W element separation and high-precision W isotope determination method for ultralow sample quantity rock

Abstract

The embodiment of the invention provides a W element separation and high-precision W isotope determination method for ultralow sample quantity rock, which comprises the following steps: selecting a rock sample to be determined, and weighing and dissolving the rock sample to obtain a sample dissolving solution; sequentially carrying out two-column chemical separation and purification on the sample dissolving solution by respectively adopting an AG1X8 resin column and a TEVA resin column, and separating out the W element to obtain a high-purity W element sample to be determined; the method comprises the following steps: respectively establishing a cup structure for W isotope composition determination and a cup structure for O isotope composition determination, and determining a high-purity W element to-be-determined sample to respectively obtain nWO3 data of W isotope and data of all O isotope compositions; and performing deoxidation correction on nWO3 data according to all O isotope composition data, and correcting W isotope mass fractionation to obtain a high-accuracy and high-precision W isotope ratio. According to the method, the chemical process background is reduced, the recovery rate of W is improved, and the accuracy and precision of W isotope testing are improved.

Description

Technical Field

[0001] The disclosed embodiments belong to the technical field of W isotope tracing and dating, and specifically relate to a method for separating the W element of ultra-low sample amount rocks and determining W isotopes with high precision. Background Art

[0002] In the study of cosmochemistry and geochemistry, 182 Hf- 182 The W radioisotope system is an important dating and tracing tool. Because its parent Hf is a strong lithophile element, and its daughter W is a siderophile element, this special property makes it play an irreplaceable role in the study of the Earth and other planets in the solar system, which cannot be replaced by other isotope systems whose parent and daughter are both lithophile (such as Rb-Sr, Sm-Nd, etc.) or siderophile (such as Re-Os, etc.). 182 Hf decays to 182 The half-life of W is only 8.9 Ma, and both Hf and W are trace elements. 182 W / 184 The change in W ratio is less than 10ppm, so 182 W / 184 High-precision determination of the W ratio is particularly important.

[0003] The existing W element separation methods mainly include: 1) Using the conventional 2-4 column method to separate W. The 2-4 column separation method is currently commonly used, that is, using anion or cation resins, as well as special resins to gradually separate matrix elements and interfering elements, and finally obtain the purified W element. This method can only achieve high-precision analysis of W isotopes in large sample volumes (the total amount of W is greater than 0.5 micrograms or 1.0 micrograms, and the corresponding rock sample volume requires one to several grams, or even more than ten grams). And the amount of resin and solvent used is large (up to 300

[0004] mL~500mL), the separation process is time-consuming and has a high background. For precious extraterrestrial material samples, such as lunar and Martian samples, it cannot meet the requirements of high-precision W isotope determination.

[0005] 2) Use NaOH alkaline solution precipitation method and special resin column method to separate W, that is, use NaOH to precipitate the matrix elements, evaporate the supernatant containing W, and then use special resin to further separate the W element. This method can separate W from small sample amounts (about 0.3 grams), but it cannot separate W from major elements such as Na, Mg, and Al. Therefore, for samples with high content of Na, Mg, and Al, when using TIMS for W isotope determination, obvious matrix interference may occur, thereby affecting the accuracy of W isotope determination.

[0006] The existing methods for determining W isotopes mainly include: 1) using MC-ICPMS instrument to perform high-precision determination of W isotopes. In this method, the instrument memory effect is strong, and how to remove the memory effect when determining multiple samples is a technical problem.

[0007] 2) Using conventional thermal ionization mass spectrometry (NTIMS), i.e., using the traditional 10 11 The Ω amplifier is connected to the Faraday cup and the W 16 The W isotope and interfering element isotope in the form of O3 were determined using 10 12 Ω or 10 13 The Ω amplifier is used to measure the heavy oxygen isotope molecules (W 16 O2 18 This method can only achieve high-precision determination of large sample quantities (the total amount of W is greater than 500 nanograms, and the corresponding rock samples require one to several grams, or even more). For samples that do not meet the requirements, 182 W / 184 The accuracy of W measurement will decrease as the signal intensity of W decreases. In addition, this method can only obtain 18 O / 16 O ratio, and W 16 O2 17 Because the signal is often below the detection line, 17 O / 16 O ratio can only be measured by 18 O / 16 The O ratio is calculated based on the assumed O isotope mass fractionation line, and its error and accuracy can lead to 182 W / 184 The precision and accuracy of the W ratio deteriorates.

[0008] In view of the above problems, it is necessary to propose a method for W element separation and high-precision W isotope determination of ultra-low sample amount rocks that is reasonably designed and effectively solves the above problems. Summary of the invention

[0009] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art and provide a method for separating the W element and determining the W isotope of ultra-low sample amount rocks with high precision.

[0010] The present disclosure provides a method for separating the W element and determining the W isotope of ultra-low sample amount rocks with high precision, the method comprising:

[0011] Selecting a rock sample to be measured and weighing it, and dissolving the weighed rock sample to be measured to obtain a sample solution;

[0012] The sample solution is subjected to two-column chemical separation and purification respectively by using an AG1X8 resin column and a TEVA resin column, the W element is separated and purified, and a high-purity W element sample to be determined is obtained;

[0013] The cup structure for determining the W isotope composition and the cup structure for determining the O isotope composition are respectively established, and the isotope thermal ionization mass spectrometry is performed on the high-purity W element sample to be determined, and the W isotope composition is respectively obtained. n WO3 data and all O isotope composition data;

[0014] According to the above-mentioned total O isotope composition data, n The WO3 data were corrected for oxygen removal, and then the W isotope mass fractionation produced during the instrument measurement process was corrected and calculated to obtain a W isotope ratio with high accuracy and precision.

