Analysis method for measuring nickel isotope in geological sample

Abstract

The technical scheme of the invention discloses an analysis method for determining nickel isotope in a geological sample. In an alkaline medium of ammonia water, most metal elements easily form hydroxide precipitates, when the ammonia water and a rock sample solution generated through acid digestion are subjected to a co-precipitation reaction, most matrix elements (Mg, Al, Ca, Ti, V, Cr, Mn, Fe and Sn) form precipitates, but the solubility of nickel hydroxides in the ammonia water is relatively high, and especially in the presence of excessive ammonia, the nickel hydroxides in the rock sample solution have relatively high solubility. A soluble ammonia complex [Ni (NH3) 6] < 2 + > can be formed, so that separation is realized. According to the method, nickel double diluents are added during early-stage sample treatment, and a sample and standard sample intercalation method is combined in a testing process, so that isotope fractionation of nickel in a chemical treatment process and an analysis process when excessive ammonia water is used for coprecipitating nickel isotopes can be effectively corrected; the bottleneck that the nickel isotope cannot be detected by using an ammonia water coprecipitation method in the traditional technology is solved.

Description

Technical Field

[0001] The present invention relates to the field of laser ablation inductively coupled plasma mass spectrometers, and in particular to an analytical method for determining nickel isotopes in geological samples. Background Art

[0002] Nickel isotopes, as important geochemical tracers, provide a unique tool for studying key scientific questions such as planetary material evolution, early Earth accretion and core-mantle differentiation, crust-mantle magmatism, surface geochemical cycles, and paleo-ocean evolution. High-precision nickel isotope composition determination methods are the cornerstone of nickel isotope geochemical research. Geological samples (such as rocks, ores, and sediments) often contain high concentrations of matrix elements (such as Si, Fe, Mg, and Ca) and interfering ions (such as Co, Cu, and Zn). Chemical separation is required to remove impurities and avoid signal interference or isotope fractionation during mass spectrometry.

[0003] The conventional sample extraction methods currently include: 1. Chelation extraction method, specifically using dimethylglyoxime (DMG) to selectively chelate nickel ions in the solution, while Fe³⁺, Mg²⁺ and other ions do not react (precious metal ions such as Pd, Pt It needs to be removed in advance with a cation exchange resin) to separate nickel from other matrix elements. However, the use of DMG nickel-specific resin for nickel separation and purification has the following disadvantages: (1) DMG's chelation of nickel is highly dependent on the pH value of the sample, and changes in pH value lead to a decrease in nickel recovery; (2) When eluting the chromatography column loaded with DMG-specific resin, an acetone-hydrochloric acid mixture is used as the eluent. Since highly volatile nickel tetracarbonyl substances may be formed in this process, nickel loss may occur; (3) Noble metal ions (such as Pd and Pt) need to be separated in advance; (4) Some DMG may remain in the sample solution. In MC-ICP-MS analysis, due to the mass discrimination effect of the mass spectrometer, the isotope measurement value may deviate from the actual value, affecting the accuracy and precision of the nickel isotope analysis results. The second method is the Fe-Mg co-precipitation method, which uses Fe³⁺ or Mg²⁺ hydroxide as a carrier to enrich Ni²⁺ through adsorption or co-precipitation. However, for Ni isotopes, Fe-Mg and other co-precipitation systems introduce many matrix elements, which interfere with Ni isotope analysis. The third method is the Fe / Co co-precipitation method, which uses Fe(OH)³ or Co(OH)² as a carrier to enrich Ni²⁺ through adsorption or solid solution formation (e.g., Ni²⁺ replaces sites in the Fe³⁺ lattice). However, this method has low selectivity and requires the use of ion exchange resins (such as AG-MP-1 anion resin) to remove interfering ions such as Co and Cu.

[0004] Ammonia is commonly used to adjust pH. When ammonia is used to adjust the pH to alkaline, metal ions such as Fe³⁺, Al³⁺, Mn²⁺, and Cu²⁺ will form hydroxide precipitates. Co-precipitation causes many interferences and poor separation effects. However, nickel hydroxide has a high solubility in ammonia, especially in the presence of excess ammonia, and will form a soluble ammonia complex [Ni (NH3)6]. 2+ , resulting in incomplete precipitation. At that time, this method still had problems such as incomplete recovery and poor separation effect. Therefore, the current existing technology believes that ammonia water is not suitable as an exclusive co-precipitation method for nickel.

