seal again and shake for 5-6 minutes, let stand to separate into layers, and aspirate the upper clear liquid again. High-purity silicon nanopowder was washed 6-8 times with S13, hydrochloric acid and high-purity deionized water. The final precipitate was the pretreated silicon nanopowder. S2. Weigh the silicon nanoparticles pretreated in step S13, add deionized water, and prepare a silicon nanoparticle suspension of a preset concentration.

6. The preparation method according to claim 5, characterized in that, The method for preparing phosphoric acid solution is as follows: Weigh concentrated phosphoric acid solution, add deionized water in proportion, and prepare a phosphoric acid solution with a concentration of 0.2-0.4 mol / L. The method for preparing aluminum nitrate solution is as follows: First, pass a high-purity aluminum nitrate standard solution with a concentration of 1000 ppm through LN Spec resin to remove iron, further reducing the sample floor of Fe, and at the same time recover the purified aluminum nitrate solution to obtain the solution.

7. A method for testing micro-samples of iron isotopes, characterized in that, Specifically, this method uses a silicon nanoparticle suspension as a highly sensitive emissive agent to enhance the ionization efficiency of iron samples, while employing dilute phosphoric acid and aluminum nitrate solutions to assist ionization, and using a high-purity rhenium filament as a sample carrier to test trace amounts of iron isotopes; the specific steps include the following: C1. First, apply the prepared phosphoric acid solution, silicon nanopowder suspension and aluminum nitrate solution to the surface of the high-purity rhenium filament in sequence. After the emissive has evaporated, apply the iron sample to the filament surface. Adjust the current to 1.2 amperes to evaporate the iron sample. Then, continue to increase the current until the filament turns dark red and hold for 2 to 4 seconds. Then, return the current to zero. C2. The iron isotope analysis data are obtained by loading a high-purity rhenium filament holder containing the iron sample into a thermal ionization mass spectrometer for testing.

8. The method for testing iron isotopes in trace samples according to claim 7, characterized in that, In step C1, the amount of iron sample spotted is 400–4000 ng.

9. The method for testing iron isotopes in trace samples according to claim 7, characterized in that, In step C2, the ionization temperature of the high-purity rhenium filament during the thermal ionization mass spectrometry test is 1350–1450 °C.

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