[0015] Optionally, the two-column chemical separation and purification of the sample solution is performed using an AG1X8 resin column and a TEVA resin column respectively, so as to separate and purify the W element and obtain a high-purity W element sample to be determined, including:

[0016] Loading 2.5 mL to 3.0 mL of AG1X8 resin into a resin column to obtain the AG1X8 resin column, and pretreating the AG1X8 resin column;

[0017] The sample solution was evaporated to dryness, and redissolved in 0.5 mL to 1 mL of a mixed acid solution of 1 M HCl and 0.5 M HF, and the redissolved sample solution was slowly added to the pretreated AG1X8 resin column;

[0018] Slowly add 6 mL to 7 mL of a mixed acid of 1 M HCl and 0.5 M HF to the AG1X8 resin column to elute the major matrix elements and most of the trace elements;

[0019] Slowly add 6 mL to 7 mL of a mixed acid of 6 M HNO3 and 0.2 M HF to the AG1X8 resin column to elute some interfering elements and the W element;

[0020] The W-containing solution separated by the AG1X8 resin column was evaporated to dryness, and then redissolved in 0.3 mL to 0.5 mL of a mixed acid solution of 9 M HCl and 0.02 M HF;

[0021] Loading 0.5 mL to 0.6 mL of TEVA resin into a resin column to obtain the TEVA resin column, and pretreating the TEVA resin column;

[0022] Slowly adding the re-dissolved W-containing solution into the pre-treated TEVA resin column;

[0023] Slowly add 2.5 mL to 3.0 mL of a mixed acid of 9 M HCl and 0.02 M HF to the TEVA resin column to elute the remaining interfering elements;

[0024] 2.5 mL to 3.0 mL of a mixed acid of 3 M HCl and 0.02 M HF was slowly added to the TEVA resin column to elute the W element, obtain a high-purity W solution, and complete the separation of the TEVA resin column.

[0025] Optionally, the AG1X8 resin column is pretreated, comprising:

[0026] Slowly add 5 mL to 6 mL of a mixed solution of 6 M HNO3 and 0.2 M HF to the AG1X8 resin column for the first wash; Slowly add 5 mL to 6 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column for the second wash;

[0027] Slowly add 5 mL to 6 mL of ultrapure water to the AG1X8 resin column to make the AG1X8 resin column in a neutral state; slowly add 8 mL to 10 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column to make the medium of the AG1X8 resin column the same as the medium of the sample dissolving solution.

[0028] Optionally, the TEVA resin column is pretreated, comprising:

[0029] Slowly adding 3 mL to 5 mL of a mixed solution of 3 M HCl and 0.02 M HF to the TEVA resin column for the first wash; Slowly adding 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF to the TEVA resin column for the second wash;

[0030] Slowly add 3mL to 5mL of ultrapure water to the TEVA resin column to make the TEVA resin column in a neutral state; slowly add 3mL to 5mL of a mixed solution of 9M HCl and 0.02M HF to the TEVA resin column to make the medium of the TEVA resin column the same as the medium of the W-containing solution after the AG1X8 resin column is separated and redissolved.

[0031] Optionally, the cup structure established for determination of W isotopic composition includes:

[0032] 182 WO3 ˉ , 183 WO3 ˉ , 184 WO3 ˉand 186 WO3 ˉ The ion beam is connected by the second low cup L2, the first low cup L1, the center cup C and the second high cup H2. 12 Ω amplifier for receiving;

[0033] 180 WO3 ˉ The ion beam is connected to the fourth low cup L4 10 13 Ω amplifier for receiving;

[0034] 181 TaO3 ˉ The ion beam is connected to the third low cup L3 10 13 Ω amplifier for receiving;

[0035] 185 ReO3 ˉ The ion beam is connected to the first high cup H1 10 11 Ω amplifier for reception.

[0036] Optionally, the cup structure for determining the W isotope composition is used to perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, comprising:

[0037] Instrument measurement parameter settings: Measure in the negative ion mode of the TIMS instrument;

[0038] The baseline of the instrument is measured once a day before the start of measurement, with a pre-wait time of 50s to 60s and a measurement time of 1200 cycles × 1.05s;

[0039] 10 11 Ω, 10 12 Ω and 10 13 The gain of the Ω amplifier is calibrated every three days, and the calibration current is a virtual current of 0.12V;

[0040] The W element of each sample was measured for 40 cycles × 20 blocks, each data was integrated for 16 s / 32 s, the idle time was 10 s to 12 s, and the peak was aligned every 5 blocks;

[0041] During the measurement, the oxygen pressure was maintained at 0.5×10 -7 mbar~1.0×10 -7 mbar, regulated by a micro air valve, each measurement lasts 7.5 to 8 hours, and the evaporation zone temperature is 1300°C to 1350°C during W isotope determination.

[0042] Optionally, the cup structure for determining the O isotopic composition is established, comprising:

[0043] 185Re 16 O4 ˉˉ and 187 Re 16 O4 ˉ The ion beam is connected by the center cup C and the second high cup H2. 12 Ω amplifier for receiving;

[0044] 187 Re 16 O3 18 O ˉ The ion beam uses the third high cup H3 connection 10 13 Ω amplifier for receiving;

[0045] 187 Re 16 O3 17 O ˉˉ The ion beam is received by a secondary ion multiplier (SEM, IC 1C) bound to the central cup C; wherein,

[0046] The position of the cup structure determined by the O isotopic composition is the same as the position of the cup structure determined by the W isotopic composition.

[0047] Optionally, the cup structure for determining the O isotope composition is used to perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, comprising:

[0048] Before each sample measurement, a Faraday cup static receiver was used. 185 ReO4 ˉ , 187 ReO4 - and 187 Re 16 O3 18 O ˉ The SEM peak-jumping method was used to measure 187 Re 16 O3 17 O ˉ Conducting determinations;

[0049] The analysis parameters for O isotope determination are 20 cycles × 10 blocks, 4 s / 8 s for integration, 6 s to 8 s for idle time, 35 min to 60 min for one measurement, and 700 °C to 850 °C for evaporation zone temperature during O isotope determination.