[0005] Therefore, existing nickel isotope separation and purification methods, in order to prevent matrix interference and other effects, are cumbersome, require large amounts of strong acid reagents, require large amounts of resin, and are costly. For example, Wu et al. (2019) used a method that alternated between chromatographic columns loaded with cationic resin AG50W–X8 and chromatographic columns loaded with anionic resin AG1–X8, and repeated column passes to separate nickel from matrix elements (Fe, Ca, Mg, and Mn). This process is time-consuming, typically requiring several days, and is prone to cross-contamination (such as nickel background in the laboratory environment). Therefore, how to better separate nickel from other interfering elements is a key issue. It is necessary to develop a more convenient method with lower sample requirements for the testing environment to achieve better detection. Summary of the Invention

[0006] The purpose of the present invention is to effectively correct the nickel isotope fractionation caused by the chemical treatment process and analysis process when using excess ammonia co-precipitation of nickel isotopes by combining the addition of a nickel double diluent during the early sample treatment and the use of a sample-standard interpolation method during the testing process, thereby solving the bottleneck of the traditional technology that cannot use the ammonia co-precipitation method to detect nickel isotopes.

[0007] To achieve the above object, the present invention provides an analytical method for determining nickel isotopes in geological samples, specifically: S1. Weigh the rock sample powder and digest it with hydrochloric acid, nitric acid and hydrofluoric acid to obtain a clear sample solution; S2. Take a portion of the clarified sample solution and test the trace elements of the solution using ICP-MS to obtain the Ni concentration of the solution; S3. Add the double diluent in proportion to the concentration of the clarified liquid calculated in S2 and mix well; S4, mixing the mixed liquid with ammonia water, centrifuging and extracting the supernatant; S5, the extracted supernatant was evaporated to dryness, and then dissolved in dilute hydrochloric acid. After ammonium citrate and ammonia were added in sequence to adjust the pH, the sample solution was loaded into an ion chromatography column containing nickel-containing special-effect resin, and a mixed solution of ammonium citrate and ammonia, deionized water, and dilute nitric acid were added in sequence to elute the chromatography column. The eluent was taken, nitric acid and hydrogen peroxide were added, and the column was evaporated on a hot plate to remove organic matter. After evaporation, nitric acid was finally added to dissolve the column to obtain a clear sample solution. S6. The nickel isotope ratio in the sample solution is measured by a multi-collector inductively coupled plasma mass spectrometer and calibrated by the sample-standard interpolation method.

[0008] Furthermore, in step S2, 50 μL of the clarified sample solution was taken into an injection tube, and 2.5 mL of 2% w / w nitric acid was added to the injection tube to make the volume 3 mL, and then the Ni concentration in the solution was measured.

[0009] Furthermore, the optimal dilution ratio of the double diluent added in step S3 to the total amount of Ni in the solution is 0.4-0.6.

[0010] Furthermore, the concentration of the nickel isotope double diluent added in step S3 is 20 μg / g, and the isotopic abundance is: 58 Ni (0.03%), 60 Ni (0.13%), 61 Ni (45.06%), 62 Ni (54.67%), 64 Ni (0.12%).

[0011] Furthermore, in step S4, an excess amount of ammonia water is added, and the ammonia water is obtained by diluting chromatographically pure or higher purity ammonia water with deionized water, and the volume fraction of the diluted ammonia water in the solution is 25% v / v.

[0012] Furthermore, in step S5, ammonium citrate and ammonia water are sequentially added to adjust the pH, specifically by adding 1 mL of 1 mol / L hydrochloric acid, then continuing to add 0.2 mL of 1 mol / L ammonium citrate, and then continuing to add 5 mol / L ammonia water until the pH is adjusted to 9-10.

[0013] Furthermore, the method for removing organic matter in step S5 is specifically as follows: the temperature is set to 80° C., the time is set to 3 hours; after evaporation to dryness, 1 mL of 2% w / w nitric acid is finally added for dissolution.

[0014] Furthermore, the mixed solution of ammonium citrate and aqueous ammonia used for eluting the ion chromatography column in step S5 is a mixture of 1 mol / L ammonium citrate and 5 mol / L aqueous ammonia in a volume ratio of 4:1. The pH of the mixed solution must be determined to be between 9 and 10 using pH test paper before use. If the pH is lower than 9, an appropriate amount of 5 mol / L aqueous ammonia must be added to adjust the pH of the mixed solution to between 9 and 10 before use.

[0015] Beneficial effects:

[0016] 1) Existing techniques require 108 mL of strong acidic chemical reagents during the separation and purification process, resulting in high reagent consumption. Some processes also utilize large amounts of volatile and irritating, high-concentration organic solvents (such as the toxic and hazardous reagent acetone), posing health risks to operators and requiring specialized operating environments or protective measures. However, this method requires only 6 mL of strong acidic reagents for nickel separation and purification, eliminating the need for toxic and hazardous organic reagents. Instead, nickel separation and purification is accomplished using only ammonia coprecipitation and an ion chromatography column containing a nickel-specific resin, resulting in simpler operation and greater user friendliness.

[0017] 2) The combination of nickel double diluent and sample-standard interpolation can effectively correct nickel isotope fractionation throughout the entire chemical treatment process and analysis process, solving the bottleneck of traditional technology that cannot use ammonia co-precipitation method to detect nickel isotopes.

[0018] 3) The entire device is simple and does not require complicated operations and harsh experimental conditions, which greatly improves the efficiency of nickel isotope analysis.

[0019] 4) For currently conventional geological samples, the nickel isotope measurement values ​​in various geological samples analyzed using the method provided by the present invention are consistent with the reference values ​​within the analytical error. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The embodiments of this specification will be further described in the form of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not restrictive, and in these embodiments, the same numbers represent the same structures, wherein: Figure 1 In this specification, the Ni isotope ratio (δ 60 Ni / 58 Ni) changes. DETAILED DESCRIPTION

[0021] In order to more clearly illustrate the technical solutions of the embodiments of this specification, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of this specification. For ordinary technicians in this field, this specification can also be applied to other similar scenarios based on these drawings without paying any creative work. It should be understood that these exemplary embodiments are provided only to enable technicians in the relevant fields to better understand and implement this specification, and do not limit the scope of this specification in any way. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0022] In recent years, multi-cup inductively coupled plasma mass spectrometry (MC–ICP–MS) has become the mainstream instrument for determining nickel isotope composition. To obtain high-precision nickel isotope data, complete separation of nickel from other matrix elements is a prerequisite for accurate nickel isotope determination using MC–ICP–MS. Currently, ion exchange chromatography is the primary method for separating and purifying nickel from samples. This method separates different elements based on the varying affinities of different ions for resin active groups. Because nickel is a trace element in geological samples and its content varies widely (0.00001–0.1%, w / w), and the composition and content of matrix elements vary across different geological samples, existing separation and purification processes typically utilize alternating columns loaded with cationic resin AG50W–X8 and anionic resin AG1–X8, with repeated column passes, to separate nickel from matrix elements (Fe, Ca, Mg, and Mn). This entire separation and purification process is cumbersome, time-consuming, requires large amounts of resin, and is costly. In addition, a variety of chemical reagents (including various inorganic acids and organic reagents) are required in the separation and purification process, and the reagent consumption is large. Some processes use a large amount of high-concentration organic solvents that are volatile and irritating, which pose certain health risks to operators and require special operating environments or protective measures.

[0023] Existing nickel isotope separation and purification processes are cumbersome, require large amounts of strong acid reagents and resin, and are costly. For example, Wu et al. (2019) used a method that alternated and repeated column passes of AG50W–X8 chromatographic columns loaded with cationic resins and AG1–X8 chromatographic columns loaded with anionic resins to separate nickel from matrix elements (Fe, Ca, Mg, and Mn). The separation and purification process required the use of 108 mL of strong acid chemical reagents, resulting in high reagent consumption. Some processes also involved the use of large amounts of volatile and irritating, high-concentration organic solvents (such as the toxic and hazardous reagent acetone), posing health risks to operators and requiring specialized operating environments or protective measures.

[0024] The ammonia coprecipitation method of the present invention can greatly simplify the nickel separation and purification process. In the alkaline medium of ammonia, most metal elements easily form hydroxide precipitates. When ammonia coprecipitates with the rock sample solution generated by acid digestion, most matrix elements (Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Sn) form precipitates. However, nickel hydroxide has a high solubility in ammonia, especially in the presence of excess ammonia, forming a soluble ammonia complex [Ni(NH3)6]. 2+ Therefore, nickel remains in the supernatant, which can effectively avoid the influence of most matrix elements on nickel isotope analysis.