[0050] Optionally, obtaining a high-purity W element sample to be determined includes:

[0051] The W element solution obtained by two separations using the AG1X8 resin column and the TEVA resin column was placed on a hot plate and evaporated to dryness, and redissolved in 1 μL to 2 μL of a mixed solution of 7% M HNO3 and 4% M HF to obtain the high-purity W element sample to be determined.

[0052] Optionally, the n The WO3 data is deoxygenated and then the W isotope mass fractionation generated during the instrument measurement is corrected and calculated to obtain highly accurate and precise W isotope ratios, including:

[0053] According to the determination of ReO4, the accurate three oxygen isotope compositions are calculated, among which the calculation formula of O isotope composition is: 18 O / 16 O = 1 / 4 × I ( 187 Re 16 O3 18 O - ) / I( 187 ReO4 - ), 17 O / 16 O = 1 / 4 × I ( 187 Re 16 O3 17 O - ) / I( 187 ReO4 - );

[0054] Subtract the isotopic interference of TaO3 and ReO3 on WO3;

[0055] Based on the calculated O isotope composition, deoxygenation correction was performed;

[0056] To perform a mass fractionation calibration: Use 186 W / 184 W = 0.92767, corrected by exponential law.

[0057] The method for separating the W element and determining the W isotope of ultra-low sample amount rocks in the embodiments of the present disclosure adopts a two-column chemical separation method for chemical separation of the W element, which can completely separate the W element from matrix elements and interfering elements. By simplifying the separation process and reducing the amount of resin and solvent used, it not only reduces the background of the chemical process to as low as 40pg, but also increases the recovery rate of W to more than 97%, making high-precision W isotope determination of small sample amounts (20 mg to 400 mg) possible.

[0058] The method for separating the W element and determining the W isotope of the rock with an ultra-low sample amount according to the embodiment of the present disclosure is to establish a cup structure for determining the W isotope composition and a cup structure for determining the O isotope composition, and to use a Faraday cup and a 10 11 Ω, 10 12 Ω and 10 13 The isotope thermal ionization mass spectrometry method of static measurement with three different types of amplifier combinations is used to statically measure low-content or low-sample rock samples of W, obtain all five isotopes of tungsten, and monitor the isotopic interference of tantalum and rhenium; through Faraday cup, 10 12 Ω and 10 13 The combination of two different types of amplifiers and an ion counter (SEM IC 1C) and a rationally designed cup structure for the determination of O isotopic composition were used to determine the ReO4 16 O. 17 O and 18 O all three O isotopes, solving the problem of low W signal in small sample amounts and 17 O abundance is too low (natural abundance is about 16 1 / 2600 of O, 18 The problem of being unable to obtain accurate and high-precision measurement data of 1 / 5 of O) is solved, and the high-precision and high-precision determination of oxygen isotope composition and the high-precision and high-precision test of W isotope are realized.

[0059] The method for separating the W element and determining the W isotope of ultra-low sample rocks in the disclosed embodiment can obtain the best W isotope test accuracy consistent with that determined by the conventional method when the sample amount is only 1 / 10 or less of the conventional amount. This method is particularly suitable for precious samples such as the moon and Mars, and can still obtain high-precision data when a large number of samples cannot be obtained, providing technical support for the scientific research of my country's current lunar and Mars exploration programs. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a flow chart of a method for separating the W element in ultra-low sample amount rocks and determining the W isotope with high precision according to one embodiment of the present disclosure;

[0061] Figure 2 This is the elution curve of the MISA multi-element mixed solution in one embodiment of the present disclosure. DETAILED DESCRIPTION

[0062] In order to enable those skilled in the art to better understand the technical solutions of the embodiments of the present disclosure, the embodiments of the present disclosure are further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0063] like Figure 1As shown, the embodiment of the present disclosure provides a method S100 for separating W elements and determining W isotopes with high precision in ultra-low sample amount rocks, and the method S100 comprises:

[0064] S110, selecting a rock sample to be measured and weighing it, and dissolving the weighed rock sample to be measured to obtain a sample solution.

[0065] Specifically, the dissolution of silicate samples (including Earth rocks and meteorites)

[0066] The process can be as follows:

[0067] A plurality of rock samples of different lithology were selected, wherein the lithology and W element concentration of each sample were different. 20 mg to 400 mg of each rock powder sample was weighed and placed in a 15 mL Teflon bottle.

[0068] Add 1 mL of concentrated HF and 2 mL of concentrated HNO3 into the Teflon bottle respectively, seal the Teflon bottle, place it on a hot plate, and keep it at 120°C for 2 to 5 days.

[0069] The dissolved sample solution was evaporated at 120° C. until it was dry; 3 mL of 50% by volume concentrated HCl was added again, placed on a hot plate, kept warm at 120° C. for 1 day, and evaporated at 120° C. after dissolution; 1 mL of a mixed solution of 1 M HCl and 0.5 M HF was added for re-dissolution to obtain the sample solution.

[0070] Specifically, the dissolution process for iron meteorite samples (including earth iron metal minerals) can be as follows:

[0071] Weigh about 30 mg to 100 mg of iron meteorite sample and place it in a 15 mL Teflon bottle.

[0072] Add 2 mL of aqua regia to the Teflon bottle and let it stand at room temperature until there is no reaction gas; seal the Teflon bottle, place it on a hot plate, and keep it warm at 120°C for 1 day.