[0025] However, the recovery rate of Ni using excess ammonia is not stable enough, which is specifically reflected in the following aspects: (1) The Ni recovery rate of different types of samples is unstable. Excess ammonia is added to allow the matrix elements to form precipitation and separate from Ni as much as possible. However, the content of each element in different types of samples is different, and the order of precipitation of each element and the degree of precipitation reaction are inconsistent. Therefore, the Ni recovery rate of different types of samples is unstable. (2) The matrix elements precipitate and adsorb Ni, resulting in unstable Ni recovery rate. The matrix elements may adsorb Ni during precipitation, and the adsorption amount is affected by many factors (temperature, reaction time, etc.). In actual operation, it is impossible to ensure that the adsorption amount is stable in each experiment. Therefore, the Ni recovery rate of different types of samples is unstable, and even the Ni recovery rate of the same type of samples with the same Ni loading amount may be unstable.

[0026] Based on this, the present application can effectively correct problems such as isotope fractionation caused by unstable recovery rate in the ammonia recovery Ni chemical treatment process and instrument drift during the analysis process by simultaneously using the double diluent method and the sample standard interpolation method.

[0027] Therefore, after ammonia co-precipitation, nickel isotope analysis can be achieved by MC-ICP-MS after simple nickel purification using an ion chromatography column containing nickel-specific resin.

[0028] The present invention provides an analytical technique for determining nickel isotopes in geological samples, comprising the following steps: S1. Weigh the rock sample powder and digest it with hydrochloric acid, nitric acid and hydrofluoric acid to obtain a clear sample solution; S2. Take a portion of the clarified sample solution and test the trace elements of the solution using ICP-MS to obtain the Ni concentration of the solution; S3, adding a double diluent in proportion according to the concentration of the clarified sample liquid calculated in S2, and mixing uniformly; S4, mixing the mixed solution and ammonia water uniformly, centrifuging and extracting the supernatant; S5. Evaporate the extracted supernatant to dryness, then dissolve it in dilute hydrochloric acid, add ammonium citrate and ammonia water in sequence to adjust the pH, load the sample solution onto an ion chromatography column containing nickel-specific resin, and add a mixed solution of ammonium citrate and ammonia water, deionized water, and dilute nitric acid to elute the column in sequence. Collect the eluent, add nitric acid and hydrogen peroxide, and evaporate on a hot plate to remove organic matter. The temperature is set to 80°C and the time is set to 3 hours. After evaporation to dryness, 1 mL of 2% w / w nitric acid is finally added to dissolve the sample to obtain a clear sample solution. S6. The nickel isotope ratio in the sample solution is measured by a multi-collector inductively coupled plasma mass spectrometer and calibrated by the sample-standard interpolation method.

[0029] Furthermore, the rock sample in step S1 is physically crushed in advance, sieved to obtain sample powder, and the sample is sieved through a 200-mesh sieve.

[0030] Furthermore, the sample processing in step S1 is specifically as follows: weigh 5–100 mg of rock sample powder and place it in a clean sample dissolution tank; add 1.5 mL of nitric acid and 0.5 mL of hydrofluoric acid, tighten the sample dissolution tank and shake it to fully mix the powder and the solution, then open the sample dissolution tank and add an appropriate amount of nickel isotope double diluent; tighten the sample dissolution tank, place it on a hot plate and heat it at 135 °C for 24 hours. After heating, place the sample dissolution tank in an ultrasonic machine for 20 minutes, and then place it on a heating plate and heat it for 2 hours at 135 °C; after cooling, open the sample dissolution tank, place it on a hot plate and heat it to dryness at 105–135 °C. After the solution was evaporated and cooled, 2 mL of aqua regia (hydrochloric acid: nitric acid = 3:1 (v:v)) was added, the sample container was tightened, and the sample was placed on a hot plate and heated at 110°C for 12 hours. The sample container was opened and placed on a hot plate and heated to dryness at 105°C. After cooling, 1 mL of 6 mol / L hydrochloric acid was added, the sample container was tightened, and the sample was placed in an ultrasonic machine for 20 minutes. The sample was then heated on a hot plate at 110°C for 12 hours. The sample container was then opened and placed on a hot plate and heated to dryness at 105°C. After cooling, 1 mL of 6 mol / L hydrochloric acid was added, and the sample was heated to dryness at 110°C for 2 hours. After evaporation, 1 mL of 1 mol / L hydrochloric acid was added, and the sample was heated to dryness at 110°C for 1 hour. Finally, 1 mL of 2% w / w nitric acid was added to dissolve the sample to obtain a clear sample solution.

[0031] Furthermore, in step S2, 50 μL of the clarified sample was taken into an injection tube, and 2.5 mL of 2% w / w nitric acid was added to the injection tube to make the volume 3 mL, and then the Ni concentration in the solution was measured.

[0032] Furthermore, the double dilution method in S3 refers to the three groups of Ni isotopes obtained by MC-ICP-MS testing of Ni solution with double dilution agent added ( 60 Ni / 58 Ni, 61 Ni / 58 Ni, 62 Ni / 58 The Ni isotope ratio of the double diluent was calibrated in advance and the Ni isotope ratio of the standard solution with known isotopic composition was used to correct the fractionation caused by the chemical process and instrument test through iterative calculation to obtain the corrected Ni isotope ratio.

[0033] Furthermore, the optimal dilution ratio of the double diluent added in step S3 is 0.4-0.6, that is, the Ni content in the added diluent and the Ni content in the sample should be close to 1:1. Figure 1 By adding double diluent to the standard solution and constantly changing the amount of addition, that is, the molar fraction ratio of Ni content in the double diluent to the total Ni, the Ni isotope ratio (δ 60 Ni / 58 Ni), when δ 60 Ni / 58 When Ni is close to 0‰, it is considered that the amount of nickel double diluent added is optimal.

[0034] Furthermore, the concentration of the nickel isotope double diluent added in step S3 is 20 μg / g, and the isotopic abundance is: 58 Ni (0.03%), 60 Ni (0.13%), 61 Ni (45.06%), 62 Ni (54.67%), 64 Ni (0.12%).

[0035] Furthermore, in step S4, an excess amount of ammonia water is added, which is obtained by diluting chromatographically pure or higher purity ammonia water with deionized water. The volume fraction of the diluted ammonia water in the solution is 25% v / v, ensuring that Ni forms a soluble ammonia complex [Ni (NH3)6]. 2+ .

[0036] Furthermore, in step S5, ammonium citrate and ammonia water are added in sequence to adjust the pH, specifically, 1 mL of 1 mol / L hydrochloric acid is added, followed by 0.2 mL of 1 mol / L ammonium citrate, and then 5 mol / L ammonia water is added until the pH is adjusted to 9-10.

[0037] Furthermore, the mixed solution of ammonium citrate and aqueous ammonia used for eluting the ion chromatography column in step S5 is a mixture of 1 mol / L ammonium citrate and 5 mol / L aqueous ammonia in a volume ratio of 4:1. The pH of the mixed solution must be determined to be between 9 and 10 using pH test paper before use. If the pH is lower than 9, an appropriate amount of 5 mol / L aqueous ammonia must be added to adjust the pH of the mixed solution to between 9 and 10 before use.

[0038] Furthermore, in the step of treating organic matter in step S5, the amount of nitric acid used is 200 μL, and the amount of hydrogen peroxide used is 30% (v / v) high-grade pure hydrogen peroxide, which is 200 μL.

[0039] Furthermore, the multi-collector inductively coupled plasma mass spectrometer in step S6 is a ThermoScientific™ Neptune™ MC-ICP-MS.

[0040] Furthermore, the sample-standard interpolation method in step S6 refers to that while testing the natural sample, a standard solution with a known isotope composition added with a diluent is also interpolated and calibrated with a double diluent, and then the Ni isotope composition of the standard solution and the unknown natural sample is compared to finally calculate the Ni isotope result of the sample.

[0041] Furthermore, step S6 also includes dissolving the final treated product after treating the organic matter in 2% w / w nitric acid, taking an appropriate amount into a centrifuge tube and adding 2% w / w nitric acid to dilute it into 3 mL of 200 ng / g Ni solution; introducing it into a multi-collector inductively coupled plasma mass spectrometer, and obtaining the Ni content in the sample solution through mass spectrometry measurement and isobaric correction. 58 Ni + 、 60 Ni + 、 61 Ni + 、 62 Ni + The Ni isotopic composition of the sample solution was determined by measuring the signal intensity. The multi-collector inductively coupled plasma mass spectrometer (ICP-MS) was equipped with a nebulizer with a nebulization rate of 100 μL / min and a Scott-type spray chamber. The mass spectrometer interface used for mass spectrometry measurements was a Jet sampling cone and an H-type skimmer cone. The final Ni isotopic composition was obtained by calibration using sample standard interpolation and double dilution.