[0073] The dissolved sample solution was evaporated at 120° C. until it was dry; 2 mL of aqua regia was added again, and the solution was placed on a hot plate and kept at 120° C. for 1 day. After the solution was dissolved, the solution was evaporated at 120° C. until it was dry; 1 mL of a mixed solution of 1 M HCl and 0.5 M HF was added to redissolve the solution to obtain the solution.

[0074] S120, using an AG1X8 resin column and a TEVA resin column to perform two-column chemical separation and purification on the sample solution in turn, separating and purifying the W element, and obtaining a high-purity W element sample to be determined.

[0075] Specifically, the two-column method and acids of different concentrations and types were used to chemically separate and purify the dissolved solution, that is, AG1X8 (100 mesh to 200 mesh) resin was used to separate W and matrix elements, and TEVA (TE-B100-A, 100 μm to 150 μm) resin was used to separate W and interfering elements, so as to obtain a high-purity W element sample to be determined.

[0076] Use AG1X8 resin column for the first column separation:

[0077] First, 2.5 mL to 3.0 mL of AG1X8 resin is loaded into a resin column to obtain the AG1X8 resin column, and the AG1X8 resin column is pretreated.

[0078] Specifically, 2.5 ml of AG1X8 (100-200 mesh) resin was loaded into a polytetrafluoroethylene PFA resin column with an inner diameter of 0.7 cm to obtain an AG1X8 resin column.

[0079] The specific process of pretreating the AG1X8 resin column includes:

[0080] (1) Column cleaning. Slowly add 5 mL to 6 mL of a mixed solution of 6 M HNO3 and 0.2 M HF to the AG1X8 resin column for the first cleaning. Slowly add 5 mL to 6 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column for the second cleaning.

[0081] In this embodiment, preferably, 5 mL of a mixed solution of 6 M HNO3 and 0.2 M HF is slowly added to the AG1X8 resin column for the first cleaning. 5 mL of a mixed solution of 1 M HCl and 0.5 M HF is slowly added to the AG1X8 resin column for the second cleaning.

[0082] (2) Column balancing. Slowly add 5 mL to 6 mL of ultrapure water to the AG1X8 resin column to make the AG1X8 resin column in a neutral state; slowly add 8 mL to 10 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column to make the medium of the AG1X8 resin column the same as the sample solution.

[0083] In this embodiment, preferably, 5 mL of ultrapure water is slowly added to the AG1X8 resin column to make the AG1X8 resin column in a neutral state; 10 mL of a mixed solution of 1 M HCl and 0.5 M HF is slowly added to the AG1X8 resin column to make the medium of the AG1X8 resin column the same as the medium of the upper column sample.

[0084] Secondly, after the pretreatment of the AG1X8 resin column, add the re-dissolved sample solution into the AG1X8 resin, and add different concentrations and different types of acids in turn to chemically separate and purify the solution. The specific chemical separation and purification steps are as follows:

[0085] (1) Slowly add 0.5 mL to 1 mL of the sample solution into the pretreated AG1X8 resin column.

[0086] In this embodiment, preferably, 1 mL of the sample solution is slowly added into the pretreated AG1X8 resin column to load the sample solution onto the column.

[0087] (2) 6 mL to 7 mL of a mixed acid of 1 M HCl and 0.5 M HF was slowly added to the AG1X8 resin column to elute the major matrix elements and most of the trace elements.

[0088] In this embodiment, preferably, Figure 2 As shown, 6 mL of a mixed acid of 1 M HCl and 0.5 M HF was slowly added to the AG1X8 resin column to elute the major matrix elements and most of the trace elements.

[0089] (3) Slowly add 6 mL to 7 mL of a mixed acid of 6M HNO3 and 0.2M HF into the AG1X8 resin column to elute some interfering elements and the W element.

[0090] In this embodiment, preferably, Figure 2 As shown, 6 mL of a mixed acid of 6 M HNO3 and 0.2 M HF is slowly added to the AG1X8 resin column to elute the W element. At this time, some interfering elements are eluted simultaneously with the W element, such as Zr, Ti, Hf, Ta, Re and Os, completing the separation of the AG1X8 resin column.

[0091] The W-containing solution separated by the AG1X8 resin column was placed on a hot plate and evaporated to dryness, and redissolved in 0.5 mL of a mixed solution of 9 M HCl and 0.02 M HF for separation by the second column.

[0092] The second column separation was performed using TEVA resin column:

[0093] First, 0.5 mL to 0.6 mL of TEVA resin is loaded into a resin column to obtain the TEVA resin column, and the TEVA resin column is pretreated.

[0094] Specifically, 0.5 mL of TEVA (TE-B100-A, 100 μm to 150 μm) resin was loaded into a PFA resin column with an inner diameter of 0.7 cm to obtain the TEVA resin column.

[0095] Wherein, the TEVA resin column is pretreated, specifically comprising:

[0096] (1) Column cleaning: Slowly add 3 mL to 5 mL of a mixed solution of 3 M HCl and 0.02 M HF to the TEVA resin column for the first cleaning; slowly add 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF to the TEVA resin column for the second cleaning.

[0097] In this embodiment, preferably, 5 mL of a mixed solution of 3 M HCl and 0.02 M HF is slowly added to the TEVA resin column for the first washing; and 5 mL of a mixed solution of 9 M HCl and 0.02 M HF is slowly added to the TEVA resin column for the second washing.

[0098] (2) Column equilibration. Slowly add 3 mL to 5 mL of ultrapure water to the TEVA resin column to make the TEVA resin column neutral; slowly add 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF to the TEVA resin column to make the medium of the TEVA resin column the same as the medium of the W-containing solution after separation and redissolution of the AG1X8 resin column.

[0099] In this embodiment, preferably, 5 mL of ultrapure water is slowly added to the TEVA resin column to make the TEVA resin column in a neutral state; 5 mL of a mixed solution of 9 M HCl and 0.02 M HF is slowly added to the TEVA resin column to make the medium of the TEVA resin column the same as the medium of the W-containing solution after the AG1X8 resin column is separated and redissolved.

[0100] Secondly, after the pretreatment of the TEVA resin column, the re-dissolved W-containing solution was added to the TEVA resin column, and different concentrations and different types of acids were added to the re-dissolved W-containing solution for chemical separation and purification. The specific chemical separation and purification is as follows:

[0101] (1) Slowly add 0.3 mL to 0.5 mL of the W-containing solution that has been separated and redissolved by the AG1X8 resin column to the pretreated TEVA resin column.

[0102] In this embodiment, preferably, 0.5 mL of the W-containing solution separated and redissolved by the AG1X8 resin column is slowly added to the pretreated TEVA resin column to load the W-containing solution onto the column.

[0103] (2) Slowly add 2.5 mL to 3.0 mL of a mixed acid of 9 M HCl and 0.02 M HF to the TEVA resin column to elute the remaining interfering elements.

[0104] In this embodiment, preferably, Figure 2 As shown, 2.5 mL of a mixed acid of 9 M HCl and 0.02 M HF was slowly added to the TEVA resin column to elute interfering elements such as Zr, Ti, Hf, Ta, Re, and Os.

[0105] (3) Slowly add 2.5 mL to 3.0 mL of a mixed acid of 3 M HCl and 0.02 M HF to the TEVA resin column to elute the W element, obtain a high-purity W solution, and complete the separation of the TEVA resin column.

[0106] In this embodiment, preferably, Figure 2 As shown, 2.5 mL of a mixed acid of 3 M HCl and 0.02 M HF was slowly added to the TEVA resin column to elute the W element, obtain a high-purity W solution, and complete the separation of the TEVA resin column.

[0107] The separated W element solution is placed on a hot plate and evaporated to dryness, and redissolved in 1 μL to 2 μL of a mixed solution of 7% HNO3 and 4% MHF to obtain the high-purity W element sample to be measured, which is to be used for TIMS instrument measurement.

[0108] In this embodiment, the chemical separation of the W element adopts a two-column chemical separation method, which can completely separate the W element from the matrix elements and the interfering elements. By simplifying the separation process and reducing the usage of resin and solvent, not only the background of the chemical process is reduced to 40pg, but also the recovery rate of W is increased to 97%, making it possible to determine the high-precision W isotope of small samples (20 mg to 400 mg).

[0109] S130, respectively establish a cup structure for determining the W isotope composition and a cup structure for determining the O isotope composition, perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, and obtain the W isotope composition n WO3 data and all O isotope composition data.

[0110] Specifically, as shown in Table 1, different types of receivers (FC, SEM) and different types of amplifiers (10 11Ω, 10 12 Ω and 10 13 Ω) to establish the cup structure for the W isotope composition determination. The cup structure for the W isotope composition determination specifically includes:

[0111] Four more abundant 182 WO3 ˉ , 183 WO3 ˉ , 184 WO3 ˉ and 186 WO3 ˉ The ion beam is connected by the second low cup L2, the first low cup L1, the center cup C and the second high cup H2. 12 Ω amplifier for reception.

[0112] 180 WO3 ˉ The ion beam is connected to the fourth low cup L4 10 13 Ω amplifier for reception.

[0113] 181 TaO3 ˉ The ion beam is connected to the third low cup L3 10 13 Ω amplifier for receiving. Among them, 181 TaO3 ˉ Used for monitoring 180 TaO3 ˉ right 180 WO3 ˉ interference.

[0114] 185 ReO3 ˉ Used to monitor heavy oxides 185 Re 16 O2 17 O ˉ right 186 WO3 ˉ Since W isotope determination uses the Re band as a carrier, the ReO3 signal may be very high. 185 ReO3 ˉ The ion beam is connected to the first high cup H1 10 11 Ω amplifier for reception.

[0115] It should be noted that configuration 10 12 The maximum limit of the ion beam that the Faraday cup of the Ω amplifier can receive in the negative ion state is 1.2V. In this experiment, no diluent was added to the samples used, and the maximum natural abundance was used. 184 W is calculated when 184 WO3 - When the ion beam intensity is 1.2V, 180WO3 - The ion beam intensity is less than 4.7mV and less than 10 13 The maximum limit of the ion beam that the Faraday cup of the Ω amplifier can receive in the negative ion state is 120mV.

[0116] Table 1 Cup structure composition determined by W isotopic composition

[0117] Receiver L4 L3 L2 L1 C / SEM H1 H2 Ion beam <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 180 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 181 <h2 style=";text-align:left;direction:ltr"> TaO3<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 182 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 183 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 184 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> <![CDATA[ 185 ReO3]]> <h2 style=";text-align:left;direction:ltr"><![CDATA[ <h2 style=";text-align:left;direction:ltr"> 186 <h2 style=";text-align:left;direction:ltr"> WO3]]><h2 style=";text-align:left;direction:ltr"> Atomic mass 228 229 230 231 232 233 234 Abundance.(%) 0.12 ˉ 26.5 14.3 30.6 ˉ 28.4 Amplifier(Ω) <![CDATA[10 13 ]]> <![CDATA[10 13 ]]> <![CDATA[10 12 ]]> <![CDATA[10 12 ]]> <![CDATA[10 12 ]]> <![CDATA[10 11 ]]> <![CDATA[10 12 ]]>

[0118] The isotope thermal ionization mass spectrometry is performed on the high-purity W element sample to be determined using the cup structure for W isotope composition determination established in Table 1, specifically including:

[0119] Instrument measurement parameter settings: Measure in the negative ion mode of the TIMS instrument.