[0042] Example 1:

[0043] 1) Weigh 40 mg of basalt GSR–3 rock sample powder and digest it with hydrochloric acid, nitric acid, and hydrofluoric acid to obtain a clear sample solution. The specific digestion steps are as follows: place the weighed rock sample powder in a clean sample dissolution tank; add 1.5 mL of nitric acid and 0.5 mL of hydrofluoric acid, tighten the sample dissolution tank and shake it thoroughly to thoroughly mix the powder and solution. Then, open the sample dissolution tank and add 0.278 mL of 20 μg / g nickel isotope double diluent; tighten the sample dissolution tank and place it on a hot plate to heat at 135°C for 24 hours. After heating, place the sample dissolution tank in an ultrasonic machine for 20 minutes and then heat it on a hot plate at 135°C for 2 hours. After cooling, open the sample dissolution tank and place it on a hot plate to heat to dryness at a temperature of 105–135°C. After the solution was evaporated and cooled, 2 mL of aqua regia (concentrated hydrochloric acid:concentrated nitric acid = 3:1 (v:v)) was added, the sample container was tightened, and the sample was placed on a hot plate and heated at 110°C for 12 hours. The sample container was opened and placed on a hot plate and heated to dryness at 105°C. After cooling, 1 mL of 6 mol / L hydrochloric acid was added, the sample container was tightened, and the sample was placed in an ultrasonic machine for 20 minutes. The sample was then heated on a hot plate at 110°C for 12 hours. The sample container was then opened and placed on a hot plate and heated to dryness at 105°C. After cooling, 1 mL of 6 mol / L hydrochloric acid was added, the sample was heated to dryness at 110°C for 2 hours, and after drying, 1 mL of 1 mol / L hydrochloric acid was added and the sample was heated to dryness at 110°C for 1 hour. Finally, 1 mL of 2% w / w nitric acid was added to dissolve the sample to obtain a clear sample solution. 2) Mix 25% v / v ammonia water and the clarified sample solution, centrifuge, and extract the supernatant; 3) Evaporate the extracted supernatant to dryness and dissolve it in 1 mL of 1 mol / L hydrochloric acid. Adjust the pH by adding appropriate amounts of ammonium citrate and ammonia. Load the sample solution onto an ion chromatography column containing nickel-specific resin. Elute the column with a mixture of ammonium citrate and ammonia, deionized water, and dilute nitric acid. Finally, evaporate the dilute nitric acid eluate to dryness. Add nitric acid and hydrogen peroxide and evaporate on a hot plate to remove organic matter. Set the temperature to 80°C for 3 hours. Finally, add 1 mL of 2% w / w nitric acid to dissolve the sample to obtain a clear solution. 4) The nickel isotope ratio in the sample solution was tested by multi-collector inductively coupled plasma mass spectrometry, and the analysis result was δ 60 Ni / 58 Ni = –0.03±0.11 (2SD)‰, which is within the error range and the recommended value δ 60 Ni / 58 Ni = –0.05 ± 0.05 (2SD)‰ remained consistent.

[0044] Example 2:

[0045] The difference between Example 2 and Example 1 is that: the pure peridotite standard sample DTS-1 of the United States Geological Survey USGS is used as an example (the recommended Ni isotope value is δ 60 Ni / 58 Ni = –0.07±0.05 (2SD)‰), Ni double diluent was added to the sample, and after ammonia coprecipitation and Ni special resin two-step separation, the analysis result was δ 60 Ni / 58 Ni = –0.09±0.04 (2SD)‰, which is consistent with the recommended value within the error range.

[0046] Comparative Example 1:

[0047] The difference between Comparative Example 1 and Example 1 is that: taking the pure peridotite standard sample DTS-1 of the United States Geological Survey USGS as an example, 5 mg of DTS-1 powder (the recommended Ni isotope value is δ 60 Ni / 58 Ni = –0.07±0.05 (2SD)‰), the amount of 20 μg / g double diluent added in the digestion process was 0.59 mL, and only ammonia coprecipitation and Ni-specific resin separation were performed in one step. The analysis result was δ 60 Ni / 58 Ni = 0.19 ± 0.16 (2SD), deviating from the recommended value.