[0120] The baseline of the instrument is measured once a day before starting the measurement work, each time waiting for 50s to 60s, and measuring 1200 cycles×1.05s. Preferably, each time waiting for 60s.

[0121] 10 11 Ω, 10 12 Ω and 10 13 The gain calibration of the Ω amplifier is performed once every three days, and the calibration current is a virtual current of 0.12V.

[0122] The W element of each sample is measured for 40 cycles × 20 blocks (i.e. 800 data), each data is integrated for 16s / 32s, and the idle time is 10s to 12s; preferably, each data is integrated for 32s, and the idle time is 12s. Peak centering is performed every 5 blocks.

[0123] During the measurement, the oxygen pressure was maintained at 0.5×10 -7 mbar~1.0×10 -7 mbar, regulated by a micro air valve, each measurement lasts 7.5 to 8 hours, and the evaporation zone temperature during W isotope determination is 1300° C. to 1350° C. Preferably, each measurement lasts about 7.5 hours.

[0124] In this example, the cup structure of W isotope composition determination was established by using Faraday cup and 10 11 Ω, 10 12 Ω and 10 13The isotope thermal ionization mass spectrometry method of static measurement with three different types of amplifier combinations is used to statically measure low-content or low-sample-amount rock samples of W, obtain all five isotopes of tungsten, and monitor the isotopic interference of tantalum and rhenium, thus realizing the static measurement of W isotopes with low signal and high precision.

[0125] More specifically, in this embodiment, the oxygen isotope composition is in the form of ReO4, and is determined by 185 Re 16 O4 (atomic mass 249), 187 Re 16 O4 (atomic mass 251) and heavy oxygen isotopes ( 17 O and 18 Oxide molecules 187 Re 16 O3 17 O 17 O (atomic mass 252) and 187 Re 16 O3 18 O (atomic mass is 253) is used to achieve this. Therefore, the structure of the O isotope composition determination cup shown in Table 2 is established, specifically including:

[0126] 185 Re 16 O4 ˉ and 187 Re 16 O4 ˉ The ion beam is connected by the center cup C and the second high cup H2. 12 Ω amplifier for reception.

[0127] 187 Re 16 O3 18 O ˉ The ion beam uses the third high cup H3 connection 10 13 Ω amplifier for reception.

[0128] 187 Re 16 O3 17 O ˉ The ion beam is received by a secondary ion multiplier (SEM, IC 1C) bound to the central cup C.

[0129] As shown in Tables 1 and 2, the position of the cup structure for the O isotope composition determination is the same as the position of the cup structure for the W isotope composition determination. In other words, the position of all cup structures receiving ReO4ˉ is the same as the position of the cup structure receiving WO3ˉ. Therefore, when switching between ReO4ˉ determination and WO3ˉ determination, there is no need to adjust and move the position of the Faraday cup. When measuring the sample, the temperature can be first raised to a lower ReO4 excitation temperature for O isotope determination, and then the temperature can be continued to be raised to the WO3 excitation temperature for W isotope determination, which saves measurement time.

[0130] Table 2 Cup structure composition determined by O isotopic composition

[0131]

[0132] The isotope thermal ionization mass spectrometry is performed on the high-purity W element sample to be determined using the cup structure for determining the O isotope composition shown in Table 2, including:

[0133] Before each sample was measured, the corresponding Faraday cup was used to statically receive the mass numbers 249, 251, and 253 (i.e. 185 ReO4ˉ, 187 ReO4ˉ and 187 Re 16 O3 18 Oˉ) was measured using the SEM peak-jumping method to receive the mass number 252 (i.e. 187 Re 16 O3 17 Oˉ) for determination.

[0134] The O isotope analysis parameters are 20 cycles × 10 blocks (i.e., 200 data), 4s / 8s integration, 4s to 8s idle time, 35 minutes to 60 minutes for one measurement, and 700° C. to 850° C. for the evaporation zone temperature during O isotope determination. Preferably, the integration time is 8s, the idle time is 8s, and the time for one measurement is 60 minutes.

[0135] In this embodiment, the cup structure for determining the O isotope composition is established in the W isotope determination method to accurately determine the three oxygen isotopes, which is not available in the existing W isotope determination method. 12 Ω and 10 13 The combination of two different types of amplifiers and an ion counter (SEM) and the rationally designed cup structure for the determination of O isotopic composition were used to determine the ReO4 16 O. 17 O and 18O all three O isotopes, and take advantage of the convenience of the Re filament used in W isotope determination to obtain high-signal and high-precision O isotope data, solving the problem of low W signal in small sample quantities and 17 O abundance is too low (natural abundance is about 16 1 / 2600 of O, 18 The problem of being unable to obtain accurate and high-precision measurement data for 1 / 5 of O) was solved, which avoided the deviation of the 17O / 18O ratio caused by the deviation of the assumed conditions in the past 17O / 18O ratio calculation, and achieved high-precision and high-precision determination of oxygen isotope composition and high-precision and accuracy testing of W isotopes.

[0136] S140, according to the total O isotope composition data n The WO3 data were corrected for oxygen removal, and then the W isotope mass fractionation produced during the instrument measurement process was corrected and calculated to obtain a W isotope ratio with high accuracy and precision.

[0137] Specifically, data processing: Tungsten is measured in the form of trioxide ions in a negative ion state, and the data needs to be processed offline after being exported. 1) According to the determination of ReO4, the accurate trioxygen isotope composition is calculated, where the calculation formula for the O isotope composition is: 18 O / 16 O = 1 / 4 × I ( 187 Re 16 O3 18 O - ) / I( 187 ReO4 - ), 17 O / 16 O = 1 / 4 × I ( 187 Re 16 O3 17 O - ) / I( 187 ReO4 - ); 2) deduct the isotopic interference of TaO3 and ReO3 on WO3; 3) perform deoxygenation correction on WO3 based on the calculated O isotopic composition; 4) perform W isotope mass fractionation correction: use 186 W / 184 W = 0.92767, corrected by exponential law.