[0048] Comparative Example 2:

[0049] The difference between Comparative Example 2 and Example 1 is that: the pure peridotite standard sample DTS-1 of the United States Geological Survey USGS is used as an example (the recommended Ni isotope value is δ 60 Ni / 58 Ni = –0.07±0.05 (2SD)‰), 5 mg of DTS-1 sample was selected, and no Ni double diluent was added to the sample. Only ammonia coprecipitation and Ni special resin separation were performed. The analysis result was δ 60 Ni / 58 Ni = 0.68±0.28 (2SD), deviating from the recommended value.

[0050] Example 3:

[0051] The only difference between Example 3 and Example 1 is that the geological sample used is 5 mg of peridotite DST-2b rock sample powder (the recommended Ni isotope value is δ 60 Ni / 58Ni =0.14±0.03 (2SD)), the amount of 20 μg / g double diluent added in the digestion process was 0.945 mL, and the analysis result was δ 60 Ni / 58 Ni =0.12±0.03 (2SD)‰, which is consistent with the recommended value within the error range.

[0052] Example 4:

[0053] The only difference between Example 4 and Example 1 is that the geological sample used is 100 mg of andesite GSR-2 rock sample powder, and the amount of 20 μg / g double diluent added in the digestion process is 0.0845 mL. The analysis result is δ 60 Ni / 58 Ni = –0.09±0.04 (2SD)‰, which is consistent with the recommended value within the error range.

[0054] Example 5:

[0055] The only difference between Example 5 and Example 1 is that the geological sample used is 40 mg of basalt JB-1b rock sample powder (the recommended Ni isotope value is δ 60 Ni / 58 Ni =0.16±0.07 (2SD)), the amount of 20 μg / g double diluent added in the digestion process was 0.29 mL, and the analysis result was δ 60 Ni / 58 Ni = 0.16±0.04 (2SD)‰, which is consistent with the recommended value within the error range.

[0056] Example 6:

[0057] The only difference between Example 6 and Example 1 is that the geological sample used is 40 mg of diabase W-2a rock sample powder (the recommended Ni isotope value is δ 60 Ni / 58 Ni =0.29±0.01 (2SD)), the amount of 20 μg / g double diluent added in the digestion process was 0.132 mL, and the analysis result was δ 60 Ni / 58 Ni = 0.33±0.04 (2SD)‰, which is consistent with the recommended value within the error range.

[0058] 0.09±0.04 (2SD)‰, which is consistent with the recommended value within the error range.

[0059] Example 7:

[0060] The only difference between Example 7 and Example 1 is that the geological sample used is 80 mg of shale GSR-5 rock sample powder (the recommended Ni isotope value is δ 60 Ni / 58 Ni =0.09±0.05 (2SD)), the amount of 20 μg / g double diluent added in the digestion process was 0.148 mL, and the analysis result was δ 60 Ni / 58 Ni = 0.07±0.06 (2SD), which is consistent with the recommended value within the error range.

[0061] Example 8:

[0062] The only difference between Example 8 and Example 1 is that the geological sample is 40 mg of basalt BHVO-2 rock sample powder (the recommended Ni isotope value is δ 60 Ni / 58 Ni = 0.03 ± 0.06 (2SD), the amount of 20 μg / g double diluent added in the digestion process was 0.224 mL, and the analysis result was δ 60 Ni / 58 Ni =0.04±0.05 (2SD), which is consistent with the recommended value within the error range.

[0063] Example 9:

[0064] The only difference between Example 9 and Example 1 is that the geological sample used is 20 mg of dolomite GSR-12 rock sample powder (the recommended Ni isotope value is δ 60 Ni / 58 Ni =0.14±0.04 (2SD)), the amount of 20 μg / g double diluent added in the digestion process was 0.235 mL, and the analysis result was δ 60 Ni / 58 Ni =0.12±0.06 (2SD), which is consistent with the recommended value within the error range.

[0065] The advantages of the present invention are: (1) In the nickel separation and purification process, only 6 mL of strong acid reagent is required, without the use of toxic and harmful organic reagents. The separation and purification of nickel can be completed using only ammonia co-precipitation and an ion chromatography column containing nickel-specific resin. (2) The entire device is simple, without the need for complex operations and harsh experimental conditions, which greatly improves the efficiency of nickel isotope analysis. (3) The nickel double diluent used in the present invention can effectively correct the isotope fractionation of nickel in the entire chemical treatment process and analysis process. (4) The nickel isotope measurement values ​​of various geological samples analyzed using the method provided by the present invention are consistent with the reference values ​​within the analytical error.