[0138] The following is a description of the W element separation and high-precision W isotope determination method for ultra-low sample amount rocks according to the embodiment of the present disclosure in conjunction with corresponding embodiments.

[0139] A two-column chemical separation method was designed with a W content of 100 ng and a corresponding sample amount of 20 mg to 400 mg.

[0140] The separation process has good reproducibility of elution curves for different earth rocks, stony meteorites and iron meteorites.

[0141] As shown in Table 3, the W element separation and high-precision W isotope determination method S100 of the ultra-low sample amount rock of the present disclosure embodiment was used to determine the single element W standard solution SRM3163, and the total amount of W of about 1000ng, 100ng, 50ng, 30ng and 10ng was sampled. 184 W 16 O3 - The signal intensities were measured at approximately 0.1 V, 0.25 V, 0.5 V, and 0.1 V, respectively.

[0142] The results show that when 184 W 16 O3 - When the signal strength is 0.5 to 1.0V, 182 W / 184 The ratio and precision of W are 0.864869±6ppm (2RSD, n=21, t=12 months), 184 WO3 - When the signal strength is 0.1 to 0.3V, 182 W / 184 The ratio and precision of W is 0.864868±11ppm (2RSD, n=17t=3 months). When the total amount of W reaches 30ng, the sample amount is only less than 1 / 10 of the conventional method in the past, and the best measurement precision of 4ppm~6ppm (2RSD) that can be obtained for more than 500ng can still be obtained when using NTIMS with conventional amplifiers in previous studies.

[0143] Table 3 Test data of 3W standard solution and reference material of rock samples

[0144]

[0145] As shown in Table 3, the W element separation and high-precision W isotope determination method S100 of ultra-low sample amount rock of the disclosed embodiment was used to carry out determination of a group of earth rock and meteorite samples. The selected 6 samples are basalt JB-3, BCR-2 and BHVO-2, granodiorite GSP-2, ordinary chondrite-Jilin meteorite and iron meteorite-Nandan meteorite. These rock samples represent typical rock samples of mantle, crust, stony meteorite, and iron meteorite, covering the W content range of most earth and meteorites (251-1555ng / g), among which JB-3, BCR-2 and BHVO-2, granodiorite GSP-2 are widely reported as international geological reference materials. In order to ensure the uniformity of the samples in this experiment, about 1g to 2g of each sample was weighed for dissolution. Then, the total amount of W was estimated to be about 100ng (corresponding to 20mg to 400mg of rock sample) based on the W content reference value in each sample. The samples were then chemically separated and purified for W, and then subjected to NTIMS determination.

[0146] The results show that within the error range, μ 182 The W values ​​are consistent with the reported data. 182 The W value is consistent with that reported for ordinary chondrites of the same type.

[0147] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the embodiments of the present disclosure, but the embodiments of the present disclosure are not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the embodiments of the present disclosure, and these modifications and improvements are also considered to be within the protection scope of the embodiments of the present disclosure.

Claims

1. A method for separating W from ultra-low sample amount rocks and determining W isotopes with high precision, characterized in that: The method comprises: Selecting a rock sample to be measured and weighing it, and dissolving the weighed rock sample to be measured to obtain a sample solution; The sample solution is subjected to two-column chemical separation and purification respectively by using an AG1X8 resin column and a TEVA resin column, the W element is separated and purified, and a high-purity W element sample to be determined is obtained; The cup structure for determining the W isotope composition and the cup structure for determining the O isotope composition are respectively established, and the isotope thermal ionization mass spectrometry is performed on the high-purity W element sample to be determined, and the W isotope composition is respectively obtained. n WO3 data and all O isotope composition data; According to the above-mentioned total O isotope composition data, n The WO3 data were corrected for oxygen removal, and then the W isotope mass fractionation produced during the instrument measurement process was corrected and calculated to obtain a W isotope ratio with high accuracy and precision.

2. The method according to claim 1, characterized in that The method of using an AG1X8 resin column and a TEVA resin column to perform two-column chemical separation and purification on the sample solution in turn, separating and purifying the W element, and obtaining a high-purity W element sample to be determined, comprises: Loading 2.5 mL to 3.0 mL of AG1X8 resin into a resin column to obtain the AG1X8 resin column, and pretreating the AG1X8 resin column; The sample solution was evaporated to dryness, and redissolved in 0.5 mL to 1 mL of a mixed acid solution of 1 M HCl and 0.5 M HF, and the redissolved sample solution was slowly added to the pretreated AG1X8 resin column; Slowly add 6 mL to 7 mL of a mixed acid of 1 M HCl and 0.5 M HF to the AG1X8 resin column to elute the major matrix elements and most of the trace elements; Slowly add 6 mL to 7 mL of a mixed acid of 6 M HNO3 and 0.2 M HF to the AG1X8 resin column to elute some interfering elements and the W element; The W-containing solution separated by the AG1X8 resin column was evaporated to dryness, and then redissolved in 0.3 mL to 0.5 mL of a mixed acid solution of 9 M HCl and 0.02 M HF; Loading 0.5 mL to 0.6 mL of TEVA resin into a resin column to obtain the TEVA resin column, and pretreating the TEVA resin column; Slowly adding the re-dissolved W-containing solution into the pre-treated TEVA resin column; Slowly add 2.5 mL to 3.0 mL of a mixed acid of 9 M HCl and 0.02 M HF to the TEVA resin column to elute the remaining interfering elements; 2.5 mL to 3.0 mL of a mixed acid of 3 M HCl and 0.02 M HF was slowly added to the TEVA resin column to elute the W element, obtain a high-purity W solution, and complete the separation of the TEVA resin column.

3. The method according to claim 2, characterized in that The AG1X8 resin column is pretreated, comprising: Slowly add 5 mL to 6 mL of a mixed solution of 6 M HNO3 and 0.2 M HF to the AG1X8 resin column for the first wash; Slowly add 5 mL to 6 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column for the second wash; Slowly add 5 mL to 6 mL of ultrapure water to the AG1X8 resin column to make the AG1X8 resin column in a neutral state; slowly add 8 mL to 10 mL of a mixed solution of 1 M HCl and 0.5 M HF to the AG1X8 resin column to make the medium of the AG1X8 resin column the same as the medium of the sample dissolving solution.

4. The method according to claim 2, characterized in that: The TEVA resin column is pretreated, comprising: Slowly adding 3 mL to 5 mL of a mixed solution of 3 M HCl and 0.02 M HF to the TEVA resin column for the first wash; Slowly adding 3 mL to 5 mL of a mixed solution of 9 M HCl and 0.02 M HF to the TEVA resin column for the second wash; Slowly add 3mL to 5mL of ultrapure water to the TEVA resin column to make the TEVA resin column in a neutral state; slowly add 3mL to 5mL of a mixed solution of 9M HCl and 0.02M HF to the TEVA resin column to make the medium of the TEVA resin column the same as the medium of the W-containing solution after the AG1X8 resin column is separated and redissolved.

5. The method according to claim 1, characterized in that The cup structure established for the W isotopic composition determination includes: 182 WO3 ˉ , 183 WO3 ˉ , 184 WO3 ˉ and 186 WO3 ˉ The ion beam is connected by the second low cup L2, the first low cup L1, the center cup C and the second high cup H2. 12 Ω amplifier for receiving; 180 WO3 ˉ The ion beam is connected to the fourth low cup L4 10 13 Ω amplifier for receiving; 181 TaO3 ˉ The ion beam is connected to the third low cup L3 10 13 Ω amplifier for receiving; 185 ReO3 ˉ The ion beam is connected to the first high cup H1 10 11 Ω amplifier for reception.

6. The method according to claim 5, characterized in that The cup structure for determining the W isotope composition is used to perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, comprising: Instrument measurement parameter settings: Measure in the negative ion mode of the TIMS instrument; The baseline of the instrument is measured once a day before starting the measurement work, waiting for 50s to 60s each time, and measuring 1200 cycles × 1.05s; 10 11 Ω, 10 12 Ω and 10 13 The gain of the Ω amplifier is calibrated every three days, and the calibration current is a virtual current of 0.12V; The W element of each sample was measured for 40 cycles × 20 blocks, each data was integrated for 16 s / 32 s, the idle time was 10 s to 12 s, and the peak was aligned every 5 blocks; During the measurement, the oxygen pressure was maintained at 0.5×10 -7 mbar~1.0×10 -7 mbar, regulated by a micro air valve, each measurement lasts 7.5 to 8 hours, and the evaporation zone temperature is 1300°C to 1350°C during W isotope determination.

7. The method according to claim 1, characterized in that The cup structure for the O isotopic composition determination is established, including: 185 Re 16 O4 ˉˉ and 187 Re 16 O4 ˉ The ion beam is connected by the center cup C and the second high cup H2. 12 Ω amplifier for receiving; 187 Re 16 O3 18 O ˉ The ion beam uses the third high cup H3 connection 10 13 Ω amplifier for receiving; 187 Re 16 O3 17 O ˉˉ The ion beam is received by a secondary ion multiplier (SEM, IC 1C) bound to the central cup C; wherein, The position of the cup structure determined by the O isotopic composition is the same as the position of the cup structure determined by the W isotopic composition.

8. The method according to claim 7, characterized in that The cup structure for determining the O isotope composition is used to perform isotope thermal ionization mass spectrometry on the high-purity W element sample to be determined, comprising: Before each sample measurement, a Faraday cup static receiver was used. 185 ReO4 ˉ , 187 ReO4 - and 187 Re 16 O3 18 O ˉ The SEM peak-jumping method was used to measure 187 Re 16 O3 17 O ˉ Conducting determinations; The analysis parameters for O isotope determination are 20 cycles × 10 blocks, 4 s / 8 s for integration, 6 s to 8 s for idle time, 35 min to 60 min for one measurement, and 700 °C to 850 °C for evaporation zone temperature during O isotope determination.

9. The method according to any one of claims 1 to 4, characterized in that: The method of obtaining a high-purity W element sample to be determined comprises: The W element solution obtained by two separations of AG1X8 resin column and TEVA resin column was placed on a hot plate for evaporation, and redissolved in 1 μL to 2 μL of a mixed solution of 7% M HNO3 and 4% M HF to obtain the high-purity W element sample to be determined.

10. The method according to any one of claims 1 to 4, characterized in that: The n The WO3 data is deoxygenated and then the W isotope mass fractionation generated during the instrument measurement is corrected and calculated to obtain highly accurate and precise W isotope ratios, including: According to the determination of ReO4, the accurate three oxygen isotope compositions are calculated, among which the calculation formula of O isotope composition is: 18 O / 16 O = 1 / 4 × I ( 187 Re 16 O3 18 O - ) / I( 187 ReO4 - ), 17 O / 16 O = 1 / 4 × I ( 187 Re 16 O3 17 O - ) / I( 187 ReO4 - ); Subtract the isotopic interference of TaO3 and ReO3 on WO3; Based on the calculated O isotope composition, deoxygenation correction was performed; To perform a mass fractionation calibration: Use 186 W / 184 W = 0.92767, corrected by exponential law.

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