[0066] The present invention is a breakthrough, simple and efficient, and can be quickly promoted in geological analysis laboratories.

[0067] While the basic concepts have been described above, it will be apparent to those skilled in the art that the detailed disclosure is merely illustrative and does not limit this specification. Although not explicitly stated herein, various modifications, improvements, and revisions to this specification may be made by those skilled in the art. Such modifications, improvements, and revisions are suggested in this specification and remain within the spirit and scope of the exemplary embodiments of this specification.

[0068] Similarly, it should be noted that, in order to simplify the presentation of this specification and thus facilitate understanding of one or more embodiments of the invention, the foregoing descriptions of the embodiments of this specification sometimes combine multiple features into a single embodiment, figure, or description thereof. However, this disclosure method does not imply that the subject matter of this specification requires more features than those recited in the claims. In fact, an embodiment may have fewer features than all of the features of a single disclosed embodiment.

[0069] Each patent, patent application, patent application publication, and other materials, such as articles, books, specifications, publications, and documents, cited in this specification is hereby incorporated by reference in its entirety. This excludes any application history documents that are inconsistent with or conflicting with the content of this specification, as well as any documents (currently or subsequently appended to this specification) that limit the broadest scope of the claims of this specification. It should be noted that if the descriptions, definitions, and / or terminology used in the accompanying materials are inconsistent or conflicting with the content of this specification, the descriptions, definitions, and / or terminology used in this specification shall prevail.

[0070] Finally, it should be understood that the embodiments described in this specification are intended only to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, by way of example and not limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly described and illustrated in this specification.

Claims

1. An analytical method for determining nickel isotopes in geological samples, characterized in that: S1. Weigh the rock sample powder and digest it with hydrochloric acid, nitric acid and hydrofluoric acid to obtain a clear sample solution; S2. Take a portion of the clarified sample solution and test the trace elements of the solution using ICP-MS to obtain the Ni concentration of the solution; S3. Add the double diluent in proportion to the concentration of the clarified liquid calculated in S2 and mix well; S4, mixing the mixed liquid with ammonia water, centrifuging and extracting the supernatant; S5, the extracted supernatant was evaporated to dryness, and then dissolved in dilute hydrochloric acid. After ammonium citrate and ammonia were added in sequence to adjust the pH, the sample solution was loaded into an ion chromatography column containing nickel-containing special-effect resin, and a mixed solution of ammonium citrate and ammonia, deionized water, and dilute nitric acid were added in sequence to elute the chromatography column. The eluent was taken, nitric acid and hydrogen peroxide were added, and the column was evaporated on a hot plate to remove organic matter. After evaporation, nitric acid was finally added to dissolve the column to obtain a clear sample solution. S6. The nickel isotope ratio in the sample solution is measured by a multi-collector inductively coupled plasma mass spectrometer and calibrated by the sample-standard interpolation method.

2. The extraction method according to claim 1, wherein In step S2, 50 μL of the clarified sample solution was transferred to an injection tube. 2.5 mL of 2% w / w nitric acid was added to the injection tube to make the volume 3 mL. The Ni concentration in the solution was then measured.

3. The extraction method according to claim 1, wherein In step S3, an excess amount of ammonia water is added. The ammonia water is obtained by diluting chromatographically pure or higher purity ammonia water with deionized water. The volume fraction of the diluted ammonia water in the solution is 25% v / v.

4. The extraction method according to claim 1, wherein The optimal dilution ratio of the double diluent added in step S4 is 0.4-0.

6.

5. The extraction method according to claim 1, wherein The concentration of the nickel isotope double diluent added in step S4 is 20 μg / g, and the isotopic abundance is: 58 Ni (0.03%), 60 Ni (0.13%), 61 Ni (45.06%), 62 Ni (54.67%), 64 Ni (0.12%).

6. The extraction method according to claim 1, characterized in that In step S5, ammonium citrate and ammonia water are sequentially added to adjust the pH, specifically by adding 1 mL of 1 mol / L hydrochloric acid, then continuing to add 0.2 mL of 1 mol / L ammonium citrate, and then continuing to add 5 mol / L ammonia water until the pH is adjusted to 9-10.